With good water paramters/ tank maintenance and good quality foods the shrimp can last quite a long time, I think the longest I have had a wild caught white bodied macrobrachium last in captivity has been around 3-6 months. But the outcome is always the same in the end.
Depending on the disease depends on how it is transmitted. Some shrimp diseases they believe are transmitted sexually, by male carriers that infect the females and her subsequent offspring then carry the disease doramantly until some environmental stress triggers the disease the take hold. Environmental stresses can be too hot temperature, too cold, lack of food or over crowding because of dwindling water sources, eg height of summer with little or no rain so water courses are reducing in volume.
The other theory for some shrimp diseases is that shrimp become infected when eating the already diseased corpses of fellow shrimp, and or eating the droppings of infected shrimp.
To the naked eye many shrimp diseases look similar (the few that have actually been studied for economic impacts on commercial industries), and it is only via detailed microscopic investigation can a positive identification of the disease can potentially be correctly identified.
Best of luck with your shrimp and please keep us updated with its progress.
