The dynamics of the host–parasite relationship IV. The response of sheep to graded and to repeated infection with Haemonchus contortus

Abstract

In the present experiment the response of sheep to a single infection with Haemonchus contortus at graded doses, and their responses to two subsequent infections with 3000 infective larvae, were studied. The response of the sheep was investigated by estimation of faecal worm egg counts on alternate days throughout the course of the experiment and by following the development of the parasite by differential worm counts performed on animals slaughtered at crucial times.Initial infections were established with graded doses of 500–2700 infective larvae. The proportion of infective larvae which became established at each dose, development of the worm burden and fecundity per adult worm were similar for each dose.Following first challenge infection with 3000 infective larvae there were no effects which could be related to the previous level of infection. Whereas there was no difference in egg production per female worm, a small but consistent increase in the number of retarded larvae was observed in the previously infected animals (6% of the burden was in the 4th larval stage at day 56) compared with the previously uninfected control animals (2% in the 4th stage at day 56).Following a second challenge with 3000 infective larvae an increase in the number of retarded larvae was again observed, and, in addition, egg production per female worm was reduced compared with egg production in previously uninfected sheep given a similar challenge infection.The results of the initial infections suggest that control of the growth and development of H. contortus infection by factors independent of an active host response does not occur in worm burdens established from doses as high as 2700 infective larvae.

Drug-abbreviated infections of Trichostrongylus colubriformis and development of immunity in jirds (Meriones unguiculatus)

“…During primary infection, faecal egg counts were signi®cantly lower in trickleinfected group A than in single-infected group B. Similar results have been obtained in sheep infected with Nematodirus spathiger (Donald et al 1964) and Haemonchus contortus (Dineen et al 1965). The reduction in faecal egg production observed in the trickle-infected group was most likely due to the local immunity of the host, since protective immunity to T. colubriformis in sheep is characterised by a reduction in worm establishment and in the fecundity of female worms (Dobson et al 1990a, b;Douch et al 1996).…”

“…Under the in¯uence of an immune response the posterior distribution of T. colubriformis through the gastro-intestinal tract takes place at between 10 and 15 DPI in guinea pigs (Connan 1966) and at between 15 and 25 DPI in rabbits (Bezubik et al 1988). In immune sheep, T. colubriformis was relocated posteriorly from the predilection site of the parasite in the ®rst 3 m of the small intestine to the next 6 m of the same organ (Dineen et al 1965;Taylor and Kilpatrick 1980;McClure et al 1992) and to the caecum (Elliot 1981). At the early stage of infection, resistance may develop locally at the site of heaviest parasitism, which leads to migration towards the posterior part of the gastro-intestinal tract.…”

Immunity to Helminths: Resistance, Regulation, and Susceptibility to Gastrointestinal Nematodes

“…There was also a suggestion that a cellular compartment may be involved in protection, although exactly what cells were important and how they contributed were unclear (16). This idea was extended several decades later through a series of papers from Ogilvie and colleagues (22)(23)(24), again working with N. brasiliensis in the rat, together with studies from Dineen and colleagues (25)(26)(27) using the ovine parasite Trichostrongylus colobriformis, in this case a sheep parasite adapted to the guinea pig. Ogilvie and coworkers developed the idea in the 1960s and 1970s of protective immunity operating through antibody and cells-lymphocytes-and also identified [alongside other groups, e.g., Jarrett (28,29)] the highly elevated IgE levels that were associated with worm infection.…”

The effect of Haemonchus contortus infection on haematological parameters in young Merino sheep and its significance for productivity

“…(Figure 2). (Dineen, Donald, Wagland and Offner, 1965; Erythrocyte potassium concentrations in Silverman, Mansfield and Scott, 1970). After termination of doses of H. contortus normally is less than 3 infection, a 3-or 4-week period usually was weeks, and peak egg counts are usually sufficient to enable lambs to regain normal reached at 5 to 6 weeks after infection haematocrits ( Figure 2).…”