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Avian Influenza Exam on a Brown Pelican

International Bird Rescue photo by Ariana Gastelum

Staff at International Bird Rescue's center in Los Angeles assess a brown pelican for avian influenza in a special quarantine area.

They could be working with chickens at a million-bird poultry farm, endangered condors in the wild, flamingos at the local zoo or a pet cockatiel at a clinic.

No matter how they practice, veterinarians from multiple facets of the profession are bracing for an extended onslaught of deadly avian influenza — with no clear end in sight.

An especially transmissible and persistent strain of highly pathogenic avian influenza (HPAI), first detected in 2020, is now known to be circulating on every continent apart from Australia and Antarctica, and threatening to become endemic in multiple countries. (A suspected case in Antarctica was recorded in late December, in a brown skua seabird on the tip of the Antarctic Peninsula, but the case has yet to be confirmed).

Most conspicuously, the virus is devastating poultry industries like never before. In the United States alone, 81.37 million birds in commercial or backyard poultry operations have been affected since the strain was first detected stateside on Feb. 8, 2022, according to the U.S. Department of Agriculture, making it the worst avian influenza outbreak in the country's history.

If the latest numbers coming out of the U.S. are any guide, 2024 is shaping up as another hard year. The USDA says 8.82 million commercial and backyard birds have been affected in the past 30 days — a large chunk of them in Northern California — accounting for 11% of the total number of birds affected in the U.S. so far.

The outbreak also is killing multitudes of wild birds and pushing endangered animals such as the African penguin and California condor closer to extinction.

"It's huge," said Dr. Rebecca Duerr, a veterinarian and the research director at conservation group International Bird Rescue. "It's one of the biggest threats to bird populations in our lifetimes.”

HPAI has crossed over to non-bird species, too, including wild mammals, such as foxes and raccoons, infected when they eat affected birds. A small number of cats and dogs are known to have been infected, most notably 29 cats in Poland, 25 of whom either died from illness or were euthanized, according to the World Health Organization. (Contaminated raw pet food was the suspected, but not confirmed, culprit).

Mass mortality events involving mammal-to-mammal transmission of HPAI have been reported among seals, sea lions and farmed minks. Only a handful of humans have been reported as infected worldwide, all displaying zero or mild symptoms.

"It's been shown, at this stage, that the risk to humans is very, very low," said Dr. Andrew Hennenfent, a board-certified veterinary public health expert in Iowa. "But there's always the possibility that the virus could mutate to become more harmful to humans. Influenza viruses mutate readily.” Hennenfent also is a zoonosis consultant at the Veterinary Information Network, an online community for the profession and parent of the VIN News Service.

The risk of the virus reaching pet birds is relatively low, since they're commonly kept individually or in small numbers, often caged inside homes. But that's cold comfort to Dr. Brian Speer when he imagines the disastrous consequences of the virus getting into his practice in California. One of the largest avian-only hospitals in America, it houses dozens of patients at any one time, whether they're toucans, flamingos, ostriches, vultures, parrots or backyard chickens.

"You start imagining a bad virus around every corner, on every surface — like we all felt with Covid," Speer said. "Most certainly, it messes with your mind.”

Outbreak shows few signs of waning

Avian influenza is an A-type influenza virus that comes in two categories: highly pathogenic avian influenza (HPAI) and low-pathogenic avian influenza (LPAI).

The subtype of HPAI causing so much grief right now, H5N1, was identified in 1996 in China. It has been behind several international outbreaks of HPAI, all of them relatively short in duration. For instance, when HPAI hit the U.S. especially hard in 2014 and 2015, the first case was recorded in December 2014 and the last case in June 2015, some six months later. The current, multiyear outbreak involves a new strain of H5N1, known as 2.3.4.4b.

Transported over vast distances by certain "carrier" species of migratory bird — which can be infectious without succumbing to disease — 2.3.4.4b has shown resilience throughout all four seasons of the year and spread especially far, according to a review in the journal Eurosurveillance.

