Environmental tolerance of free-living stages of the poultry roundworm Ascaridia galli

- Ascaridia galli eggs develop to fully embryonated stage at a broader constant temperature range (15-35 °C) than previously reported.
- High relative humidity and aerobic conditions are necessary for development to occur.
- Exposure to a 1-2% dilution of the disinfectant chlorocresol for 4 h or longer was ovicidal in vitro.
- Conditions for development to L3 are likely met all year round in poultry barns in temperate climates.

The poultry roundworm Ascaridia galli is re-emerging in laying hens in many European countries due to the increase in non-caged housing. A series of in vitro experiments was carried out to study the in ovo larval development (embryonation) under different environmental conditions. Between 83% and 96% of the eggs developed to L3 within 7-21 days of incubation in water between 20 and 30 °C. Twenty-six percent completed development at 33 °C and 4% at 35 °C after 31 days. At 15 °C parasite egg development was low with 8% L3 after 56 days. In another trial larval development occurred, when parasite eggs were exposed to freeze-thaw cycle (30′ to 12 h) followed by incubation for 2 weeks at 25 °C. Alkaline and acidic conditions in the range of pH 2.5-12.5 had no adverse effect on development. Oxygen and relative humidity above 70% were necessary for development to occur. Thus, some A. galli eggs may complete development at conditions prevailing in poultry barns in temperate climate zones throughout the year. Although exposure to a 1% or 2% dilution of the broad-spectrum disinfectant chlorocresol for 4 h or longer was ovicidal, further work is required to improve the method of application in the field.