Bovine Viral Diarrhea; cause, symptom, treatment and prevention in calf

04/10/2022

These PI animals will shed BVD virus at high levels for life and PI animals are therefore the most significant source of infection. TI animals shed virus at much lower levels and only for a few days.
TI calves may also test positive for BVD virus. However, due to the immune response in TI calves a repeat test 3-4 weeks later should be negative, whereas a PI should always give a positive result. It is expected that around 0.6-0.7% (6-7 calves per 1,000) will test positive for BVD virus.
PI animals can look entirely normal, particularly at birth, but may become stunted and ill-thriven. PI animals often develop a severe and always fatal wasting condition with diarrhoea and ulceration of the gut and feet, called mucosal disease (MD). This typically occurs between 6 and 18 months of age. The majority of PI animals are dead before reaching breeding age or slaughter weight, either from MD or other infections (particularly scour and pneumonia).
BVD virus persists in herds by creating further PI calves. Therefore identification and removal of PI cattle is the key to control. Vaccination to maintain immunity in breeding stock can offer further protection where susceptible pregnant cattle are exposed to BVD virus.
BVD eradication makes financial sense. A recent study estimated that the programme in the Republic of Ireland would give a cost benefit of 10:1 over the six years of the programme i.e. a return of ten euro for each one spent.

04/10/2022

Bovine viral diarrhoea (BVD) is a highly contagious viral disease of cattle that can be transmitted as easily as the common cold. It can be spread directly by infected animals, or indirectly, for example by contaminated visitors or equipment.
The majority of infections with BVD virus occur after birth. In this case animals become transiently infection (TI) before recovering and becoming virus-negative, typically within 3 weeks or less. Transient infections may occur without obvious clinical signs but depending on age, s*x and immunity they can lead to a range of reproductive problems, including abortion and poor calf health with scours and pneumonias that respond poorly to treatment.
Infection of the unborn calf between approximately 30 and 120 days of pregnancy will result in it becoming persistently infected (PI) with BVD virus if the calf is not aborted. If a calf is not PI at birth it will never be PI.

04/10/2022

How do I prevent BVDV from reentering my herd?
An effective BVDV prevention program is based on maximizing immunity and minimizing exposure of the herd to the virus. The appropriate program for each farm will vary, depending on the farm’s goals and other factors, such as open vs. closed herd, source of purchased animals, feasibility of isolation facilities, etc.

1. Vaccination
BVD vaccines are an important part of the prevention program. Vaccines are available in two forms - modified live and killed. Both forms have their advantages and disadvantages.

An advantage of modified live BVD vaccines is that they stimulate the entire immune system (both cell- mediated and humoral immunity). Therefore, it is generally recommended that every animal receive a modified live BVD vaccine at least once in its lifetime, preferably when it is 3-6 months of age. A disadvantage of modified live BVD vaccines is there may be label restrictions against using them on some or all pregnant animals, thus their use in mixed populations of bred and open animals must be carefully controlled.

An advantage of killed BVD vaccines is that they can be used on all open and pregnant animals, thus the entire herd can be vaccinated at any time. Disadvantages of the killed BVD vaccine include: a shorter duration of immunity, a reduced ability to stimulate cell-mediated immunity, and sometimes a slight drop in milk production for a day or two after vaccination. As indicated on the label, killed vaccines must be administered twice (two or three weeks apart) if the animal is being vaccinated for the first time. Only one shot is required thereafter at 4 to 6 month intervals

Both types of vaccines, if administered properly and according to the label, will provide sufficient immunity to prevent the clinical onset of acute BVD. To maintain this level of immunity, the modified live vaccine needs to be given at least annually, and the killed vaccine needs to be given every 4-6 months.

Both types of vaccines can also help prevent transmission of BVD virus to the fetus and therefore prevent abortions and/or the birth of persistently infected calves. Some clinical trials indicate superior protection of the fetus by certain MLV vaccines against some strains of virus. No vaccine is expected to afford 100% fetal protection. Thus it is still possible to occasionally have BVDV induced abortions and/or persistently infected calves in a vaccinated herd exposed to a field strain of BVD.

Vaccines are a tool for prevention, not a cure. Don’t wait for the first case of BVD to occur before deciding to vaccinate. By then many or all of the animals will already be exposed and/or infected. The added stress of vaccination may only make clinical signs worse. Similarly, if new animals will be entering the herd, it is always best to vaccinate them at least a week prior to their assembly and movement, rather than waiting until they arrive in the herd.

Keep in mind that vaccines do not induce good immunity in heavily stressed or poorly conditioned animals. So, even the best vaccination program is likely to fail in an environment with poor nutrition, stress overcrowding and without an isolation facility.

2. Biosecurity
Maintain a closed herd, if possible. Since BVD outbreaks are commonly associated with new animals entering the herd, maintaining a closed herd is the ideal approach to keep the virus out. Unfortunately, this may not be possible. Today, many farms purchase all replacements, while others temporarily send heifers to contract raisers. And these raisers typically commingle heifers from many farms before they are returned home to the milking herd.

3. If the herd is not closed, “best management” practices for moving cattle into the herd (purchased or your own)
Vaccinate with BVD vaccine two weeks prior to moving. When deciding which vaccine to use, consider the vaccine program of the herd of origin. If that herd is well vaccinated, one dose of killed BVD vaccine should be sufficient. If it is not well vaccinated, or if the history is unknown, two doses of killed (2 weeks apart) or one dose of modified live vaccine (non pregnant animals only) are be indicated.

Before moving, test all cattle not previously tested for persistent BVDV infection (BVDV carriers). Since animals can only become carriers prior to birth, previously tested cattle do not need to be retested. Do not allow carriers on the farm. Calves born to test negative pregnant replacements must also be tested.

