Some of the world’s most notorious infections — including Lyme disease, rabies and Ebola — come from zoonotic diseases. These illnesses are caused by pathogens (bacteria, viruses or other parasitic organisms), which can be passed from animals to humans.

But, even though they can lead to serious health problems, there is a gap in our knowledge when it comes to these diseases.

We don’t yet fully understand how pathogens “shift” between different host species and cause epidemics — and research is starting to show that the changing environment could be a factor.

The number of animal species that a pathogen infects is an indicator of its capability to shift to other host species and infect them, too.