Mice or Rats with severe respiratory disease will quite often get very cold due to low oxygen intake. To keep the mouse or rat warm, wrap a heating pad set on low in a towel and place it underneath one side of the aquarium. Do not place it under the entire tank, as your mouse or rat needs to be able to have a place to go if he gets too warm. You can also drape a towel over one half of the top of the tank. This will give the mouse or rat a dark place to relax in peace and will hold in some of the heat as well. Never put a heating pad in the cage, as your mouse or rat could bite into the heating elements and electrocute himself. Make sure the tank, and the room the tank is in, does not get too warm, or the mouse or rat may get dehydrated. Seventy to 72 degrees is adequate.
A very sick mouse or rat most likely will not be interested in cleaning himself. In fact, it is a good sign when a sick rat once again begins to groom. You can help keep your mouse or rat clean by wiping him down with a damp rag. Urine will need to be cleaned off so it does not burn his delicate skin. Use a wet rag to do this, but do not rinse the pet off under the faucet, as this will place an incredible amount of stress on him, which could cause him to become sicker. Sometimes even the sound of running water or a hairdryer will cause undue stress and are not recommended. Your pet needs to be kept as calm as possible during his illness. Use a soft towel to dry him off.
In addition to changing the cloth used for bedding frequently, make sure you clean the cage and any accessories regularly. Use a germicidal cleaner such as Parvosol, or a mild bleach solution. Rinse and dry the tank well before putting your pet back in if using the bleach solution.