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. 2022 Nov 1;116(11):1082-1090.
doi: 10.1093/trstmh/trac076.

An outbreak of Rift Valley fever among peri-urban dairy cattle in northern Tanzania

William A de Glanville  1   2 , Kathryn J Allan  1   3 , James M Nyarobi  1   4 , Kate M Thomas  5   6 , Felix Lankester  7   8 , Tito J Kibona  4 , John R Claxton  1 , Benjamin Brennan  9 , Ryan W Carter  1 , John A Crump  5   10   11   12 , Jo E B Halliday  1 , Georgia Ladbury  1 , Blandina T Mmbaga  6   10   12 , Furaha Mramba  13 , Obed M Nyasebwa  14 , Matthew P Rubach  10   11   15 , Melinda K Rostal  1   16 , Paul Sanka  13 , Emmanuel S Swai  14 , Agnieszka M Szemiel  9 , Brian J Willett  9 , Sarah Cleaveland  1
Affiliations

An outbreak of Rift Valley fever among peri-urban dairy cattle in northern Tanzania

William A de Glanville et al. Trans R Soc Trop Med Hyg. .

Abstract

Background: Human and animal cases of Rift Valley fever (RVF) are typically only reported during large outbreaks. The occurrence of RVF cases that go undetected by national surveillance systems in the period between these outbreaks is considered likely. The last reported cases of RVF in Tanzania occurred during a large outbreak in 2007-2008.

Methods: Samples collected between 2017 and 2019 from livestock suffering abortion across northern Tanzania were retrospectively tested for evidence of RVF virus infection using serology and reverse transcription quantitative polymerase chain reaction (RT-qPCR).

Results: A total of 14 RVF-associated cattle abortions were identified among dairy cattle in a peri-urban area surrounding the town of Moshi. RVF cases occurred from May to August 2018 and were considered to represent an undetected, small-scale RVF outbreak. Milk samples from 3 of 14 cases (21%) were found to be RT-qPCR positive. Genotyping revealed circulation of RVF viruses from two distinct lineages.

Conclusions: RVF outbreaks can occur more often in endemic settings than would be expected on the basis of detection by national surveillance. The occurrence of RVF cases among peri-urban dairy cattle and evidence for viral shedding in milk, also highlights potentially emerging risks for RVF associated with increasing urban and peri-urban livestock populations.

Keywords: Africa; Rift Valley fever, zoonoses; food microbiology; milk; population surveillance.

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Figures

Figure 1.
Figure 1.
RVFV RT-qPCR status of livestock abortions in northern Tanzania by week, November 2017–October 2019.
Figure 2.
Figure 2.
Location of wards included in the prospective cohort study of livestock abortion in northern Tanzania, 2017– 2019. The number of RVF cases identified out of total abortions investigated during the apparent outbreak period (16 May–11 August 2018) are shown.
Figure 3.
Figure 3.
Molecular phylogenetic analysis of partial sequence (802 bp) of segment S of RVFV strains obtained from Tanzanian cattle, northern Tanzania, 2018. The tree with the highest log likelihood (−2414.72) is shown. Sequences are labelled with GenBank accession number and designated strain names with country and year of origin shown in parentheses. Sequences from this study are highlighted in bold and labelled with GenBank accession numbers and unique animal individual identifiers. Clades of viral lineages as designated by Bird et al. are labelled by brackets. Sequence from the Smithburn vaccine strain is highlighted in bold italics.
See this image and copyright information in PMC

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