The regulation of populations ofOstertagia ostertagiin calves

Abstract

The course of the worm burdens of calves infected daily with larvae ofOstertagia ostertagiat five different rates was studied by making post-mortem worm counts on groups of calves killed after experiencing infection for different periods of time.The relationship between worm numbers and infection rates together with evidence that a turnover of worms occurred, led to the conclusion that burdens of adult worms were regulated primarily by a loss of worms at a rate proportional to the number present.Further, estimates based on the number of developing fourth-stage larvae indicated that the proportion of the larvae administered which became established decreased gradually as the experiment progressed.At very low infection rates, the rate of turnover of the worms was slower than at high infection rates but in all groups it remained constant through the 6 months duration of the experiment.The development of a small proportion of the larvae administered was arrested at the early fourth stage. At the highest infection rate used, the proportion of worms that became inhibited was somewhat greater.

Variation in size of Ostertagia circumcincta, a nematode parasite of sheep, induced experimentally and during preparation and preservation

“…a resistance to the establishment of worms. Since Ostertagia spp., acquired at a constant rate, are lost regularly and replaced by the incoming larvae (turnover), the worm burden of population B consisted mainly of worms accumulated over the final 30 days (Michel, 1970;Waller & Thomas, 1978). These worms had become established in a host whose previous experience had enabled it to develop a sufficiently strong resistance to further infection so as to become nearly refractory.…”

The dynamics of trickle infections with Heligmosomoides polygyrus in syngeneic strains of mice

“…Calves dosed daily with Ostertagia ostertagi and sheep with O. circumchzcta limit infection by a continual turnover of adult worms which, in combination with a gradual decrease in the proportion of new larvae that become established, results in the development of a dose-dependent equilibrium (Michel, 1969(Michel, , 1970Waller & Thomas, 1978). In contrast to this, sheep exposed daily or weekly to Haetnonchus contortus show a linear dose-dependent accumulation of worms, followed by a plateau during which time only adult worms can be recovered.…”

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

“…Dierent parasitic stages of the nematodes invading the intestinal mucosa act as a trigger for generation of the host immunological response (Anderson and Michel 1977). This host response plays an important role in determining the spatial population dynamics of the parasite (Michel 1970;Michel et al 1973). 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).…”