‘One world, one health’

Minimally invasive method of testing for pathogens could provide new paradigm for characterizing disease transmission

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DURHAM, N.C.—When Peter Larsen, senior research scientist at Duke University, heard a presentation by Duke Lemur Center veterinarian Cathy Williams, who was performing physical exams on lemurs in the rainforests surrounding a mine site in eastern Madagascar to help monitor the impacts of such activities on lemur health, he wanted to help her by using genomic technology. What developed was a minimally invasive method that could potentially determine whether unknown vectors were carrying disease from species to species, even from animals to humans.
The Duke Lemur Center was engaging in a collaboration with a nickel mining company (Ambatovy Minerals S.A.) in Madagascar to preserve the lemur population, according to Anne Yoder, director of the Duke Lemur Center and co-author of “Blood Transcriptomes Reveal Novel Parasitic Zoonoses Circulating in Madagascar’s Lemurs,” which appeared in Biology Letters, Jan. 27, 2016.
According to the article, “Zoonotic diseases are a looming threat to global populations, and nearly 75 percent of emerging infectious diseases can spread among wildlife, domestic animals and humans. A ‘one world, one health’ perspective offers us an ideal framework for understanding and potentially mitigating the spread of zoonoses, and the island of Madagascar serves as a natural laboratory for conducting these studies. Rapid habitat degradation and climate change on the island are contributing to more frequent contact among humans, livestock and wildlife, increasing the potential for pathogen spillover events.”
Larsen, the lead author of the study, designed a test to find pathogens in any organism without having information up front. The researchers used a technique called whole-transcriptome sequencing to screen for blood-borne diseases in wild lemurs, distant primate cousins to humans. The animals were found to carry several strains or species of parasites similar to those that cause Lyme disease and other infections in humans.
This is the first time these parasites have been reported in lemurs or in Madagascar, the only place on earth where lemurs live in the wild outside of zoos and sanctuaries, according to the researchers. Larsen believes that they probably came to Madagascar, which is geographically isolated, by way of imported cattle.
The researchers believe that their approach could lead to earlier, more accurate detection of future outbreaks of zoonotic diseases that move between animals and people. Many emerging infectious diseases that affect humans, including recent outbreaks of SARS, Ebola and bird flu, are zoonotic. In other words, they can spread among wildlife, domestic animals and humans. According to Yoder, “We can detect pathogens we might not expect and be better prepared to deal with them in any species.”
As Larsen explained, “Leveraging powerful genomic technologies for discovery, we can design an inexpensive method to screen various species all over the world. There may be a complex association of pathogens in domesticated species and humans, with pathogens moving from host to host.”
While standard diagnostic tests look for known pathogens, new or unexpected diseases can go undetected. Using phylogenetics, researchers can postulate pathogens that come from elsewhere in any organism without prior knowledge.
Larsen’s team analyzed 150 blood samples from six lemurs in two species, and found more than just lemur RNA in the animals’ blood. Using computer algorithms that compared the genetic material to sequences already catalogued in existing databases, they discovered several new types of parasites that had never been reported in lemurs. Changing ecological issues can spread disease from one species to another or one place to another, so the team wants to know whether the same pathogens are circulating in domesticated species and people.
The next step, according to Larsen, is to assemble a team at Duke and North Carolina State University to “get a better understanding of what is being impacted.” Wildlife experts and veterinarians are in place, and the team is identifying clinicians “to do things differently with human samples.”
Larsen concluded, “Tick-borne pathogens are still being discovered. Our method will accelerate discovery and therapeutics. Taking a ‘one world, one health’ approach, we can screen, confirm what was reported, develop rapid diagnostics that screen for a larger variety of pathogens and improve the health of a variety of populations.”

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