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An unusually long Rift valley fever inter-epizootic period in Zambia : Evidence for enzootic virus circulation and risk for disease outbreak

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Title: An unusually long Rift valley fever inter-epizootic period in Zambia : Evidence for enzootic virus circulation and risk for disease outbreak
Authors: Chambaro, Herman M. Browse this author
Hirose, Kazuyo Browse this author
Sasaki, Michihito Browse this author →KAKEN DB
Libanda, Brigadier Browse this author
Sinkala, Yona Browse this author
Fandamu, Paul Browse this author
Muleya, Walter Browse this author
Banda, Fredrick Browse this author
Chizimu, Joseph Browse this author
Squarre, David Browse this author
Shawa, Misheck Browse this author
Qiu, Yongjin Browse this author
Harima, Hayato Browse this author
Eshita, Yuki Browse this author
Simulundu, Edgar Browse this author
Sawa, Hirofumi Browse this author →KAKEN DB
Orba, Yasuko Browse this author →KAKEN DB
Issue Date: 2-Jun-2022
Publisher: PLOS
Journal Title: PLoS neglected tropical diseases
Volume: 16
Issue: 6
Start Page: e0010420
Publisher DOI: 10.1371/journal.pntd.0010420
Abstract: Rift valley fever (RVF) is a mosquito-borne disease of animals and humans. Although RVF outbreaks are usually reported at 5-15-year intervals in sub-Saharan Africa, Zambia has experienced an unusually long inter-epizootic/-epidemic period of more than three decades. However, serological evidence of RVF virus (RVFV) infection in domestic ruminants during this period underscores the need for comprehensive investigation of the mechanisms of virus perpetuation and disease emergence. Mosquitoes (n = 16,778) captured from eight of the ten provinces of Zambia between April 2014 and May 2019 were pooled (n = 961) and screened for RVFV genome by a pan-phlebo RT-PCR assay. Aedes mosquito pools (n = 85) were further screened by nested RT-PCR assay. Sera from sheep (n = 13), goats (n = 259) and wild ungulates (n = 285) were screened for RVFV antibodies by ELISA while genome detection in pooled sera (n = 276) from domestic (n = 248) and wild ungulates (n = 37) was performed by real-time RT-PCR assay. To examine the association between the long inter-epizootic period and climatic variables, we examined El Nino-Southern Oscillation indices, precipitation anomalies, and normalized difference vegetation index. We then derived RVF risk maps by exploring climatic variables that would favor emergence of primary RVFV vectors. While no RVFV genome could be detected in pooled mosquito and serum samples, seroprevalence was significantly high (OR = 8.13, 95% CI [4.63-14.25]) in wild ungulates (33.7%; 96/285) compared to domestic ruminants (5.6%; 16/272). Retrospective analysis of RVF epizootics in Zambia showed a positive correlation between anomalous precipitation (La Nina) and disease emergence. On risk mapping, whilst northern and eastern parts of the country were at high risk, domestic ruminant population density was low (< 21 animals/km(2)) in these areas compared to low risk areas (>21 animals/km(2)). Besides evidence of silent circulation of RVFV and the risk of disease emergence in some areas, wildlife may play a role in the maintenance of RVFV in Zambia.
Type: article
Appears in Collections:人獣共通感染症国際共同研究所 (International Institute for Zoonosis Control) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

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