Insects are very well known for spreading a variety of diseases that are harmful to human since ancient times. They spread diseases from one host to another either through their bite, as in the case of mosquitoes spreading yellow fever and malaria, or through their feces, as in the case of fleas spreading cat-scratch fever. A wide spectrum of insects are responsible for transmitting diseases to human, either directly, or via animal including household pets.
Among all insects, mosquitoes, consist of more than 3500 species, are most notoriously infectious, spreading malaria, yellow fever, and dengue, causing several million death yearly, affecting hundreds of millions more annually. Mosquitoes are also responsible for transmitting zika, chikungunya, lymphatic filariasis(elephantiasis), West Nile fever, and various types of encephalitis, among others. Mosquito-borne diseases are endemic in over hundreds of countries, especially in the tropic, or sub-tropic, affecting the social and economic development of nations in Africa, Asia, and South America. Increasingly, countries previously not concern about mosquito-borne diseases are seeing a rise in such cases. Yellow fever is posing a serious threat in America while West Nile fever is spreading in Europe. Despite the seriousness of mosquito-borne diseases, there is only a handful of vaccine successfully developed so far, such as vaccines for Japanese encephalitis virus infection and yellow fever. Patients with dengue, malaria, West Nile fever are primarily given supportive treatments to boost up the immune systems of infected patients.
The second biggest problematic insect is the flies. Sandflies transmitting the Leishmania parasites through bites, affecting the livelihood of some 350 million people in 98 countries in Africa, Asia, Central and South America, and southern Europe. About 12 million people are directly infected, with 2 million new cases occurring every year at casualty rate between 20-50 thousand people. Poverty, malnutrition, deforestation, and uncontrolled urbanization are factors in the spread of the disease. The female phlebotomine sandfly is blamed for the spread of the deadly Chandipura encephalitis virus in India and Africa. The disease advanced quickly from an influenza-like illness to coma and death. In 2003, 329 children developed acute encephalitis in southern India and 183 of those died. It is viewed as a serious emerging illness by world health organizations. Sleeping sickness is spread by the blood-sucking tsetse flies, affecting 36 countries in sub-Saharan Africa. The tsetse flies look quite similarly to housefly but with a distinctive characteristic of folding its wings completely with one resting on top of the other. 55 million people in the Africa continent is estimated to be at risk. As of 2010, it causes 9000 deaths annually. At the second stage of the sickness, an infected person may experience neurological symptoms of numbness, poor coordination, and confusion. Onchocerciasis, or River Blindness, transmitted through bites by blackflies that live near fast-flowing waterways can result in blindness, affecting some 17.6 million people in Africa.
Ticks and lice form the third group of insect-borne disease carriers. Deer ticks, transmitting the bacterium Borrelia burgdorferi, causes Lyme Disease with the characteristic bull’s-eye skin lesion. Lyme disease is affecting 65,000 people a year in Europe and 300,000 people a year in the United States. The disease can lead to long-term joint pains and lethargy. Epidemic typhus, transmitted by human body lice, and plague, transmitted by the flea, are still affecting small sections of people in Africa, Asia, and America. A more common benign disease spread by flea is the cat-scratch fever or otherwise known as cat-scratch disease, affecting mostly small children in the United States and other parts of the world.
Although insect-transmitted diseases pose a particular threat on the continents of Africa, Asia, and South America, and to the lesser extent, Europe, and North America, by avoiding contacts with the insect population through uses of insect netting, repellents, and appropriate clothing, and destroying harmful insect habitats, the diseases are manageable.