Parasitism

Ectoparasite- Psoroptes ovis (mange)in agoat

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• published: 26 Mar 2015
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LIKE VIDEO, SUBSCRIBE THE CHANNEL Psoroptes ovis For decades, conventional practice among acarologists has been to distinguish several species of Psoroptes among the mites that cause psoroptic mange worldwide in wild and domestic ungulates and rabbits, e.g. P. cuniculi in the ears of rabbits and various ungulates, P. equi on the bodies of English equids, P. ovis on the bodies of sheep and other ungulates (Bochkov, 2010). Distinctions between the species were based primarily on host and anatomical site infested and on morphology of the males. Recently, several workers have invalidated these criteria and used genetic analysis to show conspecificity of the traditionally different species. The earliest published description for Psoroptes mites is that for P. ovis, making this the proper designation for all such mange mites on all domestic hosts. Thus, the nomenclatural situation in Psoroptes becomes similar to that in Sarcoptes, with one morphologically and genotypically variable species occurring worldwide, albeit on a smaller spectrum of hosts and with a bit less stringent host specificity among the variants. Two other named Psoroptes spp. remain as tentatively valid taxa occurring only on wild mammal hosts (Bochkov, 2010). Psoroptic mange in both sheep and cattle seems to vary in its severity according to the variant of P. ovis present, with the most severe form being a reportable condition caused by an especially virulent genotype and known as ‘sheep scab’. This form has been eradicated from the USA, New Zealand, Canada, and Australia, although it still persists in many other parts of the world. Thus, particularly for further eradication efforts against psoroptic sheep mange, genotypic analysis of the involved mites may be an especially valuable tool (Falconi et al., 2002). Mature female Psoroptes are 550–750 µm long, with a striate cuticle and four long and 16 short dorsal somatic setae. A noticeable anterodorsal cuticular plate is present behind the mouthparts, and the midventral ovipore is an inverted U-shape. Males are about one-fourth smaller, and they have an additional, Chapter 2.9.8. — Mange OIE Terrestrial Manual 2013 5 larger posterodorsal cuticular plate, a pair of posteroventral adanal suckers, and two terminal posterior lobes, each equipped with four setae of varying lengths and structures. Nymphs and larvae are somewhat similar to adults but progressively smaller, and all Psoroptes are pearly white in colour. In all stages, the anterior two pairs of legs are thicker and more robust than the posterior pairs, which are thinner, and in the male, shortened in the fourth pair. Legs I and II terminate in pretarsal empodial suckers on long, segmented pedicels in both sexes, with similar structures on legs IV of the female and legs III of the males. The female’s third tarsus ends in two long, whip-like setae, and the male has a single short seta on tarsus IV, plus a long, thin seta accompanying the empodial sucker on tarsus III.