Anytime a shrimp is turning white, it is pretty much the beginning of the end. There are quite a few causes of a shrimp going white (viral, bacterial) but the outcome is still the same, the death of the shrimp in question.
Because the only sure fire way of knowing which disease has caused the whitening and it is the symptom of a few shrimp diseases there are a few ideas on how it is transmitted from shrimp to shrimp.
One is that all shrimp carry the disease but its stress (heat, water paramaters, tank mates) that allows the disease to then take hold. Other ideas state that the males carry the disease and when mating with females transmit it, and the shrimplets are infected. Another is that the disease is passed on in the droppings of the infected shrimp and when other shrimp eat these droppings they are in turn infected. Or that the shrimp are infected by eating the bodies of infected dead shrimp they come across in the tank.
There is no cure, your best bet is to isolate the infected shrimp and keep it and any nets and plants etc used to maintain its tank away from other shrimp and if it dies in the tank with your other shrimp do not let the unaffected shrimp eat the dead one.
This is a wild caught macrobachium I caught locally during a sevre heat wave

and a smaller one
This is what a healthy macrobachium should look like, also wild caught
As far as I know the illness should not affect fish, but they and snails may also be carriers, there is just to many unknowns and not much research into shrimp diseases.
Some more info that might help you
http
/www.fao.org/docrep/field/003/ac006e/AC006E10.htm
http
/www.enaca.org/modules/news/article.php?article_id=1802