Pathology

For other uses, see Pathology (disambiguation).

File:Renal Cell Carcinoma.jpg

A renal cell carcinoma (chromophobe type) viewed on a hematoxylin & eosin stained slide

Pathology is the study and diagnosis of disease through examination of organs, tissues, cells and bodily fluids. The term encompasses both the medical specialty which uses tissues and body fluids to obtain clinically useful information, as well as the related scientific study of disease processes.

History

Main article: History of pathology

The history of pathology can be traced to the earliest application of the scientific method to the field of medicine, a development which occurred in the Middle East during the Islamic Golden Age and in Western Europe during the Italian Renaissance.

Early systematic human dissections were carried out by the Ancient Greek physicians Herophilus of Chalcedon and Erasistratus of Chios in the early part of the third century BC. The first physician known to have made postmortem dissections was the Arabian physician Avenzoar (1091–1161). Rudolf Virchow (1821–1902) is generally recognized to be the father of microscopic pathology. Most early pathologists were also practicing physicians or surgeons.also see Egyptian mummification as pre modern necropsy might suggest as early embalming and post mortem organ removal.

Origins of pathology

Early understanding of the origins of diseases constitutes the earliest application of the scientific method to the field of medicine, a development which occurred in the Middle East during the Islamic Golden Age and in Western Europe during the Italian Renaissance.

The Greek physician Hippocrates, the founder of scientific medicine, was the first to deal with the anatomy and the pathology of human spine. Galen developed an interest in anatomy from his studies of Herophilus and Erasistratus. The concept of studying disease through the methodical dissection and examination of diseased bodies, organs, and tissues may seem obvious today, but there are few if any recorded examples of true autopsies performed prior to the second millennium. Though the pathology of contagion was understood by Muslim physicians since the time of Avicenna (980–1037) who described it in The Canon of Medicine (c. 1020), the first physician known to have made postmortem dissections was the Arabian physician Avenzoar (1091–1161) who proved that the skin disease scabies was caused by a parasite, followed by Ibn al-Nafis (b. 1213) who used dissection to discover pulmonary circulation in 1242. In the 15th century, anatomic dissection was repeatedly used by the Italian physician Antonio Benivieni (1443-1502) to determine cause of death. Antonio Benivieni is also credited with having introduced necropsy to the medical field. Perhaps the most famous early gross pathologist was Giovanni Morgagni (1682-1771). His magnum opus, De Sedibus et Causis Morborum per Anatomem Indagatis, published in 1761, describes the findings of over 600 partial and complete autopsies, organised anatomically and methodically correlated with the symptoms exhibited by the patients prior to their demise. Although the study of normal anatomy was already well advanced at this date, De Sedibus was one of the first treatises specifically devoted to the correlation of diseased anatomy with clinical illness. By the late 1800s, an exhaustive body of literature had been produced on the gross anatomical findings characteristic of known diseases. The extent of gross pathology research in this period can be epitomized by the work of the Viennese pathologist (originally from Hradec Kralove in the Czech Rep.) Carl Rokitansky (1804-1878), who is said to have performed 20,000 autopsies, and supervised an additional 60,000, in his lifetime.

Origins of microscopic pathology

Rudolf Virchow (1821-1902) is generally recognized to be the father of microscopic pathology. While the compound microscope had been invented approximately 150 years prior, Virchow was one of the first prominent physicians to emphasize the study of manifestations of disease which were visible only at the cellular level. A student of Virchow's, Julius Cohnheim (1839-1884) combined histology techniques with experimental manipulations to study inflammation, making him one of the earliest experimental pathologists. Cohnheim also pioneered the use of the frozen section procedure; a version of this technique is widely employed by modern pathologists to render diagnoses and provide other clinical information intraoperatively.

Modern experimental pathology

As new research techniques, such as electron microscopy, immunohistochemistry, and molecular biology have expanded the means by which biomedical scientists can study disease, the definition and boundaries of investigative pathology have become less distinct. In the broadest sense, nearly all research which links manifestations of disease to identifiable processes in cells, tissues, or organs can be considered experimental pathology.

Other Pertinent Topics

• History of medicine
• Anatomical pathology
• Surgical pathology
• List of pathologists
• United States and Canadian Academy of Pathology

Pathology as a science

Pathology is a broad and complex scientific field which seeks to understand the mechanisms of injury to cells and tissues, as well as the body's means of responding to and repairing injury. Disease processes may be incited or exacerbated by a variety of external and internal influences, including trauma, infection, poisoning, loss of blood flow, autoimmunity, inherited or acquired genetic damage, or errors of development. One common theme in pathology is the way in which the body's responses to injury, while evolved to protect health, can also contribute in some ways to disease processes. Elucidation of general principles underlying pathologic processes, such as cellular adaptation to injury, cell death, inflammation, tissue repair, and neoplasia, creates a conceptual framework with which to analyze and understand specific human diseases.

Adaptation to injury

Cells and tissues may respond to injury and stress by specific mechanisms, which may vary according to the cell types and nature of the injury. In the short term, cells may activate specific genetic programs to protect their vital proteins and organelles from heat shock or hypoxia, and may activate DNA repair pathways to repair damage to chromosomes from radiation or chemicals. Hyperplasia is a long-term adaptive response of cell division and multiplication, which can increase the ability of a tissue to compensate for an injury. For example, repeated irritation to the skin can cause a protective thickening due to hyperplasia of the epidermis. Hypertrophy is an increase in the size of cells in a tissue in response to stress, an example being hypertrophy of muscle cells in the heart in response to increased resistance to blood flow as a result of narrowing of the heart's outflow valve. Metaplasia occurs when repeated damage to the cellular lining of an organ triggers its replacement by a different cell type.

