Human-Animal Disease Transmission
Firs off, some vocabulary – a disease that can pass between humans and animals is called a Zoonotic disease. We actually touched on these briefly in class, when the professor mentioned that networks through which diseases spread might have nodes that aren’t just people, but also animals. Studying this area is actually a very important area in the field of epidemiology because of how much it effects our ordinary understanding of how diseases spread.
One of the most important ways in which Zoonotic diseases complicate our model is how diseases can mutate. Suppose, for example, that a disease might be successful with certain mutations in humans, but then jump to animals and start mutating again. This could remove people from the epidemic for a while, but after a while we could face a form of the disease that we don’t yet have an immunity for because it changed so much while jumping to another cluster in the network. In this way, Zoonotic diseases can be considered an SIRS (Susceptible, Infectious, Removed, Susceptible) model. This is why they can be so dangerous (recall the various epidemics of avian influenza and swine flu that we’ve seen over the last several years). No one really gets a lifetime immunity – there’s always a decent chance that the disease could come back around the network. More over, the network is far more interconnected because not just talking or accidental contact with someone. Pets, wild animals, even food can serve as an edges on which the disease can travel. In fact, according to this page, “more than 6 out of every 10 infectious diseases are spread to humans from animals.” This just goes to show how hard Zoonotic diseases can be to contain and reduce their R0 factor to low enough to stop from them from continually spreading.
Essentially, this means that controlling the k portion of R0 is particularly difficult for Zoonotic diseases. After all, even contact with common mosquitoes is a chance to transmit for many diseases (whether from the mosquito to human or vice versa). Fortunately, as the previously linked CDC page notes, there’s quite a bit we can do for basically no cost to limit this k factor at least somewhat. Important as always is proper hygiene and food handling techniques (the latter is particularly relevant when dealing with diseases that might come straight from the food, rather than from people handling the food). In addition to handling food well, eating only appropriately prepared food is also important – for instance, avoiding under-cooked meat and unpasteurized milk. Even simple steps like this can help us prevent the treat of causing epidemics the range between both human and animal populations.
(Full link for CDC source: http://www.cdc.gov/onehealth/zoonotic-diseases.html)