Tarabagans, a type of rodent found in Russia, were found to carry the most virulent strain of Yersinia pestis bacteria, which causes bubonic plague. They can transmit plague to humans through flea bites. Signs that a Tarabagan has plague include bloody vomit and a shaky walk. Plague was transmitted between humans via flea bites or direct contact with infected bodily fluids during pneumonic plague. War and poor hygiene increased plague transmission by concentrating rodent populations and fleas near humans. A pandemic refers to a major disease outbreak that spreads across a large region or worldwide.