Title: Newcastle disease Authors
|Koch, Guus -|
Submitted to: Diseases of Poultry
Publication Type: Book / Chapter
Publication Acceptance Date: November 1, 2012
Publication Date: N/A
Interpretive Summary: Newcastle disease is caused by virulent Newcastle disease virus (NDV) strains infecting avian species and can be found worldwide. Newcastle disease viruses are paramyxoviruses that are single stranded, negative sense, enveloped RNA viruses in the genus Avulavirus. In spite of vaccination, globally the disease continues to affect the poultry industry causing outbreaks and large economic losses. Even in countries like the United States where virulent NDV isolates are only found in wild birds, such as cormorants and pigeons, much money is spent on vaccinating to prevent disease and testing to make sure the disease is not present. The current vaccines when given correctly prevent disease signs and death from disease but the virus is still able to infect vaccinated animals and replicate. Viruses that replicate are then shed into the environment in feces and saliva and are able to infect other birds. The NDV isolates found in the environment and found in birds are changing slowly over time. The viruses found in the United States now are very different from those found in the 1940s or 1950s. When the genes of NDV found around the world are compared using computer software, the viruses group depending on how similar they are to each other. Some groups are found depending on the type of bird the viruses are found in. For instance the pigeon isolates will group together and the cormorant will fall into a different group. Many of the tests used to identify a virus are based on the matching of the genetic material to the solutions used in the test. If the viruses change too much it is possible the test won’t work and will have to be modified to be able to identify NDV isolates. Identification of virulent NDV is reportable to the State Veterinarian and to The World Organization for Animal Health and could affect the ability of a country to trade poultry and poultry products.
Technical Abstract: The focus of this chapter, are viruses of avian paramyxovirus serotype-1 (APMV-1). All isolates of APMV-1 are of one serotype and are referred to as Newcastle disease viruses (NDV). Newcastle disease (ND) is caused only by infections with virulent isolates of APMV-1 (virulent NDV or vNDV). Virulent NDV have an intracerebral pathogenicity index (ICPI) in day-old chickens of 0.7 or greater; or multiple basic amino acids have been demonstrated in the virus (either directly or by deduction) at the C-terminus of the F2 protein and a phenylalanine at residue 117. While infections with NDV of low virulence (loNDV) do not cause ND, they can still lead to clinical respiratory disease when other infections or suboptimal environmental conditions are present. Sometimes APMV-1 is used when discussing loNDV and NDV is used when referring to the virulent forms of NDV. However, to avoid confusion in this chapter vNDV will be used to denote strains that cause ND. Of the eleven defined APMV serotypes, serotype APMV-1 serotype is the most important APMV serotype for poultry. When comparing the number of countries reporting outbreaks of 71 important animal diseases from 2006-2009, ND was the 2nd most prevalent disease reported in 56 of the 167 member countries of the World Organization for Animal Health (OIE), and this number is likely an under reporting of the countries with the disease. Because clinical signs of infected birds vary depending on the host species, the virulence and dose of the infecting virus, and the immune status and age of the host, it can be especially difficult to recognize the disease. Clinical signs may range from 100% mortality among non-vaccinated chickens to a drop in egg production among seemingly healthy, well-vaccinated layers.