Published Date: 2012-06-04 12:18:37
Subject: PRO/AH/EDR> Theileria, bovine - Australia (02): (VI)
Archive Number: 20120604.1155307
THEILERIA, BOVINE - AUSTRALIA (02): (VICTORIA)
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Thu 31 May 2012
Source: ABC News (Australian Broadcasting Corporation) [edited]
A Melbourne parasitologist researching the deadly cattle disease [theileriosis] says cattle brought into Victoria from NSW [New South Wales] should be quarantined to avoid further spread of the disease.
Melbourne University's Dr Abdul Jabbar says about 100 cattle in Victoria have now died from theileriosis, which infects herds through a parasite carried by bush ticks.
The Victorian Department of Primary Industries has resisted demands from cattle producers to quarantine infected herds.
Dr Jabbar says if quarantine isn't an option, it should then be mandatory for cattle to be tested for theileria before they are sold interstate. "We have more than 70 outbreaks and especially in the last 6 months, 50 outbreaks so it is really increasing.
We have investigated a number of properties and in most of those properties, the disease actually occurred only in those animals which were transported from NSW."
[Byline: Libby Price]
[Theileriosis results from infection with obligate intracellular protozoa in the genus _Theileria_. The 2 most important species are _T. parva_, which causes East Coast fever, Corridor disease, and Zimbabwean theileriosis, and _T. annulata_, which causes tropical theileriosis (Mediterranean theileriosis). A number of other _Theileria_ species can infect ruminants; many of them cause mild or asymptomatic infections.
Both _T. parva_ and_ T. annulata_ are spread by ticks. It is likely the tick responsible for this outbreaks is (_Haemaphysalis longicornis_ see images at http://pds.exblog.jp/pds/1/200508/09/39/b0060239_1622729.jpg and http://www.abc.net.au/reslib/201205/r935892_9853667.JPG). More information about ticks that cause this disease may be found in ProMED-mail post 20110313.0805.
_Theileria_ sporozoites are transmitted to susceptible animals in the saliva of the feeding tick. Ordinarily, _T. parva_ and _T. annulata_ only mature and enter the saliva after the tick attaches to a host; usually, a tick must be attached for 48 to 72 hours before it becomes infective. However, if environmental temperatures are high, infective sporozoites can develop in ticks on the ground and may enter the host within hours of attachment. Transovarial transmission does not occur with either _T. parva_ or _T. annulata_. Inside the host, _Theileria_ sporozoites undergo a complex life cycle involving the replication of schizonts in leukocytes and piroplasms in erythrocytes. Cattle that recover from _Theileria_ infections usually become carriers.
The incubation period for theileriosis is 10 to 25 days.
The typical clinical signs of East Coast fever are swelling of the draining lymph node followed by generalized lymphadenopathy, fever, anorexia, and a rapid loss of condition. Other symptoms can include lacrimation, nasal discharge, corneal opacity, an increased respiratory rate, and diarrhea. Death is common in fully susceptible cattle, but more rare in cattle in endemic areas. Terminally, animals often develop pulmonary edema, severe dyspnea, and a frothy nasal discharge. Cattle with East Coast fever may also develop a fatal condition called "turning sickness." In this form of the disease, infected cells block capillaries in the central nervous system and cause neurologic signs. Some animals recover from East Coast fever and become asymptomatic carriers; others may have poor productivity and stunted growth.
Tropical theileriosis resembles East Coast fever, but jaundice and anemia may also occur. Common clinical signs in tropical theileriosis include fever, enlarged lymph nodes, pale mucous membranes, a rapid loss of condition, and sometimes hemoglobinuria.
Morbidity and mortality vary with the host's susceptibility and the strain of the parasite. The mortality rate from East Coast fever can be up to 100 percent in cattle from non endemic areas. However, in indigenous zebu cattle in endemic areas, mortality is usually low even with a morbidity of approximately 100 percent. The mortality rate for tropical theileriosis can also vary from 3 percent to nearly 90 percent, depending on the strain of parasite and the susceptibility of the animals. Theileriosis can be treated with drugs, and vaccines are available for both East Coast fever and tropical theileriosis. Recovery from one strain of _T. annulata_ confers cross protection against other strains. Cross protection does not occur with _T. parva_.
The differential diagnosis includes heartwater, trypanosomiasis, babesiosis, anaplasmosis, and malignant catarrhal fever. The parasites must also be differentiated from other species of _Theileria_.
Portions of this comment have been extracted from http://www.cfsph.iastate.edu/Factsheets/pdfs/theileriosis_theileria_parva_and_theileria_annulata.pdf. - Mod.TG
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