Tracking outbreaks before they happen

New diseases sometimes evolve from existing human illnesses, but most of the time they come from a disease that already existed in animals. When they make the jump to humans, these viruses can cause major epidemics. A new paper hopes to help predict where these outbreaks might happen, and what animals they might come from.

"Think of the model as a road map that shows where we should put funding and do surveillance," Kevin Olival, a disease ecologist at EcoHealth Alliance and an author of the study, tells Axios.

Why it matters: Zoonotic diseases, which come from animals and include Ebola, Zika, HIV, SARS and many types of flu, sicken millions of people every year.

Knowns and unknowns:

• Not every virus will jump to humans, but there are factors that can make it more likely (e.g. we're more likely to get diseases from animals we share genes with, like primates).
• We can't get diseases we don't come in contact with, so living in close proximity with the animals is a factor (think rats and birds).
• Scientists have surveyed some animal groups more than others, so there are very likely to be unknown viruses hiding.

What they did:

• The researchers created a database over 2,800 viruses associated with animals, and used it to analyze what made them most likely to infect humans.
• They used their models to estimate how many zoonotic viruses each type of animal might have, if scientists studied them thoroughly.The researchers then subtracted already-identified viruses and created a heat map that shows where undiscovered epidemics might be lurking.

What they found: Bats are more likely than any other animal to carry diseases that can infect humans, but no one seems to know why. The researchers also flagged geographic hotspots where disease might take off. According to the model, a large number of bat-carried diseases are lurking in northern South America. A smaller number of diseases from hoofed animals might be hidden in East Africa, while undiscovered primate-borne diseases cluster globally around the tropics.

This doesn't mean that we should cull all bats. "It's human ecological change that drives diseases to emerge," says Olival -- whether that's humans encroaching on the habitats of disease-carrying animals or humans changing their behavior. From there, he thinks we should examine the animals and environments to better understand what human actions might cause those diseases to make the jump.

What's next? Olival says the US Agency for International Development is already using this model to help target disease surveillance. Scientists on the joint USAID/CDC project, called PREDICT, catch animals across the world and test their blood for possible pathogens. They've already found new viruses to keep an eye on, says Olival, and it's also giving them a chance to test the model and see if diseases appear where the model thinks they will.