Q: Are there any diseases that humans can catch from their pet fish or fish can catch from humans? If so, how common are they?
Mary Barron, Albuquerque, New Mexico
A: Dear Mary,
I don't know of any diseases that pet fish can catch from their owners but there are some diseases that people can catch from pet fish. We call these diseases, those that can go from animals to humans, zoonotic diseases or zoonoses.
The first and probably most common is mycobacteriosis. This condition is sometimes called "aquarium finger." Although related to the organism that causes tuberculosis in humans, the species of Mycobacterium that fish can carry does not cause tuberculosis in humans. Sometimes fish mycobacteriosis is incorrectly referred to as "fish TB." Humans are most susceptible to this disease when they have open cuts or sores on their hands when they handle or touch fish. It's also possible to contract this disease by coming in contact with contaminated water. Finally, people who are immuno-compromised (have weak immune systems) are more likely to contract "aquarium finger" than young, healthy people.
The disease can be treated but it can take several months to cure. Generally, the lesions are restricted to the hands and extremities. This is because the fish bacteria grows best at fish temperatures (temperature of the aquarium or pond) and not human body temperature (98.6 F). Since our hands and fingers are cooler than our core body temperature, the bacteria can survive and multiply in the extremities. Here are some tips to prevent this problem (which I have never observed by the way):
Always wash your hands well after touching fish or aquarium water.
Wear latex gloves when handling fish (you may have noticed we were always wearing gloves when working with the fish in the NOVA segment).
Don't handle fish or aquarium water if you have an open cut or sore.
Aquarium water has been linked to other bacterial disease (e.g., shigellosis) of humans but this is pretty rare. Overall, fish are very safe pets for people and the incidence of zoonotic disease is low.