Title: Newcastle disease: genotypic variation and gross pathology Author
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 30, 2013
Publication Date: N/A
Technical Abstract: There are currently 18 genotypes described for class II Newcastle disease viruses and one genotype for class I. While class I viruses are globally distributed in wild birds, the class II genotypes are found more selectively in different countries. For instance the NDV isolates in genotype V are most often found in North and Central America, and those from genotype VII are mostly isolated from Asia. The clinical disease of Newcastle disease (ND) can be confused with other diseases. Often the presentation of unvaccinated chickens sick with ND consists of a bird that is depressed, not eating or moving, with ruffled feathers, possibly with conjunctivitis. Unvaccinated birds may also be found dead with no obvious signs of disease. Well-vaccinated poultry if challenged with a virulent NDV will become infected, but may show no signs of diseases except a drop in egg production that starts around one week after the challenge. Thirty days after challenge these birds may lay misshapen eggs that have shells lighter than normal. Chickens that are not well vaccinated often present with various neurological signs that don’t necessarily appear to be related to a respiratory disease, and may even look like Marek’s Disease. Gross lesions from experimentally vaccinated birds can vary depending on the genotype and sometimes the individual isolate. However, lesions such as enlarged and mottled spleens, and edema, hemorrhage and necrosis of the cecal tonsil are often found with virulent strains. Gross lesions from outbreaks (specifically the 2002 outbreak in CA) are markedly more severe, perhaps due to the partial protection from vaccination, the addition of secondary bacterial infections, and even the possibility of having multiple days of exposure (rather than one day of challenge in experimental conditions).