Bovine Viral Diarrhea (BVD) is a widespread disease of cattle caused by the Bovine Viral Diarrhea Virus (BVDV). Infection often leads to immunosuppression, affecting multiple body systems and resulting in clinical signs ranging from inapparent to severe. Since there is no direct antiviral cure for BVD, the treatment approach centers on three main strategies: providing supportive care for acutely sick animals, eliminating the source of continuous infection within the herd, and implementing strict biosecurity measures to halt further transmission.
Providing Supportive Care for Infected Animals
Treatment for animals suffering from acute BVD is primarily supportive, focusing on managing symptoms and mitigating the effects of virus-induced immunosuppression. Since the virus causes severe diarrhea, a major component of care involves combating dehydration and electrolyte imbalances. This is accomplished through the administration of oral or intravenous fluids and electrolyte solutions to restore fluid balance.
Acutely infected animals frequently develop fever and pain, necessitating the use of non-steroidal anti-inflammatory drugs (NSAIDs) to reduce discomfort and lower body temperatures. BVDV suppresses the immune system, leaving cattle vulnerable to other pathogens. This vulnerability commonly leads to secondary bacterial infections, such as pneumonia or enteritis, which are often the cause of mortality in BVD cases.
To address these secondary infections, broad-spectrum antibiotics are administered to treat or prevent bacterial complications. While antibiotics do not affect the BVD virus itself, they are an important part of supportive treatment during the period of viral immunosuppression. Animals that develop the fatal form of the disease, known as mucosal disease, do not respond to treatment and are euthanized on welfare grounds.
Locating and Removing Persistently Infected Animals
The long-term control strategy for BVD revolves around identifying and removing Persistently Infected (PI) animals. PI animals are infected with the noncytopathic strain of BVDV while still in the womb, specifically during the first four months of gestation, before their immune system is fully developed. Because the fetus recognizes the virus as “self,” the animal is born infected and remains infected for life, continuously shedding large amounts of virus into the environment.
PI animals are the most significant reservoir for BVDV and are far more efficient transmitters than transiently infected cattle. They may appear healthy but constantly expose the rest of the herd to the virus, undermining vaccination efforts and causing ongoing disease problems. Identifying PI cattle must be a priority in any outbreak management plan to eliminate the source of infection.
Diagnostic testing for PI status involves detecting the virus antigen or RNA in tissue samples, rather than looking for antibodies. The most common method is the ear notch test, where a small tissue sample is taken from the ear when calves are tagged. This tissue is tested using techniques like Antigen-Capture ELISA (ACE) or Polymerase Chain Reaction (PCR) to confirm the virus presence. Any animal testing positive must be isolated and retested after approximately three weeks to differentiate a transient acute infection from a lifelong persistent infection. Once PI status is confirmed, the animal must be permanently removed from the herd, as they cannot clear the virus and pose an unacceptable risk for disease transmission.
Immediate Biosecurity Measures During an Outbreak
Immediate action must be taken to prevent the spread of BVDV once a diagnosis is confirmed within a herd. A robust biosecurity protocol is implemented to separate infected animals from susceptible ones, limiting environmental contamination. The first step is the strict quarantine and physical separation of all animals showing clinical signs or those confirmed as persistently infected.
Movement of all cattle, including purchases and sales, must be halted. A quarantine period of two to four weeks should be established for any necessary new arrivals. Strict traffic control protocols are initiated, regulating the movement of people, equipment, and vehicles onto and within the farm. Visitors and service personnel must wear disposable outer clothing and footwear or disinfect their boots to avoid carrying the virus between pens or properties.
Thorough cleaning and disinfection of all contaminated areas, equipment, and shared instruments are mandatory to reduce the viral load in the environment. All pregnant cows and new calves must be closely monitored and tested, as the virus can cross the placenta, leading to abortions, stillbirths, or the birth of new PI calves. Protecting the breeding herd from exposure is a primary focus, often supported by vaccination programs to reduce the risk of fetal infection and the generation of PI animals.