4. Bovine Virus Diarrhea and mucosal
disease are clinically dissimilar disease
syndromes, and were originally
described as separate diseases, but
they are now known to have a common
viral etiology.
5. Bovine viral diarrhea describes the
syndrome seen predominantly in 6- 18
month old cattle as a primary infection.
6. Mucosal Disease (MD) is usually sporadic,
progressive and fatal. It would seem to occur
in a small number of congenitally infected
animals which are immunotolerant and
harbor virus in all their tissues without
showing any clinical symptoms
7. Bovine Viral Diarrhea Virus (BVDV) is a
member of the Flaviviridae family in the
genus of Pestivirus.
It is a positive sense, enveloped, single
stranded RNA virus The structure of the
virion is spherical polymorphic.
It has the ability to mutate into multiple
variants depending on environmental
pressures on the virus.
8. BVD viruses are grouped into two genotypes, Type 1 and
Type 2, based on genomic characteristics and the severity of
disease they produce in cattle.
Each genotype, 1 and 2, are divided into two biotypes-
cytopathic (cp) and non-cytopathic (ncp) based on how they
replicate in cell culture.
Cytopathogenicity does not correlate with the severity of
disease in vivo (high and low virulence strains)
Some cp strains are recovered from animals with mucosal
disease (MD), but most of the time ncp isolates are
recovered from infected animals.
9. The classic virus is ncp; cp isolates are
generated by mutations or genome
rearrangements in the original/parental
ncp strain. Most (>95%) of the field
isolates are ncp.
10. Young calf persistently infected with BVD (right) compared to similarly-
aged normal herd mate.
11. Host Range
BVD is normally an infection of cattle, but it has
the ability to cause infections in pigs, sheep,
goats,, deer, reindeer, bison,, and other wild
ruminants.
Infections of BVDV are now seen throughout the
world in all ages of cattle. Due to production and
reproduction losses, this virus has a very
significant economic impact.
12. Transmission
The virus may be present in various secretions
and semen. Spread is by direct and indirect
contact.
The mode of infection is by ingestion and
inhalation.
Transplacental infections are frequent and result
in serious consequences for the embryo/fetus.
Bulls may be persistently infected and the virus
in semen is spread by coitus an artificial
insemination.
13. Horizontal Transmission
Fomites
BVDV has been shown to spread to
susceptible animals through feed and
equipments.
One study showed that BVDV can be
transmitted between animals during
palpations if the same pair of gloves are
worn for all exams.
14. Environment
BVDV is shed in most secretions and excretions
(tears, urine, feces, mucus) and can survive outside
the host for weeks.
Calving pens and common shared areas can
become highly contaminated.
Crowding can also increase transmission if animals
are infected with the respiratory type of BVDV.
Oronasal uptake is the most common route of
transmission.
Vectors
Flies have also been shown to transmit BVDV.
Horse flies, stable flies, head flies, face flies
15. If a cow is persistently infected it will infect the fetus.
Other mechanisms of vertical transmission are:
Contaminated Semen infects the cow, which leads to
infection of the fetus.
Embryo Transfer If the embryo is transferred to a cow
that is infected, the fetus will also become infected.
Modified Live Vaccine Vaccinating pregnant cows
with live virus has been shown to infect the fetus.
Vertical Transmission
16. BVD virus can be spread in semen of persistently infected bulls or in
bulls experiencing acute BVD with transient virus infection
18. Pathogenesis:
Bovine viral diarrhea describes the syndrome
seen predominantly in 6-18 month old cattle as
a primary infection. Passive immunity may
protect up to 6 months of age explaining the
prevalence of BVD in 6-18-month old cattle.
19. Infection is via the oropharyngeal route with
primary replication in the epithelium of the
oropharynx and a rapid uptake into the
drainage lymph nodes. Viremia involves
infection of lymphocytes giving rise to a
leucopenia, and spreads to other lymphoid
tissues, particularly Peyer's patches.
20. Concurrent replication in the epithelium of
the alimentary tract results in discrete
erosions which in the oral cavity cause
excessive salivation, and in the small and large
intestine induce diarrhea. Lesions in the nasal
cavity and conjunctiva may also occur and be
associated with discharges.
22. Primary infection of pregnant cows with
BVDV may result in transplacental
infection and may give rise to a range of
problems according to the stage of
pregnancy:
23. In early pregnancy it may be a cause of infertility and
embryonic death.
In mid-gestation it will produce congenital anomalies
such as cerebella hyperplasia; it may also cause
abortion; or may result in congenital infection of
apparently normal calves. This latter group of animals
do not have antibody to BVDV but frequently excrete
virus and are therefore a source of infection; they also
are likely to develop mucosal disease.
