Ancient disease endures
Bubonic Plague transmission studied by WSU scientist
|Paul Gaylord, a welder in Central Oregon nearly died from the plague, transmitted by a cat bite. Photo courtesy of The Portland Oregonian and the Gaylord family.|
Most people have heard of the deadly plague that killed a third of Europe's population, but few realize that the cause — Yersinia pestis — is anything but ancient history. The germ is still among us, as demonstrated by a man in Central Oregon who spent a month on life support after contracting it.
This is why Viveka Vadyvaloo feeds her tiny, jumping research subjects blood infected with the same type of pathogen that ravaged medieval Europe. Working with an inactivated strain of Y. pestis, she studies how fleas pick up the disease and how they maintain and transmit it.
Contrary to what many believe, the "plague is not a disease of the past,” said Vadyvaloo, assistant professor of the veterinary college's Paul G. Allen School for Global Animal Health. Even with the advent of antibiotics, it smolders as a threat because "we don't yet fully understand the disease,” she said.
Illustration of the Bubonic Plague taken from 1411 German Bible. Artist unknown.
More than 30 species carry Y. pestis, said Vadyvaloo, now in her sixth year of researching fleas and how they spread the plague. Even in countries with good sanitation and modern medicine, the plague persists largely because of these six-legged, wingless insects that jump from host to host, she said. Once bitten, rats, squirrels, chipmunks and the sagebrush vole in Washington state become carriers as well. Less often, so do cats and humans.
Because fleas can jump up to eight inches, examining them under a microscope is almost impossible. Vadyvaloo immobilizes the jigging bugs by placing them on ice for 15 minutes, then on to the microscope's cooling plate.
"It's the only way to keep the fleas still so I can analyze them while they are alive,” she said.
The plague isn't common in the United States, but when someone does contract the disease, the Oropsylla Montana flea residing west of the Rocky Mountains is the likely culprit, explained Vadyvaloo, while holding up a mesh-capped jar the size of a beach bucket in which appeared to be grains of dark sand, pulsating and vaulting.
"If one of these fleas is a carrier of Y. pestis and it bites a rodent or human for a blood meal, they too can become carriers,” she said. Where some mammals get sick and die, others, like dogs, do not.
How a flea injects the bacteria into the host while it's drawing blood out is a fascinating aspect of Vadyvaloo's research.
Once inside the flea, Y. pestis bacteria multiply to form a Velcro-like blockage in its gut. "Unable to digest food, the flea is constantly hungry,” she said.
And so, the flea keeps biting — all-the-while regurgitating bacteria-laden blood into its hosts. A pin-head sized pool of blood can harbor up to 10,000 of the pathogens, said Vadyvaloo. Once bitten, "all it takes are five to ten of them to slip inside and infect a person.”
In Oregon, a flea probably infected a homeless cat, which in turn, infected the man, a 59-year-old welder, according to articles published in The Oregonian. The cat's neck was "swollen as if it had swallowed two key limes,” according to the newspaper. Convinced the cat was choking, the man yanked a dead mouse from its mouth and the normally friendly cat bit his hand.
From the wound, the rod-shaped bacteria traveled swiftly to the man's closest lymph nodes where they launched their onslaught.
Swollen lymph nodes are a tell-tale sign of the most common form of the disease, called bubonic plague, said Vadyvaloo. Inflammation occurs when Y. pestis multiply inside the lymph nodes to cause dark swelling or buboes.
Three days after being bitten, the Oregon man developed those buboes under his armpits, along with a high fever and intense achiness. An urgent care physician prescribed antibiotics for a diagnosis of a nonthreatening ailment called cat-scratch fever and sent him home, according to the account given by his family members. Two days later, he was hospitalized with a spiked temperature and burning lymph nodes the size of lemons, they told the newspaper. By then, his bubonic plague had advanced to the septicemic form of the disease, where a riot of bacteria is unleashed into the bloodstream and assaults the body's organs.
Antibiotics are most effective when given within the first 24 hours, according to Atlanta's Centers for Disease Control.
The Oregon man, recently removed from life support and expected to live, will lose the ends of his fingers and toes made gangrenous by bacteria and must learn to walk again, according to The Oregonian. He is the fifth person in Oregon to contract the plague since 1995. In Washington, the last human infection occurred in 1984 near Yakima, according to state veterinarian Leonard Eldridge.
"We do know that rodents here, particularly the sagebrush vole, are natural reservoirs of the disease and that plague-infected fleas are feeding on them and then spreading it to other animals,” he said.
A new study concludes that the plague, typically associated with lower-income areas, is turning up in wealthier regions. Published in the June issue of Emerging Infectious Diseases, the study found that in New Mexico, where the nation's rates of the plague are highest, people are contracting the disease in new housing developments butted against semi-arid wilderness. There, plague bacteria flourish among ground squirrels, wood rats and fleas, according to researchers.
"I think the recent incidences of plague in Oregon and in affluent New Mexico neighborhoods are examples of how the right combinations of human presence, climate, and rodents and their fleas can shift the disease's location and allow it to persist,” said Vadyvaloo.
The evolution of medicine and society — including public health programs — has slashed cases of the plague to roughly 3,000 cases globally each year, said Allen School Director Guy Palmer. But the disease continues to erupt in cycles and then go quiet. Yersinia pestis never goes away, he said. It hides in some rodent — only to be spread one day by a ravenous flea with a blocked gut.
Viveka Vadyvaloo, Paul G. Allen School for Global Animal Health, 509-335-6043, Viveka@vetmed.wsu.edu
Linda Weiford, WSU News, 509-335-7209, firstname.lastname@example.org