H5N1: The Race to Catch Up

SASKIA V. POPESCU, PhD, MPH, MA, CIC;

H5N1: The Race to Catch Up

August 23, 2024

By SASKIA V. POPESCU, PhD, MPH, MA, CIC

Publication

Article

ContagionContagion, Summer 2024 Digital Edition

Volume 09

Issue 02

Transmission to humans is limited in the US, but concerns linger, especially in the wake of the COVID-19 pandemic.

Highly pathogenic avian influenza (HPAI) A (H5N1) is a subtype of the influenza A virus that primarily affects birds. Although H5N1 has been spreading in birds, recent cases in sea lions, sea elephants, and foxes have raised concern as mammalian infections are rare. More recently, an outbreak in dairy cows in the United States has caused disquiet not only due to the rarity of the virus in mammals, but because cases have spread across multiple states. Additionally, investigators have identified 3 human cases.

This new outbreak has led to greater concern regarding the disease and our capacity to respond to and monitor the situation. According to the Centers for Disease Control and Prevention (CDC), as of June 3, 2024, 79 dairy herds have been affected across 9 states.¹ Although human-to-human transmission is rare and infections in humans are sporadic, the CDC has reiterated that job-related or recreational exposure to infected birds and mammals could increase one’s risk. However, the agency has emphasized that the current risk to the general public for H5N1 is low. Ultimately, the issue is that our response to this outbreak has been, for lack of a better word, wobbly.

As Katherine J. Wu, PhD, highlighted, the United States has struggled with both an underreaction and overreaction, noting that “the US is struggling to mount an appropriate response. Because of the coronavirus pandemic, the nation’s alertness to infectious diseases remains high. But both federal action and public attention are focusing on the wrong aspects of avian flu and other pressing infectious dangers, including outbreaks of measles within US borders and epidemics of mosquito-borne pathogens abroad. To be fair, the United States (much like the rest of the world) was not terribly good at gauging such threats before COVID[-19].”²

Better Surveillance, Data Are Crucial

Right now, we need better surveillance and data to understand how H5N1 is transmitted. Many have noted the US Department of Agriculture’s (USDA) slowness in sharing data, which has led to frustration over the lack of information regarding timelines and locations of sample collection. The slow stream of information regarding the dairy cattle cases brings to mind the data collection and analysis issues during the pandemic. Thus, many researchers and scientists have rallied to dig into what is available and try to fill the gaps in terms of viral evolution and how this outbreak started. Extensive collaboration among researchers has generated significant findings, particularly that the reassortment of the North American avian H5N1 2344b viruses occurred before the cattle outbreak, indicating that the outbreak likely occurred from a single introduction into cows, which then spread.³ It is also likely that this outbreak has been circulating among cattle for much longer than researchers realized, and a suggested origin has been a cattle farm in Texas. However, more information is needed, from understanding transmission between cows, including spread and the role of potentially contaminated equipment, to disease severity.

There also have been concerns about the safety of dairy milk. In tests, milk from infected cows showed viral fragments, which are different from live, culturable virus. In response, the US Food and Drug Administration (FDA) emphasized that pasteurization effectively inactivates H5N1 in milk. The FDA performed additional tests with the USDA to study dairy samples, underscoring that “new preliminary results of egg inoculation tests on a second set of 201 quantitative polymerase chain reaction–positive retail dairy samples, including cottage cheese and sour cream, in addition to fluid milk, show that pasteurization is effective in inactivating HPAI. This additional preliminary testing did not detect any live, infectious virus.”⁴ Simply put, pasteurization works, and consuming raw milk is never a good idea.

Contagion, Summer 2024 Edition

Check out the full Summer 2024 book, now in a new interactive digital format, here:

Click to view the issue

As well as the concern about milk, further discussion has taken place regarding the risk to humans and how the disease is transmitted as there have been limited cases historically—roughly 900 H5N1 cases across 23 countries since it was first identified in 2003. Delving into the human case, in a dairy farm worker, has shed additional light on the issue, with researchers noting that “the virus identified
in the worker’s specimen had a change (PB2 E627K) that has been associated with viral adaptation to mammalian hosts and detected previously in humans and other mammals infected with HPAI A(H5N1) viruses and other avian influenza A virus subtypes, including A(H7N9) and A(H9N2).”⁵

Despite the slow start, the USDA has issued a federal order that all lactating dairy cows must test negative for the virus before being moved across state lines. The CDC has also issued helpful guidance on testing for medical providers seeing patients who may be at high risk for exposure to H5N1. The challenge is to increase surveillance, which requires collaboration and coordination across agencies, public health departments, veterinarians, farmers, and so on. One of the biggest hurdles may be ensuring protection for workers, especially migrant workers, who may hesitate to come forward due to fears of deportation or punishment. Social determinants of health are a significant part of our outbreak response, and we saw the implications of ignoring them during the pandemic. Further, this outbreak is novel for the cattle industry, which has not implemented the same incentives as the poultry industry, such as offering financial protection for those who report illness or lose animals to culling. These dynamics can make surveillance and disease reporting challenging.

We need several things to confront this outbreak: more epidemiological data on the transmission of the virus, better interventions, and strategic surveillance. How can we ensure farmers and farms are protected but also encourage the farmers to report illness? Despite our fatigue from COVID-19, this outbreak represents a precarious moment for the US. Now is the time to establish an agile response to emerging infectious diseases while strengthening a robust surveillance network and solidifying public trust through transparency and continued communication.