24. BVD virus is most important when it infects susceptible
breeding cattle during early pregnancy causing foetal
death/abortion, and weak/premature calves.
25. Birth defects of the nervous system. Note the low head carriage
and wide stance. This calf was also very unsteady on its feet
27. Mucosal Disease (MD) is usually sporadic,
progressive and fatal. It would seem to occur in
the small number of congenitally infected
animals which are immunotolerant and harbor
virus in all their tissues without showing any
clinical symptoms.
28. If they encounter a second strain of virus then
superinfection occurs and extensive erosions
are established throughout the alimentary
tract. The outcome may be an acute fatal
disease or a chronically progressive syndrome
with the animals remaining antibody negative.
29. Congenitally infected excretor animals are an
important source of dissemination of virus and
difficult to detect since they are seronegative.
Outbreaks are usually confined to a particular
farm or to premises where cattle are frequently
bought in. The virus survives quite well on
fomites in warm weather or in indoor housing.
31. Persistently Infected (PI) animals
One of the main reservoirs for the virus is PI
cattle who are reported to shed several billion
virions a day. Contact with a PI animal is more
of a risk for transmitting the virus and causing
infection than an acutely infected animal
because the PI animals shed such a high amount
of virions.
33. Epidemiology: The virus is transmitted
easily from animal to animal and from
herd to herd by indirect means through
feed contaminated with urine or
oral/nasal secretions, feces, or aborted
fetuses and placentas.
34. The virus is transmitted directly to
susceptible hosts, rather poorly from acutely
affected cattle and very efficiently from
persistently infected animals.
35. Some persistently infected females survive to breeding
age and may give birth to persistently infected
offspring, thereby perpetuating the transmission
pattern. Where infection has been present in a herd
for some time and the majority of cattle are immune,
the introduction of susceptible animals, typically
heifers, results in sporadic losses, often continuing
over a period of years if husbandry practices remain
unchanged.
36. Where infection is absent in a herd, the
introduction of a persistently infected animal
is often followed by dramatic losses. Since the
infection also occurs in sheep and goats, as
well as swine, deer, bison, and other wild
ruminants, these species may also be sources
of virus for the initiation of infection in cattle
herds.
37. Clinical specimens: Nasal discharge, feces,
blood, blood smears, spleen, kidney, lymph
nodes, turbinates, intestine, lung, acute and
convalescent sera, and fetal liver and kidney.
Diagnosis
38. BVDV is routinely diagnosed in laboratories via serology,
antigen detection assays, virus isolation, and by viral RNA
amplification such as polymerase chain reaction (PCR).
Acute infections can be accurately diagnosed by viral
isolation derived from Buffy coat or nasal swab samples,
immunohistochemistry, and antigen-capture ELISA
assays. It is essential for these samples to be collected
while the animal is still shedding virus. If the animal is
convalescent a positive diagnosis of the virus will not be
achieved because virus is not present.
39. Serological evaluation of acute BVDV infection is
most commonly performed via serum
neutralization. It is important to note that for
serology to be most effective there must be paired
samples- acute and convalescent- for serum titers
to have any significant meaning. Although serum
titers can vary from lab to lab a four-fold change
in titer, as well as clinical symptoms that may
denote BVDV infection, are generally considered
significant.
40. For an accurate diagnosis of viral infection
via serology a clinical history of vaccination
is essential. Due to the fact that most
vaccines available to cattle producers are
modified-live vaccines, when an animal is
exposed to a field strain of virus that is
similar to the vaccine strain, the antibody
titers will be significantly higher, which may
lead to inconclusive or false laboratory
results.
41. Treatment
Currently, there is no treatment available to cure
Bovine Viral Diarrhea Virus
Treatment Options
Antibiotics for Secondary Infections
Pneumonia etc.
If the animal develops Mucosal Disease, there are
treatments to alleviate the symptoms, but the animal
will eventually die.
IV fluids for diarrhea and water loss
PIโs should be euthanized to prevent further contamination and
potential infection to the rest of the herd.
42. VaccinationVaccination does not provide complete protection against BVDV
infection
It can help to reduce the number of infections
Vaccination is not long lasting
Regular booster shots should be kept up to date according to label or
vetVaccination
Vaccinated cattle can thus become become infected and show
some symptoms but death will not occur
Pregnant cattle that are vaccinated have less chance if infected, of
transmitting the virus to the fetus.
There is still a chance of abortions in those cattle that are vaccinated
Even cattle that are vaccinated may still be able to transmit the
disease to other cattle even if there are no symptoms present.
