Figure 2. Illustrative Examples of Factors Affecting Spread (Top Row) or Control (Bottom Row) of Pandemics.

A: Typical smallpox rash with extremely contagious pustular lesions. B: The two most common species of rats (reservoirs of Yersinia pestis). C: Xenopsylla cheopis (the rat flea), one of the vectors of Yersinia pestis, which transmits the infecting bacteria from rats to human beings. D: Bifurcated needle used for smallpox vaccination during the last decades of smallpox eradication. E: Cholera bed used to rehydrate patients with severe diarrhea; the drain in the middle is used to facilitate drainage of the copious diarrheal fluid. F: Cone barrier used to prevent rats from invading or leaving ships through the mooring ropes of the ship.

Panel A from Wikipedia.com, Public Domain by CDC/James Hicks; Panel B modified from Wikipedia.com (CC BY-SA 3.0); Panel C from Pixabay.com.