I think you may hear of that someone says “people who are blood group A are mosquitoes’ magnets”, or someone mention that O type of blood always attract mosquitoes. Many of my friends have complained that their own blood types are mosquitoes’ favorite, but they have different types of blood，including A, B, O and AB (covering all types of blood). Certainly, some people are badly bitten by the mosquitoes especially in the summer. Is it because there is a specific type of blood attracting mosquitoes mostly?
In order to find the correlation or relationship between mosquitoes and blood types, some scientists did the experiment which had been published in “Nature “in 1972. The experimenters chose pairs of subjects who contrasted in ABO blood group statues to see whether physiological factors could affect the selection of human hosts for feeding by mosquito. To be specific, 102 subjects put their arms into a box which contained 20 female mosquitoes during the ten minutes’ testing time. Analysis of the blood group data reveals that the mosquitoes preferentially selected hosts of blood group O. However, the basis of this result is not obvious, although they took more than 100 times experiments (repeated experiments). Additionally, this experiment was done in the seventies of last century, the period that people had still explored mosquitoes. So this conclusion is not very convincing.
Before I try to explain the reason that mosquito like some certain types of blood, I’d like to find out that what in our body attract mosquitoes, like the heat we release， chemical components of our sweat, or something else.
Actually among these factors, CO2 (carbon dioxide) is the main clue for mosquito to find you. The airflow of CO2 can largely help mosquito to find direction and lock target. In field experiment, mosquito trap containing CO2 can trap more than 8 to 45 times of numbers of mosquitoes than mosquito trap without containing CO2. Although different types of mosquitoes may have a little difference, they usually depend on CO2 to find targets. Cooperating with 1-octen-3-ol and lactic acid (a component of human sweat), mosquitoes are easier to find targets. DEET, (N,N-diethyl-meta-toluamide) the world’s most widely used topical insect repellent, with broad effectiveness against most insects, strongly inhibits the co-receptor of mosquitoes so that DEET can work well.
So a man dripping with sweat are mosquitoes favorite because their sweat and CO2 releasing by gasping for breath have fatal attraction for mosquitoes. Also, people with faster metabolism rate easily attract mosquitoes.
Now let’s go back to the experiment I mention above. The leader of the experiment in 1972 is Corinne Shear Wood, a pioneering medical anthropologist. She did other experiments to improve the existed experiment and eliminate confounding variables, just like the experiment we saw in the SC200 class which repeating and modifying to get real conclusion. In the experiment, she segmented the landing and blood meal of mosquitoes; on close examination, she also chose the test sample with different skin pigmentation, age, sex, skin temperature, degrees of subcutaneous fat and relative nutritional status. But none of these factors could be demonstrated to be acting as host determinants. In “New Evidence for a Late Introduction of Malaria into the New World”, she points out that the result of investigation suggest that a factor which has definite attraction or repulsion value to the mosquito is related, to statistically significant degree, to the subject’s ABO blood-group status. In conclusion, it reveals that the hosts with blood-group O are often chosen by mosquito. And blood-group O has more dominant attraction than blood group A and B.
After 20 years, in 2004 Japanese scientist Yoshikazu Shirai had started to study this question again. He did three different studies that are landing preference among ABO blood groups, among secretors or nonsecretors, and among ABH antigens. He got the result that despite differences in the methods used in these studies, the landing preferences are the same; that is, O > B > AB > A. It seems that we have already gotten correct answer. But, actually, not. His experiment has different result with Wood’s. In his result, although O has much attraction than A, O doesn’t have more obvious attraction than B and AB. In addition, according to his report, Shirai said “ even the landing tests on ABH antigens do not provide an explanation for the landing preference among ABO blood groups, and there may be other unknown influences underlying the differences of ABO landing preference. In fact, ABH antigens are thought to exist on human skin in low concentrations, and we suppose that mosquitoes cannot perceive them.”
In a short, he thought that his report could not prove that blood group affect mosquito feeding habits because of the lack of clear preference among human blood groups exhibited in his study.
To sum up, currently our studies about blood groups and mosquito feeding habits are superficial. It is probably because we don’t have large sample size, or we cannot control many confounding variables. So now we don’t have exactly causal relation between blood group and mosquito feeding habits.