Entomological investigations into yellow fever outbreak in northern Ghana
Authors: Osei Joseph Harold Nyarko , Pi-Bansa Sellase , Frempong Kwadwo Kyeremeh , Ofei Mavis , Boakye Helena Anokyewaa , Ansah-Owusu Jane , Akorful Sandra-Candys Adwirba , Malm Richard Odoi-Teye , Tawiah-Mensah Christopher Nii Laryea , Abudu Mufeez , Asafu-Adjaye Andy , Addo Seth Offei , Agbodzi Bright , Bentil Ronald , Pratt Deborah , Nimo-Paintsil Shirley , Bonney Joseph Humphrey Kofi , Appawu Maxwell Alexander , Koffi Millie-Cindy Aba Aude , Coleman Sylvester , Captain-Esoah Millicent , Kubio Chrysantus , Boakye Daniel Adjei , Dadzie Samuel Kweku 
Published: November 2024

Background

Recently, arboviruses have been of concern as pathogens for emerging and re-emerging infectious diseases. In Ghana, yellow fever outbreak occurred in Savannah Region in the year 2021. A team from different institutions, organisations, and stakeholders of health with varying vital expertise was assembled to respond to this national emergency to assess, contain and/or control the rapid spread of the disease. This paper presents findings from the entomological investigations conducted during the yellow fever outbreak.

Methods

Immature stages ofAedesmosquitoes were collected from breeding containers in and around houses, and adult mosquitoes sampled using BG-Sentinel traps, human landing catches and Prokopack collections. After morphological identification of these mosquitoes, they were screened for Chikungunya, Dengue Fever, Yellow Fever, and Zika viruses using real time reverse-transcription polymerase chain reaction.

Results

In all, 12,264 breeding containers were examined. A total of 3,885 larvae and 1,186 pupae were obtained from 173 containers. Out of 1,001 houses surveyed, 130 were positive for larvae and/or pupae. The breeding receptacles included plastic (6,529), metallic (6,024), clay jar (753), tire (565), and well (34). The WHO thresholds for arboviruses larval indices were used to assess risk. A total of 1571 adults identified [Aedes aegypti aegypti(35),Aedes aegypti formosus(619), andCulex(917)] were collected with adult mosquito sampling methods or emerged from immature mosquitoes stages. None of the arboviruses were detected using qPCR.

Conclusion

Vectors had no yellow fever infections. There was a high risk of arbovirus transmission in the study areas although mosquito vectors were not positive for arboviruses.Aedes aegypti formosuswas the dominantAedesspecies. They might be drivers for yellow fever transmission during outbreak. Generally, arboviral transmission was high in all study districts. Although yellow fever virus was not detected,Aedes aegyptipopulations and transmission risk in study districts was high.

Author summary

In 2021, Savannah Region of Ghana experienced yellow fever outbreak. This spread quickly to adjoining regions. The disease is transmitted by some female mosquitoes infected with yellow fever virus. These same mosquitoes can transmit other viral infections resulting in disease outcomes such as chikungunya, dengue, and zika. A team of experts from stakeholders of health were mobilised to control and/or contain the spread of the disease to other parts of Ghana. The team carried out several activities and assessments to stop the spread of yellow fever. Notably is the investigation to determine different types of mosquitoes involved in transmitting the disease. We collected some mosquitoes and processed them for vital information that could prevent future outbreaks of the aforementioned diseases. There is no surveillance system in Ghana to pick up early warnings regarding potential viral disease outbreaks. Therefore, there is scanty information on these type of mosquitoes and viruses found in different places. We used standard procedures to assess the risk of these mosquitoes in causing future disease outbreaks. Our findings suggested a high risk of future outbreaks for any of the viral diseases tested. We therefore recommended the implementation of a mosquito surveillance system to prevent future outbreaks.