Heartwater – Ehrlichia ruminantium infection

Abstract

SummaryHeartwater is a notifiable disease that is listed by the World Organisation for Animal Health. It is caused by Ehrlichia ruminantium, an obligately intracellular Gramnegative bacterium in the order Rickettsiales and the family Anaplasmataceae. The disease is borne by ticks in the genus Amblyomma and causes heartwater, or cowdriosis, in wild and domestic ruminants, primarily in Africa, but also in parts of the Caribbean. The disease was recognised in South Africa in the 19th Century and determined to be tick borne in 1900, while the organism was identified in 1925 and first cultured in vitro in 1985. This latter achievement boosted research into the disease at a time when biology was moving into the molecular genetic age. Over the last 20 years, there have been significant improvements in our understanding of E. ruminantium, yielding major advances in diagnosis, epidemiology, genetic characterisation, phylogeny, immunology, and vaccine development. The organism is genetically highly variable; this has important implications for future control measures, and is making it difficult to develop an effective vaccine for protection against tick challenge. Research is continuing into three different types of vaccine, inactivated, attenuated, and recombinant, and the current state of development of each is discussed. KeywordsAmblyomma hebraeum -Amblyomma variegatum -Attenuated vaccine -ControlCowdriosis -Diagnosis -Economic importance -Ehrlichia ruminantium -Heartwater -Inactivated vaccine -Occurrence -Recombinant vaccine -Tick-borne disease.Rev. Sci. Tech. Off. Int. Epiz., 2015, 34 (2), 557-568 AetiologyHeartwater is listed by the World Organisation of Animal Health as a notifiable disease (1). It was known in South Africa for nearly 90 years before the causative organism was identified in 1925 as a rickettsia, originally named Rickettsia ruminantium (2, 3). The name was later changed to Cowdria ruminantium (4), from which arose the term 'cowdriosis'. Molecular phylogenetic studies of the Rickettsiales in the 1990s uncovered the real evolutionary relationships within the order and the organism was reclassified as Ehrlichia ruminantium in the family Anaplasmataceae (5). Ehrlichia ruminantium, which is transmitted by Amblyomma ticks, is obligately intracellular, infects cattle, sheep, goats and some wild ruminants, and is frequently fatal. A comprehensive account of the history and biology of E. ruminantium can be found elsewhere (6). Economic and social importanceHeartwater is a serious economic problem wherever it occurs, in an enormous area covering most of sub-Saharan Africa, its offshore islands, and several islands in the Caribbean. The disease generally prevents livestock farmers from upgrading their herds to modern high-yielding breeds, as these are more susceptible to infection than traditional stock breeds, which often have a measure of resistance (7). Since heartwater is so common in the endemic areas of Africa, farmers are usually unwilling or unable to pay for definitive diagnoses, so it is difficul...

Climatic changes and their role in emergence and re-emergence of diseases

“…Beside Anaplasma, the closely related tick-borne Ehrlichia can also infect human and animals. The diseases can be induced by Ehrlichia chaffeensis and Ehrlichia ewingii (Monocytes Ehrlichiosis) in human or heartwater in cattle (by Ehrlichia ruminantium) (Allsopp 2015;Paddock and Childs 2003;Thomas et al 2009). Other forms of ehrlichiosis can also be induced by other Ehrlichia species like Ehrlichia canis, Ehrlichia muris and Ehrlichia mineirensis.…”

“…Other forms of ehrlichiosis can also be induced by other Ehrlichia species like Ehrlichia canis, Ehrlichia muris and Ehrlichia mineirensis. As a tickborne pathogen, Ehrlichia species could be detected almost worldwide (Allsopp 2015).…”

Tick (Acari: Ixodidae) infestations in cattle along Geba River basin in Guinea-Bissau

“…This disease is endemic in most of sub-Saharan Africa (Allsopp, 2015;Camus and Barré, 1988;Provost and Bezuidenhout, 1987) and was reported in Guinea-Bissau for the first time by Tendeiro (1945). A. variegatum may also be responsible for E. bovis transmission (bovine ehrlichiosis)…”

Outwitting planarian’s antibacterial defence mechanisms:Rickettsialesbacterial trans-infection fromParamecium multimicronucleatumto planarians

“…Indeed, many of them (e.g. Rickettsia spp., Anaplasma spp., Ehrlichia spp., and Orientia tsutsugamushi ) are vectored by lice, ticks and mites, and cause mild to severe disease [1, 10], such as epidemic typhus, Rocky Mountain spotted fever [11–13], anaplasmosis, ehrlichiosis [14, 15], heartwater [16], and scrub typhus [17].…”