Bovine kobuvirus little understood by science

The virus, which causes neonatal calf diarrhea, was first identified in Japan and was recently found in the United States

A virus that causes neonatal calf diarrhea has found its way to the United States.

Bovine kobuvirus was first discovered in Japan in 2003 and it belongs to a family of viruses known as picornaviridae that also includes rhinovirus, the source of head colds and sinus infections in people, and poliovirus, the cause of polio.

“Bovine kobuvirus was first identified as a cytopathic contaminant in a cell culture medium in Japan in 2003,” said Dr. Leyi Wang, clinical assistant professor in veterinary clinical medicine with the University of Illinois. “It is unknown when the bovine kobuvirus entered the U.S. It was first discovered in the calf feces in the U.S. using next-generation sequencing technology in 2019.”

According to the report, in April 2019 a fecal sample from a calf 10 to 14 days old was submitted to the university’s Veterinary Diagnostic Laboratory in Urbana for testing for enteric pathogens. Results showed that the tests for rotavirus, coronavirus, cryptosporidium, and E. coli were positive.

NGS technology platforms perform sequencing of millions of small fragments of DNA at unprecedented speed and have revolutionized genomic research.

While bovine kobuvirus is not a new virus, it is still fairly new to science, so the scope of its effects is not fully understood. Wang said that it is possible it has been in the U.S. for a while but not recognized until now. However, the virus is found in 10 countries around the world including Thailand, Hungary, the Netherlands, South Korea, Italy, Brazil, China and Egypt.

“Data from previous studies and our own studies indicated that bovine kobuvirus might be an enteric pathogen causing neonatal calf diarrhea,” said Wang. “But this needs to be further tested by virus isolation and animal challenge studies to experimentally prove it. Enteric pathogens are contagious among calves in a herd and diarrhea is a leading cause of calf death.”

He said that, as a possible enteric agent associated with the intestines, bovine kobuvirus can enter a calf through a fecal-oral route or it could be picked up in the environment. However, it is only detectable by laboratory analysis. Four of the nine samples tested at the university’s Veterinary Diagnostic Laboratory were found with bovine kobuvirus. All of the infected cows were from Illinois.

“Farmers cannot tell what pathogens cause diarrhea in cattle since there are multiple bacteria, viruses and parasites that are causing it,” said Wang. “Laboratory differential diagnosis is needed. So far, this is not a reportable disease and there is no need to report it to state veterinarians or officials.”

Diarrhea appears to be the principle symptom of the bovine infection and no other negative associations have been observed. Wang said that since almost no one in North America is actually looking for the virus in cattle, it remains to be seen how this emerging disease fully influences bovine health.

In countries where the disease exists, bovine kobuvirus appears to be prevalent. Past studies have shown that 20.9 percent of calves (38 out of 182) younger than two months in Brazil have been infected and 26.7 per cent of calves (27 of 86) less than one month of age in South Korea have been infected.

The study conducted by the research team supported the hypothesis that bovine kobuvirus causes neonatal diarrhea and, in addition, the virus can be detected in cattle without diarrhea or without showing clinical signs of the virus.

According to the report, it appears that detection of the virus is only from fecal samples. No natural or experimental studies have reported its presence. Wang wrote that future studies, including virus isolation and virus challenge to calves, are needed to further confirm bovine kobuvirus as the causative agent in neonatal diarrhea.

Just how widespread the virus is in cattle herds in the U.S. is unknown. Continued monitoring is needed to determine rates and distribution.

“What is urgently needed are surveillance studies on herds from different states to monitor the virus in the field to see how widespread it is,” said Wang. “Scientists have access to only a few genetic sequences of this virus in public databases. We need to be sequencing these viruses to learn more about their genetic diversity and evolution.”

The research report was published recently in the journal Emerging Infectious Diseases.

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