Cell death

Necrosis is the irreversible destruction of cells as a result of severe injury in a setting where the cell is unable to activate the needed metabolic pathways for survival or orderly degeneration. This is often due to external pathologic factors, such as toxins or loss of oxygen supply. Milder stresses may lead to a process called reversible cell injury, which mimics the cell swelling and vacuolization seen early in the necrotic process, but in which the cell is able to adapt and survive. In necrosis, the components of degenerating cells leak out, potentially contributing to inflammation and further damage. Apoptosis, in contrast, is a regulated, orderly degeneration of the cell which occurs in the settings of both injury and normal physiological processes.

Inflammation

A transmission electron microscope image of an immune cell crossing from the bone marrow into the circulation

Inflammation is a particularly important and complex reaction to tissue injury, and is particularly important in fighting infection. Acute inflammation is generally a non-specific response triggered by the injured tissue cells themselves, as well as specialized cells of the innate immune system and previously developed adaptive immune mechanisms. A localized acute inflammatory response triggers vascular changes in the injured area, recruits pathogen-fighting neutrophils, and begins the process of developing a new adaptive immune response. Chronic inflammation occurs when the acute response fails to entirely clear the inciting factor. While chronic inflammation can lay a positive role in containing a continuing infectious hazard, it can also lead to progressive tissue damage, as well as predisposing (in some cases) to the development of cancer.

Tissue repair

Tissue repair, as seen in wound healing, is triggered by inflammation. The process may proceed even before the resolution of a precipitating insult, through the formation of granulation tissue. Healing involves the proliferation of connective tissue cells and blood vessel-forming cells as a result of hormonal growth signals. While healing is a critical adaptive response, an aberrant healing response can lead to progressive fibrosis, contractures, or other changes which can compromise function.

Neoplasia

Neoplasia, or "new growth," is a proliferation of cells which is independent of any physiological process. The most familiar examples of neoplasia are benign tumors and cancers. Neoplasia results from genetic changes which cause cells to activate genetic programs inappropriately. Dysplasia is an early sign of a neoplastic process in a tissue, and is marked by persistence of immature, poorly differentiated cell forms. Interestingly, there are many similarities in the gene pathways activated in cancer cells, and those activated in cells involved in wound healing and inflammation.

Choristoma

Choristoma, ectopic tissue, heterotopic tissue, or aberrant tissue, is a mass of histologically normal tissue that is present in an abnormal location.

Pathology as a medical specialty

Physicians who practice pathology diagnose and characterize disease in living patients by examining biopsies and other specimens. For example, the vast majority of cancer diagnoses are made or confirmed by a pathologist. Pathologists may also conduct autopsies to investigate causes of death. The medical practice of pathology grew out the tradition of investigative pathology, and many of the academic leaders in pathology today are accomplished in both basic science research and diagnostic practice. However, as with other specialties in medicine, most modern physician-pathologists are employed in full-time practice, and do not perform original research.

Pathology is a unique medical specialty in that pathologists typically do not see patients directly, but rather serve as consultants to other physicians (often referred to as "clinicians" within the pathology community). However, in the United States and in many other countries, pathologists receive the same doctorate training, and undergo the same medical licensure process as other physicians. Pathology is a diverse field, and the organization of subspecialties within pathology vary between nations.

Anatomical pathology

This mastectomy specimen contains an infiltrating ductal carcinoma of the breast. A pathologist will use immunohistochemistry and fluorescent in-situ hybridization to detect markers which determine the optimal chemotherapy regimen for this patient.

Main article: Anatomical pathology

Histopathology: microscopic appearance of invasive ductal carcinoma of the breast. The slide is stained with Haematoxylin & Eosin.

Histopathology: microscopic appearance of invasive ductal carcinoma of the breast. The slide is stained with an antibody (immunohistochemistry) against the ongene Her2neu. The dark-brown reaction indicates that this tumor over-expresses this gene.

Cytopathology: microscopic appearance of a Pap test. The pink cell at the center with a large nucleus is abnormal, compatible with low-grade dysplasia.

Autopsy: a brain surrounded by pus (the yellow-greyish coat around the brain, under the dura lifted by the forceps), the result of bacterial meningitis.

Gross examination: appearance of the cut surface of a lung showing the honeycomb pattern of end-stage pulmonary fibrosis.

Gross examination: appearance of a colorectal polyp (the cauliflower-shaped tumor) attached to the colon mucosa (the horizontal line at the bottom).

Anatomical pathology (Commonwealth) or Anatomic pathology (U.S.) is a medical specialty that is concerned with the diagnosis of disease based on the macroscopic, microscopic, biochemical, immunologic and molecular examination of organs and tissues. Over the last century, surgical pathology has evolved tremendously: from historical examination of whole bodies (autopsy) to a more modernized practice, centered on the diagnosis and prognosis of cancer to guide treatment decision-making in oncology. Its modern founder was the Italian scientist Giovan Battista Morgagni from Forlì.

Anatomical pathology is one of two branches of pathology, the other being clinical pathology, the diagnosis of disease through the laboratory analysis of bodily fluids and/or tissues. Often, pathologists practice both anatomical and clinical pathology, a combination known as general pathology. Similar specialties exist in veterinary pathology.

Differences with clinical pathology

Anatomic pathology relates to the processing, examination, and diagnosis of surgical specimens by a physician trained in pathological diagnosis. Clinical pathology is the division that processes the test requests more familiar to the general public; such as blood cell counts, coagulation studies, urinalysis, blood glucose level determinations and throat cultures. Its subsections include chemistry, hematology, microbiology, immunology, urinalysis and blood bank.

Anatomical pathology is itself divided in subspecialties, the main ones being surgical pathology (breast, gynecological, endocrine, gastrointestinal, genitourinary, soft tissue, head and neck, dermatopathology), neuropathology, hematopathology cytopathology, and forensic pathology. To be licensed to practice pathology, one has to complete medical school and secure a license to practice medicine. An approved residency program and certification (in the U.S., the American Board of Pathology or the American Osteopathic Board of Pathology) is usually required to obtain employment or hospital privileges.

