ABSTRACT
Introduction Arthropods are animals with segmented bodies covered by a chitin exoskel-
Arthropods may transmit infectious agents including viruses, bacteria, protozoa and helminths. Such agents may require an arthropod for perpetuation (biological transmission) or may simply contaminate an arthropod (mechanical transmission). Leishmania parasites have a complex developmental cycle within certain phlebotomine sandflies and could not move from animal to animal without the sandfly. Houseflies may have salmonella contaminating their outer surfaces or mouthparts, which may be transferred to animals by the act oflanding and crawling; but, salmonella does not need the housefly because it is an enteric commensal of many kinds of animals. Few agents can survive long enough to be transmitted by mechanical means: HIV, for example, has never been epidemiologically linked with mosquitoes or other arthropods even though it might be taken up during the act of blood feeding, probably because the virus is labile outside of host tissues and enough infected lymphocytes may never contaminate the small surface area of mosquito mouthparts.
