Day-By-Day Progress of a Potential Human-To-Human Pandemic
Gary Smith and Keith Belk
Colorado State University
Having lived through the nightmare of the 2019-2022 COVID-19 pandemic, there is little appetite among Americans for a replay by another virus. What is a pandemic? Dictionaries describe “pandemic” as: (a) a widespread outbreak disease1 and (b) a disease that is distributed or occurring widely throughout an area, a region, country, continent, or globally.2 Highly Pathogenic Avian Influenza (HPAI), caused by the H5N1 virus (colloquially called “Bird Flu”), has occurred in the USA, Canada, Europe, Australia, and New Zealand.9-15 Public-health and infectious-disease experts around the world are watching Bird Flu very, very carefully because this virus could “jump species”, acquire the capacity to attach to human cells, spread widely, and open the door to a new human-to-human pandemic.3
Bird Flu is already a poultry pandemic and it has already jumped species – from poultry to dairy cattle, swine, house cats and humans – but it has not yet succeeded in going human-to-human.4 The latest iteration of the H5N1 virus first appeared in North America in 2021.5 It circulated in wild birds and infected commercial poultry beginning in 2022; in 2024, the virus jumped into cattle. The bovine outbreak was first detected in March 2024 in dairy cattle herds in Texas and Kansas, followed in April and May 2024 by the first cases of bovine-to-human spread.6 Bovine outbreaks continued through the Summer of 2024 into more States. The virus took a toll on poultry flocks too, and a small outbreak among farmworkers in Colorado was blamed on challenging culling work in 100-degree heat.6
Five poultry workers at an egg-layer operation in northeast Colorado contracted Bird Flu.7 The workers showed mild symptoms, including “pinkeye” as well as common respiratory infections; none required hospitalization.7 Symptoms among the human Bird Flu cases included fever, chills, coughing, sore throat, and runny nose.7 Two California dairy-farm workers who contracted Bird Flu had symptoms that included conjunctivitis (i.e., eye irritation, commonly called “pinkeye”) and mild, cold-like physical illness.8 Since March 2024, in the 66 US confirmed human cases of Bird Flu, all except one (an elderly man in Louisiana has died) have recovered after “mild” illnesses; in two of the 66 cases (an adult in Missouri and a child in California) health officials have not determined how they contracted the virus.16
CDC believes that scores of cases of Bird Flu in humans have been asymptomatic and gone undetected during the 2024 outbreak.17CDC has previously considered stepping-up testing of farmworkers, their family members, and their friends, and has considered if, when, and to whom to deploy the 4.8 million doses of Bird Flu vaccine it has maintained in storage.13 Humans with Bird Flu but no known encounter with dairy or poultry could have contracted the H5N1 virus from other people via physical contact (skin-to-skin or clothing-to-skin) or airborne, but no such sequela has been identified by health officials. It is also likely that such transmission occurred via contact with raw (unpasteurized) milk, cats, wild birds, and/or non-bird wild animals.4,5,16,18,19
Health officials have confirmed presence of the H5N1 virus in dead cats and in raw milk causing California State Public Health officials, in December 2024, to suspend sales of human or pet food products that contain raw milk.5,18 Cats—wild, feral, and domesticated—have a unique sensitivity to H5N1; experts estimate that hundreds of house and barn cats have died as a result of consuming unpasteurized milk and/or raw meat/poultry from animals infected with Bird Flu.5 Cats could become capable of causing Bird Flu in humans. Infections of Bird Flu have been confirmed in 419 non-bird wild animals, including red foxes, skunks, seals, and raccoons (probably picked up by those animals eating dead birds).16 Overall, since January 2022 when the virus was first detected in the USA, more than 12,000 wild and domestic flocks and 913 dairy cattle herds have been infected.16 So far, the only species-to-species crossover from poultry-to-swine, is a single backyard pig in Oregon.6
