Why Bovine Viral Diarrhea Virus is a global challenge
Exposure, detection and monitoring of BVDV
5 September 2022
6 minute read
By: Diagnostic Monitoring is Critical to Stop the PI Calf Cycle
Bovine viral diarrhea (BVD) is a serious and costly disease for beef and dairy producers. The causative agent, the bovine viral diarrhea virus (BVDV), is a global challenge because most cattle herds are at risk for infection.
BVDV infection can cause respiratory disease, enteritis, stillbirth, abortion, and mucosal disease in beef and dairy cattle. In utero BVDV infection can induce immunotolerance, causing lifelong persistent infection (PI). Animals with PI continuously shed the virus, and they are the main source of BVDV infection in herds. Rapid detection of PI in cattle is thus essential for BVDV control.
Bovine Viral Diarrhea - Endemic Disease of Cattle Around the World
BVD is a cattle disease caused by BVDV, an approximately 12 kb, single‑stranded, positive‑RNA enveloped virus in the genus Pestivirus of the Flaviviridae family. BVDV was first discovered in 1946 in New York dairy herds and in Canada the same year. Today, it is considered an endemic disease of cattle in most parts of the world.
Symptoms of BVD can vary based on the exposed animal’s immune status and the strain of the virus they are exposed to. BVDV-1 strains are known to occur more often while BVDV-2 strains are considered more virulent [1].
If unvaccinated animals are infected with BVDV, the resulting disease will likely appear as an acute, severe sickness, characterized by bloody diarrhea, high fever (105–107°F), lack of appetite, mouth ulcers, and pneumonia. Some animals may die, while others will recover within a few weeks. Antibiotics are an ineffective treatment due to the viral nature of the disease [2].
Reproductive Transmission and Losses due to BVDV
Although the virus's name is explicitly associated with gastrointestinal disease, BVDV appears to affect many of a cow’s systems, including the reproductive, respiratory, circulatory, immunologic, integumentary, musculoskeletal, and central nervous systems. The most important economic repercussions of BVD are reproductive losses, and reproduction is the most important path of disease transmission within and among cattle populations via the generation of PI carriers.
PI Carriers
Animals with PI present a unique challenge. If a pregnant cow is first exposed to BVDV between days 42 and 125 of gestation, the virus will persistently infect the fetus due to its lack of a developed immune system. In these cases, the pregnant cow will develop antibodies to the virus; however, PI calves will continue to shed a significant amount of virus over their lives. PI calves are thus considered the main source of virus and the reason why herds allow the virus cycle to continue. Of note, an animal cannot become a PI calf after it has been born; PI carriers only develop in utero when the dame is exposed [3].
BVDV infection can also occur through contact exposure with other infected animals or contaminated fomites. Typical routes of infection include water buckets, calf feeders, feed bunks, IV equipment, nose leads, clothing or people, and cattle trucks [2].
How can BVDV exposure be minimized?
Following these best management practices can help limit BVDV exposure on a farm [2]:
- Avoid purchasing replacement animals through an auction market: These animals could have been exposed to other BVDV-infected animals. Plus, they are heavily stressed and have limited immunity.
- Place purchased animals in quarantine for 10–14 days before introducing them to the herd: Animals who are incubating BVDV may become noticeable before the entire herd is exposed.
- Set up a herd vaccination program against BVD: Work with your veterinarian to outline vaccination protocols that will prevent illness.
- Always test new animals to ensure they are BVDV-negative: BVDV carriers can shed so much virus that they can easily overwhelm even the best vaccination programs.
- Ensure semen is BVDV-free: If natural service is being used with the breeding herd, regularly test bulls for BVDV. If breeding via artificial insemination through a certified establishment, semen should already be regularly screened.
Monitoring and Detection of BVDV
Diagnostic Testing
PI calves look and act normal. It is thus vital that producers use diagnostic testing to identify PI animals and remove them from the herd. Early identification allows farmers to remove these BVDV-shedding animals from the herd as soon as possible.
PCR for Early Detection of BVDV
Polymerase chain reaction (PCR) is the most sensitive tool for early identification of PI calves. Detection of BVDV in newborn calves using other methods such as antibody-based tests can be difficult, as calves can have very high maternal antibody titers to BVDV, mainly via ingested colostrum. These maternal antibodies bind the virus and prevent its detection in antibody-based tests. This is generally known as "shielding".
High Accuracy and Large-Scale Screening
PCR tests, using either blood or tissue (e.g., ear notch) samples, can be completed in a very short period of time and provide highly accurate results. Antibody-based tests are also particularly useful for bulk-milk screening to allow diagnosis of BVDV infections in large-scale screening and eradication programs.
The Applied Biosystems™ VetMAX™‑Gold BVDV PI Detection Kit can be used to identify PI animals in mixed populations of uninfected, acute, and PI cattle. Tests that produce a presumptive positive BVDV PI–animal result should be followed up with the collection and testing of a second sample from the same animal at least three weeks after the first sample was taken. A presumptive PI animal can be ensured PI status if the second test is positive.
The VetMAX‑Gold BVDV PI Detection Kit can be used to test pools of up to 24 samples for the presence of BVDV. Pool size should be determined by the testing laboratory, based on the prevalence of BVD in the area where the samples were collected. Pooled samples yielding a positive result should then be tested individually to determine the infection status of each animal in the positive pool.
USDA-Licensed Real-Time PCR Test for Detection of BVDV
The VetMAX-Gold BVDV PI Detection Kit is the first USDA-licensed real-time PCR test for the detection of BVDV in cattle. The assay is a single-tube, real-time, reverse transcription-polymerase chain reaction (RT-PCR) in which RNA is reverse transcribed into complementary DNA (cDNA), and BVDV targets are amplified and detected in real time using fluorescent Applied Biosystems™ TaqMan™ probes.
Specificity and Sensitivity
Producers and veterinarians can have confidence in their results, as the VetMAX-Gold BVDV PI Detection Kit has proven repeatability and reproducibility in field studies. As well, it provides highly specific and sensitive detection of BVDV type 1 and type 2. Using ear notch tissue, the kit offers rapid and cost-effective detection of BVDV with results in about 1.5 hours.
Simple, Fast Workflow Automated for High-Throughput
Minimize Sample Handling and Cross-Contamination
For laboratories, the kit offers a simple, fast workflow that minimizes sample handling and reduces sample cross-contamination. The assay is easily automated for high-throughput processing using robust and reliable Applied Biosystems™ AmpliTaq Gold™ DNA Polymerase and TaqMan™ technology.
References
1. Walz PH (2019) Bovine Viral Dirrhea Virus. In: Veterinary Reproduction and Obstetrics (5th edition, p 96) Noakes D (editor). Amsterdam: Elsevier Health. https://www.sciencedirect.com/....
2. Cornell University College of Veterinary Medicine (2019) Bovine viral diarrhea: background, management and control. https://www.vet.cornell.edu/an...
3. Van Duijn L et al. (2021). Why test purchased cattle in BVDV control programs? Frontiers in Veterinary Science, 8:686257. doi: 10.3389/fvets.2021.686257
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