Insects are among the many animals that serve as disease vectors -- that is, they transmit infectious diseases to human beings through bacteria, viruses or other microorganisms. A parasite is any organism that requires a host for its own survival and does tangible harm to that host in the course of its residence. Insect parasites are responsible for numerous serious diseases and include flies, ticks, mosquitoes and many others.
The Tsetse and Other Flies
Most people recognize flies, in particular house flies, as merely an annoyance. Worldwide, however, flies are vectors for a number of serious, even fatal diseases. In sub-Saharan Africa, the tsetse fly is a vector for an organism called a trypanosome. This protozoan parasite is the causative agent of African sleeping sickness, or trypanosomiasis. This disease starts with headaches and joint pains, and can lead to central nervous system impairment -- e.g., confusion and behavioral changes -- and then death if left untreated.
In addition, the bites of phlebotomine sand flies can spread leishmaniasis, which causes skin sores and in some cases damage to internal organs.
Ticks -- The Versatile Vector
Ticks are taxonomically classified as arthropods, but in regard to parasite-borne diseases, the Centers for Disease Control and Prevention group them with insects. Ticks and their cousins are not only common parasites, but are themselves hosts for pathogenic microbes such as bacteria, viruses, protozoans and tiny worms. They are usually ectoparasites, meaning that they live on the surface of their hosts and may nourish themselves by either sucking their host's blood or digesting their tissues directly. Ticks are vectors for Lyme disease, babesiosis, Rocky Mountain spotted fever and other human maladies.
Mosquitoes the World Over
Mosquitoes infected with a range of pestilential microorganisms are a major cause of debility and death. Famously, they spread malaria, predominantly in Africa, by serving as vectors for the causative agent of the disease, a tiny, amoeba-like creature called a plasmodium. Mosquito bites are also responsible for dengue fever, yellow fever and a number of different types of encephalitis, or inflammation of the brain. In the second decade of the 21st century, West Nile virus became a major public health concern in the United States; as of 2014 there were no vaccines to prevent it and no medications to treat it, although fortunately only about 1 percent of those infected develop serious neurological illness.
Bedbugs -- The Nocturnal Bane
In much of Latin America, Chagas disease, which leads to an enlargement and weakening of the esophageal wall and heart along with other chronic problems, is spread by the bite of "kissing bugs" or triatomines, commonly called "bedbugs" in the U.S. They get the name "kissing bugs" owing to their propensity for feeding on people's faces. These pests spend their days hiding in the cracks of domiciles made of materials such as mud or thatch, and then emerge at night to feed on their hosts. The actual agent of the disease, as with African sleeping sickness, is a protozoan called a trypanosome.
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