Ringworm is certainly a nuisance. It's one of the few conditions than
can be passed from cat to human, and vice versa. The rate of
transmission of ringworm from cat to human or from human to cat is
lower than the rate of transmission among members of the same species,
but it does happen. I, too, am a volunteer with a pet rescue
organization, and I've learned that it is possible (though not common)
for ringworm to be unknowingly spread by a person (or a pet) who has
shown no symptoms.
A person who has been exposed to ringworm, who has no symptoms, and
who lives with pets has several options. You can engage in very
thorough hand-washing sessions and/or wear gloves when touching your
cats; you can have a fungal culture or ultraviolet light exam to
ascertain whether or not you have acquired the fungus; or you can seek
medical treatment for ringworm on the assumption that you might
possibly be a carrier. Since antifungal treatment is relatively safe
and inexpensive, it is occasionally recommended that even asymptomatic
humans should be treated if they have been exposed. Thorough
hand-washing is very helpful, but if you are a carrier, only the
eradication of the ringworm fungus will guarantee that you can't pass
ringworm along to your cats. You will need to see your physician if
you wish to obtain a prescription for an antifungal agent. While
veterinarians have access to good medications, they cannot legally
prescribe them for use in humans.
I have not yet found myself in this situation, but if I knew I had
been exposed to ringworm, I would go with the handwashing-and-gloves
route for at least two weeks, to protect my cats. I am personally not
very enthusiastic about taking medications which I may not need, and
the chance of an asymptomatic adult human spreading ringworm to cats
is very small.
I've gathered some online material that I hope will help. Please keep
in mind that Google Answers is not a source of authoritative medical
or veterinary advice; this material is intended for informational
purposes. For reasons of copyright, I am posting excerpts here, with
links to the sources; you may want to read these articles in their
"Ringworm is one of the more common skin infections we find in young
animals, but the name itself is somewhat misleading, for it is caused
not by a worm but a fungus.
The 'ring' part of the name is not always accurate either - although
the lesions tend to progress outwards from the centre as the fungus
invades and kills off the hair, they are not necessarily round at all.
Many species can be infected with ringworm - cats, dogs, horses,
cattle and of course humans. We probably see it most commonly in cats
- in fact some cats, mainly longhairs, may become carriers. But in
general, ringworm tends to be very much a disease of the young,
whatever the species. Humans and animals gradually build up an
immunity to it through their lives, though there are always exceptions
to the rule."
SPCA New Zealand: Ringworm
"The fungi that cause ringworm can be spread from animal to animal,
from animal to human, and even from human to animal. In both animals
and humans, healthy adults are somewhat resistant to ringworm, but
young animals and children are quite susceptible. Healthy adults can
still get ringworm, but usually the infection is mild and resolves
quickly. If you or your family members develop a rash after handling
your pets you should contact your physician immediately."
Harlequin Haven: Ringworm
"Studies show that in 30 percent to 70 percent of households where the
cat has ringworm, at least one person will get it. However, humans
have our own forms of ringworm. Athlete's foot is the classic example.
Only 3.3 percent of all human cases are caused by the same fungus that
infects dogs and cats, so you are far more likely to get ringworm from
the playground or weight room than from your furry friends.
'People with the highest risk for catching ringworm from their pet are
young children who have never been exposed, the elderly, or people
with a depressed immune system,' comments Dr. Angus. Once humans have
been exposed to a strain of ringworm, most people develop immunity and
rarely get the same strain again."
University of Illinois College of Veterinary Medicine: Ringworm
"Both the animal having the disease and any other animals and humans
who come in contact with the diseased animal should be treated with
anti-fungal therapy. It is also extremely important to isolate cats
that have active ringworm from the others while they are being
treated. If the cat's human family contains any people who are very
young, very old, or are immune-suppressed, these people are at the
highest risk for the complications from ringworm, and ringworm
treatment must be very aggressive for the well-being of all."
HDW Enterprises: Ringworm
Statistics show Microsporum canis is the leading cause of ringworm in
cats. This is a microscopic fungal organism that is very contagious
and able to spread from pet to pet, pet to human, or human to pet...
Whenever handling the cat, precautions for the owner are very
important. Always wash any exposed skin with warm water and a good
antibacterial soap. If at anytime, a human starts to have itchy areas
or skin lesions appear, they should contact their personal physician
immediately. It is important to tell them exposure to ringworm has
occurred so proper treatment can begin at once."
Essortment: Cats and ringworm
Other good resources:
Lek Pharmaceutical Group: Microsporum Canis Can Affect Humans as Well
Mar Vista Animal Medical Center: Ringworm FAQ
Veterinary Information Services: Feline Ringworm
VetInfo: Ask Dr. Mike: Infectious - Ringworm
Google search strategy:
Google Web Search: "ringworm" + "cats" + "humans"
Google Web Search: "microsporum canis" + "humans"
Google Web Search: "ringworm" + "asymptomatic carrier OR carriers"
Google Web Search: "feline ringworm"
I hope this is helpful. If anything is unclear or incomplete, please
request clarification; I'll be glad to offer further assistance before
you rate my answer.