Photo of a mosquito biting skin

Insects and their relatives — ticks, mites, spiders, and so on — are commonly known as arthropods. This group transmits a variety of diseases that are responsible for approximately 2 percent of deaths worldwide. Diseases transmitted by arthropods range from Lyme disease and West Nile fever in the United States to malaria and dengue fever in areas such as Africa and parts of Asia. In many cases, simple precautions can significantly reduce, if not prevent, the risk of transmission.

Some insect-borne diseases, such as malaria, are reappearing in areas where the disease was thought to be eradicated. Some diseases can be prevented by vaccinations or preventive use of specific medication, but for many other diseases the only preventive measure available is avoiding arthropod bites in the first place.

Preventing Bites

  • Covering as much skin as possible is an important precaution against arthropod bites. If possible, long-sleeved shirts tucked into long pants are recommended in areas where arthropod-borne diseases are common. A hat will help to protect your face.
  • When hiking in forests or jungles, pants should be tucked into socks. Open shoes should not be worn on hikes. Light colored clothes help detect ticks more easily. According to the CDC, prompt removal of attached ticks can prevent some infections.
  • Exposed skin should be covered in insect repellent containing the chemical DEET (N,N-diethyl-meta-toluamide). The higher the DEET concentration — up to 30 percent — the longer the protection provided by the repellent. Studies show that no increased protection occurs in concentrations over 30 percent. The recommended concentration for children is 20 percent, and the maximum concentration allowed for children is 30 percent. Do not use DEET-containing repellents under clothes, and wash your skin when coming back indoors. Do not spray repellent on face, instead spray on your hands and apply to face. 
  • A new controlled-formula containing 20 percent DEET is now available on the market. It provides longer lasting protection with lower concentration of DEET, while greatly minimizing the amount of DEET that's absorbed through the skin. 
  • Cover clothes and shoes in repellent containing permethrin. After spraying permethrin on clothes, allow them to dry before wearing. Permethrin will bind to fabric, and can last through five washing cycles. Never apply permethrin to skin. 
  • If you sleep in non-screened, non-air-conditioned accommodations use bed nets, preferably treated with permethrin. Nets should be tucked firmly under the mattress, or extend all the way to the floor. Before using the net, make sure it isn't torn, and check that no mosquitoes are inside the area you are going to protect with the net. Nets should have a mesh size no larger than 1.5 mm. Permethrin protection can last for months on unwashed nets. Bed nets are available in sporting goods stores.

Insect-borne Diseases


According to the WHO, malaria is found in more than 100 countries in the tropics and sub-tropics visited by over 125 million travelers each year. Since the 1970s, malaria has been on the rise reappearing even in areas where it was thought to be eradicated. Current statistics indicate that worldwide, there are an estimated 2.7 million deaths, and 300 to 500 million cases of malaria annually. (Keystone, Preventing Malaria in International Travelers, Journal of Travel Medicine, Vol 8; 3; Dec 2001)

While several drugs are available for the prevention and treatment of malaria, different drug resistance patterns have emerged around the globe. It is therefore extremely important to consult a travel medicine specialist who is familiar with the resistance patterns in your destination. A false sense of security fostered by taking the wrong preventive drug can increase the risk of exposure.

Malaria is caused by any one of four parasites from the Plasmodium family, transmitted through the bite of the female Anopheles mosquito, which bites mainly in the evening and night hours. The risk of infection is highest at the end of the rainy season. Infection at altitudes over 1500 m (approx. 4921 ft.) is rare.

Symptoms of malaria are similar to the flu, with fever, chills, head-and-muscle aches, and possibly vomiting and diarrhea. Jaundice (yellowing of the skin) and anemia (too few red cells in the blood) may also occur. Symptoms will develop no sooner than seven days after exposure, but may take months to appear. WHO recommends that travelers who visit affected countries and develop a fever within three months of returning home be tested immediately for malaria The CDC recommends being tested for malaria if fever develops within one year of returning home.

