| Description:
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Bovine coronavirus
(BCV) is recognized as the primary etiology of Winter
Dysentery (WD) of adult cows and coronaviral diarrhea
in young (3 to 21 days-old) calves. WD is a clinically
and economically important disease in many countries
including the United States and Canada. It is characterized
by high morbidity (50-100%), but low mortality (1-2%),
and occurs primarily in adult dairy cows. Bovine coronavirus survives
well at low temperatures and low levels of ultraviolet
light. Clinically, WD is characterized by severe watery
diarrhea (sometimes with blood and mucus), decreased
milk production, listlessness, depression, anorexia,
weight loss, and sometimes cough and/or nasolacrimal
discharge. Cows that recover from WD are apparently
immune from disease for 1 to 5 years, but carrier cows
can be a source of repeated outbreaks in a herd. Microscopic
lesions of WD are most evident in the spiral colon where
crypt epithelium exhibits varying degrees of degeneration
and necrosis. Grossly, hemorrhage (including petechiae)
can be found in the mucosa of both the small and large
intestine.
Coronaviral diarrhea in young calves is characterized
by profuse watery or hemorrhagic diarrhea, listlessness,
anorexia, pyrexia, and dehydration that can last 2 to
6 days in surviving calves. In some calves, feces contain
flecks of blood. Morbidity and mortality are high and
calves with bloody diarrhea can die of hypovolemiawithin
a few hours of the onset of clinical signs. Infection
is established by ingestion or inhalation of Bovine coronavirus which
replicates in "rapidly dividing" cells such
as those that line intestinal villi. Microscopic lesions
of Bovince coronavirus enteric infection in young calves can often be
observed in both the small intestine and colon. In the
small intestine, villi may be atrophic and lined by
attenuated epithelium. This lesion results in a diminished
absorptive and digestive function, and perhaps, an increased
secretory function, all of which lead to severe diarrhea.
Fluid and electrolyte loss results in dehydration, acidosis,
and hypoglycemia. In calves that recover from the acute
stages of infection, the intestinal crypt epithelium
can regenerate lost mucosa and eventually regain normal
function. Bovine coronavirus can also cause a "respiratory syndrome"
that is usually quite mild or even "sub-clinical".
Clinical signs are usually seen in calves 2 to 16 weeks
old and include sneezing (from rhinitis) and coughing
(from tracheitis). Because Bovine coronavirus can infect respiratory
epithelium, it can predispose calves to opportunistic
bacterial infections. Calves with respiratory Bovine coronavirus infection
can shed high numbers of virus in their nasal mucus
and this virus can cause enteric and/or respiratory
disease in other cattle.
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| Diagnosis: |
In the past, diagnosis
of Bovine Coronavirus in live animals was very difficult
because of common and conflicting clinical symptoms.
The virus is very labile and does not survive well in
samples, making conventional diagnostics very difficult.
It is possible to identify Bovine coronavirus by means of different
culture and floating techniques including staining.
However, these techniques are labour intensive and impractical.
Recently, a PCR-based assay for the detection of BCV
in a sample has become available. The sensitivity of
this test is remarkably greater then conventional methods
of detection and can even detect Bovine coronavirus in asymptomatic
carriers, responsible for continued spread of this disease.
Since the PCR detects specific genetic sequences unique
to Bovine coronavirus, the status of the virus (“alive”
or “dead”) is not important for diagnosis,
as long as the genetic material remains intact. This
test offers veterinarians a sensitive, specific, and
rapid diagnostic tool that can definitively confirm
the presence of Bovine coronavirus in a small blood or fecal sample.
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