HIGHLY PATHOGENIC PANZOOTIC

The USGS, among many national and international agencies, is compiling data on bird flu because the planet is experiencing a panzootic caused by highly pathogenic avian influenza (HPAI) H5N1—a panzootic is the equivalent of a pandemic in birds and animals. It’s still primarily a catastrophe for wild and domestic birds, but the CDC reports that it has also affected more than 48 species of mammals and has caused large-scale die-offs (major mortality events) amongst some, including killing more than 70% of the elephant seal pups and an unknown number of adults along the Argentinian coast in 2023.

The first known version of H5N1 was identified in 1996 at a goose farm in China. In 2005, it was detected in wild bird populations after a major mortality event when over 1,000 wild birds died suddenly at a nature reserve in China. Since then, it has been circulating widely and globally for almost 30 years, reaching the periphery of Antarctica this year. Only Australia, New Zealand, and some parts of Polynesia have no documented cases of it in wild birds (Australia is fighting an outbreak of bird flu on poultry farms, but it is not caused by H5N1). The current strain of H5N1 has been circulating in the Americas since 2021 and has caused widespread infections in wild birds, poultry, and animals.

Bird flu viruses are categorized as either low pathogenic or highly pathogenic based on how easily they spread in commercial poultry facilities. Low pathogenic avian influenza (LPAI) is widespread and endemic in certain waterfowl species—not unlike seasonal flu in humans. LPAIs typically cause relatively mild symptoms, are seasonal, and most healthy wild birds recover. Bird flu viruses are categorized as highly pathogenic avian influenza (HPAI) when they infect domestic poultry and spread rapidly through the birds kept in facilities. Obviously, this comes at a high cost to poultry and egg producers. However, historically, HPAIs do not have the same devastating effects on wild birds. HPAI H5N1 is behaving differently.

H5N1 has caused major mortality events in wild birds and has spread to bird species that haven’t been historically exposed to it. For example, it has killed large numbers of common cranes in Israel, 40% of brown pelicans in Peru, and three-quarters of the gannets breeding in Scotland. And in a development that has scientists puzzled, the gannets that survived bird flu infections changed eye color from bright blue to black. 

Bird flu also tends to be seasonal, similar to human flu viruses infecting people more in the winter months. H5N1 doesn’t have a clear seasonal profile. Jennie Rinehimer, a Washington College biology professor who specializes in behavioral ecology and uses birds as models, speculated that this aseasonality may contribute to the spread of the virus because it is actively infectious at times of the year when birds flock together for shelter or feeding, whereas other flu variants aren’t active at these times. She thinks it is also possible that this strain is just more virulent and adapted to more species. 

“I think with [the virus’] growing virulence and transmission to other types of organisms, that the public should be cognizant of that,” she said. “If people are engaging with wildlife, they should try to mitigate the amount of feeding and congregating that they’re causing those organisms to do.” She thinks people should consider not feeding birds during this outbreak because when birds congregate at feeders it could lead to introducing the virus into new species.

THE DAIRY FARM DEVELOPMENT

“This particular viral strain has shown decent transfer over into mammals, and the most prominent transfer right now is the transmission into dairy cows,” Sullivan said. “It’s concerning any time you see it cross the avian-mammal border.” According to the CDC, cattle aren’t typically affected by type A flu viruses, however, type D primarily affects cattle but doesn’t cause infection in people or birds.

Concern about the infection of dairy herds appeared to be validated when inactivated traces of the virus were found in over 20% of randomly tested milk in grocery stores, indicating a much wider spread of the virus in dairy herds. Federal and state health officials were quick to reassure the public that the pasteurized milk did not contain the active virus, and the inactivated virus that was found in the milk could not be reactivated in laboratory tests done by the USDA. The same cannot be said for raw/unpasteurized milk. Initial findings indicate that raw milk from infected cows contains high concentrations of live virus—making it unwise to drink raw milk.

In addition to deactivated traces of the virus in pasteurized milk, as of early June, there have been three documented cases of dairy farmworkers being infected. Luckily, the symptoms in all three cases have been mild, and two recovered while the third is recovering. It appears likely that the workers were infected through direct contact with infected milk rather than through respiratory dispersal. 

