# Prevalence and associated factors of human haemorrhagic fevers in Senegal: a comprehensive analysis of Hantaan, Crimean-Congo haemorrhagic fever and Rift Valley fever

## TL;DR

The study found that human exposure to several viral haemorrhagic fevers is common in Senegal, with most cases going undetected by current surveillance systems.

## Contribution

This study provides the first serological evidence of human hantavirus exposure in Senegal and highlights significant under-detection of infections.

## Key findings

- Seroprevalence rates were 15.1% for Rift Valley fever virus, 10.8% for Crimean-Congo haemorrhagic fever virus, and 2.2% for Hantaan virus.
- Exposure to Rift Valley fever was higher in the transboundary region Matam, while exposure to the other two viruses was higher in Thiès.
- Routine surveillance systems detected only a small fraction of infections, indicating widespread under-detection.

## Abstract

Viral haemorrhagic fevers such as Rift Valley fever, Crimean-Congo haemorrhagic fever, and hantavirus disease continue to threaten public health in Africa. This study assessed the seroprevalence and associated factors of these infections in Senegal.

A cross-sectional survey was conducted from September 2022 to June 2024 among asymptomatic individuals living in close contact with livestock in two regions: Matam, a transboundary area; and Thiès, a non-transboundary area with high livestock density. Participants completed standardized questionnaires, and serum samples were screened for antibodies against Rift Valley fever virus, Crimean-Congo haemorrhagic fever virus, and Hantaan virus using a Luminex-based multiplex immunoassay. Logistic regression models were used to identify independent risk factors.

Among 2,019 participants, crude seroprevalence was 15.1 percent (95 percent confidence interval: 13.5–16.7) for Rift Valley fever virus, 10.8 percent (9.4–12.2) for Crimean-Congo haemorrhagic fever virus, and 2.2 percent (1.6–3.0) for Hantaan virus. Exposure to Rift Valley fever virus was higher in Matam than in Thiès, whereas exposures to the other two viruses were higher in Thiès. Older age and male sex were consistently associated with infection, and exposure to Crimean-Congo haemorrhagic fever virus was also linked to raw milk consumption and slaughterhouse work. During the study, the national sentinel surveillance system detected only one case each of Rift Valley fever and Crimean-Congo haemorrhagic fever, indicating a substantial cases under-detection.

This study provides serological evidence of human hantavirus exposure in Senegal and confirms subclinical circulation of Rift Valley and Crimean-Congo haemorrhagic fevers. Our results suggest that routine surveillance is missing the vast majority of infections. These viruses circulate endemically within exposed populations, often in an asymptomatic or subclinical state, or manifesting with mild symptoms. This under-detection by the current monitoring system poses a significant challenge to the implementation of effective control strategies in endemic regions. This highlights the need to strengthen One Health surveillance to ensure early warning and public health preparedness.