Longitudinal study of avian influenza and newcastle disease in village poultry, Mali, 2009–2011
Newcastle disease (ND) is endemic in West Africa, which has also experienced outbreaks of highly pathogenic avian influenza (AI) H5N1 since 2006. We aimed to estimate the prevalence and incidence of AI and ND in village poultry in Mali and to identify associated risk factors. A longitudinal serologic study was conducted between November 2009 and February 2011 using ELISA commercial kits to detect antibodies. Sera (5963) were collected from 4890 different poultry. AI was rare, with a seroprevalence of 2.9% (95% confidence interval [CI] 2.3–3.5) and a seroincidence rate of 0.7 birds per 100 bird–months at risk (95% CI 0.4–1.0). AI antibodies were short lived, with a seroreversion rate of 25.4 birds per 100 bird–months at risk (95% CI 19.0–31.7). Risk factors for AI were limited: temporal variation occurred, but proximity to a water body was a risk factor only when large populations of wild waterbirds were present. ND was very common, with seroprevalence of 68.9% (95% CI 61.9–76.0) and a seroincidence rate of 15.9 birds per 100 bird–months at risk (95% CI 11.9–19.8). ND seroreversion rate was 6.2 birds per 100 bird–months at risk (95% CI 3.6–8.9). Regarding risk factors for ND, temporal variations occurred, and ND was more likely to be present in the Sudanian agro-ecological zone than in the Sahelian zone, in chickens than in other species, in flocks with higher numbers of Guinea fowl, and in flocks that had access to a waterbody. Control efforts would benefit from further increasing the ND vaccination coverage of village poultry, although this was already quite high (54.9%) for an African country. Seroconversion seemed satisfactory in vaccinated poultry, since 90.0% (95% CI 87.6–92.4) of these had ND antibodies. Further research should investigate the apparent lack of an epidemiologic role of domestic ducks for AI in Mali (unlike in Southeast Asia) and the potential role of Guinea fowl as a reservoir for ND.