Serological Evidence of Cryptic Rift Valley Fever Virus Transmission Among Humans and Livestock in Central Highlands of Kenya

Silvia Situma ^1,2,3, Evans Omondi ^4,5, Luke Nyakarahuka ^6,7

¹Department of Medical Microbiology and Immunology, University of Nairobi, Nairobi 00202, Kenya.
²Washington State University Global Health Program-Kenya, Nairobi 00200, Kenya.
³Department of Animal Science, Pwani University, Kilifi 80108, Kenya.
⁴African Population and Health Research Center (APHRC), Nairobi 00100, Kenya.
⁵Institute of Mathematical Sciences, Strathmore University, Nairobi 00200, Kenya.
⁶Uganda Virus Research Institute, Entebbe P.O. Box 49, Uganda.
⁷Department of Animal Resources and Biosecurity, Ecosystems and Veterinary Public Health, Makerere University, Kampala P.O. Box 7062, Uganda.
⁸Department of Public Health, University of Nairobi, Nairobi 00202, Kenya.
⁹Department of Biochemistry, University of Nairobi, Nairobi 00100, Kenya.
¹⁰Paul G. Allen School for Global Health, Washington State University, Pullman, WA 98165, USA.
¹¹Center for Epidemiological Modelling and Analysis, University of Nairobi, Nairobi 00202, Kenya.
¹²Kenya Medical Research Institute, Nairobi 00200, Kenya.
¹³Virology Unit, Department of Biomedical Sciences, Institute of Tropical Medicine, 2000 Antwerp, Belgium.
¹⁴Rollins School of Public Health, Emory University, Atlanta, GA 30322, USA.

⁰Department of Medical Microbiology and Immunology, University of Nairobi, Nairobi 00202, Kenya.

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January 8, 2025

View abstract on PubMed

Summary

Rift Valley fever (RVF) virus is spreading to new areas in Kenya's highlands, with recent exposures found in livestock and humans. This suggests a growing risk of future RVF epidemics in previously unaffected regions.

Area Of Science

Veterinary Medicine
Epidemiology
Public Health

Background

Rift Valley fever (RVF) typically occurs in Rift Valley fever disease hotspots, but recent small clusters have been reported in East African highlands.
The ecological factors contributing to RVF virus cycling in these highland areas during inter-epidemic periods remain unclear.

Purpose Of The Study

To investigate the occurrence of RVF virus cycling among livestock and humans in the central highlands of Kenya during inter-epidemic periods.
To identify sociodemographic and environmental risk factors associated with RVF exposure in humans and livestock.

Main Methods

A 2-year prospective hospital-based study of febrile patients (n=1468) in Murang'a County, Kenya, followed by a cross-sectional human (n=282) and livestock (n=706) survey.
Sera from patients and animals were tested for RVF virus RNA and anti-RVFV IgG antibodies. Multivariate logistic regression was used to analyze risk factors.

Main Results

No RVF virus RNA was detected in humans or livestock. However, 4.4% of livestock and 2.0% of humans tested positive for anti-RVFV IgG, indicating recent exposure.
Risk factors for human RVF exposure included male sex, raw milk consumption, and proximity to quarries. Cattle were more likely to be seropositive than sheep and goats.

Conclusions

The findings indicate recent RVF virus exposure in the central highlands of Kenya, suggesting a widening geographic dispersal of the virus.
This expanding distribution poses a greater risk for more widespread RVF epidemics in the future, necessitating enhanced surveillance and control measures.

Keywords:

Rift Valley fever virus arbovirus cryptic transmission non-epidemic period