Many pathogens are known to be transmitted to humans and animals by arthropods, most of which are blood-feeders. The pathogens transmitted include protozoans, bacteria, viruses and nematodes.
Protozoans are single cell organisms that live exclusively by mean of parasitism, mostly hematophagous. Several human and animal diseases caused by protozoa are transmitted by a variety of arthropod vectors such as mosquitoes, flies, triatomine bugs, and ticks
Malaria is by far the most important protozoan disease, which kills one to three millions people worldwide each year (WHO, 2010). The disease agent plasmodium spp. is transmitted to human by a female mosquito of the genus Anopheles, which varies according to location. The most important and best known is the Anopheles gambiae complex in Africa. With over 460 described species of anopheles, 60 are known to be vectors of malaria. The mechanism of the transmission is exclusively biological, with the pathogen undergoing cyclical development and replication within the anopheles vector. The transmission itself occurs when an infected mosquito takes its blood meal, injecting the plasmodium along with the saliva into the skin of the human host.
Babesiosis is a tick-borne illness caused by protozoa in the genus Babesia. The disease is transmitted to human by the deer tick Ixodes Scpularis during its blood meal. The majority of cases of babesiosis in the United States occurs in the northeastern part of the country.
Leishmaniasis is a zoonosis caused by a protozoan of the genera Lutzomyia andPhlebotomus. The disease is spread between human by the female of tiny insects, the sandflies which breed in the caves and burrows of rodents. The Sandflies themselves become infected during their blood meals on an infected host. The pathogen (amastigote) undergoes cyclical change to become infective and multiply to increase its number before the sandfly takes another blood meal. The disease can be found in nearly every part of the tropics but is predominant in North Africa and the Middle East.
African trypanosomiasis (sleeping sickness) is a protozoan disease found exclusively in the African savannah. The incriminated pathogen, belonging to the genus Trypanosoma is transmitted to human by the tsetse flies (genus Glossina) which feed exclusively on blood. The disease agent induces coma by invading the central nervous system and eventually leading to death.
Chagas disease also called American Trypanosomiasis is a protozoan disease that is vectored to human by the Triatomine bug Rhodnius prolixus. Both the male and the female are blood feeders and can vector the disease. In contrast to many other arthropod-borne diseases, where the pathogen transmission occurs through saliva (salivaria), in the case of Chagas disease, the transmission is exclusively through the feces (stercoraria) of the bug but still through a biological mechanism. After blood-feeding on its victim the insect releases its infected feces near the bite wound. The victim by scratching the bite causes the infection to enter its body.
Bacteria are microscopic single-cell organism that replicates through binary disease. Arthropods can potentially transmit any bacterial pathogen to human and animal through mechanical ways. The vectors of bacteria include ticks, fleas, and cockroaches. The most significant bacterial disease transmitted by arthropod is Lyme disease.
Lyme disease, first discovered in 1975, is the most common bacterial, vector-borne disease in the United States (Artsob, 2000). The disease is caused by the spirochete bacteria belonging to the genus Borrelia and transmitted to human by the bite of an infected tick (Ixodes).
Black plague is an arthropod-borne disease caused by the bacterium Yersinia pestis. It occurs primarily in wild animals, such as rats and other rodents. Human infection occurs from the bite of an infected flea that has fed on infected animals.
Typhus, spotted fever and trench fever are infections caused by rickettsia, which is microscopic Gram-negative bacteria. The pathogen is transmitted to human by lice, fleas, mites and ticks (CDC, 2009). Most often the infection occurs when scratching infectious feces into the skin of the host.
A wide number of arthropods are known to transmit viruses to their human host. More than 600 different viruses are known to be transmitted by arthropods.
Dengue fever is the most medically important arthropod-borne viral disease with a 50 to 100 million cases reported annually worldwide (Angela, 2011) . Dengue and its severe form, dengue hemorrhagic fever both are transmitted to human by a mosquito species, Aedes aegypti and potentially other Aedes species. The virus exists as 4 different serotypes (DEN-1, DEN-2, DEN-3, and DEN-4), infection to each providing immunity if any, only to that strain of the disease.
Yellow fever is caused by an arbovirus transmitted to human by several Aedes species. However, the major vector is Aedes aegypti which along can also transmit other diseases. The virus normally occurs in the forest monkeys in many parts of tropical Africa and South America (Burgess and Cowan, 1993). It does not affect monkeys which serve as reservoirs. Humans contract the disease when they get bitten by the forest-dwelling mosquitoes. Subsequently, the disease may spread from human to human Yellow Fever is a dangerous infection whose prevalence around the world has been greatly reduced due to the availability of an effective vaccine.
Colorado tick fever is a viral disease that occurs predominantly in the western United States. The virus is transmitted to human by the wood tick Dermacentor andersoni during recreational activities outdoor. Squirrels and chipmunks serve as the primary animal reservoirs.
West Nile Fever is a spreading viral disease transmitted to human and cattle by several culex mosquitos, culex pipiens being the major vector. Mosquitoes become infected when they feed on infected birds. These infected mosquitoes spread the disease to humans and other animals when they get bitten (CDC, 2005). The disease is found in many parts of the world including Africa, parts of Asia and Europe, the Mediterranean region, the Middle East and Australia It was introduced in the United states in 1999 (Dauphin and Zientara, 2007).
Many other arboviral diseases are vectored to human and cattle by arthropods including rift valley fever, chikungunya, many encephalitis (Tick-borne encephalitis, Eastern Equine Encephalitis…) and probably many other unsubscribed.
Nematodes are roundworms that can be transmitted to human by arthropods, causing many traumatic diseases.
Lymphatic filariasis also known as elephantiasis is a tropical disease transmitted to human by several species of mosquitoes in the genera Anopheles and Culex. The disease agentWuchereria bancrofti or Brugia malayi according to locations is a nematode worm (microfilaria) that invades the lymphatic system, thereby causing a massive swelling in different part of the human body, mainly the legs. The disease may not be lethal, but caused severe disabilities that alter the person’s ability to function properly in society.
Onchocerciasis is another nematode disease affecting people, leading to sight impairment in tropical regions, mainly in Africa and Latine America. The disease is caused by a nematode worm transmitted to human by a female blood-feeding black fly of the genusSimulium that breed in a fast flowing water. The most significant vector in Africa is Simulium damnosum. The fly deposits its larvae on human skin, which then burrow through, causing itching and eventually when they enter the eyes, lead to the progressive damage of eyes tissues and inevitably blindness.
Dog Heartworm disease is an infection that attacks dogs. The causative agent, a nematode Dirofilaria immitis, which is spread between dogs by mosquitos possibly Aedes vexanx and Aedes quadrimaculatus.
Many other nematodes are vectored by arthropods to human and animals.