Friday, July 20, 2018
How animal parasites find a home in humans. There has been a lot of buzz recently about a video shared by Oregon woman Abby Beckley, who describes removing worms from her eye. Researchers at the Centers for Disease Control and Prevention released a case report documenting Beckley’s infection as the first human case of the cattle eyeworm Thelazia gulosa. We certainly feel for Beckley having to go through this ordeal, and without a doubt, felt our skin crawl just thinking about it. But aside from the “creep” factor of this case, it does makes us wonder how a cow parasite ever ended up in a human eye. And it begs the more fundamental question: How are animal parasites able to infect humans? To answer this question, we need to understand more about parasites and their ecology. As a veterinarian and disease ecologist, my research examines what ecological factors influence the emergence of zoonoses — diseases that spread from animals to humans. The case of the cattle eyeworms is certainly intriguing. Transmission of parasites from one host to another can occur through several routes, depending on where the parasite resides in the host and how it is shed, for example through feces, blood or other bodily secretions. Direct contact, consumption of contaminated water or food (Cryptosporidium, Giardia), or via a vector like a tick or mosquito are all possible. Parasitic infections transmitted from animals to humans have occurred naturally throughout history.