Via Science: In Brazil, a plague of rats signals what may come in a more urban world. Excerpt:
Rats haunt the slums of Pau da Lima. Their paw prints surround drain pipes. Burrows pock dirt walls. Shriveled black feces speckle patio edges. The rodents even leave their mark in the blood of the people living here in a crowded favela on the edge of this sprawling coastal city, Brazil’s third largest. Many residents carry antibodies for Leptospira, a bacterium found in rat urine that can be deadly to humans.
“There’s so many rats. You can’t believe it. Outside, inside,” says Carlos Bautista as he sits on the step of his brick shack, looking out over a pile of sodden trash and a makeshift chicken coop.
The haunting is deeply personal for Bautista. Six years ago, his 22-year-old wife died, unexpectedly, from lung damage caused by leptospirosis. Soon after, Bautista sent his son to live in the countryside with his grandparents. “It’s better to have him alive there than to have him here” exposed to rats and disease, he says in a voice barely above a whisper.
Rats have long been one of the world’s most ubiquitous—and infamous—forms of urban wildlife, synonymous with pestilence and squalor. They’ve attracted only sporadic attention from scientists, however. Much about the secretive city rat—chiefly the Norway rat, Rattus norvegicus—remains a mystery.
But as the world’s urban population surges and more people crowd into rat-plagued neighborhoods like Pau da Lima, the rodents are getting renewed attention from researchers and public health experts. Over the past decade, scientists in a number of cities have launched efforts to better understand rat behavior and evolution, and the role they play in spreading disease.
One of the most intensive and longest-running investigations into rat-human interactions is occurring here in Pau da Lima, a chaotic jumble of buildings astride a small, hilly swathe of this city of 2.9 million people. For the last 2 decades, researchers have scrutinized the bodies, homes, and habits of favela residents—rat and human alike—while dodging encounters with gun-toting gangs.
The goal is to decipher the forces driving leptospirosis, which kills some 60,000 people annually worldwide, and find the best ways to curb a disease that experts warn is an underappreciated threat in the burgeoning slums of a more urban world.
“When we think about the slums in Jakarta or Manila or Cali, Colombia, what you see in Pau da Lima is exactly what you see in those areas, if not worse,” says Albert Ko, a physician and infectious disease expert at Yale University, and a founder of the Salvador research project. “We need to find out what solutions can be done immediately that are also generalizable to many of the urban slums.”
Ko's interest in Pau da Lima’s rats dates back to 1996, when a surge of deathly ill people, many with failing kidneys, started appearing at the Salvador hospital where he worked. At the time, leptospirosis was considered a rural disease. The corkscrew-shaped spirochete that causes it dwells in the kidneys and urinary tracts of rats and farm animals, and it infects people when their skin or mucus membranes come in contact with water contaminated by the animals’ urine. Many people show no sign of infection, or just fever and aches. But a small fraction develop severe kidney damage or massive bleeding in the lungs, although researchers aren’t sure why.
Alarmed, Ko and Brazilian colleagues spent much of a year tracking the outbreak. The results, spelled out in a 1999 article in The Lancet, were among the first alerting the world that this infection had moved to cities. Over 8 months, they found 326 severe cases, with 50 people dead, and traced the cause to a strain of Leptospira found primarily in rats. They noticed that infections surged after intense rains, and that most of the sick came from favelas on the city’s outskirts, nearly half of which had open sewers. One was Pau da Lima.