The under-reported disease is usually spread though contact with rodents, but a new study finds this trend may not hold in northern Tanzania or beyond.
Research in Asia has tied living in close quarters with rats to outbreaks of leptospirosis. The bacterial infection causes symptoms that are often mistaken for malaria. Severe cases can be life-threatening, says Professor Albert Ko at the Yale School of Public Health.
“Our group has done global burden of disease studies on this and there are over a million a cases a year and roughly 60 thousand deaths,” said Ko.
Common source of fevers
Leptospirosis is becoming recognized as a common source of fevers in Africa. But the source of the disease was unclear. It could be rats, or it could be something else, said Michael Maze, of the University of Otago.
“Well, we know that leptospirosis has many possible animal hosts,” said Maze. “I guess the story starts when we identified how common leptospirosis was the cause of severe fever in people coming to the hospital in northern Tanzania.”
Maze and an international team of researchers asked those patients about their lifestyles: how many rats they saw around their home… whether they owned livestock and if so, what kind?
They also tested blood samples for leptospirosis infections. Of the nearly 900 people tested, almost a third were infected, or had been.
The researchers also trapped almost 400 rats in nearby villages. They tested the rodents to see if they carried the leptospira bacterium like their Asian cousins. They did not.
But cattle did — they found over seven percent of them carried up to four types of leptospira that could potentially infect humans. Goats and sheep did, too, though less often.
Blood samples match
This result matched the findings from the patients’ blood samples. People who owned livestock were most likely to have leptospirosis infections, especially cattle owners.
"Leptospirosis is carried in the renal tract — so the kidney and the bladder — and comes out in the urine of infected animals,” said Maze. “So even simple things like avoiding urine while doing activities such as, for example, milking cattle would be a good first step.”
Maze recommends abattoir workers and dairy farmers wear gloves and other protective clothing.
“A cow is much bigger and it produces a much larger volume of urine and so that creates a greater opportunity for exposure,” said Maze.
But Maze and colleagues found doctors did not diagnose a single one of the patients in the study with leptospirosis. In fact, one in four active cases was misdiagnosed as malaria — even though the patients’ blood tested negative for parasites.
Maze says one reason is because symptoms of the two diseases are similar and there is not an accurate, simple test for leptospirosis that can be run in regional hospitals.
“The second reason is that clinician awareness of these diseases is low,” said Maze. “If you don’t recognize them it becomes a cycle where they’re never diagnosed so you never recognize them.”
Yale's Albert Ko says the work Maze and his colleagues have done provides a better understanding of how leptospirosis spreads.
“This is an important study specifically because it provides key information on risk factors in a high burden setting, said Ko. “In specifically among this at-risk population of vulnerable pastoralist society.”