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Zoonotic Rift Valley fever virus prevalence and risk factors in the Lake Zone of Tanzania

Leah H. Streb1*, Brian H. Bird2, Happy R. Mkali3, George Makingi4, David J. Wolking2, Walter Magesa4, Grace Mwangoka3, Jennifer K. Lane2, Rudovick Kazwala4, Woutrina Smith2 and Jonna A. Mazet2
  • 1 School of Veterinary Medicine, University of California, Davis, United States
  • 2 One Health Institute, School of Veterinary Medicine, University of California, Davis, United States
  • 3 Ifakara Health Institute (COSTECH), Tanzania
  • 4 Sokoine University of Agriculture, Tanzania

Background: Rift Valley fever (RVF) is a mosquito-borne zoonotic threat to both humans and livestock globally caused by Rift Valley fever virus (RVFV). Outbreaks have resulted in hundreds of human deaths across Africa, and the mass abortion and death associated with ruminant outbreaks can cause considerable economic loss. RVFV circulates endemically at low-levels in its primary vector, Aedes sp. flood-water mosquitoes. Outbreaks in livestock and humans are usually associated with unusually heavy and extensive rainfall. Methods: PREDICT is a large collaborative project with aims to detect and discover viruses that are zoonotic and have pandemic potential. The presented project benefitted from this established framework. We focused efforts in the Lake Zone of Tanzania, where human and animal samples were being collected to test for other emerging infectious diseases using a broadly reactive consensus RT-PCR platform (cPCR) for a range of viral families. From 2015-2019, PREDICT collected human samples from 3 surveillance sites in the Kagera and Kigoma regions of the Lake Zone. Two of these sites were health clinics that enrolled patients with febrile illness of unknown origin. The third site was a constellation of villages adjacent to protected areas and a large international refugee settlement. Human data collection at all sites was done concurrently with animal sampling in the area These regions were selected due to the high prevalence of undiagnosed fevers in humans, intense human-animal contact, and shifting disease transmission drivers. This approach aimed to assess disease emergence and prevalence at high risk interfaces. Survey data were collected with samples to allow for the analysis of risk factors. Utilizing data and samples collected from the Kagera and Kigoma regions, we determined the seroprevalence of anti-RVF IgG immunoglobulins in humans. Then bivariate analysis and multivariable logistic regression were utilized to determine associations between risk factors, such as animal contact and livelihood exposures, and seropositivity. SaTScan was used to determine spatial clustering. Results: Of 463 individuals tested, 30 were positive, yielding a seroprevalence across sampling sites of 6.5%. Seroprevalence did not differ among sites, nor did it vary by sampling season or gender (p > 0.05). Bivariate analyses were performed to determine individual variable relationships with seroprevalence. Significant livelihood exposures included animal production/slaughter (OR = 2.26, 95% CI = 0.99-5.14, p = 0.047) and beekeeping (OR = 3.95, 95% CI = 1.57-9.92, p = 0.007). Individuals that had eaten sick livestock (OR = 3.13, 95% CI = 1.19-8.22, p = 0.028), found dead livestock (OR = 3.41, 95% CI = 1.20-9.69, p = 0.032), and slaughtered livestock (OR = 2.73, 95% CI = 1.22-6.09, p = 0.011) had increased risk of being seropositive for RVFV. Significant exposures from bivariate analysis were entered into a multivariable logistic regression model, which showed that most risk of exposure to RVFV could be explained by age (OR = 2.57, 95% CI = 1.41-4.69, p = 0.002). Conclusions: Previously, only limited data existed on Rift Valley fever virus for the Kagera and Kigoma regions of Tanzania, which have been thought to be outside of the expected or endemic RVFV zone. Most risk factors associated with seroprevalence for RVFV related to contact with livestock, which could reflect animal exposure risks or be a result of these factors being connected with working outside in high risk areas. Our study is contributing to the evolving understanding of RFV and other zoonotic diseases that occur at minimal endemic levels with sporadic, severe epidemics.

Acknowledgements

This study was made possible by the generous support of the American people through the United States Agency for International Development (USAID) Emerging Pandemic Threats PREDICT project (cooperative agreement number GHN-A-OO-09-00010-00), through the US Defense Threat Reduction Agency's Biological Threat Reduction Program (contract number: HDTRA1-14-1-0053), and by the Global Underserved Communities Fellowship from the Office of Global Programs at the University of California, Davis.

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Keywords: Rift Valley fever virus (RVFV), Tanzania Africa, seroprevalence, emerging disease, Zoonotic, Livestock keepers

Conference: GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data, Davis, United States, 8 Oct - 10 Oct, 2019.

Presentation Type: Student Poster-session

Topic: Real-time field data collection and visualization platforms

Citation: Streb LH, Bird BH, Mkali HR, Makingi G, Wolking DJ, Magesa W, Mwangoka G, Lane JK, Kazwala R, Smith W and Mazet JA (2019). Zoonotic Rift Valley fever virus prevalence and risk factors in the Lake Zone of Tanzania. Front. Vet. Sci. Conference Abstract: GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data. doi: 10.3389/conf.fvets.2019.05.00026

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Received: 20 Jun 2019; Published Online: 27 Sep 2019.

* Correspondence: Mx. Leah H Streb, School of Veterinary Medicine, University of California, Davis, Davis, California, CA 95616, United States, lhstreb@ucdavis.edu