Respiratory diseases in rats may cause them to sneeze, have difficulty in breathing (more respiratory effort), lose weight, sound snuffly or have other unusual respiratory sounds, go off their food, become less active, adopt a hunched up posture or have ruffled fur. If your pet rat is showing any of these signs it is best to consult a vet sooner rather than later since seemingly minor upper respiratory problems can quickly escalate into serious problems such as pneumonia. Often stressed or poorly rats will have a red coloured discharge from their eyes and nose. This is porphyrin and generally means something is "not quite right". This is often seen in rats with Mycoplasma infections.
Although Mycoplasma is probably the most common pathogen causing respiratory symptoms in rats other bacteria or viruses may also be involved. These include Pasteurella pneumotropica, Bordetella bronchiseptica and Sendai virus. It is believed that most rats and mice are infected with Mycoplasma but most will not show clinical signs. It is passed from one rat to another by the aerosol route. Rats breathe it in when they breathe tiny droplets of water from the breath of another rat (or mouse). The disease causes damage to the lungs and since this damage is usually fairly extensive before symptoms show, this is why the disease is so difficult to treat. Some people think that there may be a genetic factor involved in this disease since some strains of rat seem more susceptible than others. Therefore breeding from affected animals is to be discouraged. Rats tend to develop mainly upper respiratory problems due to Mycoplasma, mainly the snuffles and sneezes (rhinitis) but also sinusitis and middle ear disease.
Medical treatment is often necessary if your rat is affected by respiratory symptoms; however if your rat just has slight snuffles and sneezes you may decide to adopt the "wait and see" approach. Keep a close eye on your pet to ensure that it is still active and eating and drinking normally. If it shows more than very slight signs of respiratory illness then consult your vet promptly. Usually antibiotics are given to rats suffering from respiratory symptoms. Drugs commonly used include enrofloxacin and tetracycline although there are several others which may be used on their own or in combination. Often these respiratory diseases do not respond particularly well to treatment. If the rat is very poorly sometimes fluids may be given by injection to treat dehydration and food may sometimes be given orally if the rat is not eating by itself.
Good nursing care can really help a poorly rat. Keep the cage in a draught free environment and keep it warm and clean. If you have more than one rat, keep any poorly animals separate. This will help to prevent the spread of disease and also mean that the poorly rat will not have to compete for food or be disturbed from rest by other animals. As far as possible try to reduce any stress for the rat; don't allow children to handle it while it is sick.
Try to prevent respiratory problems in rats by having good standards of hygiene (clean the cage regularly) and avoid overcrowding. It is possible that many rats have subclinical infections which do not give rise to clinical disease unless environmental factors cause the animal to be stressed.