Virginia Tech researchers identify leptospirosis as a major health threat in Botswana

May 15 2013

The newest public health threat in developing countries may not be a cinematic-quality emerging disease but actually a disease from animals that was identified more than 100 years ago.

Virginia Tech researchers have identified leptospirosis as a significant health threat in Botswana. The world's most common disease transmitted to humans by animals, according to the World Health Organization, leptospirosis is a two-phase disease that begins with flu-like symptoms but can cause meningitis, liver damage, pulmonary hemorrhage, renal failure, and even death if untreated.

"The problem in Botswana and much of Africa is that leptospirosis may remain unidentified in animal populations but contribute importantly to human disease, possibly misdiagnosed as other more iconic endemic diseases such as malaria," said disease ecologist Kathleen Alexander, an associate professor of wildlife in the College of Natural Resources and the Environment.

Under a grant from the National Science Foundation, researchers in Alexander's wildlife health and disease laboratory have identified banded mongoose in Botswana as being infected with Leptospira interrogans, the pathogen that causes leptospirosis.

The animals, although wild, live near humans, sharing scarce water resources and scavenging in human waste. The pathogen can pass to humans through soil or water contaminated with infected urine. Mongoose and other species are consumed as bushmeat, which may also contribute to leptospirosis exposure and infection in humans.

This first published confirmation of leptospirosis in wildlife in Botswana appeared today (May 14, 2013) in the journal Zoonoses and Public Health. The study, "Leptospira interrogans at the Human-Wildlife Interface in Northern Botswana: A Newly Identified Public Health Threat," was written by postdoctoral associates Sarah Jobbins and Claire Sanderson, and Alexander, who is affiliated with Virginia Tech's Fralin Life Science Institute. Jobbins is lead author and Alexander is corresponding author.

"Given the global importance of this disease, I was convinced that we were going to find Leptospira interrogans in some species in the ecosystem," said Alexander. "The pathogen had not been reported previously in the country with the exception of one cow in Southern Botswana over a quarter of a century ago.

"We looked at public health records dating back to 1974 and there were no records of any human cases," she continued. "The doctors who I talked with at the hospital said they were not expecting to see the disease in patients as they were not aware that the pathogen occurred in the country."

"This pathogen has a wide host range and can infect many animals, both wild and domestic, including dogs," said Jobbins. "Banded mongoose are not likely the only species infected in the ecosystem, but they serve as an important sentinel allowing us to identify health risks to humans."

Alexander, a veterinarian and researcher with the Center for African Resources: Animals, Communities and Land Use (CARACAL), has been conducting a long-term study of human, wildlife, and environmental health in the Chobe District of Northern Botswana, an area that includes the Chobe National Park, forest reserves, and surrounding villages.

"Our research program is directed at understanding how people, animals, and the environment are connected, including the potential for diseases to move between humans and wildlife," said Alexander. "Diseases such as leptospirosis that have been around for a very long time are often overlooked and underfunded amid the hunt for the next newly emerging disease."

"Leptospirosis was first described in 1886, but we still know little about the occurrence of this disease in Africa, despite the knowledge that it can impact human health substantially and that Africa is expected to have the highest burden of disease," said Jobbins.

With the identification of leptospirosis in the ecosystem, Alexander worries about the public health threat this disease may pose to the highly immune-compromised population of Botswana, where 25 percent of 15- to 49-year-olds are HIV positive, according to the Botswana Government's Ministry of Health.

"In much of Africa, people die without a cause being determined," she continued. "Leptospirosis is likely impacting populations in the region, but without knowledge that the organism is present in the environment, overburdened public health officials are unlikely to identify clinical cases in humans, particularly if the supporting diagnostics are not easily accessible."

The researchers looked for Leptospira interrogans in archived kidneys collected from banded mongoose that had been found dead from a variety of causes. Of the sampled mongoose, 43 percent tested positive for the pathogen.

"Given this high prevalence in mongoose, we believe that Botswana possesses an as-yet-unidentified burden of human leptospirosis," said Jobbins. "There is an urgent need to look for this disease in humans who have clinical signs consistent with infection."

Because banded mongoose have an extended range across sub-Saharan Africa, the study results have important implications to public health beyond Botswana. Across Africa, human and animal populations overlap, and many species are becoming tolerant of humans.

"Investigating exposure in other wildlife, and assessing what species act as carriers, is essential for improving our understanding of human, wildlife, and domestic animal risk of leptospirosis in this ecosystem," the researchers wrote.

The study also cited climate change predictions that the region will become more arid, concentrating humans and animals even more around limited surface water, increasing the potential for disease transmission of water-associated organisms.

"Infectious diseases, particularly those that can be transmitted from animals, often occur where people are more vulnerable to environmental change and have less access to public health services," said Alexander. "This is particularly true in Africa. While we are concerned about emerging diseases that might threaten public health — the next new pandemic — we need to be careful that we don't drop the ball and stop pursuing important diseases like leptospirosis that have already been identified as having a significant impact on human health.

"As humans move into traditional wildlife areas and transform landscapes, interactions between humans and wildlife will change in important ways," she continued. "Many wildlife species are becoming progressively more urbanized, setting the stage for increased contact with humans and the potential for transmission of diseases such as leptospirosis. The more important threat to human health likely arises from known pathogens occurring in changing landscapes."

Alexander is working together with the Botswana government to identify immediate research and management action — in particular, the need to alert frontline medical practitioners and public health officials to the potential for leptospirosis infections to occur in humans and to include this pathogen in diagnostic assessments and disease surveillance.