Skills and procedures

The procedures used in anatomic pathology include:

• Gross examination – the examination of diseased tissues with the naked eye. This is important especially for large tissue fragments, because the disease can often be visually identified. It is also at this step that the pathologist selects areas that will be processed for histopathology. The eye can sometimes be aided with a magnifying glass or a stereo microscope, especially when examining parasitic organisms.
• Histopathology – the microscopic examination of stained tissue sections using histological techniques. The standard stains are haematoxylin and eosin, but many others exist. The use of haematoxylin and eosin-stained slides to provide specific diagnoses based on morphology is considered to be the core skill of anatomic pathology. The science of staining tissues sections is called histochemistry.
• Immunohistochemistry – the use of antibodies to detect the presence, abundance, and localization of specific proteins. This technique is critical to distinguishing between disorders with similar morphology, as well as characterizing the molecular properties of certain cancers.
• In situ hybridization – Specific DNA and RNA molecules can be identified on sections using this technique. When the probe is labeled with fluorescent dye, the technique is called FISH.
• Cytopathology – the examination of loose cells spread and stained on glass slides using cytology techniques
• Electron microscopy – the examination of tissue with an electron microscope, which allows much greater magnification, enabling the visualization of organelles within the cells. Its use has been largely supplanted by immunohistochemistry, but it is still in common use for certain tasks, including the diagnosis of kidney disease and the identification of immotile cilia syndrome.
• Tissue cytogenetics – the visualization of chromosomes to identify genetic defects such as chromosomal translocation
• Flow immunophenotyping – the determination of the immunophenotype of cells using flow cytometry techniques. It is very useful to diagnose the different types of leukemia and lymphoma.

Subspecialties

Surgical pathology

Main article: Surgical pathology

Surgical pathology is the most significant and time-consuming area of practice for most anatomical pathologists. Surgical pathology involves the gross and microscopic examination of surgical specimens, as well as biopsies submitted by non-surgeons such as general internists, medical subspecialists, dermatologists, and interventional radiologists. Surgical pathology increasingly requires technologies and skills traditionally associated with clinical pathology such as molecular diagnostics.

Oral and maxillofacial pathology

Main article: Oral and maxillofacial pathology

In the United States, subspecialty-trained doctors of dentistry, rather than medical doctors, can be certified by a professional board to practice Oral and Maxillofacial Pathology.

Cytopathology

Main article: Cytopathology

Cytopathology is a sub-discipline of anatomical pathology concerned with the microscopic examination of whole, individual cells obtained from exfoliation or fine-needle aspirates. Cytopathologists are trained to perform fine-needle aspirates of superficially located organs, masses, or cysts and are often able to render an immediate diagnosis in the presence of the patient and consulting physician. In the case of screening tests such as the Papanicolaou smear, non-physician cytotechnologists are often employed to perform initial reviews, with only positive or uncertain cases examined by the pathologist. Cytopathology is a board-certifiable subspecialty in the U.S.

Molecular pathology

Main article: Molecular pathology

Molecular pathology is an emerging discipline within anatomical and clinical pathology that is focused on the use of nucleic acid-based techniques such as in-situ hybridization, reverse-transcriptase polymerase chain reaction, and nucleic acid microarrays for specialized studies of disease in tissues and cells. Molecular pathology shares some aspects of practice with both anatomic and clinical pathology, and is sometimes considered a "crossover" discipline.

Forensic pathology

Main article: Forensic pathology

Forensic pathologists receive specialized training in determining the cause of death and other legally relevant information from the bodies of persons who died suddenly with no known medical condition, those who die from non-natural causes, as well as those dying as a result of homicide, or other criminally suspicious deaths. A majority of the forensic pathologists cases are due to natural causes. Often, additional tests such as toxicology, histology, and genetic testing will be used to help the pathologist determine the cause of death. Forensic pathologists will often testify in courts regarding their findings in cases of homicide and suspicious death. They also play a large role in public health, such as investigating deaths in the workplace, deaths in custody, as well as sudden and unexpected deaths in children. Forensic pathologists often have special areas of interest within their practice, such as sudden death due to cardiac pathology, deaths due to drugs, or Sudden Infant Death (SIDS), and various others.

Training and certification

Australia

• (Also New Zealand, Hong Kong, Singapore, Malaysia, and Saudi Arabia)

Anatomical Pathology is one of the specialty training programs offered by the Royal College of Pathologists of Australasia (RCPA). The RCPA. To qualify as a Fellow of the RCPA in Anatomical Pathology, the candidate must complete a recognised undergraduate or postgraduate medical qualification and then complete a minimum of 2 years of clinical medical experience as a prerequisite to selection as a training registrar. The training program is a minimum of 5 years, served in at least two laboratories, and candidates must pass a Basic Pathological Sciences examination (usually in first year), the Part 1 examinations (not before 3rd year) and the Part 2 examinations (not before 5th year). Fellows may then continue into subspecialty training.

Canada

Anatomical Pathology (AP) is one of the specialist certificates granted by the Royal College of Physicians and Surgeons of Canada. Other certificates related to pathology include general pathology (GP), hematopathology, and neuropathology. Candidates for any of these must have completed four years of medical school and five years of residency training.

US

Anatomic Pathology (AP) is one of the two primary certifications offered by the American Board of Pathology (the other is Clinical Pathology (CP)) and one of three primary certifications offered by the American Osteopathic Board of Pathology. To be certified in anatomic pathology, the trainee must complete four years of medical school followed by three years of residency training. Many U.S. pathologists are certified in both AP and CP, which requires a total of four years of residency. After completing residency, many pathologists enroll in further years of fellowship training to gain expertise in a subspecialty of AP or CP. Pathologists' Assistants are highly trained medical professionals with specialized training in Anatomic and Forensic pathology. To become a Pathologists' Assistant one must enter and successfully complete a NAACLS accredited program and pass the ASCP Board of Certification Exam.