Previous strains of H5N1 were more harmful to commercial poultry than wild birds. "This strain is different because it is slaughtering wildlife in droves," said Duerr.

Dabbling ducks like mallards and teals appear more likely to be carriers, as opposed to diving ducks, Duerr said. Geese and pelicans are among birds hit especially hard, she added. "And it could spread in Antarctica any time. Penguins seem to be extremely susceptible to it. A lot of the slow-breeding marine birds are particularly at risk. The entire Atlantic population of northern gannets has had a huge population-level impact from this disease."

HPAI thrives more in colder temperatures, but the year-round persistence of the current strain, especially in so many migratory birds, is fueling concern that it will become endemic in North America, Europe and elsewhere. (HPAI currently is endemic in countries with less-advanced veterinary infrastructure, such as Egypt, China, India, Indonesia, Nigeria and Vietnam, according to the USDA.)

The virus is transmitted through respiratory secretions or droppings, including via contaminated food and water. Clinical signs of disease can include sudden, unexplained death, lethargy, purple discoloration of the legs and decreased egg production. There may be respiratory signs, such as coughing, sneezing, nasal discharge and difficulty breathing (dyspnea), and/or neurologic signs, such as poor coordination, rapid involuntary eye movements (nystagmus), tics and tremors. Mortality rates for the H5N1 subtype of HPAI can be 90% to 100%, according to the U.S. Centers for Disease Control and Prevention.

Standard approach is culling; vaccination still controversial

Due to high mortality rates and infectiousness, management of HPAI largely entails isolating infected flocks and killing them.

For veterinarians who discover a suspected case at a commercial poultry operation, they must immediately contact the relevant state authority and prepare for the extermination of the flock. Things typically happen fast. "Often, a farmer will come to work one morning, and a good proportion of the flock is either sick or dying, when they were all fine the night before," said Hennenfent. "In the U.S., once HPAI is confirmed, the USDA and state animal health officials call for a rapid response that includes rapid depopulation and disposal to try and limit the spread to that one site."

Extermination methods can differ by country, often due to regulatory strictures. In the U.S., for instance, the most common method of mass depopulation is ventilation shutdown-plus, a controversial practice that involves sealing the building and pumping in heat until the animals inside die, usually of hyperthermia. Death can take hours, entailing extreme suffering, but the procedure is relatively cheap and convenient. Ventilation shutdown-plus is banned or heavily restricted in many places, such as the United Kingdom and European Union, where large flocks often are culled with carbon dioxide or nitrogen-infused foam.

Vaccines for HPAI exist but their use is questionable because cross-border trade can be disrupted, in part because difficulty distinguishing between vaccinated and infected birds makes it hard to screen for infected animals. Moreover, vaccinated birds can still become mildly infected and shed the virus. France, for instance, is the sole European country to have kicked off a vaccine drive, which commenced in October for ducks only. (The decision sparked an immediate response from the U.S., which banned all poultry imports from France).

The USDA said last April that it was trialing several vaccine candidates but use still is illegal in the U.S. with one small exception — a vaccine rollout has been approved for California condors in an attempt to save America's biggest land bird from extinction.

Use of antivirals also is controversial. The U.S. Food and Drug Administration, for instance, bans the use of go-to drugs for treating influenza in humans — adamantane and neuraminidase inhibitors — in chickens, turkeys and ducks to discourage the development of drug resistance.

Speer, who also is an avian medicine consultant for VIN, doesn't see the U.S. changing its position on vaccines and antivirals soon, though he wonders what will happen if the outbreak persists. "If this becomes an endemic virus, not just some flash in the pan, there might need to be some reconsideration of that strategy," he said. "We're all hoping it'll go away, but this one's hanging on."

Duerr said vaccines perhaps could protect other wild bird species but sees limitations. "Every species is a little different: A bird is not a bird is not a bird," she said. "And so each species needs to have a safety evaluation. Does [the vaccine] actually do anything? Do they need to be re-vaccinated?

