Epidemiological study of newcastle disease virus in a live bird market in Morogoro Municipality, Tanzania
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Date
2024-05
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Sokoine University of Agriculture
Abstract
Village poultry plays a vital role in providing essential nutrition and
income for rural communities in Africa. In this context, poultry are
typically traded through live bird markets, which serve as central
trading hubs where producers connect with traders and consumers,
facilitating the flow of poultry products along the value chain. While
they serve as important trading hubs, these markets create an
environment where pathogens, like Newcastle disease virus (NDV)
and avian influenza, can easily emerge and spread. To date, half of
NDV class II genotypes have been reported in Africa (I, IV, V, VI, VII,
XI, XIII, XIV, XVII, XVIII, and XXI). The information on the circulating
NDV genotypes is still scarce despite the endemic nature of ND in
most countries on the African continent. Improving our
understanding of the epidemiology of NDV in live bird markets is
important for assessing the circulating genotypes, disease risks and
identifying factors that contribute to its persistence. A one-year
repeated cross-sectional study was employed to survey local
chickens at the Mawenzi live bird market in Morogoro municipality
for NDV presence, its temporal and spatial distribution, and risk
factors for NDV infection. The oro-cloacal and blood samples were
collected from 659 local chickens between June 2020 and May
2021. The sampling was conducted once every week and
questionnaires administered to the middlemen and traders at the
same time. The questionnaire targeted the information on the source
of the chickens, vaccination status, whether homes from where
chickens were bought keep mixed poultry species, transit time from
the villages to the market, time taken from collection of chickens
from the villages to arrival to the market. Newcastle disease virus
was detected by using reverse transcription real-time polymerase
chain reaction (RT-qPCR) and conventional PCR followed by
sequencing of PCR products. Twenty-three percent of 659 local
chickens sampled were positive for NDV based on PCR. Increased
odds of NDV infection were identified in chickens that had been in
the market for two or more days prior to sampling. Four significant spatiotemporal clusters of NDV-positive chickens encompassing 13
villages were detected between August and October 2020,
illustrating geographic hotspots of infection when NDV was most
prevalent. Furthermore, Sequencing and phylogenetic analysis
revealed the presence of sub-genotype VII.2. Similar to other live
bird markets, this market had enclosures with high densities of birds
of mixed species, limited biosecurity, and the presence of birds with
observable illness. Bird traders who source the chickens from the
villages, described long transit times in mixed enclosures with limited
sanitation practices without consideration of sick birds or vaccination
status prior to arriving at the live bird market. The detected sub-
genotype VII.2 has phylogenetic links to Zambian NDV strains
implying a Southeast dissemination of the virus, considering that it
was first detected in Mozambique. This study highlights the need to
invest in infrastructure and biosecurity for live bird markets as well
as training opportunities for increasing traders‘ knowledge on
hygiene, sanitation, animal welfare, and poultry biosecurity
measures. Moreover, the study underscores the need of active NDV
surveillance to determine the distribution of this NDV genotype in the
country and monitor its spread and contribution to the emergence of
new ND virus strains.
Description
Degree of Master of Philosophy
Keywords
Epidemiological, newcastle disease virus, live bird market, Morogoro Municipality, Tanzania