Practice settings

• Academic anatomical pathology is practiced at university medical centers by pathologists who are also university faculty. As such, they often have diverse responsibilities that may include training pathology residents, teaching medical students, conducting basic, clinical, or translational research, and/or performing administrative duties, all in addition to the practice of diagnostic anatomical pathology. Pathologists in academic settings often sub-specialize in a particular area of anatomic pathology and may serve as consultants to other pathologists regarding cases in their specific area of expertise.
• Group practice is the most traditional private practice model. In this arrangement, a group of senior pathologists will control a partnership that employs junior pathologists and contracts independently with hospitals to provide diagnostic services, as well as attracting referral business from local clinicians who practice in the outpatient setting. The group often owns a laboratory for histology and ancillary testing of tissue, and may hold contracts to run hospital-owned labs. Many pathologists who practice in this setting are trained and certified in both anatomical pathology and clinical pathology, which allows them to supervise blood banks, clinical chemistry laboratories, and medical microbiology laboratories as well.
• Large corporate providers of anatomical pathology services, such as AmeriPath in the United States. In this model, pathologists are employees, rather than independent partners. This model has been criticized for reducing physician independence, but defenders claim that the larger size of these practices allows for economies of scale and greater specialization, as well a sufficient volume to support more specialized testing methods.
• Multispecialty groups, composed of physicians from clinical specialties as well as radiology and pathology, are another practice model. In some case, these may be large groups controlled by an HMO or other large health care organization. In others, they are in essence clinician group practices that employ pathologists to provide diagnostic services for the group. These groups may own their own laboratories, or, in some cases may make controversial arrangements with "pod labs" that allow clinician groups to lease space, with the clinician groups receiving direct insurance payments for pathology services. Proposed changes to Medicare regulations may essentially eliminate these arrangements in the United States.

See also

• Pathology
• Digital pathology and Telepathology
• Clinical pathology
• Forensic pathology
• Laser capture microdissection
• List of pathologists
• History of pathology
• United States and Canadian Academy of Pathology

External links

• "Conversations with Pathologists", a website based on a book project by Sue Armstrong, sponsored by Genentech and The Pathological Society of Great Britain and Ireland
• PathReports.in: Make Anatomical pathology reporting paperless and save trees.
• PathMax, a collection of online Pathology resources
• MyBiopsy.org, information on more than 25 of the most common cancers and cancer-related conditions
• The Doctor's doctor, a very useful web site for patients and pathologists
• Pathologie Online, online Pathology resources (in German)
• Pathology Outlines, an online textbook of anatomic pathology
• College of American Pathologists
• American Board of Pathology
• CYTOPATHNET Online Resource Center for Cytopathology
• Histology Group of Victoria Incorporated
• Flickr group: Pathology and Lab Medicine: numerous photos illustrating the work of pathologists.
• Pathtalk.org: A multiple-author weblog by and for anatomic pathologists, with illustrative cases and specialty-related discussions.
• PathologyPics.com: An interactive histology database for the Practicing Anatomic Pathologist as well as Pathology Trainees.

Clinical pathology

Pathogenic organisms are grown from patient specimens in clinical microbiology labs, allowing selection of the correct antibiotics

Main article: Clinical pathology

Hematology: Blood smears on a glass slide, stained and ready to be examined under the microscope.

Bacteriology: Agar plate with bacterial colonies.

Bacteriology: microscopic image of a mixture of two types of bacteria stained with the Gram stain.

Clinical chemistry: an automated blood chemistry analyser.

Histopathology: microscopic image of invasive carcinoma with the overexpressed HER2/neu oncogene stained in brown.

Clinical pathology is a medical specialty that is concerned with the diagnosis of disease based on the laboratory analysis of bodily fluids, such as blood, urine, and tissue homogenates or extracts using the tools of chemistry, microbiology, hematology and molecular pathology. This specialty requires a medical residency.

Clinical pathology is a term used in the US, UK, Ireland, many Commonwealth countries, Portugal, Brazil, Italy, Japan, and Peru; countries using the equivalent in the home language of "laboratory medicine" include Austria, Germany, Romania, Poland and other Eastern European countries; other terms are "clinical analysis" (Spain) and "clinical/medical biology (France, Belgium, Netherlands, North and West Africa).

Licensing and subspecialities

The American Board of Pathology certifies clinical pathologists, and recognizes the following secondary specialties of clinical pathology:

• Chemical pathology, also called clinical chemistry
• Hematopathology
• Blood banking - Transfusion medicine
• Clinical microbiology
• Cytogenetics
• Molecular genetics pathology.

In some countries other sub specialities fall under certified Clinical Biologists responsibility:

• Reproductive biology including Assisted reproductive technology, Sperm bank and Semen analysis
• Immunopathology

Organization

Clinical pathologists are often medical doctors. In some countries in South-America, Europe, Africa or Asia, this specialty can be practiced by non-physicians, such as Ph.D or Pharm.D after a variable number of years of residency.

In United States of America

Clinical pathologists work in close collaboration with clinical scientists (clinical biochemists, clinical microbiologists, etc.), medical technologists, hospital administrators, and referring physicians to ensure the accuracy and optimal utilization of laboratory testing.

Clinical pathology is one of the two major divisions of pathology, the other being anatomical pathology. Often, pathologists practice both anatomical and clinical pathology, a combination sometimes known as general pathology. Similar specialties exist in veterinary pathology.

Clinical pathology is itself divided into subspecialties, the main ones being clinical chemistry, clinical hematology/blood banking, hematopathology and clinical microbiology and emerging subspecialties such as molecular diagnostics and proteomics. Many areas of clinical pathology overlap with anatomic pathology. Both can serve as medical directors of CLIA certified laboratories. Under the CLIA law, only the US Department of Health and Human Services approved Board Certified Ph.D., D Sc, or MD and DO can perform the duties of a Medical or Clinical Laboratory Director. This overlap includes immunoassays, flow cytometry, microbiology and cytogenetics and any assay done on tissue. Overlap between anatomic and clinical pathology is expanding to molecular diagnostics and proteomics as we move towards making the best use of new technologies for personalized medicine.