"You can't recapture every wild animal once a year for a booster, so it's not really practical to vaccinate the entire world against this. It's really only the wild birds that are down to tiny human-managed populations that may end up getting vaccinated."

Attempting to hold back the tide

Dr Brian Speer

Photo courtesy of Dr. Brian Speer

Dr. Brian Speer, pictured here with a cockatoo at his avian-only practice in California, sees so many unique species of bird that he perceives human qualities in his patients. "I see them as really cool people that happen to have feathers," he said. "You get to know each one of them as you would a good friend. And when your good friend needs some help, we listen to them and we help them out."

One way to avoid such awful fates for so many animals is to prevent the virus from reaching them. Prevention may involve using coverings to stop wild birds and their droppings from getting close to densely packed commercial poultry operations, where pathogens can spread like wildfire. And, since transmission often is caused by humans moving between farms with virus particles on their skin or clothing, containment methods include using disposable boot covers and disinfectant footbaths and regularly washing equipment like vehicles and egg trays.

Speer tells clients with backyard chickens who live near waterbodies like ponds that they might want to keep their birds inside since they may encounter migrating waterfowl or shorebirds.

However, keeping birds indoors for extended periods can be bad for their health, too, Speer pointed out. "We have some local zoos that, when this outbreak initially appeared, they moved outdoor birds like flamingos inside to minimize exposure," he said. "But then over month after month, some of those birds were developing health issues associated with being inside too long, and some of those zoos are having to re-examine their lockdown policy. It definitely is a multilayered challenge."

For veterinarians working in companion animal or wildlife rescue settings, disinfecting surfaces and wearing personal protective equipment when dealing with suspected cases can help. Recommending pet owners avoid feeding dogs and cats raw or poorly processed food could mitigate contamination risk.

"Normal cooking temperatures would completely kill any virus," Hennenfent said. "In raw food, transmission could be possible but is not a huge concern for me. However, in general, we advise not feeding raw meats including poultry to pets because it can increase the risk of them ingesting lots of pathogens like Salmonella and other sorts of enteric bacteria."

Crucially, all veterinarians contacted by VIN News said hospitals should establish a triage system to keep the virus away from other patients.

"Our staff are coached to weigh the risk of different scenarios," Speer said. "Should a backyard chicken owner call and say, ‘Oh my gosh, I went out to the henhouse this morning and I had six birds, and now five are dead. Can you help?' That bird's not going to come to our door. But for a person with a single backyard chicken that's had swollen sinuses for a few weeks and it needs some help, we're not going to say you can't come in."

Any suspected sufferer should be assessed in a separate room or building. Birds showing clinical signs indicative of HPAI could be euthanized if there's no time to await the results of diagnostic testing, which, according to Duerr, sadly is often the case for wild birds. "Testing, at this point, is a send-out, and it's not super fast,” she said. “And it's expensive."

In an attempt to solve that problem, Duerr is working with a doctoral student from the University of California, Davis, on developing an HPAI point-of-care test. In the meantime, many birds that don't have HPAI but display similar clinical signs to those that do will be unnecessarily euthanized.

Also of concern, Speer said he has heard of veterinarians who are avoiding treating even mildly suspect cases for fear they'll contaminate their practices. "Those colleagues that take such a hard stance are positioning far more animals to suffer without help because they're not triaging them well," he said. "The veterinarians' oath is to do our best to educate the public, alleviate pain and suffering, and to augment and enhance welfare." Offering a positive example, Speer told of a case in which a significant portion of a chicken flock in California was saved when the virus was contained to two of several barns on the property.

At the same time, he accepts that practitioners are treading a fine line, including at his own avian-only hospital. "I think the art form is to better understand the pathogen so we can substitute pathogen paranoia with targeted pathogen awareness," Speer said. "If we know what it is, how it moves, then you can sleep better at night because you know how to manage what you're up against."