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

University essay from SLU/Dept. of Biomedical Sciences and Veterinary Public Health

Abstract: As the EU ban on conventional cages (1999 EU-directive) drew closer, most European countries moved towards alternative systems. Consequently, barn and free-range systems has become increasingly popular. Regardless of how welfare has improved, this major change in husbandry likely affects the parasite transportation. Accordingly, recent reports have unanimously shown that prevalence of round worm infection, in particular Ascaridia galli has increased dramatically. Although management practices have shown to be somehow efficient with regard to parasite control in caged system, at this time there is no effective way to prevent and eliminate the existing parasite in non-caged system. For better understanding the infection dynamics of A. galli a series of experiments was carried out to study the environmental factors (temperature, relative humidity, pH and oxygen) influencing the fate of A. galli eggs within the environment. In addition, two more experiments were run to evaluate the efficacy of thiabendazole and commercial broad spectrum disinfectant Chlorocresol (Interkokask). Survivability of the eggs with regard to the age of the parasite eggs was investigated as well. The results presented herein suggest that there is a direct relationship between temperature and the percentage of viability which was increased proportionally with the temperature up to 30°C. A narrow range of temperature between 30-35°C considered as threshold temperature range. Moreover, high percentage of survival after exposure to -5°C indicates that this species is likely cold adapted. Our result demonstrated that oxygen is an essential requirement for A. galli egg development. No optimal pH at which maximum development could occur was determined. In fact it was found that intact eggs are highly adaptable to both very acidic and baric environments. Our results indicated that relative humidity has a significant effect on viability of A. galli eggs and that these eggs need highly saturated atmosphere to complete the development. Chlorocresol was found to be capable of killing A. galli eggs when presented at level of 1%. The LDA showed the inhibitory activity of thiabendazole on larval development with LD50 value of 0.052μg/ml. The results indicate that eggs of A. galli are capable of remaining viable and surviving throughout the year. Moreover, upon introduction of infective eggs to aviaries, development likely happens during all seasons. Therefore, it is essential to adopt alternative control strategies in order to lower infection risk in organic production systems which are gaining popularity.

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