NDVs are classified into velogenic, mesogenic and lentogenic
strains based on their pathogenicity (Beard and Hanson, 1984).
NDV's also differ in the severity and type of the anomalies they cause, and various pathotypes, based on pathogenicity in poultry and the patterns around the protease cleavage site of fusion protein (F), have been defined in poultry: viscerotropic velogenic, neurotropic velogenic, mesogenic, lentogenic
or respiratory, and asymptomatic (Alexander and Senne, 2008).
Pathogenicity indices such as the mean death time (MDT) in 9-10-day-old embryonated chicken eggs and the intracerebral pathogenicity index (ICPI) in 1-day-old chicks are often used to classify the virus isolates into velogenic, mesogenic, and lentogenic
Viruses of low pathogenicity or lentogenic
result in subclinical disease, whereas those of moderate pathogenicity or mesogenic generally causes clinical signs of disease, but typically result in nonlethal outcomes in chickens.
Both viscerotropic and neurotropic pathotypes cause high mortality rate accompanied by intestinal lesions or nervous signs; (c) mesogenic pathotype causes a low mortality rate and respiratory and nervous signs; (d) lentogenic
pathotype is the causative agent of clinically mild or unapparent infections of respiratory tract; and eventually (e) asymptomatic pathotype and its reflection on chicks are unapparent intestinal infections .
Study of the seroconversion of the thermostable live attenuated lentogenic
strain (local isolate) ND vaccine in layer and backyard birds.
The different expression of immune-related cytokine genes in response to velogenic and lentogenic
Newcastle disease viruses infection in chicken peripheral blood.
It belong to the family paramyxoviridae based on pathogenicity, the virus can be differentiated in to lentogenic
mesogenic, velogenic strain.
This includes viscerotropic velogenic, neurotropic velogenic, mesogenic, lentogenic
, and asymptomatic enteric forms.
ND is mostly caused by velogenic strains of NDV rather than mesogenic or lentogenic
strains which about 80-100% and 25% mortality, respectively, from disease [3-5].