Ascaridia galli eggs obtained from fresh excreta, worm uteri or worms cultured in artificial media differ in embryonation capacity and infectivity.

Ascaridia galli infection models use eggs isolated from chicken excreta, worm uteri and worms cultured in artificial media. The aim of this study was to compare the infectivity of A. galli eggs isolated from these sources under two infection regimens. A 3 × 2 factorial arrangement was employed to test the infectivity of A. galli eggs from the three sources and two modes of infection (single or trickle infection). One hundred and fifty-six Isa-Brown one day-old cockerels randomly assigned to the six treatment groups (n = 26) were orally infected with embryonated A. galli eggs obtained from the three A. galli egg sources (worm uteri, excreta or eggs shed in vitro) administered either as single dose of 300 eggs at one day-old or trickle infected with 3 doses of 100 eggs over the first week of life. Twenty-two negative control birds remained uninfected. Eggs obtained from cultured worms or excreta exhibited a higher embryonation capacity (P = 0.003) than eggs obtained from worm uteri. There were higher worm establishment (infectivity) rates from embryonated eggs originating from cultured worms and worm uteri compared with eggs obtained from fresh excreta (P < 0.0001). Trickle infection resulted in a significantly higher total worm burden (P = 0.002), establishment rate (P = 0.002) and excreta egg counts (EEC, P = 0.025) than single infection. Worm length was greater in birds infected with embryonated eggs from excreta than from uteri or cultured worms (P < 0.0001). However, mode of infection did not affect worm length (P = 0.719) and weight (P = 0.945). A strong significant positive linear correlation was observed between EECs and female worm counts at 12 weeks of post infection sampling (r = 0.75; P < 0.0001). Body weight of birds was negatively correlated with both worm burden (r = - 0.21; P < 0.01) and EEC (r = - 0.20; P < 0.05) at 12 weeks post infection. In conclusion, our results show that eggs shed by cultured worms or isolated from worm uteri had greater infective capacity than eggs harvested from excreta and that trickle rather than bolus infection resulted in higher worm establishment. These factors should be taken into account when considering artificial infection protocols for A. galli.

Establishment rate of sheep gastrointestinal nematodes in farmed red deer (Cervus elaphus).

To investigate the establishment of sheep gastrointestinal nematodes (GIN) in red deer, five red deer and five sheep aged 5-6 months were challenged with a mixed burden of sheep GIN at a rate of 327L3/kg bodyweight. The LSmean (SE) establishment rates (%) for Haemonchus contortus, Teladorsagia circumcincta, Cooperia curticei, Trichostrongylus spp. and Oesophagostomum+Chabertia spp. were 18.6 (0.03), 35.5 (0.04), 30.7 (0.04), 74.9 (0.05), 19.9 (0.06), respectively in sheep and 10.5 (0.03), 1.0 (0.04), 0.1 (0.04), 1.0 (0.05), 4.8 (0.06) respectively, in deer. Establishment rates were significantly different (p<0.05) between hosts for all genera. No Trichostrongylus colubriformis or Trichostrongylus vitrinus were seen in any deer but were present in all sheep. Trichostrongylus axei were seen in both hosts but there were relatively more which established in sheep than in deer (p<0.01). No Chabertia ovina were seen in any deer but were present in four of five sheep in low numbers. The only species of Oesophagostomum seen in either host was Oesophagostomum venulosum. These results suggest that the sheep GIN most likely to infect red deer grazing the same pastures are H. contortus, T. axei and O. venulosum.

The use of genetically marked infection cohorts to study changes in establishment rates during the time course of a repeated Ascaridia galli infection in chickens.

This study investigated the changes in establishment rates during the time course of a 6 week trickle infection of chickens with Ascaridia galli at two different dose levels, using a molecular marker. To differentiate early and late infection, two different egg cohorts (haplotype a and haplotype b, genetically identified using PCR-linked restriction fragment length polymorphism on the cox1 gene of the mitochondrial DNA) were used. Cohort-specific egg batches were produced by harvesting eggs from the uteri of female worms of the specific cohort. Fifty-six 8 week old Lohmann Brown Lite chickens were divided into seven groups and the infectivity of the egg batches was compared between two groups of chickens (P=0.6). The remaining chickens were allocated to four infection regimes and one control group. Group ab100 was trickle infected for 3 weeks with 100 eggs of haplotype a (twice weekly) followed by the same dose of eggs of haplotype b for another 3 weeks. Group ba100 was treated similarly but in the opposite order (haplotype b preceding a). A similar infection regime was applied for groups ab25 and ba25 but with a lower inoculation dose (25 eggs). All of the birds in these five groups (four infected and one control) were euthanased 2 weeks after the last inoculation. It was found that in the low-dose groups both the early and late infections established equally well, whereas in the high-dose groups the early infection was recovered in a significantly (P<0.001) higher proportion of chickens than the late infection, irrespective of genetic cohorts. Moreover, relatively higher proportions of the larvae from both the early and late infections were found in the posterior section of the small intestine. This result indicates the presence of dose-dependent resistance against reinfection and this resistance seems to act by reducing the establishment of late infection and by relocating the larvae from early infection.