Transmission
Causes
The Disease
Diagnosis
Treatment
Other Myco
References
Human carriers

Rats, like mice, carry the myco agent as an ‘inapparent infection’, similar to how humans carry the strep bacteria, but neither manifest themselves unless their host suffers some stress or illness which may lower their immune system. 
 

Transmission

Mycoplasma is spread by direct contact between mother and young, baby rats can contract the virus in the uterus, and as it affects the genital organs, it can therefore be passed during sexual contact.  Myco is can also be spread via the air, like colds and flu (‘coughs and sneezes spread diseases’)  There is little evidence to indicate that transmission can occur from cages, toys or clothes, though it is best to take all precautions and disinfect the cage and equipment regularly. 
 

Possible Causes

Ammonia is a contributing factor.  Ammonia build up can come from poor cage ventilation, dirty conditions and over crowding.  If you use an aquarium as a cage, make sure there is a wire roof to let plenty of air in, aquariums must be cleaned more often than a wire cage. 

Older animals are more susceptible, as are those with lowered immune systems for instance, recovering from an operation.  Also rats which are inbred may be more susceptible, so watch out for rats in pet shops!  There may be problems with certain colour strains, such as the Blue, which is more inbred than many other colours, (this is mainly conjecture), but it is good breeding practice to out cross regularly! 
 

Disease Development 

The disease normally develops slowly with young rats being only mildly affected, but becoming more severe in older animals. 

The disease affects the cell membranes of respiratory tract, causing inflammation in the affected tissues; large, swollen, pus and mucus filled  airways; severe damage and abscesses in lungs. 

When the disease is in the upper respiratory system, you may notice sniffling, sneezing, occasional squinting, discharge around eyes and nose, the coat may appear rough.  If infection spreads to the inner ear you may notice the neck muscles appear stiff and sore causing twisting of the neck (wry neck) 

When the disease has progressed to the lungs and pulmonary system, (possibly caused by, or made worse by ammonia, bacterial infection or Sendai Virus) you may notice; lethargy, rough coat, hunched posture, chattering, weight loss, laboured breathing and eventually death.  Unless the condition is made worse by secondary infection then this terminal stage of mycoplasma may last weeks or months. 
 

Diagnosis

The ELISA test is currently the best method of detecting mycoplasmal infection.  Ask your vet. 
 

Treatment

Antimicrobial agents, (such as echinacea or goldenseal) added to drinking water may suppress the infection and the clinical signs. 

Antibiotic treatment such as: 
Tetracycline  (try 5 to 10mg per lb, three times a day for 14 days) 
Tylosin 
Baytril (enrofloxacin) and Doxycycline in combination 

Medication to reduce inflammation, and to relax and expand the airways will be beneficial. Ask your vet to suggest something, or try a homeopathic remedy.  Anti-inflammatory drugs/remedies may be helpful in the case of wry neck which does not normally respond to treatment. 
 

Other 

Genital Mycoplasmosis is common in female rats.  This can cause a low fertility rate, small litters, fetal deaths and cause the rat to reabsorb the growing embryos.  The disease and transmission, causes and treatment methods are the same as Respiratory Myco.  It has been noticed that the fallopian tubes and uterus may become infected in rats who have Respratory Myco. 

Mycoplasmal Arthritis, attacks the middle ears, pharynx and lungs of rats.  It is not known how often this occurs.  The causes and treatment methods are the same as with Respiratory Myco.  A rat with Mycoplasmal Arthritis will limp and move with difficulty due to the pain from swollen joints.  Any joint or limb may be affected but most often  in the areas of the hips, forearms and legs 

Mycoplasma pulmonis does not affect man, although the organism may be carried in human nasal passages. 
 

References:

Diseases in ageing rats 
Monitoring for Viral and mycoplasmic infections.  
Rat Bacterial Diseases 
Abstracts