Chikungunya Outbreak in the Republic of the Congo, 2019-Epidemiological, Virological and Entomological Findings of a South-North Multidisciplinary Taskforce Investigation

Abstract

The Republic of Congo (RoC) declared a chikungunya (CHIK) outbreak on 9 February 2019. We conducted a ONE-Human-Animal HEALTH epidemiological, virological and entomological investigation. Methods: We collected national surveillance and epidemiological data. CHIK diagnosis was based on RT-PCR and CHIKV-specific antibodies. Full CHIKV genome sequences were obtained by Sanger and MinION approaches and Bayesian tree phylogenetic analysis was performed. Mosquito larvae and 215 adult mosquitoes were collected in different villages of Kouilou and Pointe-Noire districts and estimates of Aedes (Ae.) mosquitos' CHIKV-infectious bites obtained. We found two new CHIKV sequences of the East/Central/South African (ECSA) lineage, clustering with the recent enzootic sub-clade 2, showing the A226V mutation. The RoC 2019 CHIKV strain has two novel mutations, E2-T126M and E2-H351N. Phylogenetic suggests a common origin from 2016 Angola strain, from which it diverged around 1989 (95% HPD 1985-1994). The infectious bite pattern was similar for 2017, 2018 and early 2019. One Ae. albopictus pool was RT-PCR positive. The 2019 RoC CHIKV strain seems to be recently introduced or be endemic in sylvatic cycle. Distinct from the contemporary Indian CHIKV isolates and in contrast to the original Central-African strains (transmitted by Ae. aegypti), it carries the A226V mutation, indicating an independent adaptive mutation in response to vector replacement (Ae. albopictus vs Ae. aegypti).

Keywords: Aedes spp; ONE-HEALTH; Republic of Congo; arbovirus; chikungunya; mosquito; outbreak.

Figure 1

Epidemic curve of confirmed and under investigation cases. The epidemic curve shows an increase of reported cases after strengthening of the surveillance system during the mission (orange bars: cases under investigation, blue bars: confirmed cases).

Figure 2

Bayesian maximum clade credibility tree built with full genome sequences of CHIK/PNRCNG/LNSP_INMI1-2019 and CHIK/PNRCNG/LNSP_INMI2-2019 strains highlighted by as an asterisk (*), in the context of 60 full genome sequences representing the 3 major CHIKV lineages: ECSA (n = 44, including the Indian Ocean sub-lineage, n = 26; the IOL sub-lineage includes the Pakistani-Italian 2017 cluster, n = 12 and the Italian 2007 cluster, n = 3), Asia-Caribbean (n = 12), and West Africa (n = 4). Each record consists of accession number, place and year of detection/isolation. The parameters used in BMCC were mutation model General Time Reversible + G, strict clock model and constant size demographic model. It was tested through MCMC for at least 100 × 10⁶ generations. The bar represents time coalescent in years. Sequences harboring the A226V mutation are highlighted by black dots.

Figure 3

The Infectious bites of Aedes mosquito estimated from a mathematical model considering that mosquitoes were infected with chikungunya virus and exposed to environmental temperature, which was similar to the recorded meteorological temperature at a local weather station at Pointe-Noire, Republic of Congo.