Billions of people are at risk of contracting a mosquito borne disease each year, with over a million people dying each year. Malaria is believed to be responsible for half of mosquito related deaths each year, with the remainder being diseases such as yellow fever, chikungunya, dengue fever etc.
Mosquitos are all two-winged insects in the order of Diptera. Anopheles, Culex and Aedes are the generas to know as they are responsible for most human bites and disease transmission. Interestingly, only female mosquitoes are biters, due to the fact that they require blood to help produce eggs. They typically require a "blood meal" every 3-4 days. The males are content with flowers and nectar. Different species prefer to feed at different times, during the day. For example, the Culex mosquito which carries diseases such as West Nile, Japanese encephalitis and filariasis prefers to bite from "dusk to dawn". This helps travelers avoid bites by limiting outdoor activity during those times.
Experienced travelers should already be familiar with some of the disease that mosquitoes carry. Yellow fever and dengue fever are two common viral illnesses travelers need to be aware of. Fortunately, Yellow fever is vaccine preventable.
Malaria is another disease that travelers need to know. This blood-borne, parasitic infection is a global killer. Chikungunya fever is carried by the Asian Tiger Mosquito and the same mosquito which carries yellow fever. Zika virus and filariasis are also worth mentioning. There are many other infections carried by mozzies and they all help make up a list of reasons to not get bitten!
The things that attract mosquitoes to bite are not completely understood and involve all of the mosquito's senses. Mosquitoes lock on to their target with the help of visual and thermal clues, plus a very developed sense of smell. The time of day a mosquito chooses to bite help illustrate what clues it uses to find your body. Day biters are believed to have a more developed visual sense and are attracted to darker colors, such as your favorite black t-shirt. Lots of movement helps draw attention as well. Dusk to dawn biters are known for a more elaborate heat sensing system, being attracted to the heat and moisture of the skin. People who sweat more are also believed to be more attractive to mosquitoes. Perfumes, scented soaps, and lotions are also likely attractants. Several good hypotheses exist about the likelihood of mosquito attraction to carbon dioxide, the gas exhaled from breathing. Certain types of mosquitoes carry a fondness for certain body locations such as ankles, face or hands. Several well-written studies have shown some statistics:
Travelers need to use all of their savvy to prevent bites and stay healthy on their trip. The first line in mosquito bite prevention is clothing. Lighter colors are advised and long sleeves and pants act as a barrier to the attacking mosquito. Think of the clothing as a suit of armor that is difficult for the insect to penetrate. Caution must be used as wearing long sleeves and pants in hot, tropical environments can lead to overheating and dehydration.
Bed nets are another first line of protection, acting as a mechanical barrier to keep mosquitoes away from you while you are lounging in bed. Travelers who are staying in climate controlled hotels with permanently closed windows are likely able to do without nets. However, those in more rural areas or hotels with open windows and lots of outside access should be prepared with a bed net. Bed nets are a major method of disease mosquito-spread disease, in developing countries.
Permethrin is an insecticide that kills or stuns bugs. Developed from the flower Chrysanthemum, permethrin should be applied directly to clothing or fabrics. The application should be made to tents, bed nets, shirts, pants and curtains. Studies have shown that permethrin lasts for approximately 2 weeks and is non-staining, almost odorless and can remain through several washings. Proper application is typically done with a spray, using just enough to moisten the fabric and the allowing 2-4 hours to dry. Permethrin also provides protection against other disease-carrying insects such as mites, fleas, ticks, and flies. Most "mosquito coils", burned to prevent mosquitoes in a limited area, contain permethrin. Even though the chemical has a low ability to be absorbed through the skin and has a very low toxicity to mammals, it should not be applied directly to the skin. There are better measures to be applied, to your skin.
DEET (N,N-diethyl-meta-toluamide) is the premier choice for mosquito bite prevention. DEET is an older compound with its safety and efficacy very well studied. First used by the military in the 1940's and entering civilian use in the 1950's, DEET has been the subject of many studies looking at user safety and adverse reactions. Working by disrupting the mosquito's sense of smell, it helps to "jam the radar" of the mosquito trying to find a target. Intensive testing of over 20,000 other compounds has shown DEET to be the best in terms of duration of protection and types of insects it repels. DEET is effective at repelling fleas, ticks, mosquitoes, and chiggers.
Typical commercial preparations of DEET include gels, lotions, sprays and it can be found in various concentrations, up to 100%. Most travel medicine literature agrees that a concentration of 35% DEET is optimum, providing decent protection for several hours and limiting potential skin irritation side effects. The American Academy of Pediatrics advises the use of only a 10% DEET concentration, in children less than 12 years. Typically, the higher the concentration of DEET, the longer the protection time afforded. One study looked at 12.5% DEET offering 6 hours of protection, while 25% compounds only provided 8 hours.
DEET has been used by millions of people, for over 50 years. Studies conducted by the US EPA looked at chronic and acute exposures, potential to cause cancer and possibility of birth defects. These studies showed no formulation change was necessary, to improve safety profile. There are, however, cases in medical literature of DEET toxicity. Of most interest and concern is the report of 14 cases of encephalopathy (brain disorder), of which 13 cases were in children younger than 8 years of age. Many of the cases involved long-term use of excessive doses and inappropriate use of the products. Most common calls to poison control centers involve the accidental spraying of DEET in the eyes. Over the last 50 years of use, DEET has shown a remarkable safety profile.
Despite the efficacy and safety profiles of DEET and Permethrin, some travelers may elect to try and protect themselves with "natural mosquito repellents". Many natural compounds have been evaluated for anti-mosquito properties. Some include eucalyptus, garlic, citronella and vitamin B. Citronella, derived from the grass Cymbopogon, is the most promising. Studies have shown protection against bites, but for shorter times than DEET. One study showed a 10% citronella compound provided 84% protection over 4 minutes, versus a 14% DEET solution that gave 96% protection. Another study has confirmed that the same 5% citronella offered 88% protection over a 2 hour period. Generally, citronella will require more frequent applications for decent protection.
Citronella candles and incense have been proven to deter mosquitoes in backyards, porches, and rooms. Investigations have shown a 42% reduction in bites from those nearby candles versus those who had no protection.
This has been a "holy grail" for mosquito bite prevention, but no effective data has been shown. Ingestion of certain foods has long been believed to act as bite deterrents but has yet to be proven despite many attempts. Mosquito attraction is a complex system involving multiple methods, other than simply sense of smell. Garlic, onions bananas and even oral preparations of vitamin B have all been disproved.
Mosquitoes carry disease that can, at the least, ruin a trip with unwanted illness. Severe infections, carried by mosquitoes, can result in death. Prevention of mosquito bites is a key feature of travel health and needs to be thought of, well in advance of a trip. Considerations in selecting an appropriate mosquito repellent include:
Most importantly, the decision to use nothing is foolish. A combination of 35% DEET skin spray and permethrin-treated clothing is considered the most effective method. People who used this combination method of protection showed a 99.9% protection over 8 hours. This was in stark contrast to those who were unprotected and received an average of 1,188 bites per hour! Another thing to remember is that it only takes one infected mosquito bite to make you sick!
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