Transmission routes and vector potential of the poultry red mite Dermanyssus gallinae

Sammanfattning: The poultry red mite, Dermanyssus gallinae is a blood-feeding ectoparasite causing irritation, stress, and in severe infection, anemia and death of its avian host. This parasite not only causes welfare problems in poultry but also financial losses in egg production worldwide. The aims of this thesis were to elucidate the transmission routes of D. gallinae to poultry facilities and to investigate the potential of the parasite to be a vector of Erysipelothrix rhusiopathiae, the agent causing poultry erysipelas. Investigation of the 5.8S ribosomal RNA (rRNA) gene and the two internal transcribed spacers (ITS) of D. gallinae from poultry premises and wild birds in Sweden indicates that wild birds are of minor importance in the infection of D. gallinae to poultry farms. Instead there are indications that mites from wild birds in Sweden could be separate species. The transmission of D. gallinae to poultry is therefore most likely to follow another path. Population genetic analysis using the mitochondrial cytochrome oxidase c subunit I (COI) gene as a molecular marker revealed that most farms had a homogenous population of D. gallinae. This investigation included farms from Norway and Sweden and no common haplotype was found across countries. This implies that transmission is connected to the egg-producing system and most likely one or a few common sources of infection are present. However, the exact nature of these sources could not be identified. The bacterium E. rhusiopathiae could be isolated from D. gallinae collected from a farm during an outbreak of poultry erysipelas, and mites and hens were infected by the same bacterial strain. This means that D. gallinae is a potent reservoir of this agent. However, under experimental conditions uptake and transmission could not be demonstrated and therefore the vector competence of D. gallinae with regard to the erysipelas agent is still uncertain. The mite should, however, not be excluded as a potential vector possibly spreading the infection within and between farms.