Dengue in Africa : sustained and silent circulation of multiple serotypes and genotypes, detected in travelers from 2010 to 2014

Introduction Dengue is caused by 4 different related viruses, DENV 1 to 4, transmitted to humans via Aedes mosquitoes. The disease is endemic in more than 100 countries. In Africa, the estimated dengue burden is 15 million of clinical cases and about 48 millions of inapparent infections. However, dengue remains largely unrecognized in Africa. Due to the lack of laboratory confirmation, a febrile syndrome is frequently misdiagnosed as malarial infection. The circulation of different dengue serotypes is also poorly documented. However, some information is provided by reports of dengue infections in travellers returning from Africa. In the present study we attempt the identification of dengue serotypes and genotypes circulating in Africa from 2010 to 2014 detected in travellers returning to Europe. Methods We collected samples from viraemic travellers returning from Africa who attended TropNet clinics in Europe from 2010 to 2014. Sequences of the Envelope gene were used to identify the serotype and genotype. Results During the study period we identified 3 DENV serotypes circulating in Africa. DENV 1 strains were detected in East Africa in 2010 (Eritrea) and in 2012 (Kenia), whereas in Central Africa in 2013(Angola and DRC). Strains from East Africa were grouped within Asian genotype, close to virus isolated in previous years in Djibouti and Kenia; we found American /African genotype in Central Africa. Both genotypes have circulated in West Africa for many years. DENV 2 strains were detected in West Africa (Senegal) and in East Africa (Tanzania) in 2014. Dengue 2 from Tanzania belongs to cosmopolitan genotype, but form a distinct clade different from the old African group. However, DENV 2 from Senegal surprisingly fell into genotype America /Asia. To our knowledge this is the first time identified in Africa. Finally, DENV 3 was detected in 2010 in Mali and Burkina Faso and again in Burkina Faso in 2013. All DENV 3 belong to genotype III and form a cluster with the African strains identified since 2008. Conclusion DENV 1 of both genotypes was identified previously in Africa indicating endemic transmission as well as with DENV 3. Meanwhile, a new DENV 2 appeared in Tanzania, introduced from South East Asia, and in Senegal from the Americas. These results confirm silent and sustained circulation of dengue in Africa and show the usefulness of travelers for sentinel surveillance to unmask the dengue problem in Africa.