The bump on a young California girl's hand was mysterious -- and growing. It wasn't until she had seen two doctors and undergone a biopsy that her family realized the cause: The child had gotten in the way of a hungry iguana with a sweet tooth, resulting in what may be the first documented infection of a rare bacterial infection in a human from an iguana bite.
The girl, who is not named in a scientific presentation on the case that will be given at the European Congress of Clinical Microbiology and Infectious Diseases in April, is still recovering after her unexpected ordeal, which started on a vacation in March 2022.
The girl and her family had taken a trip to Costa Rica. While enjoying one of the country's many beautiful beaches, the girl's parents gave her a snack. But it turns out that she wasn't the only one who was hungry: A wild iguana popped up as the girl ate her cake by the water.
Iguanas are common in Costa Rica. They're harmless herbivores, known mostly for sunning themselves under trees and eating fruits and leaves, but experts say this animal must have developed a sweet tooth.
The iguana ran up to the girl and bit her on the back of her left middle finger, causing her to loosen her grip on the cake. The reptile then ran off with the snack, but it did leave something else behind.
Dr. Jordan Mah, an author of the presentation and an expert in medical microbiology, worked on the lab testing for the case as a part of the Department of Pathology at Stanford University. Mah said the girl's parents probably weren't thinking about the bite when they took her to a doctor because of the bump on her hand.
"I think when they went to get medical attention for the bump initially, the bite kind of slipped their mind because they didn't see it as a potential exposure, because it just healed. And it was only later on during the course of treatment, as it got worse, that it kind of jogged their memory and they brought it to the doctor's attention," he said.
Mah says the parents had been immediately responsive after the iguana encounter. The wound looked superficial, but they took the girl to a local clinic, where staffers disinfected the wound with alcohol and gave her five days worth of antibiotics.
The wound appeared to have cleared up in about two weeks. It was only five months later, when her parents noticed a dime-size bump on the girl's hand in the same spot, that they thought they should take her to another doctor. The girl told them it didn't hurt, and there were no other symptoms.
Her pediatrician thought the bump might be a harmless cyst and told her parents to keep an eye it. But when the bump continued to grow and began causing mild pain, her parents took the girl to an orthopedist, who suggested a biopsy.
The doctor removed the 2-centimeter mass. Scientists took a closer look at the growth in the lab and discovered that the child had a rare infection with Mycobacterium marinum, a non-tuberculous mycobacterium that more commonly causes a tuberculosis-like illness in fish.
It's ubiquitous in fresh and salt water but rarely infects humans. Typically, when humans are infected, it's after a wound has been exposed to the bacteria in water. Most people who get these infections develop a rash that may spread in a spherical pattern. It may develop a nodule with pus or turn into an ulcer.
Most antibiotics alone don't typically work on these kinds of infections, so doctors started the girl on rifampin, an antimicrobial, and clarithromycin, an antibiotic often used for skin infections. The infection responded well to the treatment.
"Typically, with these infections, because they take a very long time to grow and they're a little bit more fastidious, you need to treat them for a longer period of time, sometimes several months," Mah said. "So she's doing better. I wouldn't say 100%, but she's doing a lot better than she was initially."
Mah believes this is the first time a human has gotten this kind of infection from an iguana bite. He wanted to present the case to warn clinicians of the possibility.
Growing M. marinum in the lab required a lower temperature than most bacteria. This particular bacteria likes to grow at about 82 to 86 degrees Fahrenheit. Most bacteria are cultured around 95 to 98.6 degrees, so the diagnostics were slightly different. With lizards and iguanas having lower body temperatures than humans, Mah said, they may be the perfect hosts for this kind of bacteria.
"There is we know a lot about animal bites and bacteria, infections, following, let's say, dogs or cats, but there really isn't much for lizards, let alone iguana," he said. "I don't think people should be afraid, but doctors should be aware of the possibility."
Iguanas that were native to South and Central America and Mexico have become an invasive species in South Florida, Hawaii, Texas and Puerto Rico, so people may have more encounters with them. But experts who work with iguanas say they are usually pretty harmless, so there is no reason to be afraid of them.
Anna Meyer, operations manager at Iguanaland, Florida's largest reptile zoo, said the behavior of the one in this case is not typical.
"Typically, they will go about their day and not want to bother anyone or be bothered by anyone. But like any wildlife, if they start associating people with food, they're going to risk coming closer," Meyer said. In this case, other tourists in Costa Rica might have fed the wild iguana until it became habituated to people and developed certain expectations of them.
"That's an animal who's just become accustomed to people providing it with food," Meyer said. It probably realized it could get a "higher-value food" from the toddler without much danger to itself.
The lesson here, she said, is that no one should feed wildlife, because it makes the animal think that stealing food from a child is, well, like taking candy from a baby.
"There's more calories in cake than in a mango or leaves," she said.
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