Prevalence of the poultry red mite, Dermanyssus gallinae, in different types of production systems for egg layers in Sweden.

This study was undertaken between May and December 1994 to investigate the prevalence of hematophagous mites in Sweden. A particular aim was to establish the relationship between occurrence of mites and certain types of production systems for egg layers. Initially a postal questionnaire study was performed. Some months later this was followed up by inspections, sampling, and interviews on farms. The only mite species found was the red poultry mite, Dermanyssus gallinae. Although this species was found to be present in cage batteries, deep-litter systems, and backyard flocks, it was less prevalent among birds housed in cages. About 4% of the cage systems were found to be affected both according to the results of the postal inquiry and from the field study. However, discrepancies in prevalence were found when comparing the results obtained with these two investigations regarding alternative, deep-litter systems and backyard flocks. According to the inquiry, 21% of the deep-litter flocks were afflicted whereas 33% were found to be afflicted in the field investigation. Among the backyard flocks, 19% were afflicted whereas as many as 67% of the flocks were found to be afflicted upon inspection. These discrepancies were probably due to the fact that the situation had actually changed in some farms during the study period, but possibly also to inherent methodological errors. Farmers were also interviewed with focus on methods of husbandry and control strategies. Most farmers answered that they were combatting the mites by cleaning the empty houses and using chemicals such as organophosphorous compounds, carbamates, and synthetic pyrethroids. In several instances the problems were still not solved despite these curative or preventive measures. A control program for D. gallinae is suggested by regular screening and certification of the ectoparasite status of the birds before their transfer to production sites.