Hosts normally fight infections themselves via their immune system. Mammalian hosts react to infections with an innate response, often involving inflammation, followed by an adaptive response. Pharmaceuticals can also help fight infections.
The branch of medicine that focuses on infections and pathogens is infectious disease medicine.
In children the presence of cyanosis, rapid breathing, poor peripheral perfusion, or a petechial rash increases the risk of a serious infection by greater than 5 fold. Other important indicators include parental concern, clinical instinct, and temperature greater than 40 °C.
{|class="wikitable" |+Comparison of viral and bacterial infection |- ! Characteristic ! Viral infection ! Bacterial infection |- || Typical symptoms | In general, viral infections are systemic. This means they involve many different parts of the body or more than one body system at the same time; i.e. a runny nose, sinus congestion, cough, body aches etc. They can be local at times as in viral conjunctivitis or "pink eye" and herpes. Only a few viral infections are painful, like herpes. The pain of viral infections is often described as itchy or burning. | The classic symptoms of a bacterial infection are localized redness, heat, swelling and pain. One of the hallmarks of a bacterial infection is local pain, pain that is in a specific part of the body. For example, if a cut occurs and it is infected with bacteria, pain will occur at the site of the infection. Bacterial throat pain is often characterized by more pain on one side of the throat. An ear infection is more likely to be diagnosed as bacterial if the pain occurs in only one ear. A possibly infected cut that produces pus and milky-colored liquid is most likely infected. |- | Cause || Pathogenic viruses || Pathogenic bacteria |}
Wound colonization refers to nonreplicating microorganisms within the wound, while in infected wounds replicating organisms exist and tissue is injured. All multicellular organisms are colonized to some degree by extrinsic organisms, and the vast majority of these exist in either a mutualistic or commensal relationship with the host. An example of the former would be the anaerobic bacteria species which colonize the mammalian colon, and an example of the latter would be the various species of staphylococcus which exist on human skin. Neither of these colonizations would be considered infections. The difference between an infection and a colonization is often only a matter of circumstance. Organisms which are non-pathogenic can become pathogenic given specific conditions, and even the most virulent organism requires certain circumstances to cause a compromising infection. Some colonizing bacteria, such as Corynebacteria sp. and viridans streptococci, prevent the adhesion and colonization of pathogenic bacteria and thus have a symbiotic relationship with the host, preventing infection and speeding wound healing.
The variables involved in the outcome of a host becoming inoculated by a pathogen and the ultimate outcome include:
As an example, the staphylococcus species present on skin remain harmless on the skin, but, when present in a normally sterile space, such as in the capsule of a joint or the peritoneum, will multiply without resistance and create a huge burden on the host.
Persistent infections occur because the body is unable to clear the organism after the initial infection. Persistent infections are characterized by the continual presence of the infectious organism often as latent infection with occasional recurrent relapses of active infection. There are some viruses that can maintain a persistent infection by infecting different cells of the body. Some viruses once acquired never leave the body. A typical example is the herpes virus which tends to hide in nerves and become reactivated when specific circumstances arise. Persistent infections cause millions of deaths globally each year. Chronic infections by parasites account for a high morbidity and mortality in many underdeveloped countries.
===Primary and secondary infections=== Primary and secondary infection may either refer to succeeding infections or different stages of one and the same infection such as in acute herpes labialis infection. In the latter case, acute infection may also be used, as in acute HIV infection.
Indirect contact occurs when the organism is able to withstand the harsh environment outside the host for long periods of time and still remain infective when specific opportunity arises. Inanimate objects that are frequently contaminated include toys, furniture, door knobs, tissue wipes or personal care products from an infected individual. Consuming food products and fluid which have been contaminated by contact with an infecting organism is another case of disease transmission by indirect contact.
A common method of transmission in under developed countries is fecal-oral transmission. In such cases, sewage water is used to wash food or is consumed. This results in food poisoning. Common pathogens which are transmitted by the fecal-oral route include Vibrio cholerae, Giardia species, rotaviruses, Entameba histolytica, Escherichia coli, and tape worms. Most of these pathogens cause gastroenteritis.
All the above modes are examples of horizontal transmission because the infecting organism is transmitted from person to person in the same generation. There are also a variety of infections transmitted vertically - that is from mother to child during the birthing process or fetal development. Common disorders transmitted this way include AIDs, hepatitis, herpes, and cytomegalovirus
Methicillin-resistant staphylococcus aureus predominantly affects the skin and is considered to be a super bug as it is very resistant to antibiotics. This bacteria is known to generate a variety of toxic enzymes which can lead to vomiting, diarrhea, shock and sepsis. MRSA is quite common in hospitals and today there is a great cause for concern about its spread.
The most common persistent infections in North America include: HIV, hepatitis, herpes simplex, and, common to all mammals, endogenous retroviruses, which play a crucial role in placentation and therefore act as symbionts. Hepatitis B and C are usually acquired from the use of dirty needles, blood transfusions, or sexual intercourse. HIV has similar modes of transmission. Once hepatitis has been acquired, it becomes a chronic disorder. While some individuals with hepatitis B may remain asymptomatic, many will show active symptoms and remain infectious. In the long term, both hepatitis B and C can cause liver failure or liver cancer. In some cases, the signs and symptoms of liver damage may not appear for 20 years after the infection was initially acquired. Other persistent infections include: recurrent ear infection in children, tuberculosis, Lyme disease, Chlamydia, and malaria. The problem with recurrent infections is that the organism continues to damage the body which eventually results in symptoms. As the body weakens, the individual develops weight loss and extreme fatigue.
When infection attacks the body, anti-infective drugs can suppress the infection. Four types of anti-infective or drugs exist: antibacterial (antibiotic), antiviral, antitubercular, and antifungal. Depending on the severity and the type of infection, the antibiotic may be given by mouth, injection or may be applied topically. Severe infections of the brain are usually treated with intravenous antibiotics. Sometimes, multiple antibiotics are used to decrease the risk of resistance and increase efficacy. Antibiotics only work for bacteria and do not affect viruses. Antibiotics work by slowing down the multiplication of bacteria or killing the bacteria. The most common classes of antibiotics used in medicine include penicillin, cephalosporins, aminoglycosides, macrolides, quinolones and tetracyclines.
Techniques like hand washing, wearing gowns, and wearing face masks can help prevent infections from being passed from the surgeon to the patient or vice versa. Frequent hand washing remains the most important defense against the spread of unwanted organisms. Nutrition has to be improved and one has to make changes in life style- such as avoiding the use of illicit drugs, using a condom, and entering an exercise program. Cooking foods well and avoiding eating foods which have been left outside for a long time is also important. Do not take antibiotics for longer than needed. Long term use of antibiotics leads to resistance and chances of developing opportunistic infections like clostridium difficile colitis. Vaccination is another means of preventing infections by facilitating the development of immune resistance in vaccinated hosts.
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