Coronaviruses in Avian Species – Review with Focus on Epidemiology and Diagnosis in Wild Birds

Milek, Justyna; Blicharz-Domanska, Katarzyna

Epidemiology. It is well known that IBV is ubiquitous in most parts of the world in regions with intensive poultry production, where it causes huge economic losses. IBV strains are responsible for diseases of the respiratory, urogenital, and digestive tracts of domestic fowl (Gallus gallus). However, there are many reports of IBV presence in other bird species, which indicate that the virus can cross the species barrier. Recently, IBVs homologous to vaccine H120 and field IBV strains were found in healthy domestic teal (Anas) and peafowl (Pavo cristatus), respectively. This indicates that the virus can replicate in these bird species without clinical signs (30) . Moreover, a virus similar to field IBV inoculated into specific-pathogen-free chickens caused nephritis and high mortality, in contrast to H120-like IBV which revealed itself to be apathogenic. These findings indicate the possible role of these birds as asymptomatic carriers of IBV and the possibility of virus transmission to susceptible chicken populations. Similar conclusions were drawn from Chinese and Brazilian studies which showed the presence of Mass-like IBV strains in wild peafowl and pigeons (16, 38) . The detection of virus closely related to the H120 IBV vaccine strain in faeces of free living ducks and whooper swans also suggested cross-species infection from a poultry population to synanthropic birds (22) . The presence of gammaCoV was also found in wild birds sampled in Poland. IBV-like strains were identified in Anseriformes, Charadriiformes, and Galliformes, and the detected gene fragments were highly similar to the most frequently detected lineages of IBV in this geographical region, i.e. Mass, 793/B and QX (13) . Similarly, IBV strains were identified in studied samples from wild birds of the Corvidae, Ardeidae and Anatidae families in Egypt, and some of them had S1 gene fragments highly homologous to the Ma5 vaccine strain. Such findings suggest the possibility for vaccine strains to spillover to wildlife which may serve as the asymptomatic host, enabling these strains to undergo some genetic changes. Such modified virus could then spillover in the reverse direction back to a poultry population, and the possibility of its higher pathogenicity could not be ruled out (36) . Recently, interesting results for the presence of both gamma-and deltacoronaviruses in quails were reported (39) (40) (41) . The identified gammaCoVs revealed a similarity to IBV strains unique to South America (40) . Furthermore, in some cases, both genera of the viruses were identified simultaneously (41) .