Vector-borne diseases of dogs are caused by a diverse group of protozoal, bacterial and helminth parasites. In analogy with the big five, most dangerous, African wildlife species, five vector-borne diseases stand out for their most significant impact on companion animals, in particular dogs.
Two of these big five canine vector-borne diseases (VBD) are caused by protozoan parasites responsible for babesiosis and leishmaniosis. Two other groups of VBD are bacterial pathogens consisting of Lyme disease-causing spirochetes and a diverse group of intracellular bacteria (=Rickettsiaceae) responsible for ehrlichiosis, rickettsiosis and anaplasmosis. The fifth VBD group consists of helminth parasites, which are capable of inducing dirofilariosis or heartworm in dogs.
The big five canine VBD are grouped together because arthropod vectors transmit them. Mosquitoes, ticks and sandflies serve as vectors, which behave as living shuttles, carrying disease-causing organisms between animals. In some cases, these vectors transmit pathogens to people from animal reservoirs (in which case the disease is known as zoonotic).
The protozoal parasites (Babesia, Leishmania) are vectored by ticks and sandflies, respectively. A diverse range of tick species transmit the bacterial pathogens (Borrelia, Ehrlichia, Rickettsia and Anaplasma). Finally, different species of mosquitoes carry the nematodes (Dirofilaria), which cause heartworm in dogs.