The first case of sexual transmission of dengue in Spain

Dengue virus (DENV) is a common precipitant for febrile illness among travellers. Non-vector-borne transmission of DENV is possible albeit rare. The role of sexual transmission in dengue remains to be determined. The absence of DENV in semen has been discussed previously in this journal.1 The study in Singapore that comprised five male patients with acute DENV infection demonstrated the lack of shedding of DENV in their semen. Notwithstanding the limited sample size, the results highlighted the likely triviality of sexual transmission of DENV. Studies of larger sample size may be warranted in this regard. Recently, the European Centre for Disease Prevention and Control (ECDC) reported the first case of sexual transmission of DENV in Spain.2 The affected individuals (both males; aged 36 and 41, respectively) developed symptoms of dengue infection in September 2019. Although the full details related to genetic sequencing of DENV were not included in the report by ECDC, semen analyses confirmed the presence of DENV in semen of both individuals. Furthermore, the virus strain of both individuals was discerned to be identical and, importantly, similar to the DENVs that were circulating in Cuba. Notably, only one of the two patients had travelled to Cuba and the Dominican Republic, both of which are dengue-endemic regions, in late August 2019. This is the first case report of male-to-male sexual transmission of DENV globally. A probable case of female-to-male sexual transmission of DENV has been reported previously in South Korea.3 Similar to the incident in Spain, only one patient had a history of travelling to Indonesia, one of the dengue-endemic countries in Southeast Asia. Sexual transmission of the flavivirus family to which DENV belongs is not unheard of, illustrated by several confirmed cases of sexually transmitted Zika virus prior to its outbreak in the USA.4 The case report in Spain reminds the travel medicine community of the importance of non-vector-borne DENV transmission among travellers. It is worth noting that a retrospective study that analysed a 20-year hospital discharge records database in Spain for dengue-related admissions did not report any secondary cases of dengue infection.5 Specifically, none of the dengue-related admissions was related to sexually transmitted DENV. The solitary case in Spain indicates that sexual transmission of DENV may be rare. Nevertheless, the emergence of documented cases in Spain and South Korea warrants attention from the travel medicine community. Sexual transmission of DENV has never been truly established, but the recent case in Spain illuminates the possibility of this non-vector-borne transmission route. Future research of larger sample size may provide a better insight into this plausible mode of transmission. This could have implications for the advice provided by travel medicine practitioners as well as for the management of dengue. Novel discovery pertinent to dengue would augment the ongoing battle against one of the most important causes of fever in returned travellers. None received. None declared.