It was a real problem on the long voyages of discovery and trade to Asia, killing nearly the whole crew of some ships.
Typhus was a fever, spread by mites, lice and fleas. It was very common in crowded places like ships and prisons. It was even known as ship fever and goal fever.
Epidemics of typhus could destroy whole armies. One French army attacking the Italian city of Naples lost 30,000 men to the disease and had to retreat.