Nationwide surveillance identifies yellow fever and chikungunya viruses transmitted by various species ofAedesmosquitoes in Nigeria
Authors: Nwangwu Udoka C. , Oguzie Judith U. , Nwachukwu William E. , Onwude Cosmas O. , Dogunro Festus A. , Diallo Mawlouth , Ezihe Chukwuebuka K. , Agashi Nneka O. , Eloy Emelda I. , Anokwu Stephen O. , Anioke Clementina C. , Ikechukwu Linda C. , Nwosu Chukwuebuka M. , Nwaogo Oscar N. , Ngwu Ifeoma M. , Onyeanusi Rose N. , Okoronkwo Angela I. , Orizu Francis U. , Etiki Monica O. , Onuora Esther N. , Adeorike Sobajo Tope , Okeke Peter C. , Chukwuekezie Okechukwu C. , Ochu Josephine C. , Ibrahim Sulaiman S. , Ifedayo Adetifa , Ihekweazu Chikwe , Happi Christian T. 
Published: January 2024

Background

Since its reemergence in 2017, yellow fever (YF) has been active in Nigeria. The Nigeria Centre for Disease Control (NCDC) has coordinated responses to the outbreaks with the support of the World Health Organization (WHO). The National Arbovirus and Vectors Research Centre (NAVRC) handles the vector component of these responses. This study sought to identify the vectors driving YF transmission and any of the targeted arboviruses and their distribution across states.

Methods

Eggs, larvae and pupae as well as adult mosquitoes were collected in observational, analytical, and cross-sectional surveys conducted in sixteen YF outbreak states between 2017 and 2020. Adult mosquitoes (field-collected or reared from immature stages) were morphologically identified, and arboviruses were detected using RT-qPCR at the African Centre of Excellence for Genomics of Infectious Diseases (ACEGID).

Results

Aedesmosquitoes were collected in eleven of the sixteen states surveyed and the mosquitoes in nine states were found infected with arboviruses. A total of sevenAedesspecies were collected from different parts of the country.Aedes aegyptiwas the most dominant (51%) species, whereasAedes africanuswas the least (0.2%). Yellow fever virus (YFV) was discovered in 33 (∼26%) out of the 127Aedesmosquito pools. In addition to YFV, the Chikungunya virus (CHIKV) was found in nine pools. Except forAe. africanus, all theAedesspecies tested positive for at least one arbovirus. YFV-positive pools were found in six (6)Aedesspecies while CHIKV-positive pools were only recorded in twoAedesspecies. Edo State had the most positive pools (16), while Nasarawa, Imo, and Anambra states had the least (1 positive pool). Breteau and house indices were higher than normal transmission thresholds in all but one state.

Conclusion

In Nigeria, there is a substantial risk of arbovirus transmission byAedesmosquitoes, with YFV posing the largest threat at the moment. This risk is heightened by the fact that YFV and CHIKV have been detected in vectors across outbreak locations. Hence, there is an urgent need to step up arbovirus surveillance and control activities in the country.

Author summary

Epidemics of arboviral infections are fast becoming the norm across Africa, especially in Nigeria, where sporadic epidemics ofAedes-borne Yellow Fever (YF) have been on the rise since 2017. A nationwide surveillance was conducted to detect the arboviruses and the vectors transmitting them during large YF outbreaks across Nigeria.Aedesmosquitoes collected from 57 local government areas/outbreak locations, covering 16 out of the 36 states in Nigeria, were reared to adulthood, morphologically identified to species level and assayed using qRT-PCR to detect six epidemiologically important arboviruses (Dengue, Chikungunya (CHIKV), Zika, YF, West Nile and O’nyong nyong). SevenAedesspecies (includingAe. aegypti, Ae. albopictus, Ae. circumluteolus, Ae. vittatus, Ae. simpsonicomplex, Ae. luteocephalus,andAe. africanus), were caught, withAe. aegyptiandAe. albopictusthe most widespread and predominant. Only YF and CHKV were found in mosquito pools from 9 states, with onlyAe. aegyptipools positive for CHKV, while YF virus was found predominantly in this species andAe. albopictus. This study provides a baseline for widespread distribution of the majorAedesvectors, and their arboviral transmission profiles, which can enhance evidence-based control measures, and strengthen nationwide surveillance systems to forestall future outbreaks of public health magnitude.