Newcastle disease virus in West Africa: new virulent strains identified in non-commercial farms

Abstract

Forty-four Newcastle disease virus (NDV) strains, obtained between 2002 and 2007 from different poultry species in Nigeria, Niger, Burkina Faso and Cameroon, were phylogenetically analysed based on partial F sequences. Lineage 2 viruses were genetically identical or similar to the locally used LaSota vaccine strain and were mostly detected in commercial farms. Lineage 1, 3 and 4 strains were only sporadically found, and their origin was less clear. Twenty-one strains from backyard farms and live bird markets formed three new clusters within lineage 5, tentatively named 5f, 5g and 5h. All of these strains were predicted to be virulent based on their F protein cleavage site sequence. Minimal genetic distances between new and previously established sublineages ranged from 9.4 to 15.9%, and minimal distances between the new sublineages were 11.5 to 17.3%. Their high genetic diversity and their presence in three different Sub-Saharan countries suggest that these new sublineages represent the NDV variants indigenous to West Africa.

Newcastle disease in Nigeria: epizootiology and current knowledge of circulating genotypes

“…Over the years, epizootiology of ND in Nigeria has been based mostly on conventional methods viz: serological [6,69,71,75,83,85,92] and virus isolation with biological characterization [5,28,40,48,62,70,74,96]. Recently, however, attempts were made by using molecular techniques at defining the genotypes and molecular epidemiology of the circulating virus in West and Central Africa including Nigeria [19,99,[101][102][103]108].…”

“…The introduction of seemingly healthy, but inadvertently infected new bird to an existing flock has been reported to result in an outbreak of ND and highly pathogenic avian influenza (NVRI unpublished data, 2006). Also, reports of isolation of virulent NDV from apparently healthy birds have been documented [18,22,28,62,99]. In all of these reports, free-range local chickens and ducks were involved.…”

“…1a) each has been described and are responsible for the current ND outbreaks being experienced across the sub-region. These genotypes and sub-genotypes are in circulation and have not been detected elsewhere outside the sub-region, making them indigenous [19,95,99,[101][102][103]108]. All NDV genotypes that have been reported to be circulating in Nigeria are shown in Fig.…”

“…The diagnoses are rarely confirmed using laboratory-based diagnostic methods (virus isolation and pathotyping) knowing well that NDV infection is not pathognomonic; this will present unreliable results as revealed by our laboratory data unpublished data). Enzootic status of ND can be upheld based on the continuous circulation of velogenic strains of different genotypes reported to be in circulation in both apparently healthy, wild bird and sick/dead birds in live bird markets, free-range and commercial poultry [19,98,99,102,108]. As of 30th May 2016, only 8 out of the 18 countries constituting the West Africa sub-region have sequences of NDV in the sequence repositories.…”

“…The none detection of this genotype could be as a result of poor surveillance system which exists in Nigeria as well as the sub-region as a whole. Initially, due to the genetic relatedness of the currently circulating genotypes indigenous to West Africa, earlier studies on NDV genotyping in West Africa, grouped the viruses to lineage 5 and 7 (genotype XIV and VII) [19,94,99]. The classification was later streamlined to genotypes XIV, XVII, and XVII with the existence of the unified nomenclature for the classification of NDV as proposed by Diel et al [25] and expanded by Snoeck et al [101].…”