overview
- This year, the bird flu outbreak has led to several alarming developments, with at least 64 human infections.
- Experts outlined several indicators that the spread of the virus is moving in the wrong direction.
- These include the recent detection of the virus in wastewater and signs of dangerous mutations.
The lingering threat of bird flu appears to be escalating.
This year has witnessed a series of troubling events related to the virus spread. Since April, at least 64 individuals have tested positive for the virus, marking the first U.S. case in 2022 apart from one. Dairy herds in 16 states were affected this year. The Centers for Disease Control and Prevention confirmed the nation’s first severe case of avian influenza in a critically ill patient in Louisiana. California Governor Gavin Newsom declared a state of emergency this week due to the growing outbreak in cattle and poultry.
“The warning signs are transitioning from green to yellow,” stated Dr. Peter Chin-Hong, a professor of medicine at the University of California, San Francisco specializing in infectious diseases. “Numerous indications are pointing in an unfavorable direction.”
While no human-to-human transmission of avian influenza has been recorded, the CDC asserts that the immediate public health risk remains low. However, concerns are escalating based on four key indicators.
For instance, the avian influenza virus known as H5N1 is rapidly spreading among animals, including cattle, that frequently interact with humans. Moreover, detections in wastewater suggest that the virus has not only impacted livestock but also various other areas.
Additionally, there are instances of human cases where the source of infection is unidentified, along with studies on the virus’s evolution indicating that it has adapted to human receptors required for inter-human transmission. Fewer mutations have been observed.
Experts warn that when considering these indicators together, the virus is on track to potentially become the next pandemic.
“We are currently in a very precarious situation,” remarked Scott Hensley, a microbiology professor at the University of Pennsylvania.
Extensive circulation creates new pathways to humans
Since the onset of the avian influenza outbreak in 2022, the virus has spread to wild birds, domestic poultry, and wild mammals like sea lions, foxes, and black bears. Over 125 million poultry have perished from infectious diseases or been culled in the United States, as per the U.S. Department of Agriculture.
In March, an unexpected occurrence unfolded when dairy cows fell ill, experienced reduced feed intake, and produced discolored milk.
Research indicates that the virus likely spread swiftly and effectively among cows through raw milk, as infected cows excreted significant virus amounts from their mammary glands. Raccoons and domestic cats are also susceptible if they consume raw milk.
The more animals infected, the higher the risk of transmission to humans who come in contact with them.
“The more individuals infected, the higher the likelihood of variant emergence,” mentioned Jennifer Nuzzo, an epidemiology professor and head of the Pandemic Center at Brown University’s School of Public Health. “I don’t want to give the virus the opportunity to trigger a pandemic.”
Prior to this year, influenza prevention efforts did not focus on cows.
“We hadn’t considered dairy cows to be influenza hosts, at least not significant ones,” mentioned Andrew Bowman, a veterinary preventive medicine professor at Ohio State University in an interview with NBC News this past summer.
However, the virus has been detected in at least 865 herds in 16 states and in raw (unpasteurized) milk sold in California. For domestic cats that consume raw milk.
“Currently, raw milk and related products pose a direct risk to communities and consumers,” stated Chin-Hong. “A year ago, or even just months ago, the risk was significantly lower.”
Cases with unknown exposure sources
Most human H5N1 infections occur among poultry and dairy farm workers. However, in some mysterious instances, the source of infection remains unidentified.
One such case was reported in Hospital in Missouri in August, with subsequent recovery. Another instance involved children in California who tested positive in November.
Furthermore, Delaware health authorities reported a case of H5N1 infection this week in an individual with no known exposure to poultry or cattle. Although CDC testing did not confirm avian influenza as the virus, the case is considered “probable.”
In British Columbia, Canada, a teenager was hospitalized in early November after contracting H5N1 despite no apparent contact with farm animals or wildlife. The genetic makeup of the virus suggested similarity to strains found in waterfowl and poultry.
Such unexplained cases are causing concern among experts.
“This implies that the virus has a wider reach, and more individuals may have encountered it than previously thought,” mentioned Nuzzo.
Increased concentration of avian influenza in wastewater
Scientists are actively monitoring wastewater for virus fragments to better comprehend the geographical spread of the avian influenza epidemic.
Amy Lockwood, CDC’s director of public health partnerships and Verily, a company offering CDC wastewater testing services, stated that in recent months, “detections are increasing in frequency across a broader geographic spectrum.” A program known as Wastewater SCAN is in place.
Earlier in the month, approximately 19% of facilities monitored within the CDC’s National Wastewater Surveillance System across at least 10 states reported positive detections.
It is uncertain whether the detected virus fragments originated from animals or humans. For instance, some may stem from wild bird droppings entering storm drains.
“At this stage, we do not believe these signify human-to-human transmission, but there are numerous H5 viruses present,” revealed Peggy, CDC’s Director of Infectious Disease Control and Innovation.
Lockwood and Peggy mentioned that wastewater detections are concentrated near dairy processing facilities and poultry farms. However, puzzling hotspots have emerged in regions devoid of such agricultural operations in recent months.
“We are observing infections in areas where we do not automatically identify the source,” Lockwood noted, adding, “It’s a game of large numbers.”
Another mutation?
Until recently, virologists believed that multiple mutations were necessary for H5N1 to transition easily among humans.
However, a study published in Science magazine this month revealed that a cattle-circulating strain of the virus could bind to human receptors following a single mutation (Note: The study focuses solely on viral proteins, not the entire infectious virus).
“We are not implying that a pandemic is more imminent due to this finding. We simply want to highlight that the risk has elevated as a result,” explained Jim Paulson, co-author of the study and the director of molecular medicine at Scripps Research.
Separately, scientists have detected concerning elements in another virus variant found in a Canadian teen who fell severely ill in recent months. Virus samples indicated mutations that could enhance human-to-human transmissibility.
A CDC spokesperson stated that these mutations were unlikely present in the virus when the boy was infected.
“These mixed changes in the virus probably occurred following prolonged infection in the patient,” the spokesperson explained.
The strain of the virus in the first severe bird flu case in the U.S., announced on Wednesday, matched the one that infected the Canadian teenager.
Dr. Demetre Daskalakis, head of the National Center for Immunization and Respiratory Diseases, revealed that the CDC is analyzing patient samples to identify potential concerning variants.
Meanwhile, Hensley expressed concerns that the flu season could expedite virus evolution. If an individual is co-infected with seasonal influenza and avian influenza, genetic code segments can be exchanged between the two.
“Mutations are unnecessary; it’s simply a genetic code exchange,” Hensley asserted, emphasizing the importance of farmworkers receiving flu shots to reduce such opportunities.
Upcoming trials and vaccines
Experts highlighted various measures that can be taken to track bird flu spread more effectively and prepare for a possible pandemic, some of which are already in progress.
The USDA extended mass milk testing to a total of 13 states on Tuesday, accounting for approximately 50% of the national supply.
Nuzzo emphasized that efforts need to be intensified swiftly.
“We have delayed comprehensive bulk milk testing for too long, as it is a common method for detecting outbreaks on farms,” she stated.
Simultaneously, Andrew Trister, Verily’s chief medical and scientific officer, mentioned that the company is enhancing wastewater analysis to identify concerning mutations.
USDA additionally approved field trials to administer H5N1 vaccine to cattle. Hensley’s lab conducted tests on a new mRNA vaccine in calves.
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