Enhancing surveillance for dengue fever in Oyo State, Nigeria - a one health approach.

Background: Dengue fever (DF) poses a growing global threat, necessitating a comprehensive one-health approach to address its complex interplay between human, animal, and environmental factors. In Oyo State, Nigeria, the true burden of DF remains unknown due to underdiagnosis and misdiagnosis as malaria, exacerbated by poor health-seeking behavior, weak surveillance systems, and inadequate health infrastructure. Adopting a one-health approach is crucial to understanding the dynamics of DF transmission.

Methods: A cross-sectional study was conducted from January 2022 to April 2023 in 10 high-risk LGAs of Oyo State. It involved screening DENV in 289 febrile human blood samples and 1,015 Aedes species mosquitoes. Viral RNA from human and mosquito specimens was extracted and analyzed using RT-qPCR. A one-step lateral flow immunoassay cassette test kit detected DENV-specific IgM and IgG in humans. DENV IgM-positive participants were screened for Lassa Virus (LASV) to rule out coinfection due to an outbreak of Lassa fever. Mosquitoes recovered were morphologically identified and classified using appropriate taxonomical keys. Meteorological data was obtained from the Nigeria Meteorological Agency. Data was abridged as proportions and correlation analysis was performed.

Result: The overall seroprevalence of DENV was 128/289 (44.2%) with 19/289 (6.6%) and 109/289 (37.7%) being IgM and IgG positive respectively. DENV was detected all year round with more cases in the rainy season. LASV and DENV coinfection were detected in a participant. DENV RT-qPCR analysis in febrile patients and mosquitoes was negative. There was a high abundance of Aedes aegypti (79.5%) in all the locations surveyed with Aedes albopictus (12.3%) detected in Ido LGA and Ibadan South-East LGA and Aedes simpsoni (9.1%) in Iwajowa LGA. DF shows moderate to strong positive correlations with Aedes mosquito population, humidity, and rainfall (r = 0.419-0.61, p < 0.05), and a negative correlation with temperature (r =-0.465, p < 0.05).

Conclusion: The study reveals a significant burden of DENV in Oyo State. The presence of both IgM and IgG antibodies suggests past exposure and possible recent circulation of the virus. The co-detection of LASV and DENV in one participant highlights the likely potential for co-infection. Although DENV was not detected in febrile patients and mosquitoes through RT-qPCR, the high abundance of Aedes species underscores the risk of transmission. These findings emphasize the need for enhanced surveillance systems, strengthened laboratory services, targeted vector control, and increased awareness.