Arthropods that transmit microbes are called vectors. Some microbiologists consider vectors as another example of indirect transmission. Arthropods are often small animals with numerous legs. Examples of arthropods that may spread disease-causing microbes include organisms like ticks which have 8 legs and are called arachnids; other examples include lice, fleas, mosquitoes, flies, and roaches which have 6 legs and are called insects. Many diseases including malaria, Q-fever, plague, encephalitis, Rocky mountain spotted fever, and lyme disease have arthropod vectors.

In some cases the arthropod is a mechanical vector and transports microbes on its legs or other body parts. The two most well known mechanical vectors are the housefly and cockroach. Twenty different species of disease-causing microbes have been identified on the bodies of flies; and up to 40 different microbes have been transmitted by cockroaches.

If the microbe uses the insect or arachnid as a host for growth and reproduction, the arthropod is called a biological vector. Disease microbes infect the arthropod and multiply. The microbes causing malaria and yellow fever accumulate in the salivary glands; and the microbes causing lyme disease gather in the tick’s gut. The biological vectors have interesting methods of inserting the disease microbes during the biting process----the mosquitoes put saliva into the wound, fleas defecate into the bite, and tsetse flies regurgitate in to the wound resulting from the bite.

Eliminating and controlling vectors is an important way of reducing the transmission of pathogens responsible for causing communicable diseases. In addition to programs like mosquito spraying, health workers try to screen and test suspect carriers. Isolation and quarantine, as well as enforcing universal precautions (gloves, masks, goggles) when exposure to body fluidw is a possibility will reduce the transmission of microbes.