An outbreak of antibiotic-resistant skin infections at the San Diego Zoo last year began when a zookeeper infected an elephant calf that was being hand-raised because its mother couldn't care for it, according to a zoo and county health department investigation. The calf, in turn, infected as many as 20 of its human caretakers.
It is the first known instance of methicillin-resistant Staphylococcus aureus, or MRSA, in a zoo elephant and the first known transmission of the superbug from a zoo animal to a human, according to the Centers for Disease Control and Prevention, which published results of the investigation Thursday.
But it is emblematic of a rising concern that these skin infections, which have become a leading cause of admissions to emergency rooms nationwide, are being passed back and forth between people and animals, including family pets.
"It is a significant public health problem," said Dr. Kimberly May, a veterinarian and spokeswoman for the American Veterinary Medical Assn., based in Schaumburg, Ill.
"One of our biggest concerns is that the person has it, then the animal picks it up from them, then the person thinks they're clear of it, and the animal gives it back to them."
MRSA strains isolated from household pets typically are human strains acquired from human contacts, May said.
Pets, as well as humans, can carry the bacterium on their skin or in their nostrils without becoming ill. If MRSA infects a cut or scrape and gets into the bloodstream, it can cause serious illness and even death in animals or people.
The 2-month-old calf, a female African elephant that was never formally named, was euthanized in February 2008 for reasons unrelated to MRSA, zoo officials said. Its infections had healed after treatment with topical, oral and intravenous antibiotics, but it nevertheless failed to thrive.
The calf was born in November 2007 and was separated a month later from its mother when she couldn't produce enough milk for it. When it failed to gain weight, zoo veterinarians inserted a central line for tube feeding. The incision became infected, and MRSA abscesses developed on the calf's leg and elbow.
None of the zoo's other elephants, including the calf's mother, were found to be infected with or colonized by the bacterium.
The strain isolated from the elephant calf was USA300, which has become infamous for causing infections in wrestlers, football players and others who engage in contact sports. The bacterium is spread through skin-to-skin contact or sharing personal items such as towels or sports equipment.
The 20 zookeepers who developed confirmed or suspected MRSA infections had prolonged, close contact with the youngster -- bottle-feeding it, playing with it, lying alongside it and using their mouths to blow into its trunk, a technique to encourage the calf to take milk from a bottle.
"They really tried to do the things that would best facilitate the calf recovering, doing things the mother would do with the calf," said Dr. Donald Janssen, the zoo's associate director of veterinary services.
Fifty-five zoo employees, including elephant keepers, members of the zoo's nursery staff, veterinarians and nutritionists, provided round-the-clock care for the calf. Three of the 55 were found to carry MRSA in their nostrils. The investigators concluded that one of them probably infected the calf.
"That's the most likely hypothesis," said Dr. David Sugarman, a San Diego-based CDC epidemic intelligence services officer who participated in the investigation.
Most of the human skin infections were mild boils and lesions on the hands, forearms and wrists, the report said. It recommended better hygiene and infection controls such as washing hands before and after handling animals, wearing protective clothing, and cleaning equipment and surfaces.