Experimental Ascaris suum infection in the pig: worm population kinetics following single inoculations with three doses of infective eggs

Abstract

To study population kinetics during primary Ascaris suum infections, 3 groups of 52 pigs each were inoculated with 100, 1000, or 10,000 infective eggs. In all groups, the majority of larvae was found in the liver on day 3 post inoculation (p.i.) and in the lungs on day 7 p.i. Liver white spots, caused by migrating larvae, were most numerous at day 7 p.i., whereafter they gradually healed, and only low numbers of granulation-tissue type white spots and lymphonodular white spots persisted at days 21-56 p.i. Independent of dose level, 47-58% of the inoculated eggs were recovered as larvae in the small intestine on day 10 p.i., but most larvae were eliminated at days 17-21 p.i. This elimination started earlier and removed a higher percentage of the worms with increasing inoculation dose, resulting in small strongly aggregated worm populations by day 28 p.i. (k of the negative binomial distribution was low: 0.2-0.4) without significant differences between groups. Thus, overdispersion, which is a characteristic of both porcine and human ascarosis, is found here under experimental conditions where aggregation factors like host behaviour, transmission rate, host status etc have been partly or totally controlled.

Assessing the zoonotic potential ofAscaris suumandTrichuris suis: looking to the future from an analysis of the past

“…Most larvae are expelled from pig (and probably also human) hosts at an early stage, when they are too small to be observed by the naked eye (Roepstorff et al, 1997;Nejsum et al, 2009). Macroscopic Ascaris worms in faeces are seen only in a minority of cases.…”

The development of a mouse model to explore resistance and susceptibility to early Ascaris suum infection

“…Recent comparative studies on larval migration in pigs and mice have led to the suggestion that the mouse is a suitable model for exploring susceptibility in the early phase of A. suum infection Slotved et al 1998) as the pattern of migration of the larvae is analogous. The recovery of larvae from mice has been shown to be higher when compared to other abnormal hosts such as rabbits, guinea-pigs and rats (Douvres and Tromba, 1971) and even pigs (Roepstorff et al 1997). Relative host size and parasite size contribute to this higher recovery.…”

Investigating the underlying mechanism of resistance to Ascaris infection

“…Furthermore, on return to the small intestine post migration, pre-adult larvae shift distally and are expelled between days 14-21 p.i. This pattern of self-cure expulsion was observed during experimental single infections and did not appear to be influenced by the size of the inoculation dose [28].…”

“…in pigs coincides with the healing of GT-WS [28]. Peréz et al [40] Increased liver pathology has been shown to be related to a reduction in lung larval numbers in repeated experimental inoculations [26,29,42] and in consistently naturally-exposed herds [26].…”