New Mosquito Species Could Derail Fight Against Malaria

By Wilson Odhiambo

Urban’ Kenya has been alerted because new mosquito species, Anopheles stephensi, threatens to derail decades of effort made in the fight against malaria.

According to a report by experts from the Kenya Medical Research Institute (KEMRI), the species was first noted during routine mosquito surveillance in Saku and Laisamis villages in Marsabit County. The report states that, unlike the traditional mosquito vector, the Anopheles stephensi can adapt to man-made habitats that include plastic containers, discarded car tyres and open sewer lines—this makes urban centres a hot spot for their prevalence.

Anopheles stephensi is endemic to South Asia and Arabian Peninsula, where it is a known carrier for two malaria variants Plasmodium falciparum and P. vivax. It was first noted at the Horn of Africa ten years ago in Djibouti, after which it was later tracked down in Ethiopia, Somalia, and Sudan in 2019.

Stagnant water in one of Nairobi’s residential areas. Credit: Wilson Odhiambo/IPS

The species is also known to survive through different climatic conditions, which can enable it to cause problems all year round if left uncontrolled.

‘’This mosquito most likely spreads through ships coming in from Asia since genetic analysis of many of the samples collected in Africa shows they are closely related to those found in Asia. Once they got to Africa, it is highly likely they have been transported southwards on the road,’’ said Dr Eric Ochomo, the project’s lead researcher and an entomologist at the KEMRI, Kisumu.

‘’It breeds in a wide range of habitats, mostly water storage containers that are not covered, manholes, overhead tanks, poorly dumped plastic containers etc.’’

Malaria has been a perennial problem in Kenya and Africa, given the vast tropical conditions that favour mosquitos and unreliable health facilities that make its control and treatment an almost impossible hurdle.

A researcher from KEMRI’s Entomology Department tests stagnant water for the new species of mosquito. Credit: KEMRI’s Entomology Department

While being a nuisance in Africa, most malaria cases and mortalities have been recorded in rural areas, characterized by a lack of adequate medical amenities, unreliable infrastructure, and a lack of knowledge among residents.

Urban areas have usually been spared the malaria burden due to access to proper medical facilities and a good understanding of the disease and how to control and prevent it.

This notion may, however, change for the worse as this new mosquito species threatens the demographics and steps made in the fight against malaria in Africa.

‘’This species is different from the traditional mosquito for two main reasons; A) its diversity of breeding habitats means it can breed in rural and urban settings alike, which means that it is not restricted to rural habitats like the Anopheles gambiae, Anopheles arabiensis and Anopheles funestus which are the most common vectors in Kenya at the moment. B) It can transmit both Plasmodium falciparum and Plasmodium vivax parasites. We currently have very low levels of P. vivax transmission in Kenya, and this could be increased by this vector,’’ Ochomo explained to IPS.

Despite the 2020 world malaria report showing a significant decrease in malaria deaths over the past two decades (from 84 percent in 2000 to 67 percent in 2019), it remains one of Africa’s leading causes of death, especially among pregnant women and children under the age of five.

The report stated that 51 percent of the global malaria deaths were in Africa, with Burkina Faso (4%), the Democratic Republic of the Congo (11 percent), Nigeria (23 percent), Mozambique (4 percent), Niger (4 percent) and Tanzania (5 percent).

In Kenya, most malaria cases are centred around the malaria endemic areas, including the coastal and lake regions, which form prime breeding spots for female anopheles mosquitos. For the cases reported in towns such as Nairobi, a follow-up on the patient’s movements often reveals that they recently visited or through one of these malaria-endemic places and got infected.

According to the Centers for Disease Control (CDC), about 3.5 million malaria cases are reported in Kenya annually, with about 10,700 mortalities. Out of this, western Kenya (lake region) usually records the highest number of cases at 45 percent.

The lake and coastal regions are categorized as malaria-endemic due to the favourable temperature and humid conditions they provide for mosquito breeding.

With most people in central Kenya and the highland areas having little exposure to malaria infections, this new vector could prove problematic given their immune system’s primitiveness to the disease.

The 2020 Kenya malaria indicator report says that low-risk malaria areas include Nairobi, Nyandarua, Nyeri, Kirinyaga, Murang’a, Kiambu, Machakos, Makueni, Laikipia, Nakuru, and Meru. Most of these areas are considered urbanized compared to most parts of Kenya.

Seasonally, areas that experience malaria outbreaks include Tana River, Marsabit, Isiolo, Meru, Garissa, Wajir, Mandera, Turkana, Samburu, Baringo, Elgeyo Marakwet, Kajiado. This is mainly due to the arid and semi-arid conditions experienced throughout the year that do not favour mosquito breeding.

‘’What this means is that we are going to have more incidences of malaria because this vector can thrive in both rural and urban settings and many other geographical regions,’’ says Dr Alex Owino, Medical Superintendent, Katulani Sub-County Hospital, Kitui.

‘’Kitui county falls under the low-risk malaria areas, with the few cases recorded being mainly from patients who had recently travelled outside the county,’’ he told IPS.

Owino explained that controlling malaria was easy when there were specific places where the host mosquito was known to favour. However, with this new vector being able to spread widely, it becomes a threat to the efforts made in the fight against malaria.

Being a developing country, parts of urban Kenya are characterized by poorly planned housing facilities, inadequate drainage systems and poor waste disposal management. Nairobi, for instance, is also known for hosting the largest slum in the country, Kibera, coupled with the Nairobi dam, which has, for years, made the headlines for having all manner of pollution destroying it.

All these conditions have been a recipe for various diseases, such as cholera and typhoid, causing health problems, especially in the slum areas. Now, malaria may have just added to the burden that these town dwellers have to deal with.

Ochomo said that, unlike the traditional malaria-causing mosquitoes, Anopheles gambiae and Anopheles funfests, the Anopheles stephensi is an invasive species that could bring malaria transmission to these areas where there is a large number of naive (have never had malaria) individuals.

‘’These individuals could get far more severe symptoms than people who have been exposed since birth,’’ he told IPS.

Wilson Opudo, a public health and infectious diseases specialist, also believes that the ongoing changes in climate conditions are likely to increase the malaria burden by creating mosquito breeding zones in areas where they were not a concern.

‘’Despite malaria being known to favour certain parts of Kenya, the recent changes in climate which have resulted in temperature increase and hydrological changes may help form new areas for the malaria vector breeding thus bringing malaria to places where it initially did not exist,’’ Opudo told IPS.

‘’This will put a lot of pressure on the malaria control commodities currently available for the endemic areas of Africa and could result in increased disease burden,’’ he added.

Ochomo concluded that its presence in urban settings means controlling this new vector will rely on properly managing waste disposal, covering water containers, and draining stagnant water.

‘’There is very little information available on the behaviour of the adult mosquitoes and an urgent need to invest in the research on this to inform what control methods would be applicable for the adult mosquitoes,’’ said Ochomo.

IPS UN Bureau Report