Rev 02/26/2024
Stomach Worm
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Haemonchus (Rudolphi, 1803) Cobb, 1898
Among the parasite species that infect domestic ruminants, male specimens of H. similis are easily distinguished, because they have shorter spicules than those of H. placei and H. contortus. Also, distances of the barbs to distal end of the spicules of H. similis are longer.
Until recently, the sheep parasites of the genus were called H. contortus and the cattle species H. placei. However, there is now increasing evidence that these are both H. contortus with race adaptations to parasitism of cattle and sheep (Talamini do Amaranti, 2011)
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Paleartic, Neartic, Oriental, Ethiopian, Neotropical, Australian.
Sheep are the primary host of H. contortus while cattle are the primary hosts of H. placei.
Parasitic gastroenteritis caused by Haemonchus spp. is a major cause of economic losses in the livestock industry.
It impairs weight gain and increases mortality in cattle and small ruminants, especially in tropical and subtropical areas. T
Many reports of H. contortus, particularly in cattle might actually represent misidentification of H. placei because of difficulties in species identification.
Haemonchus contortus is considered primarily a parasite of domestic sheep but also infects numerous other domestic and wild ruminants.
Haemonchus placei is primarily a parasite of domestic cattle but it has been reported from other domestic and wild ruminants
Haemonchus similis is a parasite of domestic cattle in South America, North America, and rarely in other widely scattered localities where it has been moved with the cattle trade
Six additional species of Haemonchus occur primarily in wild African ruminants (Lichtenfels and Pillit, 2000).
Haemonchus contortus cuts into host stomach tissues with a single dorsal tooth. It feeds on the released blood, fluids and cell contents.
The nematode secretes an anti-coagulant.
The eggs hatch after being expelled in the feces of the host.
The first larvae hatch 14-17 hours after being passed through the feces and then go through a lethargic state for 8-10 hours. This is the first molting period.
The first three juvenile stages of the organism are free-living. The second larval stage is reached 40 hours later and in 3-5 days the organism becomes infective.
When the infective stage is reached, the nematode moves onto the foliage of plants where it is ingested by grazing vertebrates.
Females are larger than males and have a higher metabolic rate.
Haemonchus cuts into host stomach tissues with a single dorsal tooth. It feeds on the released blood, fluids and cell contents.
De-worming lambs.
The prophylaxis of parasitic gastroenteritis relies heavily on anthelmintic treatments. However, their frequent use has led to the appearance of resistant parasite populations, which have been jeopardizing the livestock industry worldwide.
Proper identification of the various species, as well as knowledge regarding the epidemiology of parasitic gastroenteritis, is essential for the establishment of sustainable strategies of parasite control. Until recently, it was difficult to distinguish between H. placei and H. contortus, because of their similar morphology.
Chopra, A.K. 1982.Observations on non-specific phosphomonoesterases in relation to glycogen content in three nematodes in sheep. pp.191-193.Springar-Garwhal, eds. Journal of Comparative Physiology and Ecology.8:3.
Croll, N.A. 1976.The organization of Nematodes. Academic Press, London, New York, San Francisco.
Gibbons, L. 1986. SEM Guide to the morphology of Nematode parasites of vertebrates. CAB International, United Kingdom.P.191.
Lee, D.L. 1976.Physiology of Nematodes. MaCMillan Press. Columbia University.
Lichtenfels, J.R. and Pillit, P.A. 2000. Synlophe paterns of the Heamonchinae of ruminants (Nematoda: Trichostrongyloidea). J. Parasitol. 86:1093-1098.
Talamini do Amaranti, A.F. 2011. Why is it important to correctly identify Haemonchus species? Rev. Bras. Parasit. Vet. 20:263-268
Wertjuk, M. 1964. On the infective larvae of the gastointestinal nematodes of sheep, and their identification.pp.361-404. Journal of Parasitology.2:19.
Plus material from Rebecca E. Line, 1995.
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