The population dynamics of Hyostrongylus rubidus infections of pigs after infection with 2500 to 40 000 larvae

Abstract

The population dynamics of H. rubidus infections in 307 growing pigs have been studied, with single infection doses of larvae ranging from 2500 to 40 000. Five groups of growing pigs (1 to 5) were infected with 2500, 5000, 10 000, 20 000 and 40 000 infective larvae of H. rubidus respectively and the establishment, rate of worm loss, worm growth and fecundity studied. It was found that the numbers of larvae established were directly related to the initial size of larval dose administered, more becoming established with increasing dose. The infections were patent earlier and the loss of adult worms was more rapid the higher the rate of infection. By the 6th week of infection slightly less than 99 per cent of the worms in the two highest infection groups (4 and 5), about 96 per cent in group 3 and 94 per cent in groups 1 and 2 had been lost. At necropsy the female worm length and numbers of eggs contained in the uterus were not related to the size of the larval dose. More female than male worms were recovered at slaughter, the sex ratio widening as the infection progressed. The faecal egg count on the day of slaughter did not correlate with the worm burden at necropsy, nor did the absence of eggs in the faeces indicate the absence of egg-bearing worms in the gut.