Move animals with your own truck, directly from farm to farm. Do not purchase them through an auction market or move them with unknown cattle due to the high risk of exposure to BVDV under these conditions.

Isolate all new arrivals (purchased or your own heifers) for two to three weeks in a well-ventilated area, away from the rest of the herd, yet close enough to permit frequent checking for any signs of disease. If any diseases are noted, remove the affected animals immediately, and call the veterinarian to establish a diagnosis and treatment regime. During isolation, administer a booster vaccine, especially if the vaccine history is unclear or if the previous owner’s vaccine program was inadequate.

4. Ongoing testing for BVD carriers (persistent infection)
Continual exposure to BVDV from one or more persistently infected carriers may cause infection in vaccinated animals, so the herd may experience sporadic abortions and infertility. Since exposure to BVDV from any source can result in a cow giving birth to a BVDV carrier, one can never be sure an animal is not a carrier until it tests negative. Therefore, it is recommended that all purchased cattle be tested before entering the herd, and all newborn calves be tested.

What is the NYSCHAP BVD prevention module?
The New York State Cattle Health Assurance Program (NYSCHAP) offers a specific module to prevent and control BVD. This module is a structured program for BVD prevention that is based on a series of “best management” practices. It is implemented on the farm in conjunction with the core module of NYSCHAP as a joint effort between the State Veterinarian (NYS Dept. of Ag and Markets) and your herd veterinarian. Together, these veterinarians discuss with farm owners and managers the important aspects of BVD prevention. In addition, they tour the farm to establish the level of risk for BVD, they develop a farm management plan to control and prevent the disease, and they establish a system to monitor the success of the program.

All participants will be recognized and identified by a certificate stating the level at which their herd is enrolled in the NYS Cattle Health Assurance Program. This certificate will serve as evidence to cattle buyers and consumers that animals, milk, and meat from this herd have a value-added component in the form of reduced risk for both cattle diseases and foodborne pathogens.

04/10/2022

Bovine Viral Diarrhea
Bovine viral diarrhea is caused by BVDV, a pestivirus. Cattle are the natural host, but other animals such as alpacas, deer, sheep, and goats are also affected. BVDV preferentially infects cells of the immune system, including macrophages, DCs, and lymphocytes. The associated lesions in lymphoid tissues are severe lymphoid depletion in mesenteric lymph nodes and Peyer's patches, whose intestinal surface may be covered by a fibrinonecrotic membrane. Histologically, there is marked lymphocytolysis and necrosis of germinal centers in Peyer's patches and cortices of lymph nodes. There is thymic atrophy because the thymus is markedly depleted of lymphocytes and may consist of only collapsed stroma and few scattered lymphocytes. BVD is discussed in detail in Chapters 4 and

04/10/2022

How to Treat Bovine Viral Diarrhea
While this virus has no cure, practicing supportive therapies such as increasing feed and water intake will temporarily help to improve the well being of your cattle. Infected calves should be culled to prevent the spread of BVD.

How to Prevent Bovine Viral Diarrhea
You can vaccinate your heard to protect them against BVD. These vaccinations can be costly, but they can also save the lives of your livestock. While vaccines alone cannot prevent BVD entirely, they can lessen the severity of its symptoms.

Alternatively, ranchers may choose to avoid the spread of BVD by making infected cattle less infectious, thus rendering them less likely to spread the illness. Giving your cattle the right antibodies once you notice signs of BVD will decrease the degree to which they shed the virus

25/06/2022

25/06/2022

VIRUS TAXONOMY AND CHARACTERISTICS
Bovine viral diarrhea virus is the prototypic member of the genus Pestivirus within the family Flaviviridae.4 Strains of BVDV can be classified in vitro as cytopathic (CP) or noncytopathic (NCP), and this classification of the virus is referred to as the biotype. This differentiation is based on the effect of the virus on cultured cells, with CP strains causing vacuolation and cell death within cultured cell monolayers. Importantly, the effect of the virus in cultured cells does not correlate with virulence because strains of BVDV causing severe clinical disease are mainly NCP strains.5 In addition, only NCP strains of BVDV have been demonstrated, both naturally and experimentally, to induce persistent infection.6 The NCP biotype predominates in the cattle population, and distribution data from diagnostic laboratories have indicated that NCP isolates are the most common field isolate and account for approximately 65% to 90% of BVDV isolates.7 The NCP biotype is often the source for CP strains, which arise by mutations and recombinations in the NCP strain.8

Because BVDV is an RNA virus, mutation and variation occurs. This variation includes antigenic, genetic, and pathogenic variation. Although there is considerable antigenic variation, all pestiviruses are antigenically cross-reactive. Therefore BVDV exists as one serotype. Genetic heterogeneity exists among BVDV isolates, and phylogenic analysis of BVDV genomic sequences has led to the conclusion that there exist two genotypes of BVDV, BVDV 1 and BVDV 2.9 These two genotypes are now considered separate species within the Pestivirus genus.4,10 Subgenotypes of both BVDV 1 and BVDV 2 are described. Specific differences in the viral nucleic acid sequences are the basis for genotyping. The classification of genotype is independent of biotype because of CP and NCP BVDV 1 and BVDV 2 strains. Several techniques are available for identifying the different genotypes of BVDV, but most genotyping procedures involve the use of molecular biology techniques that take advantage of sequence differences in specific genome segments. Differences in BVDV genotype may define antigenic differences. With respect to the distribution of genotypes within the cattle population, the BVDV 1 genotype is isolated more frequently than the BVDV 2 genotype.