Seroprevalence of major respiratory diseases of chickens in central Ethiopia in different chicken production systems.

In Ethiopia, most chicken disease outbreaks and mortalities are attributed to a respiratory syndrome known as "fengil" with variable clinical signs and undefined etiology. The main goal of this study was to determine whether key respiratory pathogens that could contribute to the fengil syndrome circulate in Ethiopia. Specifically, we aimed to determine the seroprevalence of infectious laryngotracheitis virus (ILTV), infectious bronchitis virus (IBV), Newcastle disease virus (NDV), Mycoplasma gallisepticum (Mg), and avian metapneumovirus (aMPV). A cross-sectional survey was conducted in 158 scavenging and 42 small and medium-scale intensive chicken holdings in the East, West and North Shewa Zones of central Ethiopia. Blood from 495 chickens was collected and serological tests were used to determine exposure to these pathogens. Vaccination against NDV was the only immunization practiced with a significantly higher vaccination rate in the intensive than the scavenging system. Serological evidence of a high level of exposure to all pathogens was detected, including the first report on the seroprevalence of aMPV, ILTV, and IBV in the East Shewa Zone. The chicken and holding seroprevalence rates were respectively 91% and 94% for IBV, 34% and 57% for aMPV, 47% and 66% for Mg, 27% and 51% for ILTV and in unvaccinated flocks, 39% and 53% for NDV. These pathogens could contribute to the fengil syndrome, commonly ascribed to NDV. The seroprevalence of aMPV and ILTV was higher in chickens under the scavenging system. Exposure to multiple pathogens was common, with more than 50% of chickens positive for three or more pathogens in the scavenging system. This was reflected in significant positive associations between seropositivity to ILTV, Mg, ILTV, and IBV. The role of these pathogens in the causation of respiratory disease in the field requires further investigation.