When any animal from a population is diagnosed with ringworm, the following questions arise: what do you do about the other animals in the environment? Do they all need to be cultured? Must they all be isolated while awaiting culture results? Will they all need treatment?
The answers to these questions are dependent on several factors. Not all animals in the same house or even the same room as a ringworm-infected animals will become infected themselves. The risk of infection depends on the animal’s individual immune status and grooming habits, the overall cleanliness of the environment, and the level of proximity between the exposed and infected animals. Some questions to ask include: What is the baseline sanitation level? Is this a highly cleanable environment such as a bank of stainless steel cages in an otherwise empty room? Is this a home with lots of scratching posts, furniture and carpeting to collect spores? Somewhere in between, such as a bank of cages in a messy room, with lots of junk piled about? Is bleach or Accel used on a routine basis for disinfection? How closely exposed were the animals? Were they each in separate cages, with minimal handling by staff likely to be carrying infection on their clothing? Was there some shared space such as an exercise area or “get acquainted room” where the animals comingle or spend time without cleaning between occupants? Are cats allowed to wander loose during cleaning but caged separately otherwise?
Is there evidence of spread? Has more than one animals been affected? Are all affected cats from one area of the shelter, or has it shown up in more than one room? Are animals that have been in the shelter long term (> 2-4 weeks) affected? (This suggests acquisition of infection in the shelter, as opposed to coming in already infected).
If the environment is basically clean, animals are generally kept reasonably separated, and overall animal health is good, it is not uncommon for animals to survive a minor exposure without becoming infected. Ideally, all exposed animals will be toothbrush-cultured, but this is often impractical and may not be necessary in a reasonably well-run shelter.
On the other hand, toothbrush cultures all around are generally required in a foster home where there are extensive opportunities for contact, in a cage-free cat shelter or group cat room, or any time there is evidence of significant spread (multiple cats affected). For more information on interpretation of fungal cultures ("pathogen scores") and management based on culture results, please see Dermatophyte Treatment in a Nutshell.
In the event of a true outbreak, many shelters will find it impossible to shut down intake for the duration of treatment. In such cases, it will be necessary to create a clean, separate area for new incoming cats. If this is impossible, a single dip in lime sulfur at intake can reduce the chances of infection if cats must be admitted to a contaminated environment. Please note that this is not recommended as a routine intake procedure for cats and kittens.
As is always the case, prevention of an infectious disease outbreak is far cheaper and easier on all concerned than management of an outbreak. After an outbreak of any kind, all personnel should meet to ensure that all staff and volunteers understand how the situation came about and what methods of control were most effective in ending the outbreak. From this informational meeting, a plan to prevent outbreaks in the future should be developed, written down, posted and distributed, so that all involved are aware of their role in prevention of future outbreaks.