To date, only dairy herds and not beef herds have been infected, and the virus is concentrated in the cows’ udders and their milk. The most compelling hypothesis for the transmission in cattle is that milk residue from an infected cow remains in the milking machines and can infect the next cow hooked up to the machine. Because industrial dairy farms raise calves at centers before sending them to different herds across the country, this might explain how the virus has spread so widely. The good news is that a virus that spreads through direct contact with raw milk is less of a threat to other species and certainly not a transmission method that is likely to cause a pandemic.

The infections of the farm workers also have some positive takeaways. The three workers that we know were infected have had mild symptoms, with conjunctivitis (pink eye) the most common symptom. The latest patient has shown some respiratory symptoms that will need to be monitored, but there has been no human-to-human spread.

In less promising news, cats that drank the raw milk of infected cows also became ill. Half of them died, and the other half had to be humanely euthanized. In a study in the journal Emerging Infectious Diseases, researchers confirmed the cats died of H5N1 infections, had high viral loads in their brains and nervous systems, and showed neurological symptoms prior to death. 

SOME REASSURING FACTS

Given how fresh the trauma and disruption of the Covid pandemic is, it would be irresponsible and clinically wrong to claim H5N1 will cause another deadly pandemic. 

The Covid virus was new to humans, and human immune systems couldn’t mount the sort of robust defense they do with pathogens they have some previous exposure to. Flu viruses, on the other hand, are old and perennial enemies, and there’s the possibility we may have some immunity from previous encounters with the flu even if this bird flu variant does reassort and change radically. Equally important, we have stockpiles of vaccines and anti-viral medications such as Tamiflu that the CDC and FDA say are likely to be effective against H5N1. 

In a breakthrough, researchers at the Perelman School of Medicine at the University of Pennsylvania announced in May that they had successfully created experimental vaccines targeting H5N1 using the mRNA technology they developed to create the first Covid vaccines. The advantage of this technology is that, in the event of people-to-people transmission of the virus, it can produce vaccines rapidly, and they can be customized to target the genetic profiles of emerging strains of the virus.

RAW MILK FROM INFECTED COWS CONTAINS HIGH CONCENTRATIONS OF LIVE VIRUS—MAKING IT UNWISE TO DRINK RAW MILK.

AN EVOLVING AND ONGOING PANZOOTIC

Rinehimer, as a behavioral ecologist, is somewhat conflicted about the virus and its function in nature. In general, she thinks viruses and other challenges to species, like predation or competition for food, are natural parts of the evolutionary dance. These pressures on species drive evolution and sometimes drive weaker or poorly adapted species into extinction. “In the absence of humans,” she said, “extinction is normal. Extinction is a good thing for the long-term health of the biodiversity of our planet.”

With H5N1 she has some reservations. “The problem these days is that humans have had their hands in so many other aspects of nature that we’ve thrown things out of whack so profoundly,” she said. “In my opinion, we have some kind of moral responsibility to right the wrongs.” She thinks we should intervene with species that human actions have driven to the edge of extinction and has some practical advice for people to help birds survive this catastrophe. “The two biggest issues for birds are domestic cats and window collisions, which kill billions every year,” she said. Individuals can make a survival difference to many bird species by taking actions such as not letting cats outside or using readily available remedies to make windows visible to birds.

David Kramar joined Washington College this spring as director of the River and Field Campus. He specializes in natural resource management and has a particular passion for raptors and other birds of prey. He notes that research into bird flu has historically been focused on commercial poultry and natural reservoir species such as waterfowl. “Less well-known is the extent to which avian influenza is found in species that tend to exhibit less communal behavior, such as our raptor populations.”

While working with The Raptor Center at the University of Minnesota, he learned of the infection rates amongst birds of prey. “As of the end of December 2023, the Raptor Center had tested 2,162 individuals with a positive incident rate of 262 individuals, or roughly 12% of all individuals tested,” he said. Infection rates in Maryland, Virginia, and Delaware are less known, and he would like to fill in the data gap. He is in the process of setting up a collaboration between Washington College, the Virginia Department of Wildlife Resources, and the Eastern Ecological Science Center to trap eagles and sample for bird flu. He hopes to have this up and running and start adult trapping over the winter of 2024–25.