Experimental infections with Trichostrongylus colubriformis (Giles, 1892) Loos, 1905 in lambs: worm burden, growth rate and host resistance resulting from prolonged escalating infections

Abstract

Lambs were infected at daily intervals from 3 weeks of age with increasing doses of infective larvae of Trichostrongylus colubriformis, according to an exponential infection schedule designed to simulate the pattern of infection experienced by grazing lambs during the spring and early summer in Britain. The faecal egg counts and the worm burdens in the lambs followed a similar exponential trend for 12 weeks after initial infection.The T. colubriformis burdens in these lambs appeared to be cumulative during the first 12 weeks, after which the animals developed a resistance to further reinfection, which was very strong by 16 weeks after initial infection. However, even lambs which were refractory to new infection continued to harbour large numbers of adult worms, which caused clinical disease in most of the lambs.There was no evidence to suggest that either a turnover of the worm burden, inhibition of larval development or the sudden loss of established parasites played any major role in the regulation of the burdens of T. colubriformis in these young lambs.The removal of the established burden 16 weeks after initial infection in one lamb appeared to result in a partial loss of resistance to a challenge infection given 10 days later.

Worm burdens, acquired resistance and live weight gains in lambs during prolonged daily infections with Trichostrongylus colubriformis (Giles, 1892) Loos, 1905

“…However, the results of recent studies on T. colubriformis infections in lambs by Gibson & Parfitt (1972, 1973, in which lambs were infected at a constant rate of 2000 larvae per day, 5 days per week from 8 or 12 weeks of age, and by Chiejina & Sewell (1974), in which the lambs were exposed to an escalating rate of infection from 3 weeks of age, suggest that the immunological control of this parasite in young lambs differs from that in many other host^-parasite systems. In particular these young lambs were incapable of rejecting an established burden.…”

Caractéristiques des populations de Ostertagia sp. chez les Ovins naturellement infestés de la région de Moulay-Bouazza (Maroc).

“…La période sèche correspond donc à une population vieillissante, avec une densité vermineuse faible, une proportion de femelles importante, un nombre d'oeufs par femelle très inférieur à celui de la saison humide. Ces résultats sont en accord avec ceux d'autres auteurs (Michel, Lancaster, Hong, 1978 ;Chiejina et Sewell, 1974) lorsque l'on considère que le facteur essentiel est la densité parasitaire. Toutefois la proportion des femelles lisses évolue de façon différente pour Michel, Lancaster et Hong (1978) lors d'infestations expérimentales de bovins par O. ostertagia : les hautes densités sont associées à un pourcentage faible de femelles lisses.…”

“…Certains facteurs ont déjà été envisagés : le sex-ratio (Grundmann, Warnock, Wassom, 1976), le polymorphisme de l'appareil supra-vulvaire chez Haemonchus contortus (Lej ambre, Whitlock 1968;Lej ambre, Ractliffe 1976 ;Lejambre, Whitlock 1976 ;Cabaret 1979). Les études relatives au nombre d'oeufs présents dans les femelles de Nématodes sont rares et concernent Trichostrongylus colubriformis (Chiejina et Sewell, 1974) chez les Ovins, Strongylus sp. ou T. axei (Ogbourne, 1971) chez le cheval.…”

Responses of the humid zone ecotype of the Nigerian West African Dwarf sheep to mixed infections with Haemonchus contortus and Trichostrongylus colubriformis

“…Animals in group A were placed on a regimen of weekly escalating infections (Chiejina and Sewell 1974;Chiejina et al 2005) of 500, 1,000, 2,000 and 4,000 infective larvae (L 3 ) of a mixed culture of H. contortus (60%) and T. colubriformis (40%) per animal starting from day 0 (week 1) to day 21 (week 4) of the study. Animals in group B were used as uninfected control.…”