The Science

An arthritic form of Mycoplasma Pulmonis.

It has been suggested that poor cage sanitation and abrasions of the extremities are factors involved in helping the organism to get into the joints. Since the organism appears to be of low virulence, the healthiness immune system of a rat may be a major factor in the outcome of infection.

This form of Mycoplasma resides in the pharynx (throat), middle ears, and lungs of rats. Although it is often considered to be the principal agent involved in arthritis in rats, the disease has been rarely reported.

The organism is transmitted by direct contact between mother and babies (i.e. placental), by sexual transfer, other animal carriers and can even be passed on to baby rats while travel through the birth canal, but only if the mother is infected with myco. It is also airborne over short distances.


Rats with arthritis will generally limp and move with difficulty due to pain. Affected joints are hyperemic and swollen. Any of the joints in the limbs and vertebrae can be affected.


Probably best diagnosed by a Vet, who will listen to your rats breathing to see if the lungs are infected and may take a tissue sample from the nasal pharynx, trachea, uterus, or lungs.


Although there is no actual cure for Mycoplasma pulmonis, there are several antibiotic treatments that have shown good success rates in keeping the symptoms at bay. The disease will eventually run its course, and death will occur, but by giving strong courses of antibiotics this can be delayed for long periods of time.


Strict husbandry standards, exclusion of wild rodents, serologic and postmortem monitoring, good ventilation, and low population densities in cage and room contribute to the maintenance of a Mycoplasma-free colony.
Hysterectomy in female rats is the only really guaranteed way of having a myco free colony, however this is not always advisable as it is an extremely major operation.