Transmission

Transstadial transmission of E. canis occurs within the Brown Dog tick, Rhipicephalus sanguineus, whereas transovarial transmission has not been confirmed so far. All tick stages can be infected while feeding on infected dogs. Subsequently these ticks drop off, molt and acquire another canine host. Ticks can obtain E. canis only if engorgement occurs during the acute phase of the disease in dogs.

Nymphal and adult Brown Dog ticks are capable of transmitting E. canis for at least 155 days following detachment from the infected host. If the tick acquires an uninfected host and harbors a sufficient number of organisms, infection of the new host may occur. It is not known how long the tick must feed to transmit the organism. Infected dogs from endemic areas may travel to non-endemic areas, but lacking suitable vectors, they are no threat to other dogs.

In the American Dog tick, Dermacentor variabilis, experimental transmission of E. canis to nymphs and experimental transmission from infected D. variabilis adults to the host was successful. The tick is suspected as additional vector in the USA, but epidemiological importance is unclear.

Finally, Ehrlichia spp. infection may also be introduced in susceptible dogs by blood transfusion.

Dissemination of Ehrlichiae

Ehrlichiae are obligate intracellular bacteria which attack white blood cells, a feature even more specialized at the species level:

• E. canis infects canine monocytes and lymphocytes but only rarely infects neutrophils;
• E. ewingii infects canine granulocytes;
• E. chaffeensis infects predominantly monocytes and macrophages.

Further information

• Breitschwerdt, E.B.: Canine and feline anaplasmosis: Emerging and infectious diseases. Proceedings of the 2nd Int. CVBD Symposium, 2007, 6-15 (Download)
• http://www.cdc.gov/ticks/diseases/ehrlichiosis