A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: 15 May 2009
Source: Canadian Cattlemen Magazine [edited]
Eight cattle herds in eastern Manitoba are under federal quarantine
in what may mean a temporary end to Canada's status as free of
anaplasmosis, the Manitoba Co-operator reported Thursday [14 May 2009].
Dr. Lynn Bates, a veterinary program officer with the Canadian Food
Inspection Agency (CFIA) in Winnipeg, told the Co-operator's Ron
Friesen the herds are in an area west of the Winnipeg River in the
rural municipalities of Lac du Bonnet and Alexander.
Within the 8 herds are a total of 305 infected cattle, or "reactors,"
detected through a periodically conducted national bovine serological
survey, Bates said.
Anaplasmosis is a reportable livestock disease in Canada, caused by a
parasite of red blood cells. It affects domestic and wild ruminants
but only cattle show clinical signs.
The disease can be transmitted in infected red blood cells by biting
insects and through contaminated instruments such as hypodermic
needles and dehorning equipment.
Since anaplasmosis is blood-borne and it's not possible to avoid
insects, changing needles frequently and disinfecting dehorning
equipment in between use are the best ways to limit exposure to the
disease, said Dr. Wayne Lees, Manitoba's chief veterinarian.
"If you're in an endemic area or an area where you think anaplasmosis
is an issue, it's probably a worthwhile expense," Lees told the Co-operator.
The cause of the outbreak is not certain, but the disease was most
likely brought into the area by infected livestock imported from the
U.S., Bates said.
Anaplasmosis, endemic in much of the lower continental U.S., is not a
regulated disease in that country but costs the U.S. cattle industry
an estimated USD 300 million per year.
Canada is considered anaplasmosis-free, but the Manitoba cases, the
province's 1st since 1970, may change that status. CFIA was obliged
to report the case to the World Organisation for Animal Health (OIE),
Bates told the Co-operator.
Canada, until 2004, required anaplasmosis testing of live cattle
imported from the U.S. during the biting insect season. But new rules
in 2004 allowed U.S. feeder cattle from 39 states considered
"low-risk" for the disease into Canada without testing at any time of year.
[Anaplasmosis, formerly known as gall sickness, traditionally refers
to a disease of ruminants caused by obligate intraerythrocytic
bacteria of the order Rickettsiales, family Anaplasmataceae, genus
_Anaplasma_ . Cattle, sheep, goats, buffalo, and some wild ruminants
can be infected with the erythrocytic _Anaplasma_ . Anaplasmosis
occurs in tropical and subtropical regions worldwide (around 40o N to
32o S), including South and Central America, the USA, southern
Europe, Africa, Asia, and Australia.
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 2nd or 3rd
trimester of gestation. Anaplasmosis may also be spread through the
use of contaminated needles or dehorning or other surgical instruments.
Animals with peracute infections succumb within a few hours of the
onset of clinical signs. Acutely infected animals lose condition
rapidly. Milk production falls. Inappetence, loss of coordination,
breathlessness when exerted, and a rapid bounding pulse are usually
evident in the late stages. The urine may be brown, but, in contrast
to babesiosis, hemoglobinuria does not occur. A transient febrile
response, with the body temperature rarely exceeding 106 F (41 C)
occurs at about the time of peak rickettsemia. Mucous membranes
appear pale and then yellow. Pregnant cows may abort. Surviving
cattle convalesce over several weeks, during which hematologic
parameters gradually return to normal.
Many states do not regulate anaplasmosis because it is not contagious
from animal to animal but is transmitted through vectors. It does
result in a decrease of production and some animal loss, which these
latter 2 are the reason for concern.
Portions of this comment have been extracted from:
Anaplasmosis, cattle - Canada (MB) 20090503.1662]