A study published in PLOS One last month (17 August) shows that poor urban planning in Kenya could aid the re-emergence of dengue and yellow fever, transmitted through mosquitoes: Aedes aegypti and Aedes bromeliae.
Dengue, a viral disease spread by day-biting mosquitoes, “is the fastest spreading vector-borne viral disease” and has reached more than 100 countries, according to the WHO. Patients with the non-severe form of dengue develop high fever, flu-like symptoms and stomach pain, the severe form could result in the death of 20 per cent of patients with the disease. Meanwhile, yellow fever, a viral disease spread by infected mosquitoes could kill about 50 per cent of those infected with its severe form within seven to ten days, says WHO.
“Our study is helping to identify areas where the vector is present in high abundance that can sustain transmission of the virus.”
Rosemary Sang, Kenya Medical Research Institute
The study was conducted in the outskirts of three Kenyan cities — Nairobi and Kisumu, which have no known history of dengue outbreak and Mombasa, which is prone to dengue outbreak — from October 2014 to June 2016 during the wet and dry seasons.
Researchers from Kenya-based International Centre of Insect Physiology and Ecology (icipe) and South Africa’s University of Pretoria measured the abundance of the mosquitoes Ae. aegypti and Ae. bromeliae.
According to the study, 7,424 Ae. aegypti and 335 Ae. bromeliae were collected from all sites, made up of 100 houses for each city and season.
“Ae. aegypti remains the only known dengue vector in Kenya with sufficient abundance in the major cities to sustain transmission,” the authors note. “It is highly abundant and the risk values are indicative of high risk of dengue transmission in Kilifi and Kisumu.”
Rosemary Sang, a co-author of the study and a consultant scientist at the icipe, tells SciDev.Net that dengue outbreak in Kenya has only occurred in few specific locations in the coast and that the research team “wanted to establish the risk of spread of outbreaks to other areas”.
Sang, a principal research scientist at the Arbovirology Unit, Kenya Medical Research Institute, adds that more experiments are underway to determine if these vectors can transmit the viruses.
“Our study is helping to identify areas where the vector is present in high abundance that can sustain transmission of the virus should the disease get imported through infected travellers from outbreak countries or regions,” explains Sang, adding that this will be important for early warning and implementation of preventive measures.
Omu Anzala, a professor of medical microbiology at the University of Nairobi, lauds the study for increasing knowledge and understanding of newly emerging pathogens. “Being able to understand and predict whether there is impending epidemic is very important,” Anzala tells SciDev.Net. “We should be doing this regularly, looking at indicators of early warning so that we are better prepared [during disease outbreak].”
Anzala encourages research uptake by policy makers to enable them act quickly on outcomes of studies on emerging disease outbreaks.
This piece was produced by SciDev.Net’s Sub-Saharan Africa English desk.