Risk is defined as a combination of the likelihood of the disease and the impact of that disease, should it occur. Impacts can be to animal, human, or environmental health, to businesses, or financial in nature.

When considering risk in relation to PPE selection, we need to think about the likelihood of exposure to a pathogen, and the impact that that pathogen could potentially have on our health, or the health of others via transmission.

In this case, we have a horse displaying neurological signs. Differential aetiological diagnoses for development of acute neurological signs in horses include Hendra virus, Australian Bat Lyssavirus (ABLV) and Japanese Encephalitis virus. Each of these viruses can cause morbidity and mortality in people, so the potential impacts are severe. However, Japanese Encephalitis virus is transmitted via mosquitoes, not directly from horses to humans, so human infection is very unlikely. ABLV is not known to be directly transmissible from horses to humans, but it is known that lyssaviruses are present in the saliva of clinically infected animals and therefore may pose a risk to handlers. This mode of transmission has been well documented for Hendra virus. Therefore, the estimation of risk should rate Hendra virus as greatest risk, then ABLV and then Japanese encephalitis.