Real-time PCR data express the different distribution of avian Metapneumovirus and Mycoplasma synoviae in broiler chickens experimentally infected with one or both pathogens. Preliminary results.

Mycoplasma synoviae (MS) is an avian bacterial pathogen whose importance has grown considerably in the last years in many European countries (1). MS infection is related to respiratory disease, synovitis and EAA (2). As for many other pathogens, the severity of the respiratory disease can be enhanced by the co-infection with other viral or bacterial pathogens. Although the increased relevance of Metapneumovirus (aMPV) as a cause of respiratory disease in broilers in the field, less is known regarding its co-infection with Mycoplasma spp. in chickens and especially with MS. The aim of the present study was to experimentally reproduce the infection between aMPV and MS in commercial broiler chickens. The possible synergistic relationship between the two pathogens was evaluated through the analysis of the real-time PCR (aMPV and MS) results. For the experimental study, 160 1-day-old chicks were randomly divided in 4 groups (A, B, C and E) and housed in Montair® isolators. Group A (positive AMPV control) was inoculated via the oculo-nasal route with avian Metapneumovirus, group C received, via the same route, Mycoplasma synoviae and group B was infected with both pathogens (oculo-nasal administration). Group E acted as negative control. Group A and B received aMPV at day 15 of age and 3 days later (18-days old) group B and C were infected with MS. The experimental design was chosen in order to reproduce as much as possible the natural infection. At different times after the aMPV infection 5 animals/each group were randomly selected for post mortem evaluations, swabs were collected from respiratory and systemic tissues and submitted to real time aMPV PCR (3) and real time MS PCR (4). During the trial, which lasted until day 35 of age of the animals, serological and tissue specimens were collected for further investigations (data not shown). The infections were successfully reproduced and chickens showed clinical respiratory signs. There were no significant differences between the A (aMPV) and B (aMPV+MS) group in the total number of aMPV positive PCR, but the trend in A and B during the time was different, actually, in the B group the outcome of positive aMPV PCR was delayed and lengthen during the trial and the nasal turbinates were positive for the whole length of it. The B group (aMPV+MS) showed a higher number of positive PCR for MS, either in the respiratory tract (especially in nasal turbinates, trachea and lungs) or in systemic tissues, such as spleen, cloaca, kidney, and brain, expressing a wider dissemination of Mycoplasma synoviae in the animals. The preliminary data regarding the real time PCR results suggests the possible mutual/additive relationship between the two pathogens in broiler chickens, which seems to be related to a wider and a prolonged presence of MS and aMPV in the host.