"Logger's pox" was 19th century American frontier slang for the telltale injury seen on men who incurred the wrath of gangs of loggers or railroad workers who wore logging boots. The soles logging boots of the day were covered in sharp iron spikes so that forest workers could better climb the trunks of trees.
Loggers and railroad men generally only had enough money for the one pair of boots, so they'd definitely be wearing their spikes when they went out to drink off their aching backs and job stress. Barfights were common, and if someone was stupid or unlucky enough to take on a group of loggers, the loggers' standard fighting tactic would be to knock their opponent down and stomp the crap out of them.
Survivors of fights with loggers would have, aside from bruises and broken ribs, dozens of raw, oozing puncture wounds on their backs, arms and legs from being stomped with the spikes. The wounds were bound to be infected given the filthiness of bar floors and town streets. So, they soon resembled the ulcerated pustules left by smallpox infection and garned the nickname "logger's pox". Tetanus was likely a common complication of logger's pox.
Reference: Firestorm at Peshtigo: A Town, Its People, and the Deadliest Fire in American History by Denise Gess and William Lutz, 2002.