A rat that sneezes a lot, has more tears than normal or has crusty eyes, or has an audible wheeze or crackle, is showing signs of a respiratory infection.

Respiratory infections in rats are often caused by viruses.  Many times the viruses are harbored in older rats that aren’t showing any outward signs of infection yet they are still capable of infecting younger rats.  This is one reason why it is important to avoid mixing rats of different ages and different origins together.

One of the common causes in young rats is Sialodacryoadenitis virus/SDA virus which usually causes nasal discharge, red tears, and congestion for about 3 weeks.  There are many other viruses that can cause disease.

This young rat has red nasal discharge and a small amount of red crust in the corners of the eyes. It has a distinct clicking sound when it breathes. It is most likely infected with SDA virus.

Another common cause of respiratory infection is Mycoplasma pulmonis.  Mycoplasma often responds well to antibiotics but in some cases it may go on to cause pneumonia despite appropriate treatment.

There are a variety of bacteria that are “secondary invaders”.  This means they do not cause disease on their own but can make infections caused by viruses or mycoplasma more serious.  If left untreated, these bacterial infections quickly develop into pneumonia.

Unfortunately, there is no rapid test that can tell if a rat has a virus, mycoplasma, a bacteria, or some combination.  Mycoplasma and bacteria respond to antibiotic treatment and usually improve after 7 days of antibiotics.  Viruses do not respond to antibiotic treatment and a rat may continue to have a clear to pink nasal discharge, sneezing, and watery eyes for about 3 weeks.

If a rat is on antibiotics for 7 days and is not getting better but is not getting worse, it often has a viral infection. If a rat on antibiotics starts to have more trouble breathing, or has a change in the color of its nasal discharge, it needs to be re-examined to determine if it has developed pneumonia, a very serious infection that requires more intensive therapy.

Hygiene is very important to limit the spread of this disease.  If your rat is sick, wash and disinfect your hands before handling any other rats.  Clean the cage and wash and disinfect the cage and food bowls and water bottles every day until the upper respiratory infection resolves.

Other rats that have been exposed to an infected rat may come down with the disease within 2 weeks.