Published Date: 2009-03-13 23:57:49
Subject: PRO/AH/EDR> Theileria, bovine - Australia: (NSW), RFI
Archive Number: 20090313.1045
THEILERIA, BOVINE - AUSTRALIA: (NEW SOUTH WALES), REQUEST FOR INFORMATION
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: 13 Mar 2009
Source: ABC rural [edited]
Ticks bring disease to NSW cattle
A cattle disease spread by bush ticks has left
one producer in northern New South Wales with 35
dead cattle. Greg Bailey from Dorrigo lost 3
grown animals to Theileria, and the remainder aborted or died soon after birth.
He says it appears his cattle were more
vulnerable because they were brought in from
outside the region. "I'm supposed to be an
experienced cattleman and I actually didn't know
anything about the disease," he says.
"And I would've thought that the relevant
agencies may have prior to now let people know
that it is around and be more positive about
saying 'Look, we all know the risks of bringing
in cattle from other areas, but once this thing
is prevalent, just don't do it'."
[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. The most important vector for _T. parva_
is _Rhipicephalus appendiculatus_. _R.
zembeziensis_ in southern Africa and _R. Duttoni_
in Angola can also spread East Coast fever. _T
annulata_ is transmitted by ticks in the genus Hyalomma.
_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 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 nonendemic
areas. Howwever, 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 crossprotection against other
strains. Crossprotection 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_.
This particular outbreak in Australia is a little
out of where we typically think of Theileria
occurring. And the article does not give us
enough information to understand the type of tick
carrying the disease. Therefore, to accurately
define the disease is difficult. More
information on this outbreak would be greatly appreciated.
Portions of this comment have been extracted from:
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