The two most worrisome diseases guinea pigs can pass to humans are salmonella and ringworm. While it is possible for guinea pigs to pass lymphocytic choriomeningitis to humans, the guinea pig must first be infected by a wild mouse that gets into your home or the place where you purchased the pet. People are affected by guinea pig diseases when they don't properly handle their pet and then fail to wash their hands. In the case of salmonella, the disease can pass to humans through handling and cage cleaning. Ringworm is mostly passed to the elderly and children under the age of 5 due to their weaker immune systems. Lymphocytic choriomeningitis is most problematic for pregnant women. The disease can cause birth defects and mental retardation.
Always wash your hands thoroughly after handling your pet. If you know for sure your pet is sick with the salmonella virus, also be sure to wash your clothing after handling. Signs that your guinea pig has the virus include, weight loss, depression, changes in the coat, dehydration, loss of appetite and fever. Ringworm can be passed by handling the pet, that's why it's essential to wash your hands immediately after handling the pet. Lastly, pregnant women should try not to handle guinea pigs or clean their cages without the proper protection and/or proper handwashing. This not only prevents salmonella and ringworm, but is essential for preventing lymphocytic choriomeningitis.
The ultimate protection against these diseases is to protect your pet from them. Salmonella is a disease that can easily be avoided by cleaning fruits and vegetables thoroughly before feeding them to your pet. You should also take care to remove soiled bedding and clean your guinea pig's cage weekly. Ringworm can also be prevented through regular cage maintenance. Remove uneaten food daily to prevent a buildup of material.
It is pretty rare for you to pick up any of these dieseases if you take good care of your pigs, but make sure to take precaution.