Published Date: 2012-03-25 20:41:17
Subject: PRO/AH/EDR> Theileria, bovine - Australia: (NS)
Archive Number: 20120325.1080410
THEILERIA, BOVINE - AUSTRALIA: (NEW SOUTH WALES)
A ProMED-mail post
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International Society for Infectious Diseases
Date: 21 Mar 2012
Source: South Coast Register [Edited]
Dangerous cattle disease prompts warning for farmers
A significant outbreak of the cattle disease Theileriosis has cost a southern Shoalhaven farmer tens of thousands of dollars.
District veterinarian with the South East Livestock Authority in Bega, Ian Lugton said the disease was caused by protozoan blood parasites known scientifically as _Theileria orientalis_.
He said the disease was similar to the tick fevers of northern Australia in that the blood's red cells were destroyed and affected stock becomes anaemic, jaundiced and ill.
Mr Lugton said Theileria had been present in Australian coastal districts for many years without causing significant illness. However one pathogenic strain capable of killing affected stock, the Ikeda variant, had emerged in recent years.
Theileriosis was initially encountered on the NSW North Coast but has been diagnosed as far south as Victoria. It is believed that once cattle are infected with Theileria organisms they carry the infection for life and are capable of transmitting it to other cattle through bush ticks and other biting insects such as sucking lice and March flies.
Cattle that have never been exposed to any Theileria strains previously (naive) may develop severe disease when exposed to the Ikead strain.
Mr Lugton said the typical scenario associated with a Theileriosis outbreak was when naive susceptible heavily-pregnant cattle were introduced to a coastal district from further inland.
After a month or more the cows begin to abort late-term calves or begin lactation only to develop a fever, severe anaemia and jaundice.
Affected animals may appear lethargic, depressed and weak. Many will dry off and some will die.
Mr Lugton said disease, now thought to be Theileriosis, was first noticed in the Milton area in January 2009 in introduced stock.
A significant outbreak involving a couple of mobs of introduced cattle from southern NSW to the Yatte Yattah area occurred in spring 2011. Mr Lugton said the outbreak cost the owner tens of thousands of dollars from stillbirths and deaths among cows at calving.
He said an "unfortunate consequence" of the event was that the local area now had a plentiful supply of donors of infected blood which arthropods can use to transmit infection to susceptible cattle.
If the infection is transmitted to cattle which have not been exposed to another strain of Theileria, and if the cattle are not heavily pregnant or otherwise stressed, then the infection is likely to remain unapparent. Mr Lugton can be contacted at South East Livestock Health and Pest Authority on 6492 1283.
[By Stuart Carless]
[More information about ticks that cause this disease may be found in ProMED-mail post 20110313.0805.
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.
_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 per cent 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 per cent. The mortality rate for tropical theileriosis can also vary from 3 per cent to nearly 90 per cent, 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
Bega, Australia may be found on the interactive HealthMap at: <http://healthmap.org/r/21Se - Mod.TG]