Invasive mosquitoes could unravel malaria progress
LONDON, Nov 2, (Agencies): Scientists say an invasive mosquito species was likely responsible for a large malaria outbreak in Ethiopia earlier this year, a finding that experts called a worrying sign that progress against the disease is at risk of unraveling.
The mosquito species, known as Anopheles stephensi, has mostly been seen in India and the Arabian Gulf. In 2012, it was discovered in Djibouti and it has since been found in Sudan, Somalia, Yemen and Nigeria. The mosquitoes are suspected to be behind a recent rise in malaria in Djibouti, prompting the World Health Organization to try to stop the insects from spreading further in Africa.
On Tuesday, malaria scientist Fitsum Tadesse presented research at a meeting of the American Society of Tropical Medicine in Seattle, suggesting that the invasive mosquitoes were also responsible for an outbreak in Ethiopia.
In January, health officials in Dire Dawa, a major transportation hub, reported a rapid rise in malaria. Tadesse, lead scientist at the Armauer Hansen Research Institute in Addis Ababa, jumped in with his team to investigate. They tracked more than 200 malaria cases, examined nearby mosquito sites and tested invasive mosquitoes for the malaria parasite.
They didn’t find many of the mosquitoes that usually spread malaria in Africa. Instead, they found high densities of the invasive mosquitoes. Tadesse and colleagues concluded the invasive mosquitoes were “strongly linked” to the outbreak.
“This new evidence is terrifying,” said Thomas Churcher, a professor of infectious disease dynamics at Imperial College London, who was not connected to the research.
He said most malaria spread in Africa has been in rural areas, as native mosquitoes don’t usually like breeding in polluted cities or artificial containers like buckets. But the invasive mosquitoes can thrive in such conditions.
“If these mosquitoes get a toehold in Africa, it could be phenomenally bad,” he said. The main mosquito-control measures used in Africa - like bed nets and indoor spraying - aren’t likely to work against the invasive bugs, since they tend to bite people outdoors.
Surveillance
Still, Churcher said patchy surveillance means scientists don’t know how common the invasive mosquitoes are or how much malaria they’re causing.
Ethiopian malaria researcher Aklilu Getnet said officials have seen a major rise in the disease this year. He blamed longer rainy seasons and the conflict in northern Ethiopia, which has drained resources away from malaria.
“We are very worried,” he said, saying that until recently, Ethiopia had seen a big drop in malaria. “What we are seeing now is a significant increase.”
Anne Wilson, an infectious diseases expert at the Liverpool School of Tropical Medicine, said African communities might consider adapting measures used in India to fight the mosquitoes, like introducing fish that eat the larvae or prohibiting containers with standing water.
She said slowing progress against malaria is further complicating efforts to stop the parasitic disease, which is estimated to kill more than 600,000 people every year, mostly in Africa.
“We’re waiting to see the impact of new tools like pesticides and vaccines,” she said. “But if this mosquito starts to take off, we may be out of time.”
Meanwhile, research in Africa found a one-time dose of an experimental drug protected adults against malaria for at least six months, the latest approach in the fight against the mosquito-borne disease.
Malaria killed more than 620,000 people in 2020 and sickened 241 million, mainly children under 5 in Africa. The World Health Organization is rolling out the first authorized malaria vaccine for children, but it is about 30% effective and requires four doses.
The new study tested a very different approach - giving people a big dose of lab-made malaria-fighting antibodies instead of depending on the immune system to make enough of those same infection-blockers after vaccination.
“The available vaccine doesn’t protect enough people,” said Dr. Kassoum Kayentao of the University of Sciences, Techniques and Technologies in Bamako, Mali, who helped lead the study in the villages of Kalifabougou and Torodo.
In those villages during malaria season, other research has shown, people are bitten by infected mosquitoes on average twice a day.
The experimental antibody, developed by researchers at the U.S. National Institutes of Health, was given by IV - difficult to deliver on a large scale. But the encouraging findings bode well for an easier-to-administer shot version from the same scientists that’s in early testing in infants, children and adults.
The US government research was published Monday in the New England Journal of Medicine and presented at a medical meeting in Seattle.
The antibody works by breaking the life cycle of the parasite, which is spread through mosquito bites. It targets immature parasites before they enter the liver where they can mature and multiply. It was developed from an antibody taken from a volunteer who received a malaria vaccine.
Research
The research involved 330 adults in Mali who got either one of two different antibody doses or a dummy infusion. All were tested for malaria infection every two weeks for 24 weeks. Anyone who got sick was treated.
Infections were detected by blood test in 20 people who got the higher dose, 39 people who got the lower dose and 86 who got the placebo.
The higher dose was 88% effective, compared to the placebo. The lower dose was 75% effective.
Protection might last during the several months of a malaria season. The idea is to someday use it alongside other malaria prevention methods such as malaria pills, mosquito nets and vaccines. Cost is uncertain, but one estimate suggests lab-made antibodies could be given for as little as $5 per child per malaria season.
Lab-made antibodies are used to treat cancer, autoimmune diseases and COVID-19, said Dr. Johanna Daily of Albert Einstein College of Medicine in New York, who was not involved in the study.
“The good news is now we have another, immune-based therapy to try to control malaria,” Daily said.
Malaria is a serious and sometimes fatal disease caused by a parasite that commonly infects a certain type of mosquito which feeds on humans. People who get malaria are typically very sick with high fevers, shaking chills, and flu-like illness. Four kinds of malaria parasites infect humans: Plasmodium falciparum, P. vivax, P. ovale, and P. malariae. In addition, P. knowlesi, a type of malaria that naturally infects macaques in Southeast Asia, also infects humans, causing malaria that is transmitted from animal to human (“zoonotic” malaria). P. falciparum is the type of malaria that is most likely to result in severe infections and if not promptly treated, may lead to death. Although malaria can be a deadly disease, illness and death from malaria can usually be prevented.
About 2,000 cases of malaria are diagnosed in the United States each year. The vast majority of cases in the United States are in travelers and immigrants returning from parts of the world where malaria transmission occurs, including sub-Saharan Africa and South Asia.