No clear exposure source in Missouri H5 avian flu case

The investigation into a recent human H5 avian flu case in Missouri, the first of its kind picked up through flu surveillance, show that the source still isn't known, but early genetic analysis suggests that the virus is closely related to the one infecting dairy cattle, federal health officials said today.

At the US Department of Health and Human Services (HHS) briefing, Nirav Shah, MD, JD, principal deputy director for the Centers for Disease Control and Prevention (CDC) said state health officials are continuing the investigation, diving deeper into potential exposures.

On the animal side, California reported two more H5N1 outbreaks in dairy cows, as the state continues to investigate how the virus made its way to the farms.

Virus traces show similarity to cow strain

Shah said it wouldn't be unusual to not find a likely exposure source. For example, he said that, of about 500 human swine flu cases identified since 2010, about 8% had no clear exposure to the virus.

The probe hasn't turned up any evidence of human-to-human spread or any unusual rises in flu activity in Missouri, he added. “Evidence points to a one-off case,” Shah said.

The concentration of virus RNA in the patient's sample was extremely low, and so far, CDC scientists haven't been able to piece together the full genome, which might yield clues about the source and flag any potential markers for increased risk of spread. So far, testing hasn't been able to pinpoint the neuraminidase, which is the "N" portion of H5N1.

Though sequencing is still under way, results so far suggest that the virus is closely related to the one circulating in dairy cows, Shah said. "We're throwing everything we've got at this."