Calf Diarrhea Pathogen Information:
Rotavirus
Introduction:
Rotavirus is a member of the viral family reoviridae. Rotaviruses are divided
into various subtypes, which can infect people, calves, young pigs and foals.
Epidemiology:
Rotavirus is essentially ubiquitous in the environment of domestic animals. In
serological surveys, most adult cattle have been found to have antibodies to
rotavirus. Rotavirus may be found in the feces of healthy animals. Although it
is most commonly found as part of a mixed infection, rotavirus is considered a
primary diarrheal pathogen. Subclinical infection may be prevalent on many
farms, and healthy adults and calves can shed viruses in their feces that
become a source of infection for calves. Rotavirus can also spread as an aerosol,
particularly when conditions are humid. Calves with diarrhea due to rotavirus
are commonly between 4 days and 3 weeks of age. Diarrheic calves shed
especially high numbers of viruses in their feces, and the virus is stable in
feces and resistant to many common disinfectants. Recovery from disease does
not protect the calf against subsequent re-infection.
Zoonotic
risk: Human and Bovine strains of rotavirus are specific to their hosts, so
rotavirus is not considered a risk for transmission from one species to
another.
Clinical
features / specific therapy of rotavirus infection: Colostral protection of a
calf against rotavirus infection is most effective when antibodies are present
in the gut lumen of the calf. Because of this, protection drops sharply when
antibody-rich colostrum is replaced by milk or milk replacer that does not
contain protective antibodies. This generally takes place when the calf is
about 3 days old. Disease often occurs soon after, when the calf is 4 or 5 days
old, but also commonly occurs up to 2 weeks of age. Infection with rotavirus is
frequently accompanied by infection with another enteric pathogen or
pathogens, such as Cryptosporidium parvum(link) or E. coli(link).
By
destroying the intestinal villi of the small intestine, rotavirus causes
maldigestion and malabsorbtion, without decreasing intestinal secretions. This
results in acute-onset voluminous diarrhea with a semi-formed to watery
consistency. The lower right quadrant of the abdomen may be distended due to
filling of the small intestine with fluid. Diarrhea is accompanied by
increasing depression, dehydration, weight loss, and loss of electrolytes.
Calves with rotavirus diarrhea may or may not have a fever.
There is no
specific therapy for rotavirus infection. Mild cases of diarrhea caused by
rotavirus alone will generally resolve within a week. Younger calves tend to be
more severely affected than older calves, and calves greater than 2 weeks of
age rarely have severe signs if the rotavirus infection is uncomplicated by the
presence of other pathogens.
Diagnosis/
Necropsy findings/ Sampling goals:
Diagnosis
of rotaviral infection can be achieved by several laboratory methods (e.g.
ELISA, IFA, PCR) which can isolate rotavirus particles in the feces of an
affected calf. Viruses are more easily isolated from the feces of an animal
which has had diarrhea for 24 hours or less. Serological testing is also
available for rotavirus. It is advisable to test simultaneously for other
diarrhea causing agents, as infections with rotavirus are frequently
accompanied by other enteric infection.
Necropsy findings are
non-specific and include dehydration, fluid-filled intestines, and a distended
abomasum. Samples taken at necropsy and submitted for laboratory analysis
should include preserved samples of all intestinal segments for histopathology,
and chilled (not frozen) samples of the contents of the jejunum, ileum, and
colon for virus isolation.
Specific
Prevention Measures/ Vaccination: The primary approach to controlling Rotaviral
infection in calves involves standard management approaches to limiting the
spread of diarrheal pathogens among calves. Isolation of calves with diarrhea
is of particular importance since clinically ill calves shed high numbers of
rotavirus particles in their feces and can continue to do so for several weeks
following recovery. It is particularly important to minimize viral exposure in
calves between 3 days and 3 weeks of age, as these calves are most susceptible
to illness due to rotaviral infection. Older calves do develop some age-related
resistance to infection.
There are
several commercially available rotaviral vaccines designed to be administered
to pregnant cows in order to boost specific anti-rotaviral immunity in their
colostrum, but none of these has been clearly demonstrated to be effective in
the prevention of rotaviral infection in calves. This is thought to be due to
the fact that humoral immunity in the calf provides only limited protection
against infection, whereas very good protection is provided by the presence of
anti-rotaviral antibodies in the gut lumen of the calf. Even a well-vaccinated
cow will switch from production of colostrum to production of regular milk,
which is much lower in antibodies, during her first few days after calving, so
even with vaccination her milk will become considerably less protective after
the first few days. With dairy calves this point may be moot as many dairy
calves are removed from their dams after one or two meals of colostrum and are
fed whole milk or milk replacer thereafter.
One
approach that has been shown to be beneficial for limiting rotaviral infection
in calves is the extended feeding of colostrum or products containing specific
antibodies in the form of dried milk from hyperimmunized cows or immunoglobulins
produced in the egg yolks of chickens. These products, or colostrum from the
home farm, can provide some protection to the calf when they are fed along with
milk or milk replacer for the first thirty days of the calf’s life, as they
maintain the presence of protective anti-rotaviral antibodies in the gut lumen
of the calf.
