Early 2022 saw an increase in malaria cases in Dire Dawa (Ethiopia), with over 2,400 people being sickened. The spike in infections was the work of an invasive mosquito species that’s spreading across Africa, scientists report.
This evidence, presented at the American Society of Tropical Medicine and Hygiene’s annual meeting in Seattle on November 1, shows that an invasive vector can be transmitted. drive malarial outbreaks. The species can also thrive in urban areas, potentially posing a threat to millions more people on the continent.
Anopheles StephensiThis mosquito is a native to India, and the Persian Gulf where it is a major vector. PlasmodiumParasites cause malaria in people (SN: 10/26/20). The primary vector of malaria in Africa is Anopheles gambiae. A. stephensiThe species was first found on the African continent in Djibouti, in 2012. It has since been discovered in Nigeria, Somalia, Ethiopia and Somalia.
It wasn’t clear what kind of malarial burden the invasive mosquito could bring to Africa, says Fitsum Girma Tadesse, a molecular biologist at the Armauer Hansen Research Institute in Addis Ababa, Ethiopia. In the eight years after the mosquito’s arrival in Djibouti, the country reported a 40-fold increase in yearly malaria cases, Tadesse says. However, no one has ever linked the two. A. stephensiTo the increase.
So when malaria cases suddenly rose in Dire Dawa — from 27 cases to 260 in just three weeks in early 2022 — Tadesse and his team jumped in to investigate.
The researchers tracked 80 patients in the city who had sought care for malaria at a local or university clinic, as well as 210 patients who had sought treatment for other reasons, and they screened the patients’ household members for malaria. The team also scanned the patients’ neighborhoods for the presence of mosquito adults and larvae within a 100-meter radius of households, or in the cases of students that visited a clinic, dormitories.
The team discovered that malaria patients lived mainly near water sources infected by the invasive mosquitoes. A. stephensi. Dorms and households located near aquatic habitats harbouring A. stephensiLarvae were three times more likely than those who weren’t near water sources to have a family member or dormmate test positive for malaria. And most of the adult mosquitoes the team caught — 97 percent — were of the invasive species, the only mosquito species that the researchers found carrying Plasmodium parasites.
A. stephensi “prefers to breed in water storage containers that are typically common in rapidly expanding urban settings,” Tadesse says. The native mosquito species A. gambiaeHe adds that people tend to use natural water sources such as small pools in rural areas, and are therefore more likely to drink from them. There is a concern that the growth of A. stephensiThe mosquito could be exploiting many new water sources, just like the urbanization of Africa.
“This expands the malaria problem from a predominantly rural problem to an urban problem,” says Teun Bousema, an epidemiologist at Radboud University in Nijmegen, the Netherlands.
Another research group did a 2020 study and concluded that the spread of the invasive mosquito could be catastrophic. Additional 126 million city dwellers could be at-riskYou could contract malaria.
“The spread of Anopheles Stephensi is concerning because this species has a number of characteristics that make it difficult to control,” says Tanya Russell, a medical entomologist at James Cook University in Townsville, Australia, who was not involved in the study. The insects can lay eggs in almost any water source and can also survive long periods without drying out. “This is very uncharacteristic for malaria vectors.”
Russell states that the main vector control methods for malaria-carrying mosquitoes are insecticide-treated bednets and indoor spraying of a residual insecticide. However, this has changed since. A. stephensi also bites outdoors, the mosquito’s spread may blunt the efficacy of these tools.
The key next steps, Tadesse says, are interventions to reduce transmission of the deadly parasites, including targeting the mosquito’s larval phase with chemicals and encouraging communities to cover and secure water containers to prevent mosquitoes from laying eggs in them.
“The window of opportunity to do something about this species is closing,” Bousema says. “So, I really think this calls for very urgent action.”
