Tyzzer's disease is caused by a bacterium called Bacillus piliformis. This bacterium cannot be cultured because it has to live inside the cells of the animal, so diagnosis of this disease can only be confirmed by post-mortem examination. Recently weaned animals are most susceptible to this disease.
The signs of this disease are diarrhoea, lethargy, anorexia and death; unfortunately the prognosis for affected individuals is very poor. Try to prevent this disease by employing excellent hygiene regimes and reducing stress to the animals. If you have several rats in your colony and some of them are affected with Tyzzer's disease you could try treating them all with tetracycline to try to prevent the spread of the disease.
If you do decide to treat your rats affected by Tyzzer's disease they will need excellent nursing care. Keep them in a warm draught free environment isolated from all other pets. Your vet will advise you on the drugs which will be required but these may include antibiotics, fluid therapy, corticosteroids, and vitamin supplementation. Always take care of sick animals after you have seen to your healthy pets and wash your hands and all equipment afterwards to prevent the transmission of disease.