Ehrlichia ruminantium

Heartwater
Amblyomma hebraeum, a vector of heartwater disease
Scientific classification
Kingdom:
Bacteria
Phylum:
Proteobacteria
Class:
Alphaproteobacteria
Order:
Rickettsiales
Family:
Ehrlichiaceae
Genus:
Ehrlichia
Species:
E. ruminantium [1]
Binomial name
Ehrlichia ruminantium
(Dumler, 2001)
Synonyms
  • Cowdria ruminantium (Cowdry 1925) Moshkovski 1947 (Approved Lists 1980)

Heartwater (also known as cowdriosis, nintas, and ehrlichiosis) is a tick-borne rickettsial disease of domestic and wild ruminants.[2] It is caused by Ehrlichia ruminantium (formerly Cowdria ruminantium) - an intracellular Gram-negative coccal bacterium (also referred to as Rickettsia ruminantium). The disease is spread by bont ticks, which are members of the genus Amblyomma. Affected mammals include cattle, sheep, goats, antelope, and buffalo, but the disease has the biggest economic impact on cattle production in affected areas. The disease's name is derived from the fact that fluid can collect around the heart or in the lungs of infected animals.[3]

The disease is common in sub-Saharan Africa and some of the West Indian islands. It was first identified in sheep in South Africa in the 1830s, and had reached the Caribbean by 1980.[3] The ticks that carry the disease occur in Africa and the Caribbean, and feed on a wide variety of vertebrate hosts. In the Caribbean, at least, the cattle egret has been implicated in the spread of heartwater, since it colonized the islands in the 1950s.[3] Animals often acquire the disease when moved onto pastures where infected ticks are found.

There are reports of zoonotic infections of humans by E. ruminantium, like for other Ehrlichia species, such as those that cause human ehrlichiosis.[4][5][6]

Cowdriosis is notifiable to the World Organisation for Animal Health.

Clinical signs

Clinical disease is more common in young animals and non-native breeds. The clinical signs of disease are caused by an increased vascular permeability and consequent oedema and hypovolemia.

The symptoms include neurological signs such as tremors and head pressing, respiratory signs such as coughing and nasal discharge, and systemic signs such as fever and loss of appetite. Physical examination may reveal petechiae of the mucous membranes, tachycardia, and muffled heart sounds. Cowdriosis can also cause reproductive and gastrointestinal disease. It is frequently fatal.

Diagnosis

On post mortem examination, a light yellow transudate that coagulates on exposure to air is often found within the thorax, pericardium, and abdomen. Most fatal cases have the hydropericardium that gives the disease its common name. Pulmonary oedema and mucosal congestion are regularly seen along with frothy fluid in the airways and cut surfaces of the lungs.

To definitively diagnose the disease, C. ruminantium must be demonstrated either in preparations of the hippocampus under Giemsa staining or by histopathology of brain or kidney.

Treatment and control

During the early stages of disease, animals may be treated with sulfonamides and tetracyclines. In advanced disease, prognosis is poor.

Tetracyclines can also be used prophylactically when animals are introduced into an area endemic with cowdriosis. A live blood vaccine is available for protection of young stock, but animals may require treatment for the disease after vaccination. Ectoparasiticides, used as dips, can be used to reduce exposure the animals exposure to bont ticks. In areas endemic for heartwater, the use of dips against other ticks of domestic animals, such as Rhipicephalus (Boophilus) and Hyalomma species is likely, and this will usually contribute to control of vectors of E. ruminantium.

References

  1. ↑ Dumler JS, Barbet AF, Bekker CP, Dasch GA, Palmer GH, Ray SC, et al. (November 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 six 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 (Pt 6): 2145–2165. doi:10.1099/00207713-51-6-2145. PMID 11760958.
  2. ↑ Peter TF, Burridge MJ, Mahan SM (May 2002). "Ehrlichia ruminantium infection (heartwater) in wild animals". Trends in Parasitology. 18 (5): 214–8. doi:10.1016/s1471-4922(02)02251-1. PMID 11983602.
  3. 1 2 3 "Heartwater". Animal and Plant Health Inspection Service. U.S. Department of Agriculture. Archived from the original on 2008-04-13. Retrieved 2008-04-13.
  4. ↑ Allsopp MT, Louw M, Meyer EC (December 2005). "Ehrlichia ruminantium: an emerging human pathogen?". Annals of the New York Academy of Sciences. 1063 (1): 358–60. Bibcode:2005NYASA1063..358A. doi:10.1196/annals.1355.060. PMID 16481543. S2CID 35037984.
  5. ↑ Gaddy HG (August 2020). "Using local knowledge in emerging infectious disease research". Social Science & Medicine. 258: 113107. doi:10.1016/j.socscimed.2020.113107. PMC 7292947. PMID 32563166.
  6. ↑ Esemu SN, Ndip LM, Ndip RN (2011-01-01). "Ehrlichia species, probable emerging human pathogens in sub-Saharan Africa: environmental exacerbation". Reviews on Environmental Health. 26 (4): 269–79. doi:10.1515/REVEH.2011.034. PMID 22435325. S2CID 26448157.

Additional references

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