Several studies have found that mosquitos may prefer to bite individuals with Type O blood over other blood types. However, it is important to note that a number of factors may influence the insect’s choice in host including a person’s hormones, carbon dioxide emission, perfumes, and alcohol intake, among others.
As the hot 2021 summer months brought increased mosquito activity across much of the U.S., Snopes readers wanted to know if the buzzing pests were attracted to one type of blood over another. A deeper look through the scientific literature revealed that among other factors — like hormone levels or scents — there is evidence to suggest that mosquitoes may be more attracted to people with Type O blood — or at least these individuals were more likely to be bit.
To understand why these individuals are more likely to be pestered by the biting bugs, we must first understand what a blood type is.
What Are Blood Types?
A person’s blood type is inherited and determined by the presence or absence of substances known as antigens, which can trigger an immune response if they are foreign to the body, according to the Red Cross. The four major blood groups — A, B, AB and O —are determined by the presence or absence of two such antigens, A and B, that are found on the surface of red blood cells. But there is also a protein known as the Rh factor which is present (+) or absent (-) to make up the eight most common blood types: A+, A-, B+, B-, O+, O-, AB+ and AB-.
Type O positive is the most common with more than one-third of Americans with this type. Type O negative, on the other hand, is known as the "universal" blood type and is the most common blood type used for transfusions when a patient’s blood type is unknown. (To find out your blood type, a sample of your blood must be sampled or taken by a medical professional.)
What Does the Science Say?
The American Mosquito Control Association notes that there are more than 3,000 species of mosquitoes, and though host preference may vary depending on region and species, several studies have supported the claim that mosquitoes might be more attracted to those with Type O blood over others.
One such species, Aedes aegypti, is the major vector of Dengue in Sri Lanka. In 2019, scientists at the University of Sri Jayewardenepura in Sri Lanka set out to determine how certain blood types may influence a mosquito’s ability to rear offspring. Laboratory-reared female mosquitoes were exposed to all four blood groups at once in separate feeders. After feeding, the DNA of blood in mosquitoes was extracted and identified and the mean number of eggs per individual was determined. The researchers found that the highest preference was observed for the blood group O. However, no one blood type was found to influence a mosquito’s egg production over another, begging the question: Why might mosquitoes prefer one type of blood over another? (More on that later.)
A small-scale study conducted in 2004 also found that of 64 test subjects, those with blood Type O were significantly likely to have a mosquito land on them than on other blood groups A, B and AB.
A 2009 study published in Virology Journal found that individuals with O+ blood type were more susceptible than other group types to get chikungunya, a virus spread to people through the bite of an infected mosquito. The findings suggested that some people may have a genetic predisposition to the disease or perhaps are more likely to be bitten and infected by virus-carrying mosquitoes.
In 1974, researchers at Oxford University found that when physiological variables were accounted for, mosquitoes preferred the blood from hosts of blood group O. But a study conducted in 2014 and published in the peer-reviewed journal Acta Tropica found that mosquitoes were more likely to feed on either artificial membrane blood feeders — or directly on human hands — of those with AB type (40%) when compared to other groups of A (24%), B (21%), and O (15%). While the latter study does not prove that mosquitoes are more inclined to bite Type O individuals, the findings further add evidence that parasites like mosquitoes may prefer certain genetic factors like blood.
Interestingly, in both of the above studies, individuals with AB blood types were shown to have more severe cases of malaria than those of other blood types — a finding that researchers suggest indicate mosquito preference could serve as a sort of natural selection for population control.
Why Do We Want to Study Mosquito Preference?
Understanding how and why mosquitoes choose a host is not just a matter of comfortability. In much of the world, it can be a matter of life or death. The Centers for Disease Control and Prevention (CDC) calls the mosquito the “world’s deadliest animal” and credits the long-legged insect with spreading diseases like malaria, dengue, West Nile, yellow fever, Zika, chikungunya, and lymphatic filariasis. The transmission of diseases through mosquitoes kills more people than any other critter in the world. In 2017 alone, an estimated 435,000 people around the world died from malaria alone and millions more became ill with the disease.
Knowing what blood types a mosquito might be attracted to can help health experts and individuals take the necessary precautions to avoid being bit by one (more on that later). Additionally, understanding what individuals may be more likely to experience disease severity can help in the treatment of infection.
Other Factors to Consider
But blood type is not the only factor that may influence a mosquito’s choice in a host. Virginia Tech researchers wrote in the journal Current Biology that mosquitoes have the ability to learn which humans will be the most advantageous for feeding.
“How mosquitoes determine which individuals to bite has important epidemiological consequences. This choice is not random; most mosquitoes specialize in one or a few vertebrate host species, and some individuals in a host population are preferred over others,” wrote the study authors in 2018.
These factors can include pregnancy and hormonal fluctuations during various stages of a menstrual cycle, as well as carbon dioxide, the compounds contained in sweat, alcohol intake, and even a preexisting malaria infection.
How to Protect Yourself from Mosquito Bites
The CDC recommends wearing insect repellent, covering up with long clothing, and using screens and fans on doors and windows to avoid mosquitos.
“Mosquitoes bite during the day and night, live indoors and outdoors, and search for warm places as temperatures begin to drop. Some mosquitoes hibernate in enclosed spaces, like garages, sheds, and under (or inside) homes, to survive cold temperatures,” wrote the health agency.
For more information on mosquito-caused diseases and how to prevent them, visit the CDC's mosquito central.