By David K. Randall
May 16, 2019 | 3:15 AM
Bubonic plague bacteria taken from a patient in 2003. (Center for Disease Control / AFP / Getty Images)
The steamship caused the last global outbreak of bubonic plague. Climate change could cause the next one.
Longer, hotter weather patterns are extending the breeding season of rats and rodents, leading to a steep increase in their numbers in places like Los Angeles, New York and Houston. Over the last decade, urban rat populations are up by 15% to 20% worldwide, thanks to a combination of climate changes and a greater preference among humans for urban living, increasing the amount of trash available for scavengers, according to estimates from Bobby Corrigan, a rodent control consultant and one of the nation’s leading rat experts.
The swelling number of rodents isn’t just an urban nuisance. More importantly, all those additional rats and squirrels can serve as hosts for fleas carrying the plague-causing bacterium Yersinia pestis. The disease is already endemic among fleas that feast on rural squirrels in California, Arizona, Wyoming and other states. Climate change could make it possible for plague-carrying fleas to thrive in more places than they do now, bringing the disease into closer contact with humans.
“Any climate change conditions that increase the number of fleas [also increase] the distribution of plague,” said Dr. Janet Foley, a professor of medicine and epidemiology at UC Davis.
Already, public health officials increasingly find themselves battling rare and dangerous diseases associated with rats. An employee at Los Angeles City Hall who recently contracted typhus blamed the disease on flea bites she suffered as a result of the building’s rat infestation, while a cluster of patients suffering from the rare disease leptospirosis, an often-fatal condition spread by rat urine, were identified in the Bronx in 2017. An outbreak of bubonic plague due to contact with diseased squirrels prompted Russia to close its border with Mongolia last week.
While many major cities face the problem of increasing rat populations, Los Angeles finds itself in unique danger of disease because of its rapidly growing homeless crisis. As more people live in closer contact with rodent fleas that can carry the plague bacterium, preventing an outbreak of one of the most frightening diseases in human history will require a stronger push to eradicate potential hosts.
Eliminating rats and squirrels to save human lives saved Los Angeles once before. In 1924, fleas from an infected rat bit a man named Jesus Lajun who lived on what was then called Clara Street, near the current-day Twin Towers Correctional Facility downtown. Within six weeks, nearly everyone who had come into contact with Lajun during the roughly 48 hours between the time he caught the disease and the time he died from it was dead. The trail of victims included not only his immediate family members but also those of a neighbor who cared for him when he was too weak to leave the house.