Veterinarians and producers trying to protect herds from bovine viral diarrhea virus may be in for a tougher fight than they bargained for.
"We may have another strain of BVDV to worry about," said Dr. Robert Fulton, head of the Department of Veterinary Pathobiology at the Oklahoma State University College of Veterinary Medicine. Dr. Fulton spoke about new BVDV findings at the recent Conference of Research Workers in Animal Diseases in Chicago.
Scientists first identified BVDV in New York state dairy herds in 1946. More than 50 years later, BVDV infections are in cattle of all ages throughout the world and have a major economic impact on the cattle industry.
Programs aimed at controlling the disease focus on vaccination, surveillance, and good management practices. Scientists have identified two species of the virus, called BVDV-1, with subgroups 1a and 1b, and BVDV-2, with subgroups 2a and 2b. Since 2b was not known to exist in the United States, vaccines have targeted the other three groups. The 2b group is prevalent in South America.
In the spring of 2003, veterinarians at Oklahoma State were alerted to an outbreak of BVD in a herd with calves that were well vaccinated against the disease. Out of 250 heifers, 32 were persistently infected. When scientists set out to identify which of the three subgroups was the culprit, subtyping revealed it was BVDV-2a—but different from the BVDV-2as used in vaccines, Dr. Fulton said. He believes a persistently infected animal may be the source, but he didn't have access to all of the animals to test them.
Julia Ridpath, PhD, lead scientist for the BVD Detection and Control Project at the National Animal Disease Center in Ames, Iowa, wonders whether the animals were vaccinated under stress, or some other factor interfered with how the vaccine worked. "I don't think that this necessarily means that new type 2s are out there that the vaccine cannot protect against," she said.
Subsequent to this investigation, the Oklahoma researchers found a calf with pneumonia in a feed yard. When they investigated, they discovered, much to their surprise, that BVDV-2b was the agent.
Dr. Fulton is concerned that the current vaccines may not protect against the newly identified agents. If so, the news is unsettling for veterinarians who are already having a tough time controlling the disease.
Dr. Ridpath is not as pessimistic. According to her, the new combination vaccines that target both BVDV-1 and BVDV-2 should give a broad antigenic presentation to the immune system and, theoretically, provide broad protection.
She says the identification of BVDV-2b in this country may have epidemiologic consequences, but it's too early to tell. "It may be important from an epidemiological standpoint," Dr. Ridpath said. "Is it something emerging in the United States? We primarily have (BVDV-2a). Now, will we switch to 2b, because of importation or some other reason? It's just something we have to watch develop, over time."