In Europe

Recently, EFLM has chosen the name of "Specialists in Laboratory Medicine" to define all European Clinical pathologists, regardless of their training (M.D, Ph.D or Pharm.D) .

In France, Clinical Pathology is called Medical Biology ("Biologie médicale") and is practiced by both M.D.s and Pharm.Ds. The residency lasts four years. Specialists in this discipline are called "Biologiste médical" which literally translates as Clinical Biologist rather than "Clinical pathologist".

Place of work

See Medical laboratory.

Tools

Microscopes, analyzers, strips, centrifugal machines...

Macroscopic examination

The visual examination of the taken liquid is a first main indication for the pathologist or the physician. The aspect of the liquid, in addition, conditions the analytical assumption of responsibility that follow and the validity of the end-results.

Microscopical examination

Microscopic analysis is an important activity of the pathologist and the laboratory assistant. They have many different colourings at their disposal (GRAM, MGG, Grocott, Ziehl-Neelsen, …). Immunofluorescence, cytochemistry, the immunocytochemistry and FISH are also used in order make a correct diagnosis.

See also: staining

This stage allows the pathologist to determine the character of the liquid: “normal”, tumoral, inflammatory even infectious. Indeed, microscopic examination can often determine the causal infectious agent, in general a bacterium, a mould, a yeast, or a parasite, more rarely a virus.

Physical Analyzers

See Automated analyser.

The analysers, by the association of robotics and spectrophotometry, allowed these last decades a better reproducibility of the results of proportionings, in particular in medical biochemistry and hematology.

The companies of in vitro diagnosis henceforth try to sell chains of automats, i.e. a system allowing the automatic transfer of the tubes towards the various types of automats of the same mark. These systems can include the computer-assisted management of a serum library.

These analysers must undergo daily controls to guarantee a result just possible, one speaks about quality control. These analysers must also undergo daily, weekly and monthly maintenances.

Cultures

A big part of the examinations of clinical pathology, primarily in medical microbiology, use culture media. Those allow, for example, the description of one or several infectious agents responsible of the clinical signs.

Values known as “normal” or reference values

Detailed article: Reference range.

See also

• Pathology
• Medical laboratory
• Anatomic pathology
• Medical technologist
• Veterinary pathology
• Clinical Biologist

External links

• American Association for Clinical Chemistry
• American Society for Clinical Pathology
• American Board of Pathology
• College of American Pathologists
• European Federation of Clinical Chemistry and Laboratory Medicine

Oral and maxillofacial pathology

In the United States, subspecialty-trained doctors of dentistry, rather than medical doctors, can be certified by a professional board to practice Oral and Maxillofacial Pathology.

Training of medical pathologists

Pathology in the United States

In the United States, pathologists are allopathic (MD, MBBS, MBChB, etc.) or osteopathic (DO) physicians, that have completed a four-year undergraduate program, four years of medical school training, and three to four years of postgraduate training in the form of a pathology residency. Training may be within two primary specialties, as recognized by the American Board of Pathology: Anatomic Pathology, and Clinical Pathology, each of which requires separate board certification. Many pathologists seek a broad-based training and become certified in both fields. These skills are complementary in many hospital-based private practice settings, since the day-to-day work of many clinical laboratories only requires the intermittent attention of a physician. Thus, pathologists are able to spend much of their time evaluating anatomic pathology cases, while remaining available to cover any special issues which might arise in the clinical laboratories. Pathologists may pursue specialised fellowship training within one or more sub-specialties of either anatomic or clinical pathology. Some of these sub-specialities permit additional board certification, while others do not.

Pathology in the United Kingdom

In the UK pathologists are medical doctors registered with the UK General Medical Council. They will have completed an undergraduate medical education which in most countries lasts 4-6 years. The training to become a pathologist is under the oversight of the Royal College of Pathologists. Typically a one year training attachment is followed by an aptitude test. This is followed by further specialist training in surgical pathology, cytopathology, and post mortem pathology. There are two examinations run by the Royal College of Pathologists termed Part 1 and Part 2. The Part 2 examination is designed to test competence to work as an independent practitioner in pathology and is typically taken after 5 years specialist training. All post-graduate medical training and education in the UK is overseen by the Postgraduate Medical Education and Training Board. It is possible to take a specialist part 2 examination in paediatric pathology or neuropathology. It is possible to take a special diploma in dermatopathology or cytopathology, recognising additional specialist training and expertise.

Veterinary pathology

Main article: Veterinary pathology

For the journal, see Veterinary Pathology (journal).

Mammary (breast) cancer on a dog.

Mast cell tumor on dog.

Veterinary pathologists are veterinarians who specialize in the diagnosis of diseases through the examination of animal tissue and body fluids. Like medical pathology, veterinary pathology is divided into two branches, anatomical pathology and clinical pathology. Other than the diagnosis of disease in food-producing animals, companion animals, zoo animals and wildlife, veterinary pathologists also have an important role in drug discovery and safety as well as scientific research.

Veterinary anatomical pathology

Anatomical pathology (Commonwealth) or Anatomic pathology (U.S.) is concerned with the diagnosis of disease based on the gross examination, microscopic, and molecular examination of organs, tissues, and whole bodies (necropsy). The Indian, European, Japanese and American Colleges of Veterinary Pathologists certify veterinary pathologists through a certifying exam. The American College of Veterinary Pathologist certification exam consists of four parts - gross pathology, microscopic pathology, veterinary pathology, and general pathology. Only the general pathology section is shared between the anatomic and clinical pathology examinations. Anatomic pathologists are employed in a number of different positions, including diagnostics, teaching, research, and the pharmaceutical industry.

