BVD impersonator difficult to diagnose

KANSAS CITY, Mo. — HoBi-like viruses may cause symptoms resembling bovine viral diarrhea disease, but genetic sequencing shows it is a different species.

The virus, which was named after the two scientists who identified it in 2004, is part of the pestivirus family that includes various strains of BVD in cattle, classical swine fever in hogs and border disease virus in sheep.

“BVD is an umbrella term for a plethora of clinical presentations,” said Julia Ridpath, lead scientist at the Agriculture Research Service’s National Animal Disease Center in Ames, Iowa.

“We started to look at the genetic comparisons and things we called BVD were actually border disease, things we called border disease were BVD. We found out there were two different species of virus that that cause BVD1 and BVD2.”

BVD1 has been found throughout the world and was first described in 1946, while BVD 2 discovered in 1987 and is everywhere but Australia.

HoBi-like virus has been found in Asia, South America and Europe. Some have incorrectly called it BVD3 because it presents like BVD.

The virus was first found in bovine fetal serum that may be used in embryo transfer and other procedures.

There is little regulation against the use and sale of fetal bovine serum, and labelling its origin does not necessarily reflect where it was collected.

“They believe the introduction of HoBi-like virus into Europe was the result of using contaminated fetal bovine serum from Brazil,” she told a BVD symposium in Kansas City April 7.

There is a possibility an expensive embryo transfer could be infected and result in a persistently infected calf with BVD-like symptoms.

A virus that acts like BVD is troublesome because commonly used tests may detect a virus but cannot differentiate which one it is.

It has not been found in North America, but surveillance needs to continue to see which viruses are circulating in beef and dairy herds.

Ridpath’s research team partnered with Novartis, now Elanco, to test BVD vaccines against HoBi-like virus. Neither killed vaccines or modified live vaccines worked particularly well against the HoBi-like virus.

“Think what it is going to be like when we have a number of our animals that are naive to the HoBi-like virus. Think of the damage it is going to do,” she said.

Persistently infected animals are a common problem with BVD. Cows infected with the virus between 60 and 125 days of pregnancy end up having a persistently infected calf that is a carrier for life. It may look normal but infect others through secretions, especially nose-to-nose contact. Others are born deformed or so weak they die quickly.

It was thought the cow would become immune unless it was also persistently infected. However, there will be another persistently infected calf if the cow picks up the HoBi-like virus.

“Our whole old wives tale about if you had a (persistently infected) animal, you are safe for the rest of your life, is not true if we had HoBi- like viruses walk in,” she said.

There are other emerging pestiviruses.

Atypical porcine pestivirus appears to be widespread in the United States and may be the cause of congenital tremors in pigs. DNA sequencing discovered that it had the same general genetic organization as the others in this family.

Wildlife may also be affected.

A virus called pronghorn has been seen in mule deer, antelope, mountain goat and bighorn sheep.

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