For a tiny insect, the mosquito is an enormous threat to global health. Female mosquitoes transmit deadly viruses like dengue and chikungunya that continue to take lives despite efforts to limit their spread. In the East African country of Tanzania, for instance, two dengue outbreaks in 2018 and 2019 saw urban regions struggling with thousands of people infected.
Despite the endemic threat of dengue and other mosquito-borne diseases, limited research has been done to map the prevalence of the dengue virus (DENV) and the chikungunya virus (CHIKV) in Tanzania.
“Surveilling [mosquito-borne viruses] in regions like Tanzania is difficult as infected individuals generally present similar clinical symptoms,” explained Lisa Ng, Executive Director of the A*STAR’s Infectious Diseases Labs (ID Labs) as well as Biomedical Research Council (BMRC). “A DENV or CHIKV infection can sometimes go undetected or misdiagnosed as malaria, which is common in Tanzania.”
As understanding the enemy is the first step towards combating it, Ng collaborated with Beatrice Chipwaza and Fredros Okumu, scientists from Tanzania’s Ifakara Health Institute to determine the occurrence and prevalence of the DENV and CHIKV viruses during Southeastern Tanzania’s 2018 dengue outbreak. They also aimed to pinpoint the specific DENV serotypes circulating in the region at the time.
In 2018, the team enrolled 294 eligible patients from the rural Kilombero Valley region, a community hit particularly hard by the outbreak, and collected blood samples. To detect the presence of DENV or CHIKV, the team extracted RNA from the samples and performed a technique called multiplex real-time polymerase chain reaction (RT-PCR), allowing them to simultaneously screen samples for CHIKV and the four DENV serotypes.
Unlike previous dengue outbreaks in the region, which were primarily caused by DENV-2, the 2018 outbreak had all four known DENV serotypes in circulation. The team also reported the detection of the DENV-4 serotype for the first time in Tanzania, as well as low frequencies of CHIKV.
All in all, these results reveal that all DENV serotypes and CHIKV may already be endemic in the Kilombero Valley region. This is particularly concerning for the community as immunity against one DENV serotype does not translate to immunity towards the others. In fact, having all four serotypes in circulation may increase the number of potentially fatal secondary DENV infections.
These findings can help local public health officials make targeted and timely interventions to prevent future outbreaks. “These include targeted strategies like vector control efforts in communes and the provision of mosquito nets and repellent to the general public,” said Ng.
Building on the data collected, future studies will explore the transmission dynamics of the different mosquito-borne diseases within the region. Additionally, Ng and colleagues will investigate the prevalence of co-infections with other mosquito-borne diseases by studying patients with malaria and other febrile illnesses.
The A*STAR-affiliated researchers contributing to this research are from the Infectious Diseases Labs (ID Labs) and the Singapore Immunology Network (SIgN) .
