A Longitudinal Study of Epidemiological occurrence of Antidodies Against Newcastle Disease Affecting Village Indigenous Chickens in Boro and Jarso of Ethiopia
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Date
2012-04-20
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Addis Ababa University
Abstract
A longitudinal study to monitor epidemiological occurrence of antibodies against Newcastle
disease (ND) virus, potential risk factors for these occurrence and outbreaks in scavenging
village chickens was conducted in eight villages within two districts of Oromia region. A
total of 985 blood samples were collected from 800 individual birds in 400 household
chicken flocks during two sampling periods. None of the birds enrolled in the study was
vaccinated against ND. A haemagglutination inhibition (I-II) test was used to determine
antibody titres against ND virus. The bird-level ND seroprevalence pooled across all
samplings was 11.1 %, while accounting for each season 10.1 % and 13.8% of wet season and
dry season, respectively. The bird-level incidence rate for the period between the first and
the second sampling was 4.3%. The flock-level ND seroprevalence (at least one bird tested
had antibodies against ND virus) pooled across all samplings was 19.4%. The result indicated
that village chickens in Horo and Jarso were exposed to ND virus; there was a higher
seroprevalence of infection in Jarso than Horo despite insignificant association either in
flock-level or bird-level. Univariant risk factor analyses indicated that flock-level
seroprevalence of ND was significantly associated with different market-sheds, villages,
offering of rain feed, frequency of contact during wet season, mode of waste disposal, and
housing (p<0.05). None of the factors investigated was significantly associated with bird
level incidence. Management had significant association with disease outbreak. Thus, despite
occurring year round; in current study outbreaks during rainy season were mainly due to
management factors and severe at times of climatic stress and had been known to worsen the
outcome of the outbreak. The experimental study investigated the effect of concurrent
parasitic and viral diseases on the immune response; as well as differences in protection
between indigenous ecotype and improved breeds of chickens. This was done using the
antibody response towards ND vaccine virus in both chickens ecotypes/breed with and
without parasites. Multivariant analysis showed that there was a significant reduction in NDV
specific antibody production post vaccination in individuals with parasites compared to
antihelmintic treated chicken in both breeds. However, this finding confirmed that there was
a significant dramatic reduction in NDV specific antibody production post vaccination in
indigenous ecotype compared to improved breeds (p< 0.05).
Though breeds differ genetically in their immune responsiveness to the antigen, and being
protected following challenge; difference in their susceptibility to the virulent challenge virus
needs to be ruled out.
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Keywords
Incidence, Indigenous, ND, Outbreak, risk factor, seroprevalence