Veterinary clinical pathology

Clinical pathology is concerned with the diagnosis of disease based on the laboratory analysis of bodily fluids such as blood, urine or cavitary effusions, or tissue aspirates using the tools of chemistry, microbiology, hematology and molecular pathology. The Indian, European, Japanese and American Colleges of Veterinary Pathologists certify veterinary clinical pathologists. The American College of Veterinary Pathologists certification exam consists of four parts: General Pathology (shared with the Anatomic Pathology certifying examination), Cytology and Surgical Pathology, Hematology, and Clinical Chemistry. The credential, DACVP (Diplomate, American College of Veterinary Pathologists) is usually followed by a parenthetical notation of "(Clinical Pathology)" to distinguish DACVP counterparts certified for anatomic pathology. The European credential is DipECVCP (Diplomate of the European College of Veterinary Clinical Pathology). Clinical pathologists are employed in diagnostic pathology, veterinary and medical teaching, research, and the pharmaceutical industry.

See also

• Veterinary Medicine

External links

• American College of Veterinary Pathologists
• European College of Veterinary Clinical Pathology
• European College of Veterinary Pathologists

Plant pathology

Main article: Phytopathology

For the journal, see Plant Pathology (journal).

"Phytopathology" redirects here. For the journal, see Phytopathology (journal).

"Plant disease" redirects here. For the journal, see Plant Disease (journal).

Life cycle of the black rot pathogen, Xanthomonas campestris pathovar campes

Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Not included are ectoparasites like insects, mites, vertebrate, or other pests that affect plant health by eating of plant tissues. Plant pathology also involves the study of pathogen identification, disease etiology, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, pathosystem genetics, and management of plant diseases.

Overview

See also: Morphological symptoms of plant diseases

Control of plant diseases is crucial to the reliable production of food, and it provides significant problems in agricultural use of land, water, fuel and other inputs. Plants in both natural and cultivated populations carry inherent disease resistance, but there are numerous examples of devastating plant disease impacts such as the Great Famine of Ireland and chestnut blight, as well as recurrent severe plant diseases like rice blast, soybean cyst nematode, and citrus canker. However, disease control is reasonably successful for most crops. Disease control is achieved by use of plants that have been bred for good resistance to many diseases, and by plant cultivation approaches such as crop rotation, use of pathogen-free seed, appropriate planting date and plant density, control of field moisture, and pesticide use. Across large regions and many crop species, it is estimated that diseases typically reduce plant yields by 10% every year in more developed settings, but yield loss to diseases often exceeds 20% in less developed settings. Continuing advances in the science of plant pathology are needed to improve disease control, and to keep up with changes in disease pressure caused by the ongoing evolution and movement of plant pathogens and by changes in agricultural practices. Plant diseases cause major economic losses for farmers worldwide. The Food and Agriculture Organization estimates indeed that pests and diseases are responsible for about 25% of crop loss. To solve this issue, new methods are needed to detect diseases and pests early, such as novel sensors that detect plant odours and spectroscopy and biophotonics that are able to diagnose plant health and metabolism.

Plant pathogens

Further information: lists of plant diseases

Powdery mildew, a biotrophic fungus

Fungi

Most phytopathogenic fungi belong to the Ascomycetes and the Basidiomycetes. The fungi reproduce both sexually and asexually via the production of spores and other structures. Spores may be spread long distances by air or water, or they may be soilborne. Many soil inhabiting fungi are capable of living saprotrophically, carrying out the part of their life cycle in the soil. These are facultative saprotrophs. Fungal diseases may be controlled through the use of fungicides and other agriculture practices. However, new races of fungi often evolve that are resistant to various fungicides. Biotrophic fungal pathogens colonize living plant tissue and obtain nutrients from living host cells. Necrotrophic fungal pathogens infect and kill host tissue and extract nutrients from the dead host cells. Significant fungal plant pathogens include:

Rice blast, caused by a necrotrophic fungus

Ascomycetes

• Fusarium spp. (Fusarium wilt disease)
• Thielaviopsis spp. (canker rot, black root rot, Thielaviopsis root rot)
• Verticillium spp.
• Magnaporthe grisea (rice blast)
• Sclerotinia sclerotiorum (cottony rot)

Basidiomycetes

• Ustilago spp. (smuts) smut of barley
• Rhizoctonia spp.
• Phakospora pachyrhizi (soybean rust)
• Puccinia spp. (severe rusts of cereals and grasses)
• Armillaria spp. (honey fungus species, virulent pathogens of trees)

Fungus-like organisms

Oomycetes

The oomycetes are fungus-like organisms. They include some of the most destructive plant pathogens including the genus Phytophthora, which includes the causal agents of potato late blight and sudden oak death. Particular species of oomycetes are responsible for root rot.

Despite not being closely related to the fungi, the oomycetes have developed similar infection strategies. Oomycetes are capable of using effector proteins to turn off a plant's defenses in its infection process. Plant pathologists commonly group them with fungal pathogens.

Significant oomycete plant pathogens include:

• Pythium spp.
• Phytophthora spp., including the potato blight of the Great Irish Famine (1845–1849)

Phytomyxea

Some slime molds in Phytomyxea cause important diseases, including club root in cabbage and its relatives and powdery scab in potatoes. These are caused by species of Plasmodiophora and Spongospora, respectively.

Bacteria

Crown gall disease caused by Agrobacterium

Most bacteria that are associated with plants are actually saprotrophic and do no harm to the plant itself. However, a small number, around 100 known species, are able to cause disease. Bacterial diseases are much more prevalent in subtropical and tropical regions of the world.

Most plant pathogenic bacteria are rod-shaped (bacilli). In order to be able to colonize the plant they have specific pathogenicity factors. Five main types of bacterial pathogenicity factors are known: uses of cell wall–degrading enzymes, toxins, effector proteins, phytohormones and exopolysaccharides.

