Vector-borne diseases and how to avoid them

Malaria, the most deadly vector-borne disease, kills over 1.2 million people, mostly children, while Dengue viruses infect up to 100 million people annually. Here’s how to avoid both and others like them.

What are vector-borne diseases?

Vector-borne diseases are diseases transmitted and carried by hosts such as mosquitoes, ticks, fleas, biting flies, fresh-water snails and others. The vector is the biological host of the disease-causing pathogen, which may be a virus, bacterium, protozoan or parasite. The pathogens are replicated in the vector host and then transferred to humans and/or animals.

Well-known vector-borne diseases include the following:

• • Malaria

• • Schistosomiasi/bilharzia

• • Viral heamorrhagic fevers such as Dengue and Lassa fever

• • Reckettsial disease

• • Typhus

• • Rift Valley fever

• • Yellow fever

• • Trypanosomiasis, namely African sleeping sickness (with tsetse flies as vectors) and American chagas disease (with reduviid bugs as vectors.)

Mosquito, fly, gnat and midget-borne diseases

These insects attack exposed skin and transfer diseases such as malaria, Dengue fever, Rift Valley fever and yellow fever, encephalitis (Japanese, California, Saint Louis, Eastern and Western equine and West Nile virus) via their bites. Of these, malaria and Dengue fever need special mention.

Malaria is a serious and potentially fatal disease with symptoms such as high fevers, shaking chills and other flu-like symptoms. Most cases in sub-Saharan Africa are of a most virulent type of malaria. The vector of malaria is the female Anopheles mosquito.

Dengue fever is a viral disease endemic throughout the tropics and subtropics where infected mosquitoes prefer to feed during the daylight hours and inside homes. No vaccine is available.

Tick-borne diseases

Ticks are able to host more than one disease-causing agent at any time with which to infect humans. They are more active during the warmer months and prefer areas with high grass, bushes and woods with lots of leaf litter. Different species of tick and bacteria are involved in causing tick-bite fever, and the different forms of the disease have different names. Typical symptoms include a black mark where the bite occurred, relapsing and recurring high fevers, headaches, muscular pain and a rash.

Other common vector-borne diseases

• • Lassa fever is transmitted from animals to humans by a specific kind of wild rodent.

• • Typhus is caused by the rickettsia bacteria. There are different kinds of typhus either caused by lice and mites on humans and mites and fleas on rodents or some species of ticks. The most effective way to prevent typhus is inoculation with the typhus vaccine.

• • Bilharzia (schistosomiasis) is caused by parasitic worms called schistosomes that lay their eggs in the intestines, the bladder and liver of humans. Bilharzia is common in the tropics where bilharzia-transmitting snails are found in ponds, streams, rivers and irrigation canals. Blood in the urine may indicate urinary bilharzia.

Precautions

There are quite a few precautions that travellers can take to avoid being infected with the abovementioned diseases. First and foremost is the necessity to be vaccinated where a vaccine is available or to take preventative medicines as in the case of malaria. Second, avoid being bitten by disease-carrying vectors such as mosquitoes, ticks, fleas, etc.

Mosquitoes can be kept at bay with the use of insect repellents and sprays, insecticide-treated bed nets and by staying indoors with screens and air conditioning or fans. The mosquitoes that cause Dengue fever typically live indoors in dark, cool places, such as in closets, under beds, behind curtains and in bathrooms.

Take extra care during peak mosquito biting hours (dusk to dawn). Use insect repellents and protective clothing (long pants and long-sleeved tops). Remember that mosquitoes that cause Dengue fever typically bite during daylight hours.

Limit exposure to tick bites by wearing light-coloured clothing (long pants and sleeves), using insect repellent and tucking your pant legs into your socks, checking for ticks frequently, and washing and drying your clothing in a hot dryer.

Stay out of the water in areas where bilharzia is endemic and check your clothes and luggage for unwanted stowaways before you leave.

 

Sources

 

Hirst, K. Tick-Borne Diseases. Retrieved from: http://archaeology.about.com/cs/healthandsafety/a/safety2_2.htm
Mosquito-borne diseases. Retrieved from: http://www.cdc.gov/ncidod/diseases/list_mosquitoborne.htm
Penrith, M. Vector-borne diseases. Retrieved from: http://web.up.ac.za/default.asp/ipkCategoryID=16729
Vector borne disease. Retrieved from: http://www.fpnotebook.com/id/vector/VctrBrnDs.htm
Vector-borne diseases. Retrieved from: http://www.who.int/heli/risks/vectors/vector/en/FAQ/10723/P.Gigli; UNEP/Topham