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BackgroundThe nematophagous fungus Pochonia chlamydosporia can degrade ascarid (e.g. Ascaridia galli) eggs in agar and soil in vitro. However, it has not been investigated how this translates to reduced infection levels in naturally exposed chickens. We thus tested the infectivity of soil artificially contaminated with A. galli (and a few Heterakis gallinarum) eggs and treated with P. chlamydosporia. Sterilised and non-sterilised soils were used to examine any influence of natural soil biota.MethodsUnembryonated eggs were mixed with sterilised (S)/non-sterilised (N) soil, either treated with the fungus (F) or left as untreated controls (C) and incubated (22 °C, 35 days) to allow eggs to embryonate and fungus to grow. Egg number in soil was estimated on days 0 and 35 post-incubation. Hens were exposed to the soil (SC/SF/NC/NF) four times over 12 days by mixing soil into the feed. On day 42 post-first-exposure (p.f.e.), the hens were euthanized and parasites were recovered. Serum A. galli IgY level and ascarid eggs per gram of faeces (EPG) were examined on days -1 and 36 (IgY) or 40 p.f.e. (EPG).ResultsEgg recovery in SF soil was substantially lower than in SC soil, but recovery was not significantly different between NF and NC soils. SF hens had a mean worm count of 76 whereas the other groups had means of 355–453. Early mature/mature A. galli were recovered from SF hens whereas hens in the other groups harboured mainly immature A. galli. Heterakis gallinarum counts were low overall, especially in SF. The SF post-exposure IgY response was significantly lower while EPG was significantly higher compared to the other groups.ConclusionsPochonia chlamydosporia was very effective in reducing ascarid egg numbers in sterilised soil and thus worm burdens in the exposed hens. However, reduced exposure of hens shifted A. galli populations toward a higher proportion of mature worms and resulted in a higher faecal egg excretion within the study period. This highlights a fundamental problem in ascarid control: if not all eggs in the farm environment are inactivated, the resulting low level infections may result in higher contamination levels with associated negative long-term consequences.

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Thick-shelled eggs of animal-parasitic ascarid nematodes can survive and remain infective in the environment for years. The present study evaluated a simple in vitro method and evaluation scheme to assess the relative effect of two species of soil microfungi, Pochonia chlamydosporia Biotype 10 and Purpureocillium lilacinum Strain 251 (Ascomycota: Hypocreales), on the development and survival of eggs of faecal origin of three ascarid species, Ascaridia galli (chicken roundworm), Toxocara canis (canine roundworm) and Ascaris suum (pig roundworm). Ascarid eggs were embryonated on water agar with or without a fungus, and the resulting viability of the eggs was evaluated on days 7, 14, 21, 28, 35 and 42 post exposure (pe) by observing eggs in situ. On days 7-42 pe, P. chlamydosporia had reduced the viability of A. galli and T. canis eggs by 64-86% and 26-67%. Corresponding reductions for P. lilacinum Strain 251 were only 15-29% and 4-28%. In contrast, A. suum eggs were extremely resistant to both fungi (2-4% reduction). The differences in results are likely due to different morphologies and chemistry of the egg shell of the three ascarid species. The current in vitro method and evaluation criteria allow for a simple, repeatable and non-invasive evaluation of the ovicidal effects of microfungi. This study demonstrates that P. chlamydosporia Biotype 10 may be utilised as a biocontrol agent to reduce A. galli and T. canis egg contamination of the environment.

Eggs of chicken ascarids (Ascaridia galli and Heterakis spp.) are believed to be hardy and survive for long periods. However, this has not been evaluated quantitatively and our study therefore aimed to determine development and recovery of chicken ascarid eggs after burying in pasture soil. Unembryonated eggs were mixed with soil, placed in sealed nylon bags and buried at 7 cm depth in pasture plots April (spring, n = 72) and December 2014 (winter, n = 72). Eight randomly selected bags per season were used to estimate pre-burial egg recovery [0 week post-burial (wpb)]. Eight random bags were removed at 5, 12, 23, 38, 52, 71 wpb per season and additionally at 104 wpb for spring burial. The content of each bag was analysed for numbers and development stages of eggs. Eggs buried in spring were fully embryonated within 12 wpb. In contrast, eggs buried in winter were developing between 23 and 38 wpb, so that all viable eggs seemed to be fully developed by 38 wpb. About 90% eggs disappeared within 23 wpb (spring) and 38 wpb (winter). Small proportions (2-3%) of seemingly viable and infective eggs were still recovered up to 2 years after deposition. In conclusion, most eggs buried in temperate pasture soil seem to experience a heavy mortality within a few months after the deposition, especially during warm periods. However, a small proportion of eggs may survive and remain infective for at least 2 years.