When Bird Flu first showed up in poultry flocks and dairy herds, what did we do to abate it? We knew that it originated from wild migratory birds,16,20 it was being transmitted to humans largely among those who worked with poultry and/or dairy cattle,21,22,23 we needed to implement biosecurity practices during animal production,18,23,24 we should test for the virus in more animals and people (for presence, and to understand how the virus is evolving)10,25 and that we could be on the verge of starting a human pandemic.12,25,26 Beginning with its jump-of-species from wild birds to domestic poultry in 2022, farmers were advised to do more to equip farmworkers with personal protective equipment and train them to disinfect contaminated poultry houses, and that they needed to install sound-alarm cannons to scare-off virus-laden wild birds that threaten to infect domestic poultry.27
Some farmworkers are being taught to “break the chain” of infectious disease transmission by following COVID-19 directives of wearing a mask, not working if sick, and improved personal hygiene.28 State, federal, other country and world public-health authorities have encouraged stronger surveillance of wild birds, poultry, cattle, and people; more H5N1 testing of animals and humans; and strict biosecurity measures—especially the establishment of “control” or “buffer” zones (with a radius of 4.3 to 6.2 miles) around an infected facility.10,11,17,18,24,29 APHIS insists that biosecurity is the best weapon in fighting the HPAI infection; done correctly, it can stop future introductions of the virus and avoid actions that contribute to its spread.30
Federal, State, and Local government actions to stem the flow have included the following: (1) August 2022: APHIS—indemnifying use of euthanasia on poultry farms.30 (2) April 2024: USDA—testing for Bird Flu if cattle crossed State lines and covering farmer’s costs for voluntary testing of farm animals.31 (3) July 2024: CDC—educating farmworkers about biosecurity, vigilance, and Seasonal Flu vaccinations.6 (4) August 2024: USDA—expanding Bird Flu testing of beef (meat) entering the nation’s food supply:32 and State of California—declaring a State Of Emergency on Bird Flu.6 (5) October 2024: State of Washington—administering both H5N1 and Seasonal Flu vaccines to farmworkers.13 (6) November 2024: USDA—testing of bulk raw milk across the US;31 and CDC--widening the testing of farmworkers, animals, and livestock facilities.6 (7) December 2024: Los Angeles CA County—suspending sales of raw milk products for human and pet consumption;5,19 State of Michigan—requiring producers to adhere to biosecurity measures;33 and APHIS—updating its 2022 indemnity program for HPAI on poultry farms.
Despite everything that the industry and government has done, our success rate is dismal. Day-by-day, we watched the USA’s Bird Flu outbreak increase: (a) from 0, to 12,000 wild and domestic flocks from February 2022, through December 2024 with 133 million dead domestic birds (some died from the disease; most were euthanized to prevent spread of the disease); (b) from 0, to 913 herds of dairy cattle from March 2024 through December 2024; and (c) from 0, to 66 confirmed human cases from May 2024 through December 2024; only one person died, most patients had mild symptoms.6,13,16,31-39 APHIS paid $1.1 billion to >1,200 producers for the death or euthanasia of domestic poultry.30 In early 2025, APHIS announced $306 million for HPAI monitoring and preparedness; $103 million will go to State and Local Agencies to step up monitoring of farmworkers exposed to Bird Flu-infected animals and $306 million will prepare the nation for a potential pandemic of the virus.24,34,35
H5N1 first emerged globally in 1996, in geese, in China; there have been approximately 900 human infections with Bird Flu since 2003 with about half of those cases resulting in death of a patient.39 The current strain of H5N1 has caused widespread devastation and economic hardship in the agricultural community, but the real danger is that it may achieve human-to-human transmission. Influenza viruses, including H5N1, mutate quickly; this makes it challenging to develop a single vaccine that remains effective against variants over time.39 Many experts put H5N1 at the top of their lists of pandemic threats due to how widespread it is among animals and how rapidly it appears to be mutating.16
Most of the human cases have been among farmworkers which shows that the Bird Flu virus isn’t very good at infecting humans; but when people are exposed to high enough concentrations of it, the virus finds a way.21 Health officials say risk of human-to-human transmission of Bird Flu remains low—but that could change. A 13-year-old girl in Canada became so sick with H5N1 in late 2024 that she had to be put on a ventilator.9 The affected Canadian teenager caught Bird Flu from an unknown source, is in critical condition, and has tested positive.37 Pigs have not been implicated in the girl’s case but pigs can be infected with swine, bird, and human flu viruses making them prime “mixing vessels”; the viruses could potentially combine to form a new strain capable of spreading widely among humans.17,37 That’s what happened during the 2009 “Swine Flu” pandemic; humans could be a mixing vessel.6,37 If Bird Flu viruses (not good at residing in the human nose) combine with Seasonal Flu viruses (good at residing in the upper respiratory tract), the product virus will spread person-to-person as a sick person coughs, sneezes or even talks.37
