Silent invaders: Mosquitoes and sandflies spreading in new areas

Mosquito sucking blood from human skin. [Courtesy/GettyImages] A recent study on malaria vectors in arid regions, particularly in northern Kenya has revealed surprising findings: the emergence of new vectors responsible for both leishmaniasis and malaria. Dr Damaris Matoke-Muhia, a research scientist at the Kenya Medical Research Institute (Kemri), shared preliminary results from an ongoing study in parts of northern Kenya, showing that leishmaniasis, a neglected disease, is re surging. The disease is now appearing in new geographical areas across the country. "It could become a major public health problem in the near future if not addressed promptly," warns Dr Matoke. A team of KEMRI scientists conducting research on malaria and leishmaniasis observed key trends that prompted them to examine certain familiar traits of the disease. Ahead of the release of the full study results, Dr Matoke described these findings as crucial. She is currently leading research on malaria and leishmaniasis, and notes that Leishmaniasis is spreading in Kenya. "Initially, the disease was mostly confined to regions where is it known to be endemic, remote, arid and semi-arid areas and prevalence was high in some of these locations," she explained. "However, since 2023, we're seeing the disease expand geographically. Places like Tharaka Nithi and Kajiado are now reporting cases of visceral leishmaniasis," she added. In Marsabit County and areas like Turkana, the study is identifying more cases, with the disease reaching additional villages despite its prior presence in the region. "The disease is clearly expanding geographically," Dr Matoke stated. Dr Matoke spoke of research that has been ongoing for three years. Originally designed as a malaria-leishmaniasis study, the work unexpectedly revealed the invasion of Anopheles stephensi, a foreign mosquito species, in the county. Anopheles stephensi is an invasive, highly adaptable malaria vector native to South Asia and the Middle East that has recently spread across Africa, with detections in Djibouti, Ethiopia, Sudan, Somalia, Nigeria, Ghana, and now Kenya. Unlike traditional African malaria mosquitoes, this species thrives in urban and peri-urban environments, breeding in man-made containers, which could significantly increase malaria transmission in cities. "This shows that our work in vector science is bearing fruit," she said, noting that the study has allowed her team to identify new vectors for both malaria and leishmaniasis. Leishmaniasis is transmitted by the bite of infected sandflies of the Phlebotomine species. In Kenya, for many years, Phlebotomus martini, female sandflies, has been the main vector of visceral leishmaniasis, or kala-azar. "However, our recent research shows the emergence of Phlebotomus orientalis in areas like Marsabit, Turkana and Mandera, where this new vector is gaining ground," she explained. Previously, P. orientalis was mainly found in Sudan, Ethiopia and parts of the Sinai region in Egypt. Ecological conditions Dr Matoke-Muhia attributes this shift to ecological changes, noting that the vector is now moving into Kenya. The study also revealed surprising findings, with larger numbers of sandflies being recorded in areas where they were not previously expected. Extending the research to regions with similar ecological conditions in northern Kenya, the team identified Kajiado as another area where the vector has been found. "Our research has mapped the distribution of these vectors in the country, and recently, Kajiado County has emerged with particularly interesting findings," Dr Matoke said. In 2021, cases of visceral leishmaniasis were reported in Kajiado. Two young men transferred to Kimalel in Baringo County for treatment showed clear symptoms of the disease. The full extent of leishmaniasis in the county only became clear when scientists from KEMRI and ICIPE conducted a survey. "When we went in, we realised the disease was widespread, with cases appearing across various parts of Kajiado county," she explained, noting that both visceral and cutaneous forms of leishmaniasis were present. The scientists have already published findings confirming the occurrence of both types of leishmaniasis in the county. With this information now public, the team has moved to sensitize the community and work with the Kajiado County government and the Ministry of Health to establish treatment centers and strengthen disease management. The other development is that, apart from Phlebotomus martini and Phlebotomus orientalis, we are now seeing a new sandfly species, previously known as a vector of leishmaniasis in Asia and the Middle East, appearing in Kenya," Dr Matoke said. The ongoing study has also identified Phlebotomus alexandri as a new vector in Isiolo County, with large numbers now observed in neighbouring Marsabit. Dr Matoke and her team are currently investigating its role in the transmission of visceral leishmaniasis. "Through our mapping and ongoing research, we have detected Phlebotomus alexandri in Marsabit, Turkana, Wajir, and Kajiado," she explained. Interestingly, while the disease previously affected older children and teenagers aged 12 to 18, the researchers are now seeing infections in much younger children, even those under two years. This trend has recently been observed in Marsabit county. Housing structures The scientists believe the youngest children may be exposed either through sandfly bites at home or while accompanying their parents during pastoral activities, and they are analysing the data to understand these patterns. As part of control measures, the scientists are recommending several interventions for both county and national governments in the affected areas. "The disease requires urgent attention, and control efforts should include interventions such as bed nets," Dr Matoke said. However, she notes that housing structures and sleeping patterns in semi-arid areas often make the use of insecticide-treated nets impractical. "In such settings, bed nets can only work where people can actually sleep under them. That's why we recommend insecticide spraying as a key preventive measure," she added. Dr Matoke emphasized that spraying should ideally be done before disease cases are reported, as a proactive strategy, alongside the provision of nets where feasible. The research team also highlights environmental management, including the destruction of sandfly habitats, since the vectors often live in anthills. "Community education in affected areas is critical to prevent disease transmission," she concluded. "It is important for people to avoid sitting around anthills and to destroy inactive ones. Active anthills, which house termites, are not suitable habitats for sandflies," Dr Matoke explained. Observations show that community members are usually bitten by sandflies in the evenings, which is when infections often occur. Dr Matoke also stressed the importance of educating communities about the disease. While treatment is now available, it requires hospital admission for a minimum of 17 days. She added that patients need good nutrition to boost hemoglobin-an iron-rich protein in red blood cells that carries oxygen from the lungs to body tissues and removes carbon dioxide. Without adequate hemoglobin, patients may even require blood transfusions if their iron levels are too low. "So, we call upon the government and other partners to step in and support," Dr Matoke said, highlighting a major challenge: the company that previously produced diagnostic kits for leishmaniasis has stopped manufacturing them. To illustrate why leishmaniasis is considered a neglected tropical disease, she explained that the companies producing these kits reduced production because demand was low, as many countries do not prioritize the disease. However, she warned that if the situation remains unaddressed, leishmaniasis could affect a growing number of people in Kenya and may even rival malaria in impact.

Silent invaders: Mosquitoes and sandflies spreading in new areas

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