What do diseases like Ebola, Influenza, SARS, and Rabies have in common? Well, for one, they’re all viruses. Second, and more germane to this discussion, they’re all zoonoses–diseases that are usually harbored in non-human animal hosts but occasionally spill over into humans. Zoonoses are the subject of David Quammen’s excellent and aptly named new book, Spillover.
Quammen is in peak form with Spillover: he tracks these diseases and the researchers who study them from goat farms in Holland to bat caves in Uganda to wild meat markets on the Chinese mainland near Hong Kong. The book reads like a thriller–where exactly is Ebola lurking?– but doesn’t need fictional plot twists to keep the pages turning. Quammen’s accurate, clear, and exiting descriptions of the epidemiology, ecology, and evolution of zoonotic diseases keeps the pages turning instead.
A central message of Spillover is that a “successful” zoonosis is the result of opportunity. That is to say, the life history of many zoonotic agents does not require a pass through human populations; they will survive, reproduce, and spread just fine in their animal hosts. However, if a zoonotic disease happens to find itself in a human body, those viruses (or bacteria, or protozoans, etc.) that can survive will survive, reproduce, and possibly spread to other people. Thus, the story of zoonoses is the story of humans creating the opportunity for spillover by coming into contact with animal hosts. For example, HIV (human immunodeficiency virus) is closely related to SIV (simian immunodeficiency virus) and all evidence suggests that it spilled into human populations through the use of chimpanzees for food. Nipah, a neurological and respiratory disease in Malaysia, Singapore, and Bangladesh, likely spills over into human populations through contact with fruit bat feces, contact that is becoming more common as human cities, towns, and agricultural fields encroach on the tropical rainforests that the bats call home. In sum, close contact with wild animals greatly increases the chance of spillover.
Close contact with wild animals… Close contact… Hmmm, what is it we do again?…
Oh yeah… Uh oh!
So, if you’ve read this far, you’ve figured out my hook. This whole time, I’ve been wanting to ask, is there anything to worry about with anoles? Do any anoles, any lizards, or just reptiles in general carry any known zoonoses? Well, the short answer is yes, but the short upside is that good hygiene can remove essentially all of the risk of handling reptiles.
Infection with Salmonella bacteria seems to be the most common reptile-to-human disease. It causes no symptoms in reptiles but can cause diarrhea, nausea, vomiting, and abdominal pain in humans. Salmonella is transmitted through the fecal-oral route, so, fortunately, washing hands after handling is a reliable preventative measure.
Other very much more rare reptile zoonoses include Botulism, Campylobacteriosis, Leptospirosis, Trichinellosis, Aeromoniasis, and Zygomycosis. (Contraction of these diseases is also minimized by good hygiene and good reptile care.)
Moreover, the agents on this list, while capable of causing serious illness that should be treated promptly when spillover occurs, appear not to be cause for widespread public health concern. Transmission rates from reptiles to humans (and then humans to humans) are just too low.
One interesting thought is whether anoles or other reptiles can spread diseases to other species (termed epizoonotic diseases). I found one paper that reported that boas and pythons invasive to the US are a reservoir of inclusion body disease, which could pose a threat to native boid snakes and possibly other native snake clades as well. We also know that anoles carry lizard malaria. Could the spread of invasive anoles be taking lizard malaria into regions that haven’t known lizard malaria before, and if yes, what are the effects?
For people who would like to read more about pathogens and parasites that affect anoles, read these descriptions of Brian Falk’s work on the phylogenetics and biogeography of lizard malaria, of sexually transmitted nematodes, and of thorny-headed worms. You could also read as well as one of AA‘s earliest posts on some nasty (or beautiful, as you like it) mouth parasites, or just search ‘parasites’ on AA. Enjoy!