Bird Flu is becoming a bigger threat; it’s one mutation away from getting more dangerous to humans.40 So far, the virus is spreading primarily through close contact with infected animals, and not from person-to-person.40 Less comforting is a study published in Science41 which shows that the H5N1 strain spreading among US dairy cows is only one specific mutation away from more easily binding to human cells, a prerequisite for transmission among humans.42 We are not testing nearly enough—not nearly enough cattle or humans in particular—to understand how the Bird Flu virus is evolving.25
The latest Bird Flu case has experts worried about a potential pandemic because a child in California contracted the disease but had no contact with an infected animal. If it’s a human source, that means that a human-to-human transmission event occurred—which is a sign that a virus is on the verge of becoming a human pandemic.25 The Centers for Disease Control and Prevention (CDC) and California Department of Public Health (CDPH) are investigating the source of exposure, with initial findings showing no evidence of person-to-person transmission.43 We may be playing “Russian Roulette” by creating a situation where we have mutations or adaptation to human-to-human transmission.25 APHIS has awarded $5 million to universities and associations to find ways to flight viruses as the mutate.44 Any time a person catches H5N1, their infection is a chance for the virus to mutate in the wrong direction.45
Most recently, a senior (65YOA) in Louisiana was diagnosed with the first “severe case” of Bird Flu in the US.16,45 He was infected by his backyard chicken flock, already had respiratory problems, was hospitalized for three weeks, and died on January 6, 2025.16,22 Social and print media said his death was due to “a litany of underlying medical problems”4,46 and “the risk of an Avian Influenza pandemic in humans is low.”47 On the contrary, animal-activist group, Farm Sanctuary® claims that “Factory Farming” is going to make Bird Flu a human pandemic.48
A genetic analysis of the Louisiana man’s infection found that the Bird Flu virus had mutated while inside the man’s body which could have caused a more severe illness.16 CDC compared H5N1 DNA from his nose/throat with that of his backyard chickens and found that the virus began changing after infecting him but it was not sufficient to make the virus spread more easily from one person to another.45,47,49 CDC’s analysis found no changes in the part of the viral genome that mutates to resist antiviral drugs; so, current drug treatments should be effective against this strain of H5N1.45,47,49
As Bird Flu continues to ramp up, many are wondering what tools—namely vaccines—we have to fight it.9 CDC has encouraged people to be vaccinated with a combination of Seasonal Flu, Bird Flu, and COVID-19 vaccines to minimize the chance of genetic crossover between viral strains.6 The US already has an emergency stockpile of more than 20 million units of Bird Flu vaccines that are “well matched to the H5N1 virus”;16,39 it has the capacity to quickly make 100 million units of vaccine if necessary.16 A team of scientists has uncovered how mutations of the H5N1 make jumps from species-to-species possible and open the door to an “uncontrolled epidemic” among mammals.50 The cattle H5N1 viruses rapidly accumulate adaptations that occur at the polymerase-ANP32 interface enhance viral replications in the airway cells of avian, bovine, and human species.50 The findings of that team are consistent with previous research on existing H5N1 CVVs (candidate vaccine viruses) that are already available to manufacturers, and which could be used to make new vaccines if needed.49 The World Organization for Animal Health warns that the seasonal spread of Bird Flu won’t peak until February of 2025…which is worrisome… and has declared that HPAI “demands urgent global attention”.6,11,47
Additional Resources
Eurofins DQCI Now Offers Avian Influenza Test for Dairy Industry
Eurofins US Food Welcomes Dr. Keith Belk to Meat Testing Division
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