# Seroprevalence of dengue virus antibodies among multiple species of non-human primates in Senegal suggests that sylvatic dengue virus is maintained in non-primate reservoirs in this region

## TL;DR

This study found that monkeys in Senegal show high dengue virus exposure, but young monkeys suggest non-primate hosts also maintain the virus in the wild.

## Contribution

The study provides evidence that non-primate hosts may maintain sylvatic dengue virus in Senegal.

## Key findings

- High seroprevalence of DENV-2 was observed in three monkey species in Senegal.
- Young monkeys showed signs of infection even when the virus was undetected in mosquitoes.
- Infection rates varied between monkey species, indicating ecological or behavioral influences.

## Abstract

Dengue virus (DENV) circulates in two distinct transmission cycles: one, termed the sylvatic cycle, is enzootic to canopy-living hosts, including non-human primates and primatophilic mosquitoes, and the other, initiated by spillover from the sylvatic cycle, is endemic to humans and anthropophilic mosquitoes. Transmission dynamics of sylvatic DENV in non-human hosts has not been well characterized, and the identity of reservoir and amplification hosts is still to be determined. We investigated the role of the three common species of monkeys in the Kédougou region of Senegal in the sylvatic transmission cycle of DENV. Longitudinal surveillance of primatophilic mosquitoes in this region dating back to the 1970s revealed that sylvatic DENV-2, the only one of the four DENV serotypes found to circulate in a sylvatic transmission in West Africa, is amplified cyclically at intervals of approximately eight years based on the isolation of the virus from mosquitoes. Subsequent to the detection of DENV-2 in primatophilic mosquitoes in Kédougou in 2008, 737 monkeys, including 3 species: Chlorocebus sabaeus (n = 219), Erythrocebus patas (n = 78), and Papio papio (n = 440) were captured from 2010 to 2012 for the current study. Their age was determined using dentition and other morphological measurements. Evidence of DENV-2 infection was detected via neutralizing antibody in sera, and the annual hazard of DENV-2 infection was estimated per species using catalytic models. These analyses revealed annual hazard ranging from 0.09 to 0.42 across the three species, consistent with high levels of transmission in these populations. Furthermore, seroprevalence was moderate in individuals under one year of age, despite the lack of detection of DENV-2 in primatophilic mosquitoes for up to three years prior, suggesting that non-primate hosts contributed to the maintenance of sylvatic DENV in this region.

Dengue is often viewed as a disease that circulates mainly among people in cities, but in West Africa the virus also persists in forest environments, where it infects wild mosquitoes and animals and can occasionally spill over into humans. We set out to better understand the role of non-human primates in this forest, or sylvatic, transmission cycle. To test this idea, we collected blood samples from over 700 monkeys of three different species in southeastern Senegal between 2010 and 2012 and measured antibodies that indicate past dengue infection. We found that a large proportion of monkeys had been infected, including many young animals. Notably, young monkeys showed evidence of infection even during years when dengue virus was not detected in mosquitoes, suggesting that transmission continues quietly in the environment. We also observed clear differences in infection rates between monkey species, pointing to ecological or behavioral factors that influence exposure. Together, our findings suggest that monkeys alone are unlikely to fully maintain dengue virus transmission and that other animal hosts may also contribute. Understanding how dengue virus persists outside human populations is important, because environmental change and expanding human activity near forests may increase the risk of spillover and future outbreaks.