Viral Diarrhea Virus
noted, epidemiology and pathogenesis by BVDV are taken from Merck
Cattle are the
primary hosts for BVDV
however, the virus may
also infect sheep, goats, water buffalo and wild ruminants (Carter
2005). Infection is
directly and indirectly via host secretions. Infection therefore can be
inhalation of the virus. Artificial insemination or coitus also
facilitates the spread of BVDV as it is also shed in semen of bovine
hosts. Bovine viral diarrhea is caused by BVDV and can
exist in a variety of forms with a wide range of clinical
manifestations. These range from gastroenteric, respiratory and
syndromes to acute viral
and/or fatal mucosal disease. These syndromes are
discussed in more detail below.
BVDV has a world wide
distribution and therefore is a world wide disease. Regular vaccination
programs are commonly performed however bovine viral diarrhea continues
to play a significant role in bovine disease. Infection
can occur at any age butclinical signs are most commonly seen in
cattle between 6 months and 2 years of age.
With the many
manifestations that BVDV infection can cause, the
the concern is oriented towards the effects the virus has on
reproductive system. BVDV has the ability to cross the placenta and
fetuses at any time during gestation. The effects of fetal infection
are dictated mostly by time of infection during gestation. If a
pregnant cow contracts
during her first trimester early in gestation, fetal death may occur
fetus will be reabsorbed (Carter 2005). This can lead to infertility
fetal death does not occur, calves could abort later on in gestation,
stillborn, have malformations or be weak and unthrifty calves (Carter
2005, Merck 2005).
between 4 to 120 days of gestation most often results in immunotolerant
persistent BVDV infections. These calves can be in good or poor
often have enteric or respiratory problems (Carter 2005). Secondary
common due to the immunocomprimization of the calf as the virus targets
lymphoid tissue and impairs immunity (Carter 2005). Identification of
calves is very important for two reasons. These calves shed massive
virus into the environment and if bred, they will infect their fetus
produce more persistently infected calves (Carter 2005). Eventhough
most persistently infected calves die within the first 6 to 24 months
they act as a
source of infection for the rest of the herd.
Sick calf with BVDV
Unless noted otherwise, description of
disease by BVDV are taken from Merck (2005).
Literature suggests that bovine
viral diarrhea is the most common diagnostic explanation
with respect to bovine abortions. As described above, infection prior
to 125 days of gestation may result in fetal death, abortion,
resorption, mummification and malformations while infection after 125
days of gestation is more likely to result in persistently infected
calves. These calves
loss of condition and mucoid bloody diarrhea.
often prominent, thick and stringy nasal secretions are present
crusty skin of the muzzle area. Upon necropsy,
ulceration and erosion
upper respiratory and digestive tract is evident and due to
BVDV stong affinity
lymphoid tissue, ulceration and erosion are most often seen within the
payer’s patches and
esophagus of infected animals.
Erosions of the esogphagus from BVDV infection
Erosion of the payer's patches
of the intestine
There exists controversy in the literature concerning the exact role of
BVDV in bovine respiratory disease. BVDV is often included within the
etiologies of bovine respiratory disease complex. It has been
suggested that due to the immunosuppression and alteration of normal
defense systems from BVDV infection, cattle become susceptible to
secondary bacterial pneumonia. BVDV has also been reported to be the
most common virus associated with other viral infections of the
Bovine respiratory disease complex often arises in situations of
stress, poor management, poor environmental conditions and
malnutrition. Failure of passive transfer may also significantly
contribute to the development of bovine respiratory disease.
These additive factors depress the overal health and immunity of calves
resulting in increased susceptibility to viral and/or bacterial
infections. Commonly involved bacterial species include Pasteurella multocida, Mannheimia haemolytica and Mycoplasma bovis. Viral species
commonly associated with bovine respiratory disease complex
include Bovine Respiratory Syncytial Virus, Parainfluenza
Virus 3, and Bovine Herpesvirus-1.
Secondary bacterial pneumonia of a bovine
BVDV infection commonly
causes mucosal disease in calves that are 6 months to 2 years of age.
disease can result from both cytopathic and noncytopathic BVDV
strains. Clinical signs often include a biphasic fever,
depression, transient inappetance, rapid respiration, excessive
nasal secretions and lacrimation, and diarrhea. The
incubation period for
acute bovine viral diarrhea is 6 to 12 days with clinical signs
lasting 1 to 3 days. Clinical signs begin to resolve once
neutralizing antibodies are produced in the host. If however, infection
has significantly affected lymphoid tissue, immunosuppression becomes
evident and clinical signs and disease become more severe.
Severe BVDV infections are often associated with concurrent bacterial
or viral infections. Clinical signs include high fever, oral
ulceration, coronary band and interdigital ulceration or
erosion, diarrhea, dehydration, leukopenia and thrombocytopenia.
Extensive lymphoid depletion as well as petechial hemorrhage of
membranes is commonly observed. Severe bovine viral diarrhea
often causes high morbidity with moderate mortality and clinical signs
usually last 3 to 7 days.
infected bovine with severe diarrhea