Is A Bird Flu Pandemic Avoidable?

"I'm extraordinarily sympathetic to the general public sentiment that, like, 'Oh my God, we're so sick of infectious diseases'. We don't want alarmism."

"The best way to avoid alarmism is to avoid human infections, and do the low-hanging fruit stuff really well. [More robust biosecurity measures on farms and educating hunters], because we know a lot of animals that are harvested are at high risk [of infection with H5N1 as well [such as foxes and ducks]."

"[Should an H5N1 sample be found in infected milk] Then we're in trouble. Because if we find an infected milk sample, then the virus is almost certainly pretty widespread, because we know how rapidly the virus can spread via contaminated milking equipment."

"The CFIA [Canadian Food Inspection Agency] is taking an approach to testing commercial milk that gives them some insight into where the milk comes from. Intuitively what they would do is start looking back at the farms that were the supplier of the milk that tested positive in order to identify infected animals."

Matthew Miller, Canada Research Chair in viral pandemics

Flock of farmed geese, Henan province, China [death rate in geese, 4%]. (China Daily/Reuters)

 

The medical scientific community is now consumed with watching and waiting as the highly pathogenic avian influenza H5N1 virus -- yet another import, as it were, from China -- is spreading. While it has not yet shown up in Canada, an outbreak on dairy farms in March in Kansas and Texas is close enough for guarded concern. From dead wild birds to dairy farms, the pathogen has spread to 131 herds in a dozen American states. Human cases -- one in Texas, two in Michigan; with mild symptoms -- have also appeared, linked to the outbreak in dairy cows in the United States.

The virus has not yet been detected in Canadian dairy cattle, nor has its presence been revealed in the 600 retail milk samples tested up to June 18. There is a level of comfort in knowing the risk of transmission to humans is low and milk and milk products commercially available remain safe, according to the Canadian Food Inspection Agency. That comfort is short-lived in the realization that influenza viruses evolve continually. "I'm very worried about pigs", confides Dr. Miller, explaining that pigs can facilitate bird flu to exchange genetic material with human flu viruses; the result being a virus more adapted to transmit to humans.

The world's first plan to begin administering bird flu vaccines is set to take place in Finland when farm workers become the initial recipients. First detected in 1995 in birds in southern China and Hong Kong, since then H5N1 has become endemic in bird populations, destroying millions of both wild and farmed birds. Approximately 889 people have been infected with the virus since 2003, leading to a high proportion of deaths in the infected (52 percent). Generally the point of contact is transmission through a live or dead infected animal's body fluids; saliva, blood or feces.

And although human-to-human transmission of H5N1 rarely occurs, the high ratio of deaths to cases, in all likelihood means bird flu has the potential to "cause a major public health emergency if human exposure and viral evolution lead to sustained person-to-person transmission", concluded an editorial published the BMJ (formerly the British Medical Journal).

When H5N1 infectsm it relies on cells in almost all human tissues to allow it to replicate, not just the lungs. "It can infect all kinds of other organs, including our brain", advised Dr. Miller. Complications ranging from encephalitis (inflammation of the brain) to coma have developed in humans infected by H5N1.  Case fatality rate -- proportion of people with confirmed infections who die -- exceeds 50 percent, an astonishingly high lethality. Children and young adults experience higher critical illness with the virus.

Still, at the present time, the risk to humans is not yet sufficiently elevated to justify a mass H5N1 vaccination protocol. "My preference is that we don't find ourselves in that scenario."

"[While the U.S. has stockpiled H5N1 vaccines and other countries are soliciting tenders for emergency doses], I'm not aware that Canada has done that yet, but quite certain that it is being considered at this point."

"I'm acutely aware of public sentiment around vaccines right now, and resistance to vaccination."

"The best thing we could do is adopt a strategy like Finland is using and offer vaccine to those at high occupational exposure risk to prevent a widespread human outbreak."

Matthew Miller, McMaster Immunology Research Centre, Hamilton

Nature's Cull

"There are enough red flags that we're beholden to prepare."

"If the virus spills over into new species, it always gains an opportunity to mutate and adapt even further."

"So this is really an unprecedented level of viral activity for H5N1."

Dr.Samira Mubareka, infectious disease specialist, clinician scientist, Sunnybrook Research Institute/University of Toronto

 

"The spillover of these viruses from wild birds to mammals could cause a potentially devastating pandemic if the H5N1 viruses mutate into forms that can spread efficiently among the mammalian species."

Research study, Canadian Food Inspection Agency, published in Emerging Microbes & Infections journal

There have been fewer than a dozen Asian influenza cases confirmed among humans identified globally since 2020. Even among those no instances have been identified of H5N1 passing from human to human. Public health agencies are involved in closely watching how the highly pathogenic avian influenza H5N1 is evolving, a heightened level of alertness, the impetus of which can be traced to the still-and-ever-presence of the previous SARS-CoV-2 pathogen that upended the world community in a massive infection and fatality rate.

First identified in 1996, H5N1 had manifested itself in 2020 with a new type that was detected in late 2021 in North America. Since that date, the virus has decimated huge flocks of both wild and domesticated birds, the result of which has been millions of poultry deaths in Canada alone, from infection and from preventive culls. Dr. Mubareka advised that what has partially captured the attention of scientists is the range of species being infected by the virus.

The first Canadian case was identified in a pet dog earlier this month, among the hundreds of confirmed cases in wild skunks, foxes, mink and other mammals dating to the beginning of 2021. Farmers in Ontario and Quebec have been bracing for a potential wave of cases with the return of migratory birds (bringing the infectious virus with them). Public health agencies throughout Europe, Canada and the United States feel for the time being that risk to humans of contagion is low. There is no risk associated with consumption of cooked birds.

 

 

Scientists with the Canadian Food Inspection Agency working at a laboratory in Winnipeg where cases of H5N1 are confirmed and genetically sequenced, studied cases in 40 different wild mammals, the researchers finding the virus had undergone some "critical mutations". The critical mutations referred to by the researchers involved that part of the virus that allowed it to replicate; similar findings were reported globally.The scientists found in 17 percent of the cases changes advantaging the virus  to replicate in humans.

On the other hand, the researchers also found that the virus had not developed a preference to lock on to receptors in a human nose, mouth and throat -- the target of an influenza virus, key to human infection. Multiple surveillance networks set to monitor and track the influenza virus have been installed by the Public Health Agency of Canada, which claims to take the situation "very seriously". Its recent experience with COVID-19 aided it in building H5N1-specific plans across government departments.

The 27 member states of the European Union agreed to implement a bird flu vaccine strategy, with Mexico, Egypt and China on a list of countries inoculating chickens against H5N1. Targeted vaccination could help to prevent poultry losses and reduce the spread of the virus, advised Shayan Sharif, professor and acting dean at the Ontario Veterinary College, concerned at the possibility that the virus may mutate to become more dangerous to humans and eventually transmit human-to-human.