Novel parasitic infections
“The reality is that 30 new infections appeared in the last 30 years, and three-quarters of them are zoonotic, animal infections spilling over into the human world,” Dr. Senanayake said.
Though some of that number is the result of improved surveillance and diagnostics, a real increase has been occurring as human settlements continue expanding.
“This is just a reflection of how burgeoning human populations are encroaching upon animal habitats, and we’re getting more interactions between humans and wild animals, domestic animals and wild animals, and humans and natural flora, which is increasing the risk of this type of infection being recognized,” he explained.
The Ophidascaris worm found in this instance is in other snake species in different continents around the world, too. “Awareness of this case will hopefully lead to the diagnosis and treatment of other cases,” Dr. Senanayake added.
Though it’s certainly surprising to find this particular parasite in a human, finding a zoonotic organism in a person isn’t that strange, according to Janet Foley, DVM, PhD, a professor of veterinary medicine at the University of California, Davis. This is especially true if the usual host is closely related to humans, like primates, or spends a lot of time around them, like rats.
“There are still a lot of parasites and diseases out there in wildlife that haven’t been discovered, and we don’t know the risk,” said Dr. Foley. “But still, the risk would have to be low, generally, or we would see more human cases.”
In the United States, the roundworm common in raccoon feces is Baylisascaris procyonis and can be dangerous for people. “There have been deaths in people exposed to these worms, which do seem to prefer to travel to a human brain,” Dr. Foley said.
A 2016 Centers for Disease Control and Prevention report described seven U.S. cases identified between May 2013 and December 2015, including six that caused central nervous system disease. Another case report in 2018 involved a toddler who had eaten dirt and animal feces in his backyard.
And this past June, an Emerging Infectious Diseases case report described a B. procyonis infection in a 7-year-old with autism spectrum disorder and a history of pica. He had put material in his mouth from the ground near a tree where epidemiologists later found raccoon feces.
Still, Dr. Senanayake cautions against people jumping to conclusions about parasitic infections when they experience symptoms that aren’t otherwise immediately explainable.
The typical person who develops forgetfulness, depression, and a fever probably doesn’t have a worm in their brain or need an immediate MRI, he pointed out. “There may be other cases out there, but common things happen commonly, and this is likely to be rare,” Dr. Senanayake said.
This case demonstrates the challenge in picking a course of treatment when the differential diagnoses for hypereosinophilic syndromes is so broad.
Tricky hypereosinophilic syndromes
One of those differentials for the syndromes is parasitic infections, for which treatment would be antiparasitic agents, but another differential is an autoimmune condition that would call for immunosuppression.
“Obviously, as with this case, you don’t want to give someone immunosuppressive treatment if they’ve got a parasite, so you want to look really hard for a parasite before you start them on immunosuppressive treatment for an immunological condition,” Dr. Senanayake said.
But all the blood tests for different antibodies came back negative for parasites, “and this parasite was simply difficult to find until they pulled it from her brain,” he said.
Infectious disease physicians are always looking for the unusual and exotic, Dr. Senanayake explained. But it’s important to exclude the common, easy things first, he added. It’s after exhausting all the likely culprits that “you have to start really thinking laterally and putting resources into unusual tests.”
A version of this article first appeared on Medscape.com.