Ticks are small arthropods that feed on animals and humans and can thereby transmit zoonotic infectious diseases. The most important tick species belong to the Ixodidae family, the so-called “hard ticks” that have a shield on their hind body. In The Netherlands and much of Europe, the most common tick is the sheep tick Ixodes ricinus. In North America the most common species is Ixodes scapularis. Ixodes ticks have several life stages, including the immature larval and nymphal stages, besides the adult stage. Development to the adult stage takes on average 2-3 years and blood meals from several hosts. Nymphal and adult ticks can transmit diseases when they bloodfeed on humans, such as Lyme borreliosis, Rickettsioses and tick-borne encephalitis. Especially Lyme disease is a growing problem in Northern Europe. The numbers of ticks that are infected with Borrelia burgodorferi bacteria that cause this disease are increasing rapidly. There was a three-fold increase between 1994 and 2000 in the numbers of tick-biting incidences and Lyme diagnosis in The Netherlands. In the United States, Lyme is also a growing public health issue and is currently even the most common vector-borne disease. Nymphal ticks especially are considered high-risk Lyme disease carriers because they are tiny (1 mm) and therefore difficult to detect, may carry B. burgdorferi, and are generalized in their choice of a host.
There are many different species of flies, and several are vectors of human diseases. Black flies can transmit Onchocerciasis, and sand flies Leishmanisasis, which are both nasty parasitic diseases that infect thousands of people each year. One very important fly vector is the tsetse fly, which is found mostly in mid-continental Africa and transmits sleeping sickness (or Nagana). Sleeping sickness is caused by trypanosome parasites, and is endemic in 37 countries, causing an estimated 20,000 human deaths each year. Human sleeping sickness (also called African trypanosomiasis) can cause neurological symptoms and lethargy, and is curable but fatal when left untreated. Tsetse flies also severely impact livestock and is controlled mostly via pesticide spraying, odour-baited traps and targets, or pour-on insecticide treatment of cattle.