Bovine Viral Diarrhea (BVD)

14 يوليو 2020
Bovine Viral Diarrhea (BVD)

BVD is a general cause of hereditary respiratory and reproductive problems. In many states, it is an economically important disease, and the disease-related problems are thought to be expanding in some places

However a disease in itself, BVD is responsible for a number of transient infections that are often the source of animal health and economic issues

Causes

Bovine viral diarrhea is a infectious disease caused by bovine infectious diarrhoea virus (BVDV) in cattle and other ruminants

BVD is expressed in many ways. Either because of a congenital fetal infection, or after conception. Congenital infections can lead to resorption, abortion, mortality or live birth. Born as BVDV-infected calves may be congenitally infected fetuses that survive in utero infection (i.e., live-births). The BVDV infection in these calves will continue throughout the veal 's life, and t they will shed BVDV continuously in the farm environment

Symptoms

Clinical signs in adults are extremely variable. Acute signs of infection include fever, lethargy, loss of appetite, discharge of the eye, discharge of the nose, oral lesions, diarrhea, and decreased milk production. Chronic infection can cause signs of mucosal illness

Cerebellar hypoplasia is the most commonly recognised birth defect in calves

The signs of this are

  • Ataxia/ lack of voluntary coordination of muscle movements;
  • Tremors
  • Wide stance
  • Stumbling
  • Failure to nurse

The Calf can die in extreme cases

Transient infections include diarrhea, calf pneumonia, reduced milk production, reproductive disorders, increased other diseases and death

Losses from fetal infection include abortions; congenital defects; weak and abnormally small calves; unthrifty, persistently infected animals (PI); and death among animals with PIs

Treatment

BVD treatment is essentially limited to supportive therapy. Once the infected animals have been identified, they should be culled

Prevention

Research is ongoing to look at the potential for breeding animals that are less susceptible to the disease. At the moment, No one breed has an advantage at the moment

One approach to reduce transmission of BVD is to make infected bovine animals less infectious, and this can be done by increasing the titer of the antibody. Cattle that has antibodies when they are acutely infected with BVDV doesn't shed as much virus, and they will shed virus for a shorter period of time

The cull of persistently infected animals from the herd is necessary on farm there. Blood tests will identify Housing calves in individual hutches as opposed to group housing will decrease contact and infection risk, as will decrease density of storage

Strategic vaccination and colostrum of high quality may also diminish the proportion of sensitive cattle

A farm-based BVD control system will aim at preventing fetal infections, avoiding reproductive damage and reducing loss due to transient infections. Control is achieved with a combination of PI cattle removal, vaccination, and increased biosafety

Vaccines

BVD vaccines are available. The two categories are vaccines for modified live viruses (MLV), and vaccines for killed viruses (KV). MLV vaccines usually need only one dose during the initial immunization phase, but are more difficult to manage

KV vaccinations are generally more costly and need more than one dose during vaccination. KV vaccines, however, are less susceptible to deactivation at extreme temperatures, and are less susceptible to chemical deactivation

Diagnostics

Because persistently infected (PI) calves look and act normal, it is very important for producers to use diagnostic testing to recognize and eliminate PI animals from their herds

PCR is the most responsive tool to detect PI calves early, so farmers can eliminate these rapidly shedding animals from the herd as quickly as possible. It can be difficult to detect BVDV in newborn calves using antibody-based tests, since calves can have very high maternal antibody titers to BVDV, mainly through ingested colostrum. Such maternal antibodies bind the virus in this type of test, and prevent its detection. It is generally called shielding

PCR tests use samples of either blood or tissue (ear notch), can be performed in a very short period of time and produce extremely accurate results

Antibody-based tests are used for bulk milk screening and enable BVDV infections to be diagnosed in large scale screening and eradication