Monitoring of the Bagaza Virus Epidemic in Wild Bird Species in Spain, 2010

By the end of August 2010, high mortalities in red-legged partridges (Alectoris rufa) and pheasants (Phasianus colchicus) were detected in several hunting states in the province of Cadiz (southern Spain). Retrospective epidemiological studies revealed that the first clinical signs had been observed in late Julyearly August. The most common clinical signs were incoordination, disorientation and ataxia. The estimated mean morbidity rates were 37% in partridges and 11% in pheasants. The estimated mean mortality rates were 23% in partridges and 6% in pheasants. The estimated mean case-fatality rates were 38% and 8% in partridges and pheasants, respectively. A total of 19 clinically affected birds from 18 affected hunting states were analysed between August and November 2011. Histopathological analyses revealed encephalitis, myocarditis, leiomyositis, meningoencephalitis and neuritis as the most frequently observed lesions. Molecular analyses identified Bagaza virus (BAGV) as the causative agent of the epidemic. Further studies are needed to determine the source of introduction of the virus into Europe and to elucidate whether wild birds play a role in the epidemiology of BAGV. Surveillance in susceptible bird species, including partridges and pheasants, may be useful for the early detection of BAGV in an area.