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Newcastle Outbreak in Sweden Questions Justification for Susceptible Poultry Populations


In late October, a Newcastle disease outbreak occurred among a flock of 5,000 laying hens in Vastra Gotaland County, Sweden.  The specific case involved a sharp drop in production but no appreciable increase in mortality.  Avulavirus Type-1 (formally avian paramyxovirus-1) was isolated from the flock.  The U.K. Department of Environment Food and Rural Affairs evaluated the case and reported that pigeons were the most likely source of virus given mortality in these free-living birds in the affected county at the end of September.


The incident is reminiscent of the outbreak of clinical Newcastle disease in commercial layers in the U.K. during 1983.  The causal agent was a pigeon paramyxovirus-1 introduced into a susceptible hen population. The U.K. had previously abandoned routine Newcastle disease vaccination based on the presumption that the virus had been eliminated from the Nation.  Pigeon paramyxovirus-1 was introduced to the U.K. by racing pigeons and the vehicle of infection was contaminated feed.  A more recent case of avulavirus type-1 (paramyxovirus-1) in a mixed flock of partridges and pheasants was diagnosed in the U.K. in 2006.


Pigeon paramyxovirus-1 was introduced to the U.S. in the mid 1980’s with isolation of the virus in northeastern states and eventually extending to Texas.  The disease was suppressed and presumably eradicated by extensive vaccination of racing pigeons using inactivated pigeon paramyxovirus-1 specific emulsions.  It is significant that there was no documented case of infection of any commercial flock with pigeon paramyxovirus-1 presumably due to an acceptable level of immunity stimulated by routine Newcastle disease vaccines including Hitchner B1 and LaSota strains with or without boosting using oil emulsion vaccines.


It is questioned whether national policy should be based on attempting to exclude introduction of virus given that free living birds and migratory waterfowl can carry and disseminate viruses including avulavirus which can induce Newcastle disease-like effects in susceptible flocks.