Cats are susceptible to upper respiratory infections because they inhale viruses and bacteria as they sniff interesting smells. These diseases are caused by Feline Viral Rhinotracheitis (FVR); Feline Calicivirus (FCV); and the bacterial infection Chlamydia, also called pnoeumonitis.

The most common sign is sneezing, but coughing, runny eyes and nose and even painful eye and mouth ulcers can develop. Severe disease can lead to pneumonia. There is no cure; treatment is limited to symptomatic and supportive care. Recovered cats become carriers for life and can transmit disease to other healthy cats during "flare-ups" brought on by stress.

Disease is primarily spread by direct cat-to-cat contact, aerosol (sneezing) and by contact with contaminated items like cages, food bowls and litter boxes. The virus can also be carried on human skin, which means you may spread the infection by simply petting your cats.