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International Society for Infectious Diseases
Date: 2 May 2009
Source: Winnipeg Frepress
Dozens of cattle in Manitoba slaughtered due to disease
Dozens of cattle in eastern Manitoba have been slaughtered since
January after federal inspectors found they were infected with a
tick-borne disease that destroys the animals' red blood cells.
Canadian Food Inspection Agency disease control specialist Sandra
Stephens said inspectors are still investigating the outbreak of
anaplasmosis in the rural municipalities of Lac du Bonnet and
"We will keep looking until we turn up all negatives," Stephens said
of the ongoing testing at several cow-calf operations.
Cattle in Alberta and Saskatchewan are also being tested, as animals
from Manitoba producers often go out of province to large feedlot
This disease is not common in Manitoba and is believed to have been
introduced by an animal purchased from the United States.
Anaplasmosis is more common in the U.S. It's only been found in
Canada 7 times since 1969. An animal in Saskatchewan tested positive
Stephens said that in Manitoba, anaplasmosis is most likely spread by
ticks and biting flies.
The disease is deadly for older animals and serious but rarely fatal
in animals 1 to 2 years old. It causes fever, anemia, weakness and
Infected dairy cattle also have a rapid decline in milk production.
Stephens said the disease poses no risk to humans.
"There is no evidence tying this to infection in people," she said.
ProMED-Mail Rapporteur Susan Baekeland
[The _Anaplasma_ genus has recently been expanded to include species
transferred from the genus _Ehrlichia_ , now named _Anaplasma
phagocytophilum_ (compiled from species previously known as
_Ehrlichia phagocytophila_ , _E equi_ , and human granulocytic
ehrlichiosis agent), _A bovis_ (previously _E bovis_ ), and _A
platys_ (previously _E platys_ ), all of which invade blood cells
other than erythrocytes of their respective mammalian hosts. Bovine
anaplasmosis is of economic significance in the cattle industry.
Clinical bovine anaplasmosis is usually caused by _A marginale_ .
Cattle are also infected with _A centrale_ , which generally results
in mild disease. _A ovis_ may cause mild to severe disease in sheep,
deer, and goats.
Anaplasmosis is not contagious. Numerous species of tick vectors (
_Boophilus_ , _Dermacentor_ , _Rhipicephalus_ , _Ixodes _, _Hyalomma_
, and _Ornithodoros_ ) can transmit _Anaplasma_ spp . Not all of
these are likely significant vectors in the field, and it has been
shown that strains of _A marginale_ also co-evolve with particular
tick strains. _Boophilus_ spp are major vectors in Australia and
Africa, and _Dermacentor_ spp have been incriminated as the main
vectors in the USA. After feeding on an infected animal, intrastadial
or trans-stadial transmission may occur. Transovarial transmission
may also occur, although this is rare, even in the single-host
_Boophilus_ spp . A replicative cycle occurs in the infected tick.
Mechanical transmission via biting dipterans occurs in some regions.
Transplacental transmission has been reported and is usually
associated with acute infection of the dam in the second or third
trimester of gestation. Anaplasmosis may also be spread through the
use of contaminated needles or dehorning or other surgical
Since there are a number of vectors one wonders if Canada is so
certain they don't have the appropriate vector. Likewise, if they are
quite confident they don't have the vector then it may explain why
they are terminating the animals. However there is treatment, so this
Affected animals have decrease in appetite, milk yield and stamina.
They have thin watery blood which may not transport oxygen
efficiently and lead to difficulty breathing as the animal is not be
Diagnosis may be made on a geimsa-stained blood smear.
There is a strong correlation between age of cattle and severity of
disease. Calves are much more resistant to disease (although not
infection) than older cattle. This resistance is not due to colostral
antibody from immune dams. In endemic areas where cattle first become
infected with _A marginal_ early in life, losses due to anaplasmosis
are minimal. After recovery from the acute phase of infection, cattle
remain chronically infected carriers but are generally immune to
further clinical disease. However, these chronically infected cattle
may relapse to anaplasmosis when immunosuppressed (eg, by
corticosteroids), when infected with other pathogens, or after
splenectomy. Carriers serve as a reservoir for further transmission,
which is likely why the Canadians are terminating the animals.
However with treatment this is overcome. Serious losses occur when
mature cattle with no previous exposure are moved into endemic areas
or when under endemically unstable situations when transmission rates
are insufficient to ensure all cattle are infected before reaching
the more susceptible adult age.
Tetracycline antibiotics and imidocarb are currently used for
treatment. Cattle may be sterilized by treatment with these drugs and
remain immune to severe anaplasmosis subsequently for at least 8 mo.
Since there is treatment, that can eliminate the carrier state, they
why the deaths of the animals?
Prompt administration of tetracycline drugs (tetracycline,
chlortetracycline, oxytetracycline, rolitetracycline, doxycycline,
minocycline) in the early stages of acute disease (eg, PCV >15%)
usually ensures survival. A commonly used treatment consists of a
single IM injection of long-acting oxytetracycline at a dosage of 20
mg/kg. Blood transfusion to partially restore the PCV greatly
improves the survival rate of more severely affected cattle. The
carrier state may be eliminated by administration of a long-acting
oxytetracycline preparation (20 mg/kg, IM, at least 2 injections with
a 1-wk interval). Withholding periods for tetracyclines apply in most
countries. Injection into the neck muscle rather than the rump is
Imidocarb is also highly efficacious against _A marginale_ as a
single injection (as the dihydrochloride salt at 1.5 mg/kg, SC, or as
imidocarb dipropionate at 3.0 mg/kg). Elimination of the carrier
state requires the use of higher repeated doses of imidocarb (eg, 5
mg/kg, IM or SC, 2 injections of the dihydrochloride salt 2 wk
apart). Imidocarb is a suspected carcinogen with long withholding
periods and is not approved for use in the USA or Europe.
Portions of this comment were extracted from:
Anaplasmosis, bison - Canada (Saskatchewan) (02) 20000621.1010
Anaplasmosis, bison - Canada (Saskatchewan) 20000615.0967]
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