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This Halloween Eve, three Alexandria locations host Historic Hauntings: The Plague Is Upon Us! No, the title doesn’t refer to Old Town’s current scourge: countless J. Crew-baseball-cap-wearing, Laura Ashley-dressing potential Pat Buchanan supporters roaming around its single square mile—even though that thought gives me the heebie-jeebies more than fake fangs and bloody eyeballs. But back in the 19th century, sailing vessels entering the port of Alexandria transported even more frightful cargoes: yellow fever, cholera, and smallpox as well as other contagious diseases. Catch the holiday spirit—so to speak—as feverish sailors, desperate doctors, and other ailing ghosts wander about the waterfront to commemorate Alexandria’s pestilent past and provide a sickly atmosphere for warmup trick-or-treating from 6:30 to 10 p.m. at Carlyle House Historic Park, 121 N. Fairfax St., Gadsby’s Tavern Museum, 134 N. Royal St., and Market Square, 301 King St., Alexandria. $6. For reservations call (703) 838-4242. (Elissa Silverman)