Disease Reports Avian pneumoviruses: 1, 2, 3, 4 *5? The number of known avian pneumoviruses has doubled in the last three years. Initially known as turkey rhinotracheitis virus, the first avian pneumovirus (APV) to be discovered was in South Africa in the late 1970s, where it caused high losses from rhinotracheitis and secondary bacterial infection amongst turkeys. Subsequently pneumovirus infection was discovered in domestic fowl. During the next decade APVs were demonstrated in many countries in Europe. Initially it was believed, from serological analysis, that all isolates were of the same type. Gene sequencing showed this not to be the case. |
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The pneumoviruses could be assigned to one of two types, A and B, with large sequence differences in several genes, most notably a difference of 62% in the surface protein G gene.
APVs of types A and B were detected in more countries during the 1990s, including Asia and South America, although not in North America. Then, in 1997, a pneumovirus was confirmed in turkeys in the state of Colorado, USA, and
shortly afterwards in Minnesota. There had been difficulties detecting this virus using ELISAs developed using type A and B viruses. It transpired that the APV in the US differed extensively from these two types.
Indeed, it is likely that the *Colorado* virus will be type C; sequence data on the G protein, which defines type amongst both avian and mammalian pneumoviruses, is awaited. At about the same time that type C virus was being
discovered, researchers at Ploufragan, France, realized that two French APV isolates from the mid1980s were neither type A nor type B and not type C. These two French isolates may be candidates for yet another type of
APV. This is a fast moving field. Only last year further work at Ploufragan revealed an APV in Muscovy ducks. Preliminary analysis indicates that this isolate is more closely related to the type C virus than to the other types detected todate in Europe. Sequence data is eagerly awaited. It seems likely to me that more types of APV will be discovered. After all, there are nine types of avian paramyxovirus (APV is in the same virus family, Paramyxoviridae, as the paramyxoviruses) and 15 types of avian influenza virus. These viruses infect many species. Todate APVs have been demonstrated not only in turkeys and domestic fowl but also in pheasant, guinea fowl, duck and seabirds. There is plenty of scope for more discoveries about this increasingly interesting group of viruses. Dave Cavanagh |
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