麻豆传媒

Top brass at the CDC, the National Institutes of Health (NIH), and other agencies shared a roadmap for preventing and understanding human infection with bird flu, along with their plan for developing countermeasures against the virus that has infected more than 120 dairy herds across a dozen states.

Looking for Asymptomatic Infection

To date, more than 690 people have been monitored following exposure to the virus and 51 people have been tested. Through established testing mechanisms, only three people have been diagnosed with the highly pathogenic avian influenza A (HPAI) H5N1 virus associated with the outbreak in dairy cattle (one person in Texas and two in Michigan), said Demetre Daskalakis, MD, MPH, director of CDC's National Center for Immunization and Respiratory Diseases, during a call with reporters on Tuesday.

CDC continues to support states in monitoring for H5N1 in humans, including by providing technical assistance for a seroprevalence study conducted by Michigan's Department of Health and Human Services, the goal of which is to determine whether asymptomatic infections have occurred among people working with infected cattle.

The agency also announced for H5N1:

• Prevent infection and illness in people exposed to H5N1: study the risk of infection in humans and how to minimize it (personal protective equipment, etc.); identify indicators for severe illness; and assess the effectiveness of antivirals and vaccines, should they be used.
• Understand human infection and H5N1 illness (clinical, virologic, and epidemiologic characteristics): examine the primary modes of transmission; describe incubation times, durations of infection, and severity; use animal models to explore clinical presentations, virulence, and transmissibility; identify genetic markers of severity and track genetic changes in the virus during infection.
• Prepare for and estimate the pandemic potential of H5N1: estimate pandemic potential with the ; monitor evolutionary traits of the virus; identify candidate vaccines; evaluate antivirals; and design diagnostic tests to rapidly and accurately identify infections.

Daskalakis noted that across multiple data streams, including emergency department data on flu symptoms, wastewater surveillance, and laboratory test results, the CDC has found "no indicators of any unusual flu activity in people, including any activity related to H5N1."

Understanding the Biology of H5N1

The will focus primarily on the biology of the virus, disease pathogenesis, and transmission, according to its website.

An animal model will be used to understand how flu viruses multiply, how clinical signs of illness manifest, and potential routes of transmission, Tara Palmore, MD, an infectious diseases physician and healthcare epidemiologist for the NIH, said during the call. NIH will also research whether infected unpasteurized milk is a viable method of transmission.

Other studies will look to characterize the immune response to infection with H5N1 in cattle and animal models and examine how the immune response may impact pathology. The NIH is also testing vaccines and vaccine candidates in clinical trials against the H5N1 from the current outbreak to determine what level of protection they provide, Palmore said.

NIH is also continuing to prioritize work to develop a universal flu vaccine that could protect against several subtypes of influenza, including H5N1, and Palmore noted that "several promising candidates" are currently in early-stage clinical trials.

Separately, HHS' Biomedical Advanced Research and Development Authority (BARDA) is working to advance the development and regulatory licensure for vaccines, diagnostics, and therapeutics -- as detailed in its own -- to prevent, detect, and treat pandemic influenza infection.

"We continually develop and test vaccine candidates to sustain the U.S. vaccine action capacity to produce pandemic influenza vaccine, if needed," explained Robert Johnson, PhD, BARDA's director of the Medical Countermeasures Program.

Expanding Product Testing

Don Prater, DVM, acting director of the Center for Food Safety and Applied Nutrition for the FDA, announced a at retail locations nationally, to address what he called "remaining geographic and product gaps" from the previous sampling of the milk supply conducted in April and May.

This second sampling survey will test approximately 155 products such as aged raw milk cheese, pasteurized milk and cheeses, cream cheese, butter, and ice cream. Additional samples will be taken from areas in previous surveys to provide "a more representative picture" based on levels of dairy production in certain regions, he noted.

The FDA is also continuing to conduct studies using continuous flow pasteurization equipment that it believes mirrors those used commercially, with the goal of "validat[ing] the evidence of the effectiveness of pasteurization in ensuring that no viable HPAI H5N1 virus is present in the commercial milk supply," Prater said.

The FDA continues to warn the public against consuming raw milk and urged industry not to manufacture or sell raw milk or raw milk products. He stressed, "to date, the findings from U.S. government partners, as well as academic researchers, do not change our assessment of the safety of the milk supply."

Increasing Testing in Cattle

Finally, the U.S. Department of Agriculture (USDA), in late May, launched a which would enable dairy producers to more closely monitor their herd's health and move cows more quickly, while providing continued testing capacity and improving USDA's understanding of the virus, said Eric Deeble, DVM, acting senior advisor for H5N1 response, and Rosemary Sifford, USDA's chief veterinary officer.

The first four states to participate in the program include Texas, Nebraska, New Mexico, and Kansas, and the USDA is in "close conversation" with a dozen more possible participant states, Deeble said. The agency also expects to receive an update regarding funding in the "very near future" that would be used to compensate producers for a loss of milk production that has resulted from H5N1. Once that funding is available, Deeble said he expects "a surge" in producers participating in a range of USDA programs.

Asked whether USDA planned to start vaccinating cattle, Deeble said "we hope that through enhanced biosecurity and additional testing ... we will be able to eliminate this disease from the dairy herd in the absence of a vaccine. Although, we believe that they may be helpful down the line."

"We want to learn as much as we can about the spread of H5N1 in dairy cattle, detect the virus, [and] contain the virus where it is to prevent further spread," added Deeble.

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