Transmission risk assessment of Aedes -borne arboviral diseases in Accra, Ghana

Background

Dengue, Zika and Chikungunya are Aedes-borne viral diseases that have risen to become great global health concerns in the past years. Several countries in Africa have reported outbreaks of these diseases and despite Ghana sharing borders with some of such countries, it remains free of these outbreaks.

Recent studies in Ghana have revealed that there are antibodies and viral RNA of the Dengue virus serotype-2 among individuals in some localities in the Greater Accra Region. This is an indication of a possible silent transmission ongoing in the population, hence the need to assess the risk of transmission of these viruses within the country. This cross-sectional study, therefore, assessed the risk of transmission of Dengue, Zika and Chikungunya viruses in a domestic/peri-domestic (Madina) and a forest (Achimota Forest) population in the Greater Accra Region, Ghana.

Methodology/Findings

All stages of the Aedes mosquito (egg, larvae, pupae and adults) were collected around homes and in the forest area for estimation of risk indices. All eggs and immature stages were reared to adults and morphologically identified. The predominant species of Aedes mosquitoes identified from both sites were Aedes aegypti (98 % in Madina and 98.1% in Achimota forest). Aedes albopictus , an important arbovirus vector, was identified only in Madina at a prevalence of 1.5% but Achimota forest had the higher species diversity. Both study sites recorded high risk indices; Madina: Positive Ovitrap Index = 26.6%, Container Index = 36.8%, House Index = 19.8%, Breteau Index = 70.4%; Achimota: Positive Ovitrap Index = 34.2% and Container Index = 67.9%. RT-PCR to detect the presence of Dengue, Chikungunya and Zika viruses was negative for all pools tested.

Conclusion

All entomological risk indicators estimated showed that both sites had a high potential of an outbreak of arboviral diseases following the introduction of these viruses.

Author Summary

The detection of antibodies and viral RNA of the dengue virus serotype 2 in some communities in the urban city of Accra, suggested the possibility of silent transmission of arboviral disease within the city. We assessed the risk of arboviral disease transmission using entomological risk indices. The study was a cross-sectional study conducted in a forest and peri domestic setting located in the southern urban city of Accra.

The different stages of the Aedes mosquito were collected and, houses and containers positive for Aedes mosquitoes were also noted. The Breteau (BI), House (HI), Container (CI) and Positive ovitrap (POI) indices were determined. Real Time-PCR was conducted to determine the presence of Dengue, Zika and Chikungunya viruses in the larvae and adults collected.

Aedes aegypti was the most common species identified from both sites. Aedes albopictus another competent arbovirus vector was identified in the peri-domestic site. Almost all risk indices recorded for both sites were higher than the WHO thresholds allowed for these indices. However, real time-PCR to detect the presence of Dengue, Chikungunya and Zika viruses was negative.

The high entomological risk indicators estimated showed that both sites had a great potential of an outbreak following the introduction of these viruses, and a well-structured surveillance for these vectors is highly recommended. The detection of the presence of Ae. albopictus , an invasive species is also of great concern.