Bovine Anaplasmosis Study Guide

Overview and Clinical Importance

Bovine anaplasmosis is an infectious, non-contagious, tick-borne hemoparasitic disease of cattle caused by the obligate intraerythrocytic rickettsial organism Anaplasma marginale. It is the most prevalent tick-transmitted disease of cattle in the United States, causing economic losses exceeding $300 million annually.

Also known as "gall sickness" or "yellow-bag" due to characteristic icterus. The disease occurs in tropical and subtropical regions worldwide (40°N to 32°S), including the USA (endemic in southeastern, gulf coast, lower plains, and western states).

Etiology

Anaplasma marginale is classified in order Rickettsiales, family Anaplasmataceae. The organism appears as dense, blue-purple inclusion bodies (0.3-1.0 µm) located on or near the MARGIN of infected RBCs on Giemsa-stained smears.