Researchers worry that insufficient collection and reporting of data are hampering efforts to assess the scale of the bird-flu outbreak in US cattle — and could hold back efforts to bring the virus under control.
“We are not doing enough,” says Isabella Eckerle, head of the Geneva Centre for Emerging Viral Diseases in Switzerland. For now, the strain of the influenza virus is a long way from being able to transmit easily to and between humans. “But the moment it does, it will be an emergency.”
For now, the viral strain infecting cows, called H5N1, still prefers to bind to the receptor it uses to infect birds. This receptor is not common in the upper airways of people, says Thomas Peacock, a virologist at Imperial College London. But the virus has acquired some changes that make it better at making copies of its genome in mammals, “which is the first step of the pandemic stairs”, says Peacock. Adapting to receptors prevalent in humans is “several steps further up”.
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Scientists are eager to deploy a host of tools to monitor the pathogen’s evolution. But for these tools to be useful, Eckerle says, “you need to have the data about where the infections are happening right now” — and those data have not been forthcoming.
“Actually changing government policy based on guesses rather than information that we could get, but are not getting, is the real problem,” says Angela Rasmussen, a virologist at the University of Saskatchewan in Saskatoon, Canada.
Data deficit
Gaps in the data have been apparent since US officials first announced the outbreak in March. An analysis of viral genomes found that H5N1 probably jumped from an infected wild bird to a cow, perhaps as early as November. The virus has been circulating in cattle ever since. The delay in identifying the outbreak suggests that surveillance programmes are not robust, says Jonathan Pekar, an evolutionary biologist at the University of California, San Diego. “The infrastructure we have in place is insufficient to prevent future pandemics,” he says.
Shilo Weir, a public-affairs specialist at the US Department of Agriculture (USDA), disagrees with that assessment. “This event highlights the success of our animal health network,” Weir says. It “shows that our surveillance program is incredibly effective at early identification of emerging disease trends.”
Researchers say that surveillance has continued to falter. The USDA did not release the first viral sequences until weeks after the outbreak was announced. For many of these sequences, the agency has still not released crucial details about when, where and from which species each was collected — information that could offer insight into how the virus is moving between herds, as well as how it is evolving, say researchers. “There’s not a huge amount of information coming through, or it’s coming through very slowly,” says Peacock. “From a pandemic-potential perspective, to try and understand how bad this is and what’s going on, it’s frustrating.”
Weir says that to expedite public access, sequence data are initially shared with general ‘USA’ and ‘2024’ tags, but polished sequences with more detailed information will be uploaded on the the widely used repository GISAID.
Researchers also say that information about what percentage of all sampled animals the sequences represent hasn’t been made available. “We don’t know the full extent of testing,” says Rasmussen. That means that researchers can’t assess whether the outbreak is growing, has peaked or is experiencing a downturn, says Peacock.
Weir says that national laboratories have conducted more than 7,500 tests since the start of the outbreak. But that number does not reflect exactly how many animals have been tested because some animals might have been sampled multiple times, or swabs from multiple animals could have been pooled into one test, says Weir.
On 24 April, the USDA mandated testing of lactating dairy cows prior to their movement between states, and reporting of positive influenza A test results in livestock. The USDA expects this federal order to improve the understanding of the virus’s distribution and reduce the risk of its further spread, says Weir.
Testing shortfall
Researchers also say more sampling is needed. Almost 50 herds of dairy cattle across 9 US states have had confirmed cases of H5N1, and one infected person has been linked to the outbreak. But the actual numbers are probably much higher, scientists say. “There’s almost certainly been a lot more human cases than just the one,” says Peacock.
Cattle and people working on farms should be tested not just for the presence of viral RNA — which indicates an active infection — but also for antibodies against H5N1, which circulate in the body for longer after an infection. “This is something that should be done immediately,” says Eckerle. Antibody studies could help scientists to determine how many people and cattle have been exposed to the virus and had infections that went unnoticed, possibly because they did not show symptoms or were not tested.
Weir says that the USDA plans to adapt a commercially available antibody test for birds for use in cattle serum and milk.
The sampling of faeces and organs from infected animals would help to identify where in the body the virus is replicating, how it is being excreted and how it is spreading between animals. If the virus is spreading through contact with contaminated milk, that would be relatively straightforward to control, says Eckerle. But transmission through respiratory secretions would be more difficult to control and would make farm work more risky.
Weir says the USDA is continuing to collect epidemiological data, and to study disease pathology and transmission to better understand the virus in cattle.
Incentivizing farmers
Some of the data that researchers are calling for could already have been collected but not publicly shared, says Meghan Davis, an environmental and veterinary epidemiologist at the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland. This lack of transparency “undermines the speed and other capacities for the response”, she says.
One barrier to testing has been the lack of incentives for farmers to step forward if they suspect the virus has infected their animals, say researchers.
On 10 May, the USDA announced a plan to compensate farmers affected by H5N1 outbreaks, and those who cooperate in studies, which could see testing ramp up. Davis says these measures should have been introduced weeks ago, especially in an industry in which there are some 25,000 farms making individual decisions. Farm workers should also receive sufficient protection, so that if they fall ill they are comfortable disclosing it, says Pekar.
Information about how and where the virus has spread is important for informing the response. If the outbreak is not widespread and is moving slowly, public-health officials could decide to cull affected herds and eradicate the virus in cattle, says Eckerle. But if it is too widespread or fast-moving, they might have to resign themselves to a new reality in which cattle are a reservoir of H5N1, and focus on restricting its jump to people. “I would not say it’s too late” to decide between these two pathways, says Eckerle — but “we need data.”
This article is reproduced with permission and was first published on May 17, 2024.