Genuine concerns are beginning to emerge over a potential rise in malaria cases and a threat of dengue fever outbreak at the Kenyan coast. What is puzzling to research scientists is that even though the malaria prevalence is not going up, it is not declining either. This is not a good sign, because the danger of a sudden upsurge of disease is quite real and could lead to severe episodes.
Fight against malaria has been largely successful in this malaria endemic region so far. Disease prevalence has declined steeply from 80 per cent in the early 2000, to 8 per cent today. Even this current rate is an uptick from 4 per cent in the last five years, a development largely attributed to a lack of adequate resources required to push this trend further downwards.
Scientists are now looking at possible explanations behind this phenomenon. They are trying to understand what exactly is sustaining the disease, in what is otherwise known as “residual transmission,” according to Dr. Joseph Mwangangi, an entomologist at the Kenya Medical Research Institute (KEMRI) Wellcome Trust Programme, Kilifi.
The reason why malaria cannot be completely eliminated, he explains, is because there is something preventing it from being cleared.
At the heart of the researchers’ efforts is looking at the behavioural, socio-cultural and economic activities of the people here. This is important, because these activities might be exposing them to mosquito bites, thereby predisposing them to infection and increasing the risk of spreading malaria.
To begin with, people tend to spend more time outdoors in the evening, given the high temperatures at the coast. Also, mourners will hold night vigils outside a bereaved family’s home, during funeral arrangements. This is customary practice in many African cultures, not just at the coast but across the country too.
Research scientists are also looking into the role of bodaboda (motorcycle taxi) operators, whose contribution to sustaining disease transmission certainly cannot be ignored, given that they work all night long.
Deployment of insecticide treated nets and the application of insecticides to the walls and surfaces inside dwellings where mosquitos rest (also known as insecticide residual spraying or IRS in short), so that mosquitos are killed when they come into contact with the chemical, have done well to reduce malaria.
This of course has gone hand in hand with such intervention strategies as the intermittent preventive treatment for pregnant women and prompt diagnosis and effective treatment of all malaria cases.
But now scientists are looking for ways to move beyond insecticide treated nets, and for good reason too.
“Mosquitos are devising ways of circumventing the intervention,” says Dr. Mwangangi.
In other words, the vector is changing behavior, when it comes to insecticide treated nets and IRS. They are avoiding going into houses, choosing instead to seek a blood meal outdoors, or else wait to bite just before an individual retires to bed.
“We are realizing one thing: that this kind of response from the malaria vector might be the one responsible for having some parasites being sustained,” explains Dr. Mwangangi.
Also, since many people are sleeping under insecticide treated nets, it means that their immune against malaria is not so robust. So, in the wake of an upsurge of disease, they may be inclined to suffer severe episodes.
And of course there is the added concern of insecticide resistance, exhibited more and more by the mosquito, which, among other challenges is all the more reason why scientists are looking for alternative intervention strategies.
Perhaps of more immediate concern, is the fear of a dengue fever outbreak at the coast. This is especially the case given that all indications point to an increase of disease on a regularity that’s becoming ever so frequent.
“It is manifesting itself every February, March and April in coastal Kenya. We are having it as a major problem,” explains Dr. Mwangangi.
Dengue is a mosquito-borne viral disease, spread by the female of the species: Aedes aegyti and Aedes albopictus. According to the World Health Organisation, it causes flu-like illness, and occasionally develops into a potentially lethal complication called severe dengue.
The disease has no specific treatment. However, the WHO says early detection and access to proper medical care lowers fatality rates to below 1 per cent.
Water Not Necessary
Unlike the malaria-spreading mosquitos, the dengue vector does not need to lay eggs in water directly in order for the life cycle of a new generation to begin. Dr. Mwangangi explains that they just need any wet surface to lay their eggs, which form a shell enabling them to survive dry spells. And when they eventually come into contact with water, they become vibrant again.
Added to this survival tactic, another hardy characteristic about the dengue vector is that it passes the infection on to its progeny (unlike the malaria vector), in what is known as transovarian transmission. So, it builds infection very fast.
“However, what we are now doing is collect and screen mosquitos for a wide range of viruses,” explains Dr. Mwangangi. Besides screening for dengue fever, they are also screening for zika, chikungunya, onyongnyong, West Nile Fever and Rift Valley Fever.