The carrier status of sheep, cattle and African buffalo recovered from Heartwater

Andrew, H. R.; Norval, R. A. I.

doi:10.1016/0304-4017(89)90056-3

Cited by 104 publications

(66 citation statements)

References 3 publications

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“…It is known, however, that larvae and nymphs fed experimentally on E. ruminantium-infected sheep develop infection rates of 100% in the following instar (47), which suggests that, in the field, many ticks feed during the larval or nymphal stages on non-susceptible or non-infected hosts. In a highly managed farm environment, apparently healthy stock may constitute a dangerous disease reservoir; animals treated for heartwater can carry E. ruminantium organisms at very low levels and have been shown to remain infective to ticks for about a year (50,51). These observations show the danger posed by unsuspected carrier animals being moved to heartwater-free areas.…”

Section: Vector Competencementioning

confidence: 99%

Heartwater – Ehrlichia ruminantium infection

Allsopp¹

2015

Rev. Sci. Tech. OIE

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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...

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Section: Vector Competencementioning

confidence: 99%

Heartwater – Ehrlichia ruminantium infection

Allsopp¹

2015

Rev. Sci. Tech. OIE

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“…The genus Ehrlichia is a member of the family Anaplasmataceae, which also includes the genera Anaplasma and Neorickettsia (Dumler et al, 2001). Anaplasma and most Ehrlichia species usually cause persistent infection in their natural animal hosts (Andrew & Norval, 1989;Telford et al, 1996;Breitschwerdt et al, 1998;Harrus et al, 1998). Persistent ehrlichial infection in humans has also been documented (Dumler et al, 1993;Roland et al, 1995;Dumler & Bakken, 1996;Horowitz et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Experimental Ehrlichia chaffeensis infection in beagles

Zhang

Long

et al. 2003

Journal of Medical Microbiology

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A canine model for human monocytic ehrlichiosis was used to assess persistent infection and antigenic variation of Ehrlichia chaffeensis. Two beagle dogs were infected subcutaneously with E. chaffeensis Arkansas strain. The dogs were observed for 6 months after inoculation for clinical signs, blood chemistry changes, antibodies to E. chaffeensis and presence of E. chaffeensis in the blood. Both dogs developed thrombocytopenia, but exhibited normal body temperatures during the entire course of infection. In one dog, E. chaffeensis was cultivated for up to 74 days post-inoculation and E. chaffeensis DNA was detected in the dog's blood for up to 81 days. In the other dog, E. chaffeensis was cultured for up to 102 days and E. chaffeensis DNA was detected in the blood for up to 117 days. PCR amplification and DNA sequence analysis indicated that there was no genetic variation in the 120 kDa outer-membrane glycoprotein gene of E. chaffeensis during infection of the dogs. The dogs developed antibodies to the immunodominant proteins of E. chaffeensis, including the 175, 140, 120, 80, 50 and 28 kDa proteins, starting in the fifth week post-inoculation. The dogs maintained high antibody titres throughout the 6-month study period. These results indicate that dogs become carriers of E. chaffeensis for 2-4 months after infection without exhibiting signs of clinical disease, suggesting that dogs may serve as a natural host for E. chaffeensis.

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“…To reduce the losses caused by heartwater, it is important to detect its presence in an area and to monitor its spread. Hence, improved diagnostic methods to detect infected and carrier animals (Andrew & Norval, 1989) are essential.…”

Section: Introductionmentioning

confidence: 99%