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Study Reveals Cows Possess Human Flu Receptors, Heightening Concerns Over Bird Flu Outbreak

Study Reveals Cows Possess Human Flu Receptors, Heightening Concerns Over Bird Flu Outbreak | Credits: Getty Images

United States: During the recent days, the majority of the cows of the dairies of the United States have been showing weird symptoms, and many are also losing their lives after getting infected with the H5N1 influenza virus. According to health experts, the dairy industry in the US has been rocked, alarming health officials around the world. 

Reportedly, an urgent scientific agenda was promptly established, prompting an inquiry into the origin of the cow infection.

Undertaking this endeavor were researchers from the United States and Denmark. Their revelations, disseminated as a preliminary study, unveil the similarity in flu virus receptors between cows, humans, and birds, according to CNN Health. 

Concerns arise as cows potentially serve as reservoirs, facilitating the adaptation of the virus for improved human-to-human transmission. Although rare, such an occurrence could set the stage for a new pandemic.

Avian flu explores novel hosts

Traditionally confined to avian populations, highly pathogenic avian influenza, or H5N1, has begun infiltrating various mammals, hinting at its evolution into a human pathogen.

Commercial poultry stocks in the United States have suffered severe losses due to avian flu outbreaks. While pigs are susceptible to avian flu, cows were not previously considered probable hosts.

Since late March, the US Department of Agriculture has identified 42 infected herds across nine states. While only one individual contracted H5N1 from exposure to infected cows, the US Centers for Disease Control and Prevention assures a low risk to public health, though vigilance remains paramount.

“The findings regarding cattle are unprecedented,” remarked Dr. Lars Larsen, a veterinary clinical microbiology professor at the University of Copenhagen. Unlike in mammals, where influenza primarily affects the lungs, infected cows exhibit substantial viral presence in mammary tissue and milk.

Larsen and his team determined that H5N1 concentrations in infected cow milk exceed those found in avian hosts by a factor of 1,000. Even when diluted in 1,000 tons of milk, traces of the virus remain detectable in laboratory analyses.

Testing by the US Food and Drug Administration detected viral genetic material fragments in 20% of retail milk samples, prompting inquiries into the widespread dissemination of the virus. Subsequent investigations confirmed the absence of infectious virus in pasteurized milk, as outlined by CNN Health. 

Nevertheless, the outbreak has sparked apprehension within the agricultural sector, given the substantial economic stakes associated with bovine health. In 2022, milk and dairy products ranked fourth among US agricultural commodities by revenue, while cattle and calves sales stood second.

Viral cell entry mechanisms

Viruses require cellular entry points for infection. For COVID-19, the key is the ACE2 receptor, while for influenza, it’s sialic acid, a sugar molecule protruding from cell surfaces.

Sialic acid receptors vary across species. Avian receptors differ slightly from human upper respiratory tract receptors, influencing flu virus binding preferences.

Dr. Andy Pekosz, a molecular microbiologist at Johns Hopkins University, compares bird and human sialic acid receptors to straight and bent index fingers, respectively. Flu viruses exhibit a preference for one shape over the other.

Visual Representation | Credits: Getty Images

The sialic acid receptor profile of cows was previously unknown, as they were not believed to contract A-strain flu viruses like H5N1.

Researchers from the US and Denmark examined tissue samples from calves and cows, revealing abundant sialic acid receptors in mammary glands. Surprisingly, these receptors mirrored both avian and human variants. Lead author Dr Charlotte Kristensen notes the presence of both receptor types in nearly every cell observed, as reported by CNN. 

This discovery raises concerns about viral reassortment, a process wherein flu viruses exchange genetic material within co-infected cells. Dr Richard Webby, a study author, underscores the potential for hybrid viruses to emerge in dual-infected cells.

While the likelihood of such events remains low, the simultaneous infection of cows with avian and human flu strains presents a theoretical risk. Current low human flu infection rates mitigate this risk, though historical precedents caution against complacency.

Pigs also harbor both human and avian sialic acid receptors, with past flu infections leading to pandemic strains. The 2009 H1N1 pandemic, believed to originate in Mexican pigs, exemplifies such occurrences.

Webby suggested gradual viral adaptations as another avenue for change. Viral replication errors can yield mutations that enhance infectivity, broadening the virus’s host range.

Viral evolution

Reassortment represents a significant evolutionary leap for viruses, but gradual adaptations through drift are equally consequential.

Visual Representation | Credits: AP Photo

Dr. Sam Scarpino, a computational biologist at Northeastern University, notes the elevated risk inferred by recent findings. While preliminary, the study underscored the need for vigilance in dairy cattle transmission prevention, the reports by CNN unveiled. 

Though further research is warranted, the study’s urgency is evident. As Scarpino emphasizes, bolstered protective measures and increased research funding are imperative in combating potential influenza outbreaks among cattle.

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