BVD Antigen ELISA

Bovine viral diarrhoea, or BVD, is a virus disease of cattle that can also infect buffaloes. It can cause fever, diarrhoea, a drop in milk, poor fertility, abortion and weak or poorly growing calves. It also weakens the immune system, so other infections take hold more easily. When a pregnant cow is infected early in pregnancy, the calf can be born persistently infected, or PI. A PI calf carries the virus for life, sheds large amounts of it and may look normal or grow poorly. PI animals are a main source of the virus in a herd.

This test is an antigen ELISA. An antigen is a part of the germ itself, so the test shows whether the virus is present now, not whether the animal met it in the past. ELISA is a lab method that uses a colour change to show a result. The sample can be serum from a blood sample or an ear notch, a tiny piece of skin taken from the edge of the ear. Ear notch samples are often used to screen calves, because in very young calves antibodies from colostrum can hide the virus in a serum sample.

A positive result means virus was found, but on its own it cannot tell whether the infection is short-lived or lasting. An animal with a short, passing infection can also test positive, so your vet may repeat the test after some weeks; a second positive result supports a persistently infected animal. A negative result makes infection less likely, but timing and sample type matter. A registered veterinarian reads the result together with the animal's age, signs, herd history and other tests, such as BVD PCR or an antibody test.