The effects of bovine viral diarrhea virus (BVDV) are wide-ranging in terms of reproductive issues, adult and calf health, and production. Much as been written about BVDV over the years and much has been and is still being discovered, but in spite of that misinformation “myths” about BVDV still remain.
Dan Givens, DVM, PhD, Auburn University, discusses the plausibility of the most persistent myths about BVDV.
For example, the first three are:
Myth 1: Commingling heifers such as at synchronization or shortly before breeding presents a low risk of BVDV infection.
Busted. If the heifers to be commingled have not previously contacted each other, then prevalence studies indicate that approximately 4 of 1,000 heifers will be persistently infected (PI) and efficiently spread virus to cause infection of naive, contacted cattle. If the heifers have not been previously immunized, then the negative impact on pregnancy rates and abortions can be severe due to the timing of infection. Prior research indicates infection with BVDV at the time of estrus synchronization can decrease pregnancy rates by 20% to 50%.
Myth 2: Virus from a persistently-infected calf is not very pathogenic.
Implausible. Pathogenicity (the ability of an organism to infect a host and cause disease) is the product of infectivity (the ability of a virus to invade and establish replication within the host) and virulence (the severity of disease exhibited by infected hosts). Virus from a persistently-infected calf is very infective. To put that in perspective, prior research has shown that if you take about 60 mL of snot or spit from a PI animal and mix it in a farm pond equal to the size of an Olympic swimming pool (50 m X 25 m X 2 m), then you can go to the other side of the pond and 1 mL of collected water will contain enough virus to infect a calf 50% of the time.
When considering the virulence of BVDV, we must consider that BVDV causes a spectrum of clinical diseases that includes:
Severe, acute disease associated with leukopenia, thrombocytopenia, mucosal damage, and enteritis
Acute disease associated with immunosuppression and respiratory disease
Reproductive losses including early embryonic deaths and later abortions
Congenital defects including cerebellar hypoplasia, mandibular brachynathism, and ocular lesions
Persistent infections which can be associated with low birthweights, poor growth rates and a decreased life-span.
While the BVDV strains from PI animals may not often be associated with severe, acute disease because pregnant animals with severe, acute disease will likely abort or die in the course of an outbreak, strains of BVDV in PI animals are likely to cause the other clinical diseases that are discussed. Thus, while PI animals may not spread the most notorious of BVDV outbreaks, they are factories of infectious virus and are likely to spread other clinical diseases within the BVD spectrum.
Myth 3: Acute/transient BVDV infections will always present the same in cattle.
Busted. The outcome of acute infection with BVDV is a result of unique interplay of the viral strain, environmental stress, and the animal’s immunity. The outcome of acute infection with BVDV can be severe, acute disease associated with mucosal lesions, enteritis and bleeding disorders with a mortality rate of 25% in some populations. The outcome of acute infection with BVDV can be immunosuppression which is often linked to respiratory disease in some populations. The outcome of acute infection with BVDV can also be clinically undetectable in some populations. Thus, acute or transient BVDV infections will not always present the same in cattle.
Read about all 15 BVDV myths busted by Givens in Bovine Veterinarian here.