Virus World

The case marks the first detection of the highly pathogenic strain of bird flu on the continent. Australia has reported its first human case of the H5N1 avian influenza in a child who recently returned from India. The case marks the first time the highly pathogenic strain of bird flu, which has killed millions of birds and mammals since it began circulating in 2020, has been detected on the continent.  The child contracted the virus in India in March of this year -  likely through contact with a sick bird - and experienced a “severe infection,”  but has since made a full recovery, according to local health authorities.  Officials said contact tracing has not identified any further infections and that the risk of transmission to others was “very low”, as the virus has not yet shown evidence that it can spread between people. 

The Department of Health in the Australian state of Victoria, where the human case was identified, are also responding to an outbreak of avian influenza at a poultry farm but has said that it is an unrelated incident.  Although H5N1 infections in people are rare, the highly pathogenic virus carries an alarmingly high mortality rate. Of the 800 cases reported since the late 1990s, roughly 50 per cent resulted in death. The virus has recently broken out among dairy cattle in the US in an unprecedented outbreak.  So far, 51 herds in nine US states have been affected, although experts think it is far more widespread.  The apparent ability of the virus to spread between cows is significant because it provides more opportunities for it to evolve to better infect and spread between other mammals.  Of particular concern is whether H5N1 might now be able to infect pigs, often described as ‘mixing vessels’ for influenza and making it more likely that the virus could adapt to spread between humans.  So far this year, there have been two other confirmed human cases of H5N1. 

In Vietnam, a man died in March after direct contact with an infected bird, whilst in Texas a farm worker caught the virus from sick cattle – although his symptoms were mild. The US Centre for Disease Control is monitoring a further 300 people who have been exposed to the virus via cattle for signs of infection.  The WHO still considers the risk to humans low but urged countries to rapidly share information to enable real-time monitoring of the situation to ensure preparedness as the virus continues to spread. 

The CDC announced late Thursday that a person in Colorado has tested positive for an H5 bird flu virus — the first such recorded infection in the U.S.  The CDC did not reveal the neuraminidase subtype of the virus — the N portion of an influenza A virus’ name. The country is currently experiencing an unprecedented outbreak of H5N1 bird flu in both wild birds and in commercial poultry flocks. The man, described by Colorado health officials as being younger than 40 years old, experienced only fatigue; he is now in isolation and being treated with the flu antiviral oseltamivir. A statement from Colorado’s Department of Public Health and Environment said he is incarcerated at a state correctional facility and was culling poultry as part of a pre-release employment program. The CDC described the poultry outbreak as presumptively having been caused by H5N1. Michael Osterholm, director of the University of Minnesota’s Center for Infectious Diseases Research and Policy, was less sanguine, saying that while previous experience with H5N1 viruses suggests that human infections didn’t lead to sustained person-to-person spread, heightened surveillance is important. “Any time you’re dealing with H5N1, you sleep with one eye open,” he told STAT.

H5 viruses have long struck fear among scientists who study bird flu because of the economic damage they can wreak and their propensity to occasionally infect people. They are one of two subtypes — H7 viruses are the other — that can become highly pathogenic. That term refers to their deadliness when they infect birds. In the mid-aughts, H5N1 viruses decimated poultry flocks first in Southeast Asia and later into South Asia and North Africa. H5 viruses have also been seen to infect people from time to time, often with devastating consequences. Of just over 860 previously recorded human cases of H5N1 infection — from 19 countries — just over half have died. For a number of years, it was feared the virus might cause a potentially devastating pandemic. But when the first pandemic in decades finally occurred in 2009, it was caused by a mild swine flu virus, H1N1.  The CDC’s statement suggested it isn’t completely clear the Colorado man was actually infected. The test may have picked up virus that was “surface contaminant” — presumably virus picked up by a nose swab — that was present because of the man’s involvement in culling infected poultry. But the CDC said the individual meets the criteria as a positive case and had to be treated as such. “The appropriate public health response at this time is to assume this is an infection and take actions to contain and treat,” the statement said. The CDC statement also pointed out that the group of H5N1 viruses that are currently spreading throughout the U.S. and Europe are different from the H5N1 viruses that caused the earlier outbreaks in Asia and North Africa. This is only the second human infection caused by this clade of H5N1 viruses; the first was a man in the United Kingdom who was infected last December. His flock of poultry contracted the virus and the man tested positive for the virus, although he reportedly didn’t experience symptoms of illness.