By Cameron Webb, Ph.D., and Nur Faeza Abu Kassim, Ph.D.
Mosquitoes need blood. Although they can obtain blood from a range of animals, it is their propensity to bite people that causes so many pests and public health risks around the world. More than half a million people die each year from mosquito-borne disease, and even during the COVID pandemic, mosquito bites will infect hundreds of millions of people around the world with pathogens. , such as arboviruses and malaria parasites.
We know mosquitoes bite people, but why do they set you apart from the crowd? This is a commonly observed phenomenon, especially by scientists who need to ensure that their volunteers attract enough mosquito bites to ensure the reliability of their insect repellent research and evaluations. But what about those people who are more likely to be bitten by mosquitoes? Is it really because they have “sweet blood” or is it just the kindest thing we can say to our friends and family who are itchy and biting?
Mosquitoes pick up a cocktail of clues when looking for a blood meal. The carbon dioxide we exhale, our body temperature, the chemicals found on our skin, and perhaps even our scent choices can all determine our likelihood of being bitten. But what about our blood type? It may make sense that, as mosquitoes crave blood, our attraction to mosquito bites may be influenced by our blood type.
Recently published collaborative work between scientists from Pakistan, Malaysia, China and Australia demonstrated that mosquitoes can taste for type B blood. But the results do not mean that those with other groups blood can store insect repellent.
The research, published in December in Scientific reports, sought to determine how human blood groups influenced host-seeking behavior and mosquito fecundity. Anopheles stephensi. This mosquito is one of the most important vectors of malaria parasites in many countries ranging from South Asia to Africa. It is well adapted to urban environments and is a driving factor in malaria epidemics in Pakistan, Iran, Afghanistan and India. Its recent spread in Africa is a major concern for authorities where many countries are already suffering from the burden of mosquito-borne diseases.
Understanding the host-seeking behavior of this mosquito may provide opportunities for identifying individuals at high risk of mosquito-borne disease and therefore targeted public health actions, or it may also provide new insights into the development of mosquito control or monitoring technologies.
In a series of laboratory studies, we and our fellow researchers investigated how different types of human blood (i.e. A, B, AB, O) were digested by the mosquito and how these blood meals influenced the number of eggs developed and the survival of later immature stages. . However, it was the use of wind tunnel bioassays that provided the most fascinating result. Groups of 100 mosquitoes were released into chambers with the choice of having five individual tubes flown, each containing one of four blood types, in addition to a control, all supplied by an artificial blood supply device .
The result was surprising considering the strong preference for a particular blood type: more than 70% of mosquitoes were attracted to type B blood. This result was confirmed by some electroantennography experiments, in which tiny electrodes are attached to the mosquito’s antennae to record their blood type response, which demonstrated that mosquitoes had a significantly stronger response to type B blood.
This study was the first to show that Anopheles stephensi shows a preference for type B blood, at least in the laboratory. The result may pave the way for further investigations to translate this observed mosquito behavior into better public health outcomes for communities in countries where A. stephensi is present.
Care should also be taken in extrapolating these results from the laboratory to the field. This result helps us to understand A. stephensi and their host-seeking behavior, but there are thousands of other species of mosquitoes buzzing around the world, and such a preference is highly unlikely to exist in all of them. There are already well-documented differences in the host-seeking behavior of some of the world’s most important mosquito pests. Some prefer mammals, birds, frogs or even earthworms. However, even for mosquitoes that prefer to feed on humans, there may still be a much more complex puzzle to solve than simply determining an individual’s blood type.
The attraction of mosquitoes to humans is likely due to a wide range of factors, and it is clear that the chemical cocktail of odors produced on the skin is likely to play an important role as well. The host-seeking preferences of other medically important mosquitoes, such as Aedes aegypti and Anopheles gambiae demonstrated that there may be new combinations of chemicals that could be used to improve the effectiveness of mosquito monitoring. But it could take scientists a while to figure out the host-seeking behavior of our most “dangerous” mosquitoes. There is still so much to learn about the ecology of so many other mosquitoes, and determining who or what they are most likely to bite is still perhaps a little low on our list of research priorities.
What does all this mean if you go hiking? The important thing to remember is that just one type of mosquito is unlikely to bite you. So no matter how much of a “mosquito magnet” you think you are, no one is likely completely immune to mosquito bites, so you should always take these precautions to cover up and wear insect repellent to avoid bites of mosquitoes.
Cameron Webb, Ph.D., is Associate Professor in the University of Sydney Department of Medical Entomology and NSW Health Pathology. With over 25 years of experience as a mosquito researcher, Webb provides expert advice to local, state and federal government agencies in Australia on the management of mosquitoes and mosquito-borne diseases. Twitter: @mozziebites. Facebook: www.facebook.com/mozziebites. E-mail: [email protected]. Nur Faeza Abu Kassim, Ph.D., is an Associate Professor in the School of Biological Sciences at Universiti Sains Malaysia and COMBI Penang in Penang, Malaysia. An expert in medical and epidemiological entomology, her research focuses on mosquito-borne diseases and the role of vectors in disease transmission. She is also actively involved in community outreach programs on public health issues. Twitter: @aija81. E-mail: [email protected].