Cowdriosis, Malkopsiekte,

Heartwater, a rickettsial disease of ruminants, is one of the most important diseases of livestock in Africa. This tick-borne illness can significantly decrease productivity in regions where it is endemic. It is particularly serious in non-indigenous livestock that are moved into heartwater areas; many of these animals may die. Wild ruminants can also be infected. Most wildlife species appear to carry the organism asymptomatically, but serious illness has been reported in lechwe moved into endemic areas, as well as in experimentally infected white-tailed deer. Heartwater is readily introduced into new regions in infected animals or ticks. Known and potential host ticks are widely distributed, and can be found on a variety of animals including reptiles. On at least one occasion, leopard tortoises and African spurred tortoises imported into Florida were found to be carrying infected ticks. Once the tick vector becomes established, eradication of heartwater is difficult. One host tick, Amblyomma variegatum, was introduced into the Caribbean early in the 19 th century. During the 1970s and early 1980s, this tick spread rapidly from island to island; in some cases, it may have been carried by cattle egrets. The presence of heartwater in the Caribbean increases the risk of introducing this disease into the Americas. Ongoing programs are attempting to eradicate Amblyomma variegatum from the Caribbean. To date, these programs have succeeded in reducing the numbers of ticks on some islands and eradicating them from others, but complete eradication throughout the Caribbean remains elusive. Etiology Heartwater results from infection by Ehrlichia (formerly Cowdria) ruminantium, a small, Gram negative, pleomorphic coccus in the family Anaplasmataceae and order Rickettsiales. This organism is an obligate intracellular parasite. Strains of E. ruminantium are very diverse; while some strains are highly virulent, others appear to be non-pathogenic. E. ruminantium has a high level of genomic plasticity. Gene segments are often deleted or inserted, and genes may be disrupted. Several different genotypes can co-exist in a geographic area, and may recombine to form new strains