Vector-borne disease

Many tropical infections, including malaria, are spread from person to person or from animal to person by an arthropod vector. Vector-borne diseases are also found in temperate climates, but are relatively uncommon. In most cases part of the parasite life cycle takes place within the body of the arthropod, and each parasite species requires a specific vector. Simple mechanical transfer of infective organisms from one host to another can occur, but is rare. Some vector-borne diseases are shown in Table 2.4.

Direct person-to-person spread

Table 2-4. Infections transmitted by arthropod vectors

Disease	Infective organism	Vector
Dengue
Yellow fever West Nile fever	Flavivirus	Mosquito
Scrub typhus	Orientiae tsutsugamushi	Mite
Rickettsial spotted fevers	Rickettsia sp.	Hard tick
Tick-borne relapsing fever	Borrelia duttoni	Soft tick
Louse-borne relapsing fever	Borrelia recurrentis	Body louse
Carrión’s disease	Bartonella bacilliformis	Sandfly
Lyme disease	Borrelia burgdorferi	Hard tick
Plague	Yersinia pestis	Flea
Malaria	Plasmodium sp.	Mosquito
Lymphatic filariasis	Wuchereria bancrofti	Mosquito
	Brugia malayi	Mosquito
Onchocerciasis	Onchocerca volvulus	Blackfly
Leishmaniasis	Leishmania sp.	Sandfly
African trypanosomiasis	Trypanosoma brucei	Tsetse fly
South American trypanosomiasis	Trypanosoma cruzi	Reduviid bug

Organisms can be passed on directly in a number of ways. Skin infections such as ringworm, and ectoparasites such as scabies and head lice, can be spread by simple skin-to-skin contact. Other organisms are passed on by blood- (or occasionally other body fluid) to-blood transmission. In some cases such as HIV and hepatitis B virus this is the only route: in others such as malaria and Chagas’ disease it is an unusual alternative to the normal arthropod vector. Blood-to-blood transmission can occur during sexual contact, from mother to infant peripartum, between intravenous drug users sharing any part of their injecting equipment, when infected medical equipment is reused, if contaminated blood or blood products are transfused, or in any sporting or accidental contact when blood is spilled.

Direct inoculation

Infection can occur when pathogenic organisms breach the normal mechanical defences by direct inoculation. Some of the circumstances in which this can occur are covered under endogenous infection and blood-to-blood transmission above. Some environmental organisms may be inoculated by accident: this is a common mode of transmission of tetanus and certain fungal infections. Rabies virus may be inoculated by the bite of an infected animal.

Consumption of infected material

Although many food-related zoonotic infections are due to contamination of food with animal faeces (and are thus, strictly speaking, faeco-oral), several diseases are transmitted directly in animal products. These include some strains of salmonella (eggs, chicken meat), brucellosis (unpasteurized milk), and the prion diseases kuru and vCJD (neural tissue).

2 Comments »

1. [...] referred to as … two species, however, there are now over 30 known unique species with …Health Nova: Your Ultimate Medical Portal Routes of …african trypanosomiasis, american trypanosomiasis, bartonella bacilliformis, body louse, hard tick, [...]

   Pingback by bartonella species — March 19, 2010 @ 5:58 am

2. 

   A few workers in our area got Salmonella poisoning. It is a good thing that they did not die and they have fully recovered. ,

   Comment by Lucy Robinson — April 29, 2010 @ 10:25 am

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