Blood and Mosquitoes

By Isabel C.

Mosquitoes are ubiquitous creatures, responsible for the transmission of diseases such as malaria and yellow fever. It seems as though you can never escape them and their harsh bites. While the exhalation of carbon dioxide certainly helps them pinpoint a person’s location, blood—and the iron and protein it contains—is much more important to consider. Concerning the ABO blood-type group, your blood type can have a noticeable effect on how likely you are to be bitten by mosquitoes. It’s not a matter of sipping just any blood; there is a strategic science to it.

Image Credit: Wikimedia Commons @ Tarun.real

Only female mosquitoes are after your blood, and for good reason. In order for mosquito eggs to develop properly and yield a healthy clutch, they need iron and protein—and blood from vertebrates happens to be rich in both. When it comes to iron, there are two major sources that are found in the blood. Hemoglobin iron is mostly absorbed in the tissues of a mosquito, and therefore isn’t as craved as the other type of iron: ferric-transferrin. This is iron bound with transferrin, a protein responsible for binding and transporting the bulk of iron in the body. The difference between the two is their absorbency within a mosquito’s body. Most iron from hemoglobin, approximately 87%, ends up as waste after consumption. A measly 7% is transported to a mosquito’s eggs. In contrast, the amount of ferric-transferrin excreted by a mosquito is only about 8%, while a high 77% is distributed to the eggs. In either case there is a percentage of iron absorbed into a mosquito’s tissues, 15% for ferric-transferrin and 6% for hemoglobin iron. Because there’s an urgency to absorb as much iron as possible for the purpose of egg nutrition, mosquitoes will prioritize completing the absorption period before distributing any iron to their own body. The processing of transferrin is prioritized as well, and it is sent in hefty amounts to the eggs within a 24-hour period after the parent mosquito first consumed blood. Iron from hemoglobin likely takes much longer for a mosquito’s body to process, contributing to the excessive amount that ends up as waste rather than valuable nutrition.

Based on the high rate of distribution of ferric-transferrin, it’s natural that mosquitoes would seek out this delectable source of protein and iron to produce a healthy set of eggs. However, it’s known that the majority of iron a mosquito consumes is from hemoglobin, with only a small percentage coming from ferric-transferrin; there is simply too much iron lost from hemoglobin to contribute as substantial an amount as ferric-transferrin.

Depending on blood type, mosquitoes will display differing amounts of interest in taking a person’s blood. Why is this the case? Blood cells are not the same for every individual because of the presence of antigens, miniscule proteins that cover the surface of red blood cells. These antigens are classified as A, B, and O, with the AB blood type arising from having both an A and B antigen on a blood cell’s surface. When there are no A or B antigens present, the blood type is classified as O. DNA determines exactly which blood type you have by deciding which antigens are present in your body—these antigens, however, can appear outside of blood.

Experiments concerning the mosquito Aedes aegypti showed that participants with blood types belonging to the ABO group experienced differing numbers of mosquito bites. Those with type-O blood were the preferred target and received the majority of bites, with type-A blood being the second most preferred. It’s hypothesized that the apparent desirability of type-O blood comes from the very antigens produced by DNA. These antigens are recorded in varying bodily fluids: tears and saliva have been found to contain them. Mosquitoes are then attracted to the blood type that “stands out” among the rest, presenting itself the strongest in an array of bodily fluids. This is a compelling hypothesis that has not yet been answered.

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“What about blood makes mosquitoes want to drink it?”

Mosquitoes drink blood for the purpose of distributing the iron and protein to their eggs. Blood contains iron in hemoglobin and ferric-transferrin, the latter containing a bond between iron and protein. Both supply a mosquito with the necessary nutrients to nourish its eggs, with ferric-transferrin being most heavily sought after due to its high iron yield and rapid processing rate.

“Why is blood type a factor when it comes to mosquitoes?”

The root of all blood types is DNA, which determines the antigens that appear (or don’t appear) on the surface of red blood cells. These antigens are secreted in other areas of the body and may have a say in how desirable someone’s blood is to mosquitoes. Notably, antigens are likely more pronounced in the bodily fluids of people possessing type-O blood, making them ideal for mosquito bites.

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