Q&A: Test quickly detects invasive malaria-spreading mosquito
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Key takeaways:
- A new low-cost test can rapidly detect an invasive species of malaria-spreading mosquito, according to researchers.
- A. stephensi breeds in artificial containers and thrives in both urban and rural environments.
Researchers developed a low-cost rapid test to detect an invasive species of mosquito that has adapted to live near humans in urban environments, which they hope can be used in areas far from medical labs.
The test can detect Anopheles stephensi mosquitoes, which over the last decade have made inroads in Africa, first in Djibouti and then spreading to Ethiopia, Sudan, Somalia, Nigeria, Kenya, Ghana and Eritrea, according to the researchers.
A. stephensi can be found near water, but the mosquito is known for thriving in urban and rural environments, persisting through dry seasons by breeding in artificial containers. Interventions meant to prevent mosquitoes from spreading malaria — such as bed nets and insecticides — are less effective against A. stephensi mosquitos because, once hatched, they live outside, unlike other malaria-spreading Anopheles mosquitoes that sleep and rest inside at night, according to experts.
The world’s first two malaria vaccines have been rolled out in the last several years, but mosquito control remains a target in malaria interventions.
To help combat A. stephensi, Cristina Rafferty, a molecular biologist with the U.S. President’s Malaria Initiative at the CDC, and colleagues developed an assay that requires a heat source and reagents, which can be used with or without DNA extraction, and can confirm presence of the mosquito in about 30 minutes, even in a pooled sample of larvae or insects.
Healio spoke with Rafferty about how the test works and its potential for reducing the spread of malaria.
Healio: How does the test work?
Rafferty: It detects the specific A. stephensi invasive mosquito. The way it works is somewhat like a glorified PCR, except that instead of taking many steps, it takes one step, at one temperature and in 30 minutes. Furthermore, it is very user friendly because the interpretation is very easy. It is a pH base, which means that when there is amplification of A. stephensi, there’s change in color. The reaction starts. If there’s A. stephensi in the mix, then it turns yellow — so it is very easy to detect.
Healio: Who is going to want to use this test?
Rafferty: Ideally, we are looking at deploying this in the field, especially and obviously in Africa, where this invasive mosquito is spreading somewhat rapidly and where it really threatens to overcome all of the positive things we’ve done against malaria in the last 30 years.
This mosquito is very different than any of the mosquitoes that historically have transmitted malaria. It is an urban mosquito that likes to breed in manmade containers, and it is not seasonal, so it is there all year long. It also lives outdoors instead of feeding and resting indoors, so our typical interventions like bed nets and indoor residual spray do not work against it.
When a country is able to detect it quickly, then they can go ahead and start interventions quickly as well, which normally look at larval surveys and larval intervention, because once the mosquito emerges, it’s outdoors and is very difficult to control. So, you want to target them at the larval stage.
Larval interventions are not usually something that Africa does against mosquitoes because their normal malaria transmitting mosquitoes are not breeding in that kind of container.
Healio: How much does the test cost?
Rafferty: The cost is very similar to a standard PCR. Right now, however, in order for you to detect A. stephensi, you would have to PCR and then follow it with sequencing, which, of course, is very, very expensive — and most of the laboratories in Africa are not set up for it. They either have to send their samples elsewhere, stateside, or to a different country. That’s not only costly, but it is time consuming. The idea with this assay is that it can very quickly pinpoint A. stephensi. The results can [also] be shared with the national malaria program, which then can go ahead and make decisions about interventions much more quickly.
Healio: Is this something that other nations will invest in or is the United States going to manufacture and distribute the test?
Rafferty: It is being deployed as a tool for countries to use either individually, or other entities that might be supporting countries elsewhere can invest in it. But it is set up as a standalone assay, so anybody who is working in epidemiological surveillance can adapt it easily to their work. So, it is not being deployed just only from the CDC; it’s simply an assay that is another tool for field laboratories to use.
Healio: Is the test available yet?
Rafferty: The reagents are widely available — it’s just a matter of laboratories ordering the primers for use and the reagents. Yes, people can start using it.
It has been deployed to Kenya already, and they used it in the field to validate it and make sure that it would work in the field. There are also plans for other countries. Ghana and Ethiopia have already ordered the reagents or have them on hand, so they are deploying it to the field. I think Tanzania will be deploying it in September. There are also other entities out there that will be doing some mass trainings for different countries to expose them to the test so that they know it is available.
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