Appearance of type B avian pneumovirus in Great Britain

A survey in Britain in 1994/95 has shown that in all cases where avian pneumovirus (APV), was detected in turkeys of over 4 weeks of age, the virus was of type B. Oesophageal swabs were collected twice-weekly for up to 14 weeks in seven longitudinal surveys. RNA was extracted and analysed by reverse transcription-nested polymerase chain reaction designed to discriminate between type A and B APV. Virus of the same type as the vaccinal strain applied (type A or B) was detected from 7 and up to 35 days post-vaccination. Subsequently, type B virus only was detected when the poults were 32 to 67 days old, although in any one growing unit the period of detection was maximally one week. Episodes of increased mortality were usually associated with the detection of this type B virus a few days previously. In a single experiment inoculation of poults with virulent type A or B APV induced cross-protection although that protection was incomplete. Our results confirm that outbreaks of respiratory disease in turkeys in Britain during 1994 to 1995 were still associated with APV and that the virus was type B. In contrast, between 1985 and 1990 only APV antigenically similar to type A and B strains had been detected in Britain and in continental Europe respectively.