New diseases seldom come from nowhere. Instead, they cross over from animals to humans. Unfortunately, once they do, they sometimes literally “go viral” so quickly we struggle to catch up. A paper in Science proposes we start preparing our defenses against most virus species that might one day make the jump.

As a team of authors from five continents note; “Following each outbreak, the public health community bemoans a lack of prescience, but after decades of reacting to each event with little focus on mitigation, we remain only marginally better protected against the next epidemic.” At the moment, we usually prepare for future outbreaks of infectious disease by looking at those viruses or bacteria, such as Ebola, that have already crossed over, and thinking about the circumstances where this could happen again.

The paper's authors want us to think much bigger, cataloging all the viruses we can find in animals, and assessing their capacity to infect humans. They call the idea the Global Virome Project, and argue that with the rate of animal viral diseases infecting humans increasing in line with the expansion of human populations into new areas, the time to act is now.

At first glance, the scale of what is required looks daunting, particularly when other medium-term dangers attract so little funding. Reptile, fish, and even plant viruses exist, but seldom threaten humans. Based on the rate of discovery, the authors estimate around 1.67 million viral species remain to be discovered in mammals and birds, along with the ones we already know about.

Fortunately, not all of these are capable of infecting humans, but the paper estimates a still intimidating 631,000-827,000 are, given the right circumstances.

How much would it cost to assess all of the unknown viruses, and work out which pose dangers? The authors estimate the cost at $7 billion, based on past attempts to test for viruses. Even then a few would slip through our nets – after all, we still discover new species of mammals now and then.

Getting this sort of money when America's Centers for Disease Control and Prevention – the largest potential funder – is being cut to the bone is almost certainly unrealistic. On the other hand, the authors point out that most of the cost lies in finding the more obscure viruses, which are also, by virtue of their rarity, less threatening.

For $1.2 billion, spread over 10 years, more than 70 percent of the unknown avian and mammalian viruses could be, in the authors' words; “Discovered, characterized, and assessed for viral ecology.” Considering the 2003 SARS outbreak was estimated to cost $10-30 billion (and many lives), a cost which might have been slashed if we'd know of the virus beforehand, this could be money very well spent.