Emory’s Professor Gonzalo Vazquez-Prokopec conducted a field study in Jigjiga, Ethiopia, last summer to investigate the emergence of Anopheles stephensi, an invasive mosquito known to thrive in urban settings and spread malaria.
Originally native to South Asia, this species has made alarming inroads into Africa in the past decade and was first detected in Jigjiga in 2018. Since its arrival, stephensi have adapted to surviving the region’s prolonged dry spells, which, in Jigjiga, typically span about three months with minimal rainfall.
The proliferation of this species in the African ecosystem presents a substantial public health concern. Due to its ability to spread disease, stephensi could exacerbate the transmission of malaria — a disease that tragically claims the lives of roughly 620,000 people globally each year, and disproportionately affects the African continent, where it’s historically been a rural disease.
Anopheles stephensi on a human, about to bite Getty Images
To investigate this emergent, city-dwelling threat, Vazquez-Prokopec’s team, with funding support from the Emory Global Health Institute, partnered with Ethiopia’s Jigjiga University in 2023 to study the behavior of stephensi during the dry season, its insecticide resistance and other factors that could be pivotal in devising effective measures to safeguard communities against a potential malaria epidemic.
Vazquez-Prokopec answers questions about the adaptable stephensi, findings from the study and what Americans should make of it.
Why is stephensi different than other mosquitoes?
Stephensi often live in surface water habitats, like ponds and natural wetlands, but what makes them unique is that they can also live in city habitats where water is stored, like man-made containers, buckets, water tanks and construction pits.
When are people most likely to get bitten?
Stephensi typically bite outdoors in the late afternoon into the early evening when people are still out doing regular daytime activities.
Why are these mosquitoes spreading into urban areas?
Much of northern Africa has a long dry season where the surface water dries up. This is problematic for mosquitoes because they need water to complete their life cycle.
Researchers investigate construction site water pits for Anopheles stephensi mosquito larvae.
This problem could worsen because construction pits there are so common due to an upswing in infrastructure development. The expectation is that by 2050, over 60 percent of Africa is going to be urban, unlike any time in history.
What challenge does the emergence of stephensi in Africa present?
The challenge we have now is that stephensi is invading cities and urban areas, where many people have never been exposed to malaria because it has historically been a rural disease in Africa. This could lead to severe outbreaks and transmission of malaria.
What methods can be used to control stephensi in Africa and prevent potential malaria outbreaks?
A researcher uses the "Prokopack." Invented in 2009 by Vazquez-Prokopec using simple hardware store materials, the Prokopack is the most widely used device for collecting adult Anopheles stephensi today.
From all the available tools, what looks to be the most promising currently is larvae control because we know where they breed.
Larvivores fish, or fish that eat mosquito larvae, are often cited as a classic method malaria control. Before insecticides were invented, larvivores fish were used. And so, using these fish — which are already present in the region — at construction site water pits during the dry months could present an environmentally friendly and sustainable way to reduce the risk of a malaria outbreak.
In 2023, the U.S. had its first locally acquired cases of malaria in over 20 years. Should Americans worry about getting malaria from Anopheles stephensi?
Anopheles stephensi don’t exist in North or South America. There are other species of Anopheles mosquitoes in the U.S., but not endemic transmission. What leads to malaria transmission here is the introduction of parasites by travelers. When a traveler returns infected with malaria parasites, the parasites may be able to infect a small number of local Anopheles mosquitoes. If the mosquitoes survive the incubation period of the parasite, they may be able to infect other humans they bite. That’s a very complex set of chains that need to happen for somebody to get locally acquired malaria.
Now, what we saw with malaria in the U.S. in 2023 is a unique situation. We had one case in Texas, five in Florida and one in Maryland. Those seven people got infected, got ill and thankfully recovered, but this situation is not one of concern from a public health perspective.
The expectation is that the U.S. isn’t going to become anything like Africa with regard to malaria transmission because we have different housing and different lifestyles that prevent us from getting the number of mosquito bites that people in Africa get.
However, with climate change and other lifestyle changes, there is a logical expectation that the locally acquired malaria we saw last year isn’t going to be an anomaly. It's going to be frequent, but not necessarily to the level of Africa.
Are there any other mosquito-borne viruses people living in the U.S. should be aware of?
For people living in the U.S., the more concerning mosquito-borne virus is dengue, which is the only tropical disease that’s expanding globally. The mosquito that transmits dengue is Aedes aegypti. We don’t have it here in Atlanta, but it’s becoming more common in Florida, Texas and California.
The threat of local dengue transmission is real for these southern states currently invaded by Aedes aegypti. As in previous years, there is a high chance of observing local dengue transmission as residents visit touristic areas in other countries impacted by dengue. Also, visitors may introduce the virus if they’re infected and visit areas with Aedes aegypti.
What should you do if you’re traveling to a country impacted by dengue this summer?
There's nothing suggesting that the U.S. is going to get dengue outbreaks like in Mexico, but what we do expect are localized outbreaks. The important thing to remember is that early diagnosis, detection and confirmation of a locally acquired case versus an imported case could define the timing of a response to limit the impact on public health.
About Gonzalo Vazquez-Prokopec
Gonzalo Vazquez-Prokopec is a professor in Emory University’s Department of Environmental Sciences. As a global expert in vector ecology and control, Vazquez-Prokopec has been involved in tracing outbreaks of dengue, Zika and chikungunya for over 15 years. He is a member of the World Health Organization's Strategic Advisory Group on Dengue Immunization and participates in working groups on Anopheles stephensi control. His work aims to create a framework to better understand the linkages between people, the environment and pathogens.