Pathological and molecular investigation of velogenic viscerotropic Newcastle disease outbreak in a vaccinated chicken flocks

Abstract

Newcastle disease virus (NDV) belongs to genus and family Paramyxoviridae. There are thirteen serotypes named APMV-I (Avian Paramyxovirus-I) to APMV-13 of which NDV has been designated as APMV-1. The disease has been reported worldwide affecting both domestic and wild avian species. Morbidity and mortality rates up to 100% have been reported in cases of unvaccinated flocks. Stringent vaccination schedule is practiced in endemic/disease prone areas in order to prevent the disease. Despite this, NDV outbreaks have been reported even in cases of vaccinated populations. In this study we describe detailed pathological and molecular investigation that were undertaken in an organized poultry farm from Bareilly region, Uttar Pradesh, India, involving layer flocks which succumbed to ND outbreak in spite of following strict vaccination protocol. The mortality rate ranged from 76.80 to 84.41% in different flocks with an average mortality of 79.50%. Necropsied birds had gross lesions suggestive of viscerotropic ND including petechial hemorrhages on the proventricular tips, intestinal lumen with necrotic areas covered with hemorrhages, hemorrhagic cecal tonsils, para-tracheal edema and mottling of spleen. The characteristic histopathological lesions were mainly seen in the blood vessels and lymphoid tissues. Vascular changes characterized by congestion, edema, and hemorrhage were found in majority of the organs. Lymphocytolysis in spleen and cecal tonsils was evident. Immunohistochemical studies revealed positive signals mostly in macrophage and lymphocytes. PCR assay was done to confirm the NDV genome, which revealed an amplicon size of 356 bp. The phylogenetic analysis revealed the resemblance of the present isolate (ADS01) with class II genotype NDV XIIIA. The isolate belonged to velogenic NDV as the Minimum Lethal Dose (MLD) and Mean Death Time (MDT) for the present isolate were 10 and 41 h, respectively. Thus this study clearly demonstrates that in spite of strict vaccination regime and biosecurity procedures, ND continues to be rampant. Hence it is important to effectively administer the present vaccine in addition to strains matching to the field isolates to provide longer and optimal protection against spreading of virus by means of reducing the extent of viral shedding.

Sequential Pathology of a Genotype XIII Newcastle Disease Virus from Bangladesh in Chickens on Experimental Infection

“…The NDV infected chickens showed hemorrhagic and necrotizing lesions in the gastrointestinal tract, particularly at gut-associated lymphoid tissues (GALT), starting at 3 dpi and progressed very rapidly, which is typical of velogenic viscerotropic NDV [ 7 , 21 , 29 , 30 , 31 ]. Hemorrhages and edema in the mucosa of the proventriculus and intestine were observed at 3 dpi followed by necrosis, fusion of mucosal folds and infiltration of mononuclear inflammatory cells later on.…”

“…Similar changes in the proventriculus and intestine of chickens infected with velogenic strains of NDV were reported with a slightly delayed onset (at 4 dpi) of the changes [ 22 , 29 , 32 ]. Extensive replication of the velogenic NDV has been described in the digestive tract [ 7 , 27 ]. Following primary viremia, NDV reaches different visceral organs including liver and kidneys through blood circulation causing secondary viremia [ 26 ].…”

“…Historically, NDV strains have been classified into 4 virulence groups: velogenic (high virulence, up to 100% mortality), mesogenic (moderate virulence with respiratory signs and lower level of mortality), lentogenic (low virulence with mild or inapparent respiratory signs) and avirulent (asymptomatic) based on the clinical disease they produced in infected chickens [ 3 ]. Velogenic strains are further divided into velogenic viscerotropic causing severe gastrointestinal and visceral hemorrhages, or neurotropic causing respiratory and neurologic clinical signs and encephalitis [ 3 , 4 , 5 , 6 , 7 ]. Although all NDV strains belong to a single serotype, there is large genetic diversity among NDV isolates.…”

Molecular characterization of full genome sequences of Newcastle disease viruses circulating among vaccinated chickens in Egypt during 2011–2013

“…Currently, ND is still a serious threat to the poultry industry, even though intensive vaccination programs have been applied. Recently, some studies have reported ND outbreaks among vaccinated commercial flocks, causing up to 76.8-84.4% mortality in India [19], 70-80% mortality in Indonesia [45], 60-70% mortality in Japan [40], and 5-50% mortality in Pakistan [29]. In Egypt, ND was first reported in 1948 [6], and it was classified as an endemic disease by the beginning of the 1960s [10].…”

Pathotyping and Genetic Characterization of a Highly Virulent Newcastle Disease Virus Strain Isolated from Recent Outbreak in District Okara, Pakistan

“…At present intensive poultry production is suffering from heavy economic losses due to many reasons including infectious diseases (Abbas et al, 2017;Naseem et al, 2018). Newcastle disease (ND) is a major viral infection of the poultry and other birds, responsible for high mortality (Mariappan et al, 2018). Outbreaks of Newcastle disease are continuously reported from across all the continents including Europe, Asia, Africa, South and Central America (Hines and Miller, 2012).…”