Early diagnosis and treatment are essential— the most severe form of malaria, called falciparum malaria (caused by Plasmodium falciparum), can be rapidly fatal if treatment is delayed by more than 24 hours. Other forms of malaria are usually not life threatening, though the symptoms can come and go for years.

Malaria is especially severe in pregnant women, where it can prove fatal to the mother and the baby she's carrying. For this reason, it is strongly recommended that pregnant women not travel to malarious areas.

Several drugs are available to prevent or treat malaria. The choice of drugs will depend on several factors including the destination of travel and the health status of the traveler. It is extremely important to take the medicine exactly as directed, and for the length of time specified. Failure to follow instructions accounts for many cases of malaria in travelers.

In cases where access to medical facilities may not be possible in a timely manner, travelers will be given a "stand-by" drug (different from the one used for prevention). The stand-by drug should be taken as directed if fever develops while away from medical facilities, but medical help should be obtained as soon as possible.

Yellow Fever

Yellow fever is found in sub-Saharan Africa and areas of Central and South America. According to the WHO, yellow fever epidemics have increased in number since the 1980s.

Mosquitoes that bite during the day, most notably the species Aedes aegypti, spread the disease. The risk of infection increases in rural and forested or jungle areas, but risk does exist in urban areas. The virus that causes yellow fever infects humans and monkeys. For that reason, countries where the right mosquito species exists in proximity to monkeys are considered at risk for yellow fever, even if no human cases have been recorded there (many parts of Asia fall into this category).

Yellow fever causes initial symptoms that resemble the flu, with fever, vomiting, headaches, slow pulse and muscle aches. According to the WHO, about 15 percent of patients progress to a second phase of the disease, developing jaundice and uncontrolled internal bleeding. Half of the patients who progress that far die within two weeks after the initial symptoms appear.

Prevention, as with any other disease, is the best medicine. Follow the guidelines for avoiding mosquito bite. People who travel to areas where yellow fever is common should be vaccinated against the disease. Certain countries require the vaccine for all entering visitors, unless a medical waiver was obtained before the trip.

It is important to remember that countries that do not require the vaccine are not necessarily free of yellow fever. Countries that are at risk of yellow fever but had no cases of the disease (as explained above) will require that travelers get the vaccine to protect the country itself from the disease.

Yellow fever vaccine should not be administered to children younger than 9 months. The vaccine is considered otherwise safe for most healthy people. Because some data suggest that the vaccine may cause infection in a developing fetus, and not enough information is available on the possible consequences of such an infection, the current recommendation is not to vaccinate pregnant women.

People sensitive to eggs or egg products should not receive this vaccine because it is produced in chick embryos. Immunosuppressed individuals, such as people with AIDS or leukemia, should not receive the vaccine. A person who falls into any of these categories should carefully consider the necessity of their trip, and discuss alternatives with their travel medicine specialist. The yellow fever vaccine provides protection for 10 years.


Dengue presents an extreme risk to travelers in the tropics and sub-tropics, and according to the Centers for Disease Control, its global distribution is comparable to that of malaria. A small risk of dengue also exists in the southeastern part of the U.S. The risk of infection is higher in urban areas, and limited to altitudes below 600 m (2000 ft.).

Dengue is caused by any one of four distinct virus strains transmitted through the bite of Aedes aegypti, the same mosquito that transmits yellow fever. This mosquito bites during the day. Infection with one strain does not produce immunity to other strains, and people can have four dengue infections in their lifetime.

Symptoms of dengue include a sudden, high fever (which may occur in two waves), accompanied by extreme muscle pain and headache. A rash develops three to four days after initial symptoms appear. The symptoms can continue for several days and the only treatment is bed rest and fluids, with fever-reducing medication. This form of dengue is not life threatening.

Dengue hemorrhagic fever (DHF) is another form of dengue but far more dangerous, as it causes uncontrolled internal bleeding and has a 5 percent fatality rate. On rare occasions, dengue shock syndrome occurs as a result of DHF, with a fatality rate of up to 50 percent if it is not treated immediately.

There is no vaccine against dengue and no available medicine to prevent or treat it. The only defense against dengue and DHF is avoiding mosquito bites.

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