Malaria sleuth at UVM tracks parasite to deer
The only alarming thing about discovering malaria in white-tail deer might be that it took scientists this long to discover it.
So says Ellen Martinsen, a researcher who splits her working life between the University of Vermont’s biology department (where she earned her Ph.D.) and the Conservation Biology Institute in Washington, D.C.
Martinsen, 38, should know. Her confirmation of widespread infections in native deer was a coup: Until this year, it was commonly believed that the Plasmodium parasite had no native mammal hosts in the Western Hemisphere.
Her findings were published this February to wide acclaim in the scientific community.
Amateur scientists, including the one from the Burlington Free Press who interviewed Martinsen a week or so later in Burlington, were amply puzzled.
If deer have malaria, why aren’t they dying of it? And what’s to keep mosquitos from transmitting malaria from deer to bipeds?
With maybe just a whiff of mischief, Martinsen tossed out another eye-opener: Many of the birds in our midst, such as chickadees, cardinals and up to 75 percent of the robins, are ridden with Plasmodium.
Are deer — or robins — dropping dead of malaria?
“We don’t know,” Martinsen answered. “Not enough people are studying it.”
In the interest of public health reasons, she has redoubled her research on “host-jumping” — rare instances when a species of parasite unexpectedly broadens its diet to include animals that previously had seemed genetically off-limits.
“When parasites jump into new hosts, they usually wreak havoc,” Martinsen said.
Various strains of avian influenza, for instance, periodically have mutated into major public-health threats. Malaria parasites appear to be constrained from making that leap.
Is she sure?
Pretty much. For the benefit of a beginner, Martinsen interrupted her work in the Schall Lab at UVM to explain. She outlined the basics, championed the spirit of enquiry, praised patience and counseled against panic.
Joining her was the lab’s founder, Joe Schall, a professor emeritus in the biology department and Martinsen’s doctoral mentor.
The two scientists share an almost giddy appreciation for the lifestyle of an organism that mates in the gut of a mosquito, proliferates in the insect’s salivary gland and spills into a host creature’s bloodstream, where it chows down on red blood cells.
Are Martinsen and Schall worried that the Americas’ only native, mammal-specific malaria might someday dine on human corpuscles?
Not likely, Schall said: “It would have happened by now. The one in deer has been here for millions of years. It’s had its chance.”
Awesome distraction
Martinsen remembers nursing orphaned birds back to health as a grade-schooler.
That interest remained latent until grad school, when Schall harnessed it.
“I initially got roped into doing malaria work on birds by this guy,” Martinsen said, jabbing a thumb at her instructor.
“Ellen hates it when I brag about her, but she’s one of the top authorities on bird malaria in the world,” he rejoined.
Schall, Martinsen said, had been fundamental in sidetracking her from her main body of research: “I got majorly distracted by it.”
She summarized: In 2012, she had been sifting through the DNA contents of yet another mosquito’s salivary gland when she detected, among various Plasmodium strains, the genetic signature of blood from a white-tail deer.
“But there was no proven link,” Martinsen said. “She (the female mosquito) might have fed on a deer but picked up the parasite earlier.”
The one-time discovery in 1967 of malaria parasites in a deer in Texas was thought to be a one-time anomaly. Martinsen, with more advanced methods and networks at her disposal, was intrigued. She scanned through hundreds of frozen blood samples of deer from throughout North America.
“I put more and more effort into it,” she said. “It was building and building and then, ‘Whoa — this is so awesome!’”
There they were: Plasmodium in up to a quarter of surveyed deer populations.
“I remember the day when Ellen told me what she had found,” Schall said. “My heart skipped three beats. My mouth dropped open. It’s incredible. Ellen found Bigfoot. She found the impossible parasite.”
Loons and bobolinks and ...
Fