Colonization and organ invasion in chicks experimentally infected with Dermanyssus gallinae contaminated by Salmonella Enteritidis
Résumé
The poultry red mite, Dermanyssus gallinae is the most important and common ectoparasite of laying hens in Europe. This haematophagous mite has been experimentally demonstrated to be a vector of Salmonella Enteritidis by acquiring bacteria through the blood meal or cuticular contact. We have evaluated another route of infection by orally inoculating chicks with mites previously infected by S. Enteritidis. Two methods of infecting the mites were tested: mites contaminated by cuticular contact or during the blood meal. After the washing of mites with Paraformaldehyde, groups of 10 Salmonella contaminated mites were inoculated individually into 1-day-old chicks. The titre of the inoculum suspension was evaluated by crushing mites and further bacteriological count. It was 3x104 CFU and 2.7x106 CFU / chick respectively for cuticular contact and orally mediated contamination of mites. Each bird was found to be positive 12 days postinoculation. Salmonella colonized the intestinal tracts and invaded livers and spleens. Caecal content concentration reached a mean number of S. Enteritidis of 8.5x104 MPN Salmonella g-1. This experiment demonstrated the ability of mites to orally infect one-day-old chicks with subsequent colonization and multiplication of Salmonella. Consequently, mites infected by S. Enteritidis constitute potential reservoir hosts of this bacterium, allowing it to persist in the poultry house as a source of infection for newly introduced animals. If contaminated mites are found in poultry facilities, effective red mite control should be performed before new batches are introduced into the facility.
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