Pathogens such as Erwinia species use cell wall–degrading enzymes to cause soft rot. Agrobacterium species change the level of auxins to cause tumours with phytohormones. Exopolysaccharides are produced by bacteria and block xylem vessels, often leading to the death of the plant.

Bacteria control the production of pathogenicity factors via quorum sensing.

Vitis vinifera with "Ca. Phytoplasma vitis" infection

Significant bacterial plant pathogens:

• Burkholderia
• Proteobacteria
  • Xanthomonas spp.
  • Pseudomonas spp.
• Pseudomonas syringae pv. tomato causes tomato plants to produce less fruit, and it "continues to adapt to the tomato by minimizing its recognition by the tomato immune system."

Phytoplasmas and spiroplasmas

Main article: phytoplasma

Phytoplasma and Spiroplasma are genera of bacteria that lack cell walls and are related to the mycoplasmas, which are human pathogens. Together they are referred to as the mollicutes. They also tend to have smaller genomes than most other bacteria. They are normally transmitted by sap-sucking insects, being transferred into the plant's phloem where it reproduces.

Tobacco mosaic virus

Viruses, viroids and virus-like organisms

Main article: Plant Virus

There are many types of plant virus, and some are even asymptomatic. Under normal circumstances, plant viruses cause only a loss of crop yield. Therefore, it is not economically viable to try to control them, the exception being when they infect perennial species, such as fruit trees.

Most plant viruses have small, single-stranded RNA genomes. However some plant viruses also have double stranded RNA or single or double stranded DNA genomes. These genomes may encode only three or four proteins: a replicase, a coat protein, a movement protein, in order to allow cell to cell movement through plasmodesmata, and sometimes a protein that allows transmission by a vector. Plant viruses can have several more proteins and employ many different molecular translation methods.

Plant viruses are generally transmitted from plant to plant by a vector, but mechanical and seed transmission also occur. Vector transmission is often by an insect (for example, aphids), but some fungi, nematodes, and protozoa have been shown to be viral vectors. In many cases, the insect and virus are specific for virus transmission such as the beet leafhopper that transmits the curly top virus causing disease in several crop plants. example ( Mosaic disease of tobacco : leaves get shrink and small, chlorophyll of leaves get destroyed . Bunchy top of banana : this disease is caused by virus and in this disease plants become dwarf and all the leaves get accumulated like a rose of the branch .)

Nematodes

Main article: Nematodes

Root-knot nematode galls

Nematodes are small, multicellular wormlike animals. Many live freely in the soil, but there are some species that parasitize plant roots. They are a problem in tropical and subtropical regions of the world, where they may infect crops. Potato cyst nematodes (Globodera pallida and G. rostochiensis) are widely distributed in Europe and North and South America and cause $300 million worth of damage in Europe every year. Root knot nematodes have quite a large host range, they parasitize plant root systems and thus directly affect the uptake of water and nutrients needed for normal plant growth and reproduction, whereas cyst nematodes tend to be able to infect only a few species. Nematodes are able to cause radical changes in root cells in order to facilitate their lifestyle.

Protozoa and algae

There are a few examples of plant diseases caused by protozoa (e.g., Phytomonas, a kinetoplastid). They are transmitted as durable zoospores that may be able to survive in a resting state in the soil for many years. Further, they can transmit plant viruses. When the motile zoospores come into contact with a root hair they produce a plasmodium which invades the roots.

Some colourless parasitic algae (e.g., Cephaleuros) also cause plant diseases.

Parasitic plants

Parasitic plants such as mistletoe and dodder are included in the study of phytopathology. Dodder, for example, is used as a conduit either for the transmission of viruses or virus-like agents from a host plant to a plant that is not typically a host or for an agent that is not graft-transmissible.

Common pathogenic infection methods

• Cell wall-degrading enzymes: These are used to break down the plant cell wall in order to release the nutrients inside.
• Toxins: These can be non-host-specific, which damage all plants, or host-specific, which cause damage only on a host plant.
• Effector proteins: These can be secreted into the extracellular environment or directly into the host cell, often via the Type three secretion system. Some effectors are known to suppress host defense processes. This can include: reducing the plants internal signaling mechanisms or reduction of phytochemicals production. Bacteria, fungus and oomycetes are known for this function.

Spores: Spores of phytopathogenic fungi can be a source of infection on host plants. Spores first adhere to the cuticular layer on leaves and stems of host plant. In order for this to happen the infectious spore must be transported from the pathogen source, this occurs via wind, water, and vectors such as insects and humans. When favourable conditions are present, the spore will produce a modified hyphae called a germ tube. This germ tube later forms a bulge called an appressorium, which forms melanized cell walls to build up tugour pressure. Once enough turgor pressure is accumulated the appressorium asserts pressure against the cuticular layer in the form of a hardened penetration peg. This process is also aided by the secretion of cell wall degrading enzymes from the appressorium. Once the penetration peg enters the host tissue it develops a specialized hyphae called a haustorium. Based on the pathogens life cycle, this haustorium can invade and feed neighbouring cells intracellularly or exist intercellulary within a host.

Physiological plant disorders

Main article: Physiological plant disorders

Abiotic disorders can be caused by natural processes such as drought, frost, snow and hail; flooding and poor drainage; nutrient deficiency; deposition of mineral salts such as sodium chloride and gypsum; windburn and breakage by storms; and wildfires. Similar disorders (usually classed as abiotic) can be caused by human intervention, resulting in soil compaction, pollution of air and soil, salinisation caused by irrigation and road salting, over-application of herbicides, clumsy handling (e.g. lawnmower damage to trees), and vandalism.

Orchid leaves with viral infections

Epidemiology

Main article: Plant disease epidemiology

Epidemiology: The study of factors affecting the outbreak and spread of infectious diseases.

