An assessment of the economic impact of heartwater (Cowdria ruminantium infection) and its control in Zimbabwe

Mukhebi, A.W.; Chamboko, Tafireyi; O’Callaghan, Christopher J.; Peter, Trevor; Kruska, R.L.; Medley, Graham F.; Mahan, Suman M.; Perry, Brian D.

doi:10.1016/s0167-5877(98)00143-3

Cited by 67 publications

(36 citation statements)

References 8 publications

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“…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 difficult to quantify the economic impact of the disease. The only estimates in the literature apply to the Southern African Development Community, where total animal production losses from the disease are thought to average US$48 million annually (8,9).…”

Section: Economic and Social Importancementioning

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: Economic and Social Importancementioning

confidence: 99%

Heartwater – Ehrlichia ruminantium infection

Allsopp¹

2015

Rev. Sci. Tech. OIE

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“…There are, however, some general estimates of the economic effects of tick parasitism [5,8,[33][34][35][36] based on some of the pathogens they transmit [37,38]. Some tick-transmitted pathogens each have a particular tick species vector, so the potential distribution of each pathogen may be estimated from the distribution of its vectors.…”

Section: Background: Ticks Climate Landscape and Human Forcesmentioning

confidence: 99%

Current Limitations in the Control and Spread of Ticks that Affect Livestock: A Review

Estrada-Peña

Salman

2013

Agriculture

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Ticks are well-known parasites that affect livestock productivity. This paper reviews the current knowledge regarding the spread of ticks with their impact in animal health and the limitations to achieve effective control measures. The forecasted trends in climate play an obvious role in promoting the spread of ticks in several regions. It appears that climate warming is pivotal in the spread and colonization of new territories by Rhipicephalus microplus in several regions of Africa. The reported increase in altitude of this tick species in the mountainous regions of Central and South America appears to be driven by such general trends in climate change. This factor, however, is not the only single contributor to the spread of ticks. The poor management of farms, uncontrolled movements of domestic animals, abundance of wild animals, and absence of an adequate framework to capture the ecological plasticity of certain ticks may explain the complexity of the control measures. In this paper, we review several details regarding the relationships of ticks with the environment, wild fauna and competition with other species of ticks. Our intention is to highlight these relationships with the aim to produce a coherent framework to explore tick ecology and its relationship with animal production systems.

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“…The disease is only transmitted by ticks of the genus Amblyomma and its distribution coincides with that of its vector species (Walker and Olwage, 1987). Heartwater is a major obstacle to domestic livestock productivity in areas where it is endemic (Mukhebi et al, 1999), and is particularly serious when susceptible animals are moved from heartwater-free to heartwater-infected areas (Simpson et al, 1987). Amblyomma variegatum, the most widespread African vector of heartwater, was introduced, together with the disease, on to some Caribbean islands during the 18th or 19th centuries (Maillard and Maillard, 1998).…”

Section: Introductionmentioning

confidence: 99%

Ehrlichia ruminantium variants which do not cause heartwater found in South Africa

Allsopp

Strijp

Faber

et al. 2007

Veterinary Microbiology

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In 1994 a batch of apparently healthy goats was selected for intended export to the USA from a heartwater-free and vector tick-free region of South Africa. The animals were tested serologically for heartwater, using either or both an IFA and an ELISA test, and 52% were found to be serologically positive. A PCR assay based on Ehrlichia ruminantium 16S gene sequences gave positive results for 54% of the animals, suggesting that apparently non-pathogenic E. ruminantium variants existed in this heartwater-free area. To identify and characterise the agents responsible for the positive serological and PCR results, ticks and animal blood samples were collected from two of the three farms involved in the original survey during two successive seasons of expected peak tick activity. Ticks were kept alive for a minimum of 3 weeks to allow digestion of any blood meal before being processed.Over the two seasons, 28% of the livestock and 15% of the ticks sampled were found to be carrying E. ruminantium. E. ruminantium 16S and pCS20 sequences were detected in all of the four tick species collected from the livestock (Rhipicephalus evertsi evertsi, Rhipicephalus evertsi mimeticus, Hyalomma truncatum, Hyalomma marginatum rufipes),suggesting that some of the species may act as vectors. Animals generally carried multiple E. ruminantium 16S genotypes, whereas ticks rarely carried more than one.Infection levels in both animals and ticks were too low to generate a marked response openUP when a blood stabilate was sub-passaged in a clean sheep, preventing the subsequent establishment of any of the organisms in culture.

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An assessment of the economic impact of heartwater (Cowdria ruminantium infection) and its control in Zimbabwe

Cited by 67 publications

References 8 publications

Heartwater – Ehrlichia ruminantium infection

Heartwater – Ehrlichia ruminantium infection

Current Limitations in the Control and Spread of Ticks that Affect Livestock: A Review

Ehrlichia ruminantium variants which do not cause heartwater found in South Africa

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