Researchers who study diseases transmitted from wild animals to livestock tend to focus on a small number pathogens, most of which infect humans, a study published today in Proceedings of the National Academy of Sciences shows. Favoring the study of pathogens that directly impact humans has an obvious immediate benefit, but research on other pathogens — those that don't infect humans yet — could minimize, or even eliminate, the risk of human infection before it occurs.

In the study, researchers conducted a review of research on infectious diseases that are shared between wild animals and livestock, dating back to 1912. Thanks to an automated search and indexing approach, the researchers were able to classify 15,998 studies by disease, animal, and geography.

The analysis showed that out of 113 diseases studied, a total of 10 diseases — diseases like rabies and salmonellosis — received half of the research attention. "These 10 diseases, almost all of which can be spread from animals to people, have dominated the research agenda since the 1960s," says Siobhan Mor, an epidemiologist at the University of Sydney and a co-author of the study.

The study also showed that researchers tend to focus on certain main livestock and wildlife groups, like cattle, whereas less popular animals — bats and pigs, for instance — don't get as much attention. This might mean that diseases that involve cows are more important when it comes to transmission, but it could also indicate that scientists and the people who fund them have favorites, not to mention a limited understanding of diseases that impact less popular species.

Unsurprisingly, diseases that can be transmitted to humans are more popular study subjects than ones that can't. Given that many diseases don't start out as human diseases, this indicates that scientists probably have to play catch-up whenever a new disease starts to infect humans. "Take MERS for example: we now know that the virus was circulating in camels decades ago but that discovery only came to light when researchers started to investigate a human health problem in the Middle East," Mor says. "That’s a pattern we’re seeing time and time again; a new disease appears in humans, and livestock or wildlife are implicated after the fact."

Finally, the study hints that intense media coverage of a given disease or wildlife-livestock interaction leads to better funding. This trend could mean that funding is "driven by the perceptions of disease, rather than by the actual costs or consequence," says Christan Gortazar, an epidemiologist at the University of Castilla, in Spain, who didn't work on the study.

The world has seen 186 confirmed cases of MERS — a disease that infected camels way before it infected humans — since May 20th. Of those, 36 cases resulted in death. And 842 people have been diagnosed with the H5N1 avian influenza virus since 2003, half of whom died. As a result, researchers have spent a tremendous amount of time trying to find interventions that can stop these diseases, or minimize their effects. Still, few studies have looked at the global patterns that these types of diseases create when polled together. That's why this study matters; it's a window into the diseases and animals that get research attention and funding — and those that don't.

"Many new diseases in humans — such as MERS, SARS, and H5N1 influenza — have their origins at this interface, a trend which scientists say is increasing," Mor says. Yet "we have a tendency to prioritize human health and only regard animal health as important if and when it impacts on humans." If wildlife and livestock sectors had the resources to investigate and manage animal health issues before they became an issue for humans, they might be able to reduce the spread of diseases in animals, which would help minimize their economic impact — not the mention the likelihood of human infection.