BVDV in Alpacas

What is BVDV?
BVDV= Bovine Viral Diarrhea Viruses. This is a varied group of viruses known to infect both domestic and wild ruminants worldwide. There are 3 main subtypes of the virus found in the United States: BVDV1a, 1b, and 2a. So far only type 1b has been isolated in alpacas. In the cattle industry, the virus causes economic losses through decreased weight gains, poor milk production, reproductive losses, and death.

Clinical picture in alpacas
Most infections in alpacas appear to be mild and transient or even non-clinical. Some animals have demonstrated ill thrift, fever, anorexia, mild oral and nasal irritation, diarrhea, abortions, stillbirths and congenital defects. BVDV infections in pregnant females are also usually mild and transient; however, in-utero infection of the developing fetus has serious consequences. These range from no effect, to abortion, to birth of a persistently infected cria.

Persistent Infections (PI)
A persistently infected cria is exposed to the virus in-utero at a time when their immune system is immature and they are unable to fight off the infection. The virus is then matriculated into the forming immune system and is not recognized as a foreign pathogen. PI animals are problematic because they shed huge quantities of virus in all body fluids: respiratory and oral secretions, urine, milk, semen and feces. The co-existence of PI animals with pregnant females produces the next generation of PI animals as well as increasing the risk of pregnancy loss, birth defects and ill thrift. It is difficult to detect PI animals without testing. They may be “poor-doers” or clinically normal. To protect the alpaca population PI animals need to be identified and then euthanized or completely quarantined!

Implications of BVDV in the alpaca industry
BVDV is considered a rare disease in alpacas. There is concrete evidence that the disease has been present in theNorth American alpaca herd since 2001 and likely crossed over from infected cattle. Other species that could potentially spread the virus include sheep, goats and wildlife (deer, elk, etc.) Recent testing has identified at least 40 persistently infected alpacas. Research funded by ARF and other organizations is attempting to establish prevalence of the virus in our national herd. To control the emerging problem the focus must be on eliminating PI animals from the herd. With unity and dedication, we can control the disease in the alpaca industry

Testing
Virus Isolation: *this is the gold standard. White blood cells, serum or tissue from infected animals is processed and inoculated into cell cultures and the virus is allowed to replicate, this is a very sensitive test and allows viral typing. It is generally more expensive, time consuming, and has longer turn around time for results.

PCR: polymerase chain reaction: same samples as listed above but they are tested for the presence of virus instead of inoculated into cell cultures. It is generally less expensive and has a shorter turn around time 3-5 days.

IHC: immunohistochemical identifies virus in cells using special stains
*Note: all of the above tests if negative are approved by the AOBA and ARF to indicate an alpaca is not PI for the life of that animal when run at a laboratory experienced with alpaca BVDV testing.

Positive test results: If the any of the above 3 tests are positive it may be a short lived infection. A second sample must be collected 3-4 weeks later. If the second test is negative this indicates the animal was exposed to BVD and resolved the infection. If the second test is positive, the animal is a suspect PI and strict quarantine is imperative as well as further testing.
Negative test results: PI testing only needs to be performed once in the life of the animal because PI animals can only develop from in-utero infection.
SN: serum neutralization: demonstrates antibodies to the virus indicating exposure. This test is NOT useful to detect PI animals.

Biosecurity
Quarantine all alpacas that come to the farm or return from untested locations for a minimum of 2-3 weeks to 30 days. (shows, breedings etc.) Think about vectors: clothes, boots, wheelbarrows and manure forks. Survival of virus in environment depends on temperature and humidity. Worst case scenario is 72 hours. Bleach is a good disinfectant, remove organic material first!

Test all existing alpacas and all new arrivals to the farm for BVDV with a viral antigen whole blood test. Consider adding a clause to all contracts that provides for testing and refund if the animal is PI.

All aborted and stillborn fetuses as well as unexplained deaths should be necropsied by a veterinarian and samples tested for disease agents including BVDV. Test all low birth weight crias, poor doing crias and premature crias as well as any animals with unexplained illness.

References

www.alpacaresearchfoundation.org

www.aasrp.org

www.vetmed.wsu.edu/depts_waddl/bvdcamelids.asp

Dr Tara Timpson DVM
Presented at the SOJAA meeting February 18th 2006.