Plant disease triangle

A disease tetrahedron (disease pyramid) best captures the elements involved with plant diseases. This pyramid uses the disease triangle as a foundation, consisting of elements such as: host, pathogen and environment. In addition to these three elements, humans and time add the remaining elements to create a disease tetrahedron.

History: Plant disease epidemics that are historically known based on tremendous losses:

- Irish potato late blight

- Dutch elm disease

- Chestnut blight in North America

Factors affecting epidemics:

Host: Resistance or susceptibility level, age and genetics.

Pathogen: Amount of inoculum, genetics, and type of reproduction

Disease resistance

Main article: Plant disease resistance

Plant disease resistance is the ability of a plant to prevent and terminate infections from plant pathogens.

Structures that help plants prevent disease are: cuticular layer, cell walls and stomata guard cells. These act as a barrier to prevent pathogens from entering the plant host.

Once diseases have over come these barriers, plant receptors initiate signalling pathways to create molecules to compete against the foreign molecules. These pathways are influenced and triggered by genes within the host plant and are susceptible to being manipulated by genetic breeding to create varieties of plants that are resistant to destructive pathogens.

Management

Further information: Pest control and Antagonism (phytopathology)

Quarantine

A diseased patch of vegetation or individual plants can be isolated from other, healthy growth. Specimens may be destroyed or relocated into a greenhouse for treatment or study. Another option is to avoid the introduction of harmful nonnative organisms by controlling all human traffic and activity (e.g., AQIS), although legislation and enforcement are crucial in order to ensure lasting effectiveness.

Cultural

Farming in some societies is kept on a small scale, tended by peoples whose culture includes farming traditions going back to ancient times. (An example of such traditions would be lifelong training in techniques of plot terracing, weather anticipation and response, fertilization, grafting, seed care, and dedicated gardening.) Plants that are intently monitored often benefit from not only active external protection but also a greater overall vigor. While primitive in the sense of being the most labor-intensive solution by far, where practical or necessary it is more than adequate.

Plant resistance

Sophisticated agricultural developments now allow growers to choose from among systematically cross-bred species to ensure the greatest hardiness in their crops, as suited for a particular region's pathological profile. Breeding practices have been perfected over centuries, but with the advent of genetic manipulation even finer control of a crop's immunity traits is possible. The engineering of food plants may be less rewarding, however, as higher output is frequently offset by popular suspicion and negative opinion about this "tampering" with nature.

Chemical

(See: pesticide application) Many natural and synthetic compounds can be employed to combat the above threats. This method works by directly eliminating disease-causing organisms or curbing their spread; however, it has been shown to have too broad an effect, typically, to be good for the local ecosystem. From an economic standpoint, all but the simplest natural additives may disqualify a product from "organic" status, potentially reducing the value of the yield.

Biological

Crop rotation may be an effective means to prevent a parasitic population from becoming well-established, as an organism affecting leaves would be starved when the leafy crop is replaced by a tuberous type, etc. Other means to undermine parasites without attacking them directly may exist.

Integrated

The use of two or more of these methods in combination offers a higher chance of effectiveness.

History

Further information: Timeline of plant pathology

Plant pathology has developed from antiquity, starting with Theophrastus, but scientific study began in the Early Modern period with the invention of the microscope, and developed in the 19th century.

See also

• American Phytopathological Society
• Australasian Plant Pathology Society
• Biological control with micro-organisms
• British Society for Plant Pathology
• Burl
• Common names of plant diseases
• Disease resistance in fruit and vegetables
• Forest pathology
• Gene-for-gene relationship
• Global Plant Clinic
• Glossary of phytopathology
• Herbivory
• Horsfall-Barratt scale
• Inducible plant defenses against herbivory
• List of phytopathology journals
• Microbial inoculant
• Mycology
• Phytopharmacology
• Plant defense against herbivory
• Plant disease forecasting
• QoI
• Strobilurins
• Stunt

External links

• International Society for Plant Pathology
• Australasian Plant Pathology Society
• American Phytopathological Society
• British Society for Plant Pathology
• Contributions toward a bibliography of peach yellows, 1887–1888 Digital copy of scientist Erwin Frink Smith's manuscript on peach yellows disease.
• Erwin Frink Smith Papers Index to papers of Smith (1854–1927) who was considered the "father of bacterial plant pathology" and worked for the United States Department of Agriculture for over 40 years.
• Plant Health Progress, Online journal of applied plant pathology
• Pacific Northwest Fungi, online mycology journal with papers on fungal plant pathogens
• Rothamsted Plant Pathology and Microbiology Department
• New Mexico State University Department of Entomology Plant Pathology and Weed Science
• Pathogen Host Interactions Database (PHI-base)
• Grape Virology
• Opportunity in Plant Pathology
• Facebook page for Asian Association of Societies for Plant Pathology

Pathology and Software

As in every field, specialized software exists: the idea being to maintain Electronic medical record or Electronic health record

See also

• Important publications in pathology

External links

• American Society for Investigative Pathology
• American Society of Cytopathology
• British Neuropathological Society
• Case Records of the Massachusetts General Hospital - Clinicopathological Conference
• College of American Pathologists
• Flickr group: Pathology and Lab Medicine: numerous photos illustrating the work of pathologists.
• HistoPathology Atlas
• Immunohistochemistry protocols and troubleshooting
• Mybiopsy.org
• Pathological Society of Great Britain and Ireland
• Royal College of Pathologists (UK)
• Royal College of Pathologists of Australasia (Australia & Oceania)
• Sullivan Nicolaides Pathology - Leading Australian Pathology Laboratory.
• United States and Canadian Academy of Pathology
• WebPath: The Internet Pathology Laboratory for Medical Education
• Pathtalk.org - A community weblog about pathology-related topics.
• What is a Pathologist? - a perspective from UK pathologist Fraser Charlton.
• Pathologypics - an interactive community-driven histology atlas