Abstract
Free-range rural chickens (FRCs) dominate the poultry industry in developing countries and chickens are exposed to multi-host infections, including Newcastle disease virus (NDV). The knowledge about the characteristics of NDV from FRCs is limited. This study investigated the persistence, spread and risks of NDV from FRCs. NDV isolates (n = 21) from unvaccinated FRCs in Tanzania were characterised by conventional intracerebral pathogenicity index (ICPI) and sequence analysis of a partial region of the deduced fusion protein encompassing the cleavage site. Results showed that five isolates were screened as lentogenic, nine as mesogenic and six as velogenic. Phylogenetic analysis of the 21 isolates compared to reference sequences revealed three, four, nine and five isolates in genotypes 1, 2, 3c and 4a, respectively. Genotype 3c also included published sequences of Tanzanian isolates obtained from exotic birds and chicken isolates from Uganda. The analysis showed that NDV were persistently present among chicken populations and possibly spread through live chicken markets or migration of wild birds. Differences in amino acid sequences detected around the cleavage site separated the isolates in six types. However, cleavage site pattern could not fully differentiate mesogenic isolates from velogenic isolates.
Highlights
Free-range rural chickens (FRCs) populations dominate the poultry industry in developing countries (Permin & Hansen 1998; Regmi 2001)
Free-range rural chickens (FRCs) dominate the poultry industry in developing countries and chickens are exposed to multi-host infections, including Newcastle disease virus (NDV)
Genotype 3c included published sequences of Tanzanian isolates obtained from exotic birds and chicken isolates from Uganda
Summary
Free-range rural chickens (FRCs) populations dominate the poultry industry in developing countries (Permin & Hansen 1998; Regmi 2001). The management of FRC allows interactions between chickens and ducks, pigeons, wild birds and other animals. This predisposes chickens to multi-host infections, including Newcastle disease virus (NDV). Chickens are the most susceptible species and infections of susceptible birds with virulent NDV isolates lead to severe disease and heavy stock losses (Alexander 2001). Newcastle disease (ND) is apparently responsible for major losses in FRC populations (Spradbrow 1993). It is of economical importance in commercial poultry production and trade worldwide (Alexander 2001). Whereas much has been reported on NDV contributing to outbreaks in commercial production, knowledge is limited about the NDV circulating and causing ND oubreaks in FRC populations
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