ANAPLASMOSES

A General Introduction has been added to each disease chapter in an attempt to give a brief updated overview of the taxonomic, biological and other characteristics of the virus family or group of bacteria /protozoa that cause disease in livestock and, where relevant, involve wildlife. As the text of the three-volume book Infectious Diseases of Livestock is currently under revision the Editors are aware that there are inconsistencies between the updated introductions to chapters and the content of the chapters themselves. Once the chapters have been updated – a process that is currently underway – these inconsistencies will be removed.

Anaplasmosis is an arthropod-borne disease of cattle, sheep, goats and some wild ruminant species caused by obligate intra-erythrocytic rickettsial organisms of the genus Anaplasma in the family Anaplasmataceae*, order Rickettsiales. The parasites are biologically transmitted by ticks, but mechanical transmission by haematophagous insects and iatrogenic means also occur. Clinically, Anaplasma spp. infections in mammalian hosts may range from inapparent infection to severe disease and mortality. Generally, the disease is characterized by fever, progressive anaemia and icterus. Following subclinical infection with Anaplasma, or recovery from the disease, infected animals usually remain carriers of the parasite for life.

Differentiation of species within the genus Anaplasma was traditionally based on one or more of the following criteria: differences in host range; location within erythrocytes; morphology of the inclusion bodies; and, to some extent, pathogenicity of the organism and immunological differences.⁹ Under the traditional system only four species of Anaplasma were recognized, three of which (A. marginale, A. centrale and A. caudatum²) occur in cattle, while the other (A. ovis) occurs in sheep and goats. The changes which have occurred in bacterial classification over the last decade, as a result of the application of phylogenetic techniques, have been noted in the Introduction to the section on diseases caused by Rickettsiales and Chlamydiales.

As a result of these changes the genus Anaplasma now contains several species, previously included in the genus Ehrlichia, which are not intra-erythrocytic.³ The obligately intra-erythrocytic Anaplasma species are now known as the erythrocytic Anaplasma species.⁷ The name Anaplasma mesaeterum was proposed for an apparently distinct erythrocytic Anaplasma infective for sheep and goats⁶ but as yet there are no phylogenetic data for this organism so its provenance is uncertain.¹⁰

A variety of African and North American wild ruminant species have been found to be susceptible to A. marginale and/or A. ovis infection, but anaplasmosis in these hosts is usually mild or subclinical, and very little is known about the role that wild ruminants may play in the epidemiology of anaplasmosis in domestic animals. Uncharacterized Anaplasma spp. have been observed in, and in some instances isolated from, a number of wild ruminant species in Africa, and there is serological evidence of Anaplasma infections in an even wider host range.^{6, 8} Giraffe (Giraffa camelopardalis) is the only wild ruminant in which anaplasmosis has been associated with serious disease and mortality.^{2, 8} Anaplasma marginale⁴ and also uncharacterized Anaplasma infections¹ have been found in North American white-tailed deer (Odocoileus virginianus) but there is no evidence that these animals are an important disease reservoir for cattle.⁴

References

1. ARENS, M.Q., LIDDELL, A.M., BUENING, G., GAUDREAULT-KEENER, M., SUMNER, J.W., COMER, J.A., BULLER, R.S. & STORCH, G.A. 2003. Detection of Ehrlichia spp. in the blood of wild white-tailed deer in Missouri by PCR assay and serologic analysis. Journal of Clinical Microbiology, 41, 1263–5.
2. AUGUSTYN, N.J. & BIGALKE, R.D., 1972. Anaplasma infection in a giraffe. Onderstepoort Journal of Veterinary Research, 39, 29.
3. DUMLER, J.S., BARBET, A.F., BEKKER, C., DASCH, G.A., PALMER, G.H., RAY, S.C., RIKIHISA, Y. & RURANGIRWA, F.R., 2001.Reorganization of Genera in the Families Rickettsiaceae and Anaplasmataceae in the Order Rickettsiales; Unification of Some Species of ,Ehrlichia with Anaplasma, Cowdria with Ehrlichia, and Ehrlichia with Neorickettsia; Descriptions of Five New Species Combinations; and Designation of Ehrlichia equi and ‘HGE agent’ as Subjective Synonyms of Ehrlichia phagocytophila. International Journal of Systematic and Evolutionary Microbiology, 51, 2145–2165.
4. KEEL, M.K., GOFF, W.L., & DAVIDSON, W.R. 1995. An assessment of the role of white-tailed deer in the epizootiology of anaplasmosis in the southeastern United States. Journal of Wildlife Diseases, 31, 378–85.
5. KREIER, J.P. & RISTIC, M., 1963. Anaplasmosis. Morphologic characteristics of the parasite in the blood of calves infected with the Oregon strain of Anaplasma marginale. American Journal of Veterinary Research, 24, 676–687.
6. KUTTLER, K.L., 1984. Anaplasma infections in wild and domestic ruminants: A review. Journal of Wildlife Diseases, 20, 12–20.
7. LEW, A.E., GALE, K.R., MINCHIN, C.M., SHKAP, V. & DE WAAL, D.T., 2003. Phylogenetic analysis of the erythrocytic Anaplasma species based on 16S rDNA and GroEL (HSP60) sequences of A. marginale, A. centrale, and A. ovis and the specific detection of A. centrale vaccine strain. Veterinary Microbiology, 92, 145–160.
8. LÖHR, K.F. & MEYER, H., 1973. Game anaplasmosis: The...