Beer increases amount of mosquito bites

Carlos Brisola Marcondes

Full professor at the Department of Microbiology, Immunology and Parasi-tology (MIP) at the Biological Sciences Center (CCB) at the Federal Univer-sity of Santa Catarina (UFSC)

The skin and the exhaled air may contain substances able to affect the attractiveness of mosquitoes, differentiating individuals and creating a different attraction for children and adults, varying among races

One of the main determinants for transmission of vector-borne diseases is the frequency the reservoirs are bitten. In this way, factors able to influence this amount are of epidemiological relevance. For example, malaria control is more efficient if it targets mainly individuals that are more bitten. Pregnant women are among the individuals that attract more mosquitoes, probably due to the greater amount of exhaled air and higher body temperature.

Among many other factors, the consumption of foods and drinks may influence the attraction of mosquitoes and other blood feeding insects. Similarly, high alcohol consumption, especially in endemic areas, is a very important public health factor, since it seems to increase insect attraction. To assess this effect, some tests were developed comparing the attractiveness of mosquitoes between volunteers who ingested beer and those who did not.

In a study in Japan and another in Burkina Faso, the effect of ingestion of beer was respectively checked in Aedes albopictus and Anopheles gambiae. For the first, 350 mL of barley beer was used and on the second a non-reported amount of beer made with sorghum (8% proof) locally called dolo.

In both studies, a significant increase in the attractiveness of insects was observed, and the second showed stimulus for mosquito flight. The latter effect was assigned to alcohol dispersion in the body, with the presence of ethanol in perspiration, but considered this did not influence over attractiveness. In the first study, body temperature varied, depending on ethanol tolerance. The second study observed the reduction of body temperature and amount of exhaled CO2 (not influenced by beer) had no significant effect over attractiveness. The authors supposed that beer would increase the production of kairomones (volatile substances that hosts produced by hosts and that attract vectors) as 1-octane-3-ol, that would attract more mosquitoes.

The ingested amount of beer in the first study was very small but still able to influence mosquito attraction. More detailed tests with variable amounts and types of drinks, with exposure to vectors at different times after ingestion would be useful to understand the transmission of diseases such as malaria, dengue, Zika, Chikungunya and kala-azar.

Skin and exhaled air contain substances that affect mosquito attraction, differentiating individuals and making attractiveness among children different that among adults. There are also variations between races, but the chemical ecology of arthropods attraction is a difficult and little understood matter. This mosquito and other insects attraction process for feeding depends on other complex factors, involving smell and vision – mainly among daytime habits insects, as the tsetse fly (transmitter of the sleeping illness) and our very well-known Aedes aegypti. Skin bacteria flora also has great influence in skin odor, and it has been reported that sand flies are attracted to a Belgian cheese with substances similar to feet odors.

Some authors also suggest studies involving other beverages besides beer in order to verify whether it is the alcohol or some other substance in these drinks that affect mosquito behavior. It would also be interesting to develop tests in Brazil, with several insect groups as black flies, sand flies and biting midges, and locally consumed beverages, as cachaça. Counting only two studies in the field, it is an open area for researches, has great sanitary relevance and could be developed in laboratories or in field using olfactometers. “A coleague from Manaus reported that when his friends drank beer they attracted so many black flies as himself, who usually drinks it”.

Another factor the studies have not considered when increasing the amount of bites is the probable defense reduction against the bites (“drunk skin has no owner”). Therefore, caution when drinking, especially in high doses, since this could increase your chances of becoming infected with malaria, dengue or others.…