The presence of H5N1 avian influenza virus, better known as bird flu, among dairy cows in Texas — the second largest producer of dairy cattle — was first confirmed in late March. By then, H5N1 had likely been circulating among dairy cows for months. Six weeks later, the nine states responsible for more than one-quarter of U.S. dairy production, which accounts for 3.5% of the U.S.’s gross domestic product, had each reported H5N1 cases in dairy cows and continue to do so.
Many questions remain open about the transmission of H5N1 among dairy cows and about the possibility of the virus adapting to transmit among humans. Even with the best possible outcomes, this outbreak reveals the precipice on which the U.S. rests with respect to livestock diseases.
In the event of an infectious disease outbreak in livestock, even one that does not directly threaten human health, the costs can be catastrophic. The production of animal products (milk, other dairy products, eggs, and meat) can decrease drastically. Other costs can come from the control efforts or trade bans and loss of consumer demand. Twenty years ago, a single case of “mad cow disease” caused U.S. beef exports to plummet by more than $2.5 billion, and domestic prices fell by 16%.
News of the spread of avian influenza among U.S. dairy cows in late April led cattle futures to fall sharply at the Chicago Mercantile Exchange (the largest U.S. exchange for cattle futures). And Colombia, which buys $43 million in beef annually from the U.S., has restricted beef imports, even though no evidence has yet been found of the virus in beef cattle.
Managing diseases in livestock in a country the size of the U.S. is a huge challenge due to the frequent and extensive movement of animals across the nation. That means local animal disease problems quickly become national. In the ongoing H5N1 outbreak, cattle were moved from a farm in Texas, where infected animals had been detected in March, to farms in Ohio and Michigan that tested positive in early April for a very similar strain of the virus. This suggests that direct cattle-to-cattle transmission is occurring, and implicates animal movements in the large-scale diffusion of the virus.
National-scale movement of farm animals as they transition through the production cycle is a key component of this highly specialized industry and is unlikely to change. In the U.S., beef cattle might be born in one place, raised and fattened in another, then killed and butchered in another. The U.S. livestock industry is geographically dispersed and intensely connected: 60% of cattle born in a year cross state borders, with particular concentrations in the Plains states. This has been brought about by regional differences in livestock productivity and by economies of scale, which make it more cost-effective to ship live animals than shipping animal feed.
The U.S. has one of the most intense livestock industries in the world, primarily due to the aggregation of production over the last 50 years and the presence of large markets and mega-scale animal feedlots that are unique to the U.S. When animal movements are disseminating infection, there is a particularly high risk of infection reaching premises with lots of traffic.
Livestock markets act much as airports do for humans: they bring together animals (sometimes of multiple species) coming from many different farms, creating opportunities for contact between infected and susceptible animals before being sold and dispersed to other far-flung farms. Feedlots, facilities at which animals are fattened before slaughter or before being returned to the same or different dairy farms for stronger milk production, can also act as hubs for propagating infection.
In response to the evolving H5N1 outbreak, the USDA has placed additional influenza-testing requirements on interstate movements of dairy cows. However, the limited information available about livestock movement indicates that the movements of most cattle (dairy or beef) from or to markets occur within states. While the USDA strategy is essential in limiting the geographical diffusion of H5N1, the disease could be moving long distances within states without detection.
Given the integral role that livestock movement currently plays in U.S. agriculture, and the potential for animal movements to create pathways for the spread of pathogens, understanding the volume and structure of livestock movements across the U.S. is crucial to the success of the nation’s infectious disease management efforts. Unfortunately, livestock movements in the U.S. are only partially characterized and, in many states, only when animals cross state lines. But this information comes from veterinary inspection certificates that lack a uniform format. While this approach to tracking the movements of livestock animals aids the response to diseases, it lacks the speed and resolution required for most outbreaks, and it will not move forward the country’s preparedness in anticipation of the next livestock disease emergency.
What is needed instead is a national view of the U.S. livestock industry that incorporates the vast degree of livestock movement that occurs within the industry. This would ideally be powered by a real-time animal identification and tracking system, where the movements of individual animals are prospectively recorded from birth to slaughter as they change ownership and location. Such “animal passport systems” exist throughout the European Union and the U.K.
In the U.S., a national animal identification and tracking system has been controversial due to concerns of infringement of property and private rights of individuals, the potential cost, and the exposure of business strategies crucial to market competitiveness. But states such as Michigan and Minnesota, motivated by the threat of bovine tuberculosis, and Montana and Wyoming, plagued by chronic outbreaks of brucellosis, have implemented cattle identification and tracking systems, setting examples for a successful national system. While the establishment of these state-level animal identification programs faced some opposition from producers, the keys to their successes have included a cost-effective system, the mandatory nature of the program, and clear communication and education about the benefits of animal identification for both disease management and production management.
The use of animal tracking data in veterinary epidemiology and mathematical models would be crucial to U.S. preparedness and response to the inevitable future outbreak of an emerging livestock disease. In addition to improving animal health management, animal identification and tracking would also retain and increase export market access (currently out of reach due to unmet animal-tracking regulations), food safety assurances, and producer profitability by improved production efficiency and increased access to information.
Information provided by animal identification and tracking would make it possible to estimate the scope of a potential outbreak and plan outbreak mitigation and control strategies. Driven by data on animal demographics and movement as well as disease-specific parameters, epidemiological modeling studies could help target and hone these plans to allow maximum business continuity and minimum use of resources.
The benefits of collecting animal-movement data in real-time include evaluating the potential of an epidemic to spread, designing optimal surveillance programs and control strategies, accurate quantification of ongoing disease threats, and short- and long-term analysis of policies that may affect agricultural business practices. Each of these can help minimize the risk of the next livestock disease emergency, avoiding colossal economic and food losses, ameliorating animal welfare impacts, and mitigating the potential emergence of highly virulent strains with pandemic potential into human populations.
Shweta Bansal is a professor of biology at Georgetown University whose research focuses on how population connectivity drives the transmission and diffusion of infectious diseases in human and animal populations. Colleen Webb is a professor of biology and mathematics at Colorado State University and serves as vice provost for graduate affairs and dean. Her research focuses on data-driven modeling of disease and evaluation of preparedness and control strategies in livestock diseases.