Here is where the story gets complicated. The outcome depends on the BVD biotype and the "resistance" of the cattle involved. In the simplest case, if the cattle are adult, non-pregnant cattle and have been vaccinated against the infecting biotype previously–nothing happens. No disease, no death loss, nothing more than if they received a vaccine booster. Also, the age of the cattle is important, particularly the age of the fetus. If the fetus is exposed to a non-CPE BVD virus prior to day 120 of gestation it is possible the calf born will be an immunotolerant carrier of the virus. That is to say, the fetus may not be killed by the virus (aborted), will not mount an immune response to the virus, will shed large numbers of the non-CPE virus into the environment for as long as it lives. These immunotolerant carriers are called persistently infected (PI) cattle and usually live less than one year before dying. They are not only immunotolerant to the BVD virus, their immune system is permanently damaged putting them at risk for all other infectious diseases. Table 1 is a list of possible conditions that can result from BVD infection.
Table 1. Possible outcomes to BVD virus infection in cattle.
|
Fetal Infection |
1. Early Embryonic Death
2. Abortion
3. Stillbirths
4. Congenital Birth Defects (eye defects, brain defects)
5. PI Calves (immunotolerant and persistently infected shedders)
6. Normal Calves born with antibodies to the BVD virus |
|
Acute Infection |
1. Subclinical–no signs of disease
2. Severe BVD signs with diarrhea and lesions in the gut (mouth to anus)
3. Hemorrhagic Syndrome (failure of blood to clot normally)
4. BVD infection and respiratory disease (pneumonia)
5. Venereal disease |
|
Muscosal Disease |
1. Infection of PI calves with a CPE virus which causes severe diarrhea, weight loss, damage to the gastrointestinal system , and death. |
This table is simplified from what is known to occur in nature; however, it does point out the tremendously complicated nature of disease caused by the BVD virus.
Source: UC Davis