Genetic resistance to helminths. The influence of breed and haemoglobin type on the response of sheep to primary infections withHaemonchus contortus

Abstract

SummaryThe possible existence of strain and breed differences in the response of sheep to primary infections withHaemonchus contortuswas examined by comparing the establishment and pathogenic effects of the parasite in Scottish Blackface and Finn Dorset sheep grouped according to haemoglobin type and infected with 7–10000 3rd-stage larvae. Homozygous haemoglobin A-type sheep of both breeds had lower worm burdens and faecal egg outputs, and suffered less severe clinical and pathophysiological disturbances than animals homozygous for haemoglobin B. In addition, Scottish Blackface sheep displayed similar advantages over Finn Dorsets with the same haemoglobin type and variations in the severity of the disease as judged by a variety of pathophysiological indices correlated closely with parasite numbers. It was therefore concluded that genetic resistance operated primarily against worm establishment and that, barring the unlikely involvement of non-specific physiological factors, this was controlled by the immune response elicited. The nature of this response is unknown, but appeared to operate only against the larval stages, since the size and metabolic activities of the surviving worms were similar in all animals. In a subsequent experiment, designed to examine the response of Scottish Blackface sheep to heavy infection (45000 larvae), there was no correlation between worm establishment and haemoglobin type. This was possibly due to a delayed immune response arising from exposure to excessive amounts of antigen.

The evolution of tissue migration by parasitic nematode larvae

“…Proportion of infective larvae reaching adulthood in experimental infections with orally infecting, gastrointestinal worms. Data are from the following species and studies: Parascaris equorum (Clayton & Duncan, 1977), Ascaris suitm (Andersen et al 1973;Galvin, 1968;Tromba, 1978), Gnathostoma doloresi (Wenceslao-Ollague et al 1988), G. spinigerum (Imai et al 1989), G. hispidium (Akahane & Mako, 1986), Oesophagostominn colwnbiaman (Dobson, 1974;Dash, 1981), O. vemtlosum (Dash, 1981), Ostertagia ostertagi (Herlich, 1959;Anderson & Michel, 1977), Trichostrongylus cohibriformis (Gregg & Dineen, 1978;Dineen & Windon, 1980), T. axei (Herlich, 1959;Goldberg, 1973), Nematodirus battus (Lumley & Lee, 1981), Heligmosomoides polygyrm (Dobson, Sitepu & Brindley, 1985;Robinson et al 1989;Maema, 1986(quoted by Anderson & May, 1991), Haemottchus contortus (Altaif & Dargie, 1978;Barger & Lejambre, 1988), Trichuris muris (Wakelin, 1974(Wakelin, , 1975 and Trichinella spiralis (Murrell, 1985). (Fig.…”

Variability in the susceptibility of the fish host, Poecilia reticulata, to infection with Gyrodactylus bullatarudis (Monogenea)

“…In conclusion, the results reported in this paper are of a very preliminary nature. The demonstration of inherited differences in fish susceptibility to infection bj' monogenean parasites is of general interest, although not surprising given the volume of recent work Ouppy susceptibility to Gyrodactylus infection 543 which attest to the significance of host genetics as a determinant of the course of helminth infection in mammalian hosts (Wassom, De Witt & Groundmann, 1974;Wakelin, 1975Wakelin, , 1978Altaif & Dargie, 1978;Tanner, 1978;Brindley & Dobson, 1981;Wassom, Brooks, Cypess & Donid, 1983). The guppy -Gyrodactylus system, however, is one of great potential for future studies in this area given the ease with which both organisms can be maintained, bred and manipulated within the laboratory.…”

Opportunities for genetic improvement of sheep and cattle in the hills and uplands

“…For example, goats are generally more susceptible to gastrointestinal parasites, e.g. Ostertagia circumcincta, than sheep under Scottish conditions (F. Jackson, personal communication); Blackface sheep are more resistant to Haemonchus contortus infection than FinnDorset sheep (Altaif and Dargie, 1978); and within cattle and sheep breeds there is considerable polygenic variation to nematode infection, with heritabilities of faecal egg count often being in excess of 0-50, and with variation between known major gene haplotypes, e.g. the MHC complex (Stear, Baldock, Brown, Gershwin, Hetzel, Miller, Nicholas, Rudder and Tierney, 1990).…”