Bovine Viral Diarrhea Virus in Camelids
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1. What is BVDV?
Bovine Viral Diarrhea Virus (BVDV) is one of several world-wide
pestiviruses known to infect domestic and wild ruminants, camelids,
and swine. For cattle producers the virus causes economic losses
through decreased weight gains, decreased milk production,
reproductive losses, and death. As with most viral infections, there
is a wide range of clinical signs from inapparent infections to
diarrhea, respiratory tract infections, hemorrhage, abortions,
congenital defects, and death.
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Acute Infection
Bovine viral diarrhea refers to a mild disease caused by a BVD virus infection
in immunocompetent cattle. In general, animals develop acute BVD 10-12 days
after infection. Since BVDV infects white blood cells, whole blood (buffy coat)
is the sample of choice for isolation of BVDV from clinically ill animals.
Persistent Infection
BVDV can lead to a persistent infection in a calf if it is infected during a
certain time in gestation. If infected prior to complete development of the
fetal immune system, the virus will not be recognized as a foreign pathogen.
After birth, the calf will shed the virus and infect other animals in the herd.
Sometimes these calves look sick but they can also look perfectly healthy
thereby making it impossible to visually identify these animals.
2. Why is BVDV important to my alpacas or llamas?
This question cannot be completely answered at this time. There is much research
that needs to be performed to fully understand the implications of BVDV in
alpacas and llamas.
Research has shown that llamas and alpacas can be infected with the virus and
develop clinical signs. There have also been reports of suspected persistent
infections in crias. In cattle, persistent infected calves are the primary
source of spreading the infection to other animals. It is not known if
persistently infected crias are the primary source of herd infection in
camelids,
but it is suspected. Alpacas and llamas are sent all over North America and
lapses in biosecurity could permit a persistent infected cria to infect other
animals and herds.
3. What are some concerns among veterinarians and researchers regarding BVDV
in alpacas and llamas?
A few current questions among veterinarians and scientists requiring
investigation: Are there true persistent infections or longer transient
infections than seen in cattle? How accurately do the bovine-based tests
diagnose infections in camelids? Is there a new pestivirus specific to camelids
or a mutation of the BVD virus that appears to “prefer” camelids?
4. What are some possible clinical signs seen in alpacas and llamas?
Typical signs that a client may see include fever, oral ulcers, anorexia,
diarrhea, abortion, ill-thrift, and congenital defects.
5. How is BVDV transmitted?
The most efficient method of BVDV transmission in camelids is not known.
Transmission in cattle has been primarily by ingestion or inhalation of the
virus. The virus can be found in all body fluids (respiratory and oral
secretions, urine, milk, and semen) and feces. Transplacental (cow to fetus)
transmission also occurs. Transmission is assumed to be similar in other
susceptible species including alpacas and llamas.
6. What species can transmit BVDV?
Virus can potentially spread between domestic ruminants (cattle, sheep, goats),
camelids, and wildlife (deer, elk, etc).
7. Is there a vaccine available for alpacas and llamas?
Currently there is no BVDV vaccine licensed for use in camelids. There are
several vaccines available for use in cattle. The vaccines do not prevent
infection but reduce the clinical disease effects. At this time, it is not
recommended to vaccinate camelids until more is understood about the virus.
Unwarranted vaccination can interfere with diagnostic testing and identifying
truly infected animals.
8. Can BVDV infections be prevented?
No, BVDV infections cannot be prevented but they can be reduced. Maintaining a
closed herd, implementing strict biosecurity protocols for all incoming animals
(recommended not just for reducing BVDV infections), and periodic screening of
open herds can reduce the occurrence.
9. What diagnostic techniques are currently recommended for alpacas and
llamas?
Types of Tests Available
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Polymerase chain reaction (PCR) – nucleic acid detection, very sensitive. Will
detect persistent as well as acute (transient) infections. Diagnostic method of
choice because of excellent sensitivity.
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Antigen-enzyme-linked immunosorbent assay (Ag-ELISA) – antigen detection;
validation of this test has not been established in camelids but is being
evaluated.
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Serology (serum neutralization) – antibody detection, a single test indicates
exposure, but not active infection. Testing acute and convelescent samples and
showing a 4-fold increase in titer indicates active infection. False negatives
may occur if sample taken soon after an infection (prior to development of an
immune response), or in animals < 3 months of age when maternal, colostrum
derived, antibodies interfere with the test.
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Skin biopsy with immunohistochemistry (IHC) – antigen detection; results are not
conclusive in camelids.
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Virus isolation – Detects live virus in blood and tissues. May be required for
virus typing.
Testing Strategies:
Acute Infection:
BVDV acute infection can be diagnosed by virus isolation, polymerase
chain reaction (PCR) or serology. Virus detection must be done in the first 3-10
days after infection. A whole blood sample is the best sample for BVDV detection
by PCR or virus isolation. Paired acute and convalescent samples collected 3-4
weeks apart are required to identify four fold increase in serum antibody titers
following recovery from clinical illness.
Persistent Infection:
Definitive diagnosis of persistent infection in camelids cannot be
based upon testing done at a single time point. Detection of BVDV persistent
infection requires showing virus is present in a particular animal over time
(the infection persists). Although the BVDV antigen ELISA test done at a single
time point is used to detect BVDV persistent infection in cattle, whether or not
similar interpretation of the test in camelids is accurate is not known.
Therefore, persistent infections in camelids should be determined by detecting
virus (by PCR or virus isolation) in sequential samples collected 3-4 weeks
apart.
Tests recommended by the Washington Animal Disease Diagnostic
Laboratory (WADDL) and Washington State University Veterinary
Teaching Hospital (WSU-VTH) for testing alpacas and llamas.
Who to contact for more information?
Contact WADDL (509)335-9696 for testing questions.
Contact WSU-VTH Agriculture Animal Department, Ms. Sallie Bayly, RVT
shenson@vetmed.wsu.edu
(509-335-0711) to contact a veterinarian regarding management questions.
WADDL and WSU-VTH veterinarians who can assist you:
References:
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Goyal SM, Ridpath JF. Bovine Viral Diarrhea Virus: Diagnosis, Management, and
Control. Ames, IA: Blackwell Publishing; 2005.
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Belknap EB, Collins JK, Larsen RS, Conrad KP. Bovine viral diarrhea virus in New
World camelids. J Vet Diagn Invest. 2000;12:568-570.
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Mattson DE. Diagnostic tests and procedures for alpacas persistently infected
with bovine viral diarrhea virus.
http://www.alpacaresearchfoundation.org/papers_reports/bvdv_census.html
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Carman S, Carr N et al. BVD in alpaca: abortion and PI. J Vet Diag Invest
17:589-593, 2005.
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Evermann JF. Pestiviral infections of llamas and alpacas. Small Ruminant Res
61:201-206, 2006.
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Grooms D, Baker JC, Ames TR. Diseases caused by bovine viral diarrhea virus. In
Smith BP, ed. Large Animal Internal Medicine. St. Louis: Mosby; 2002:707-714.
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Last Edited: Oct 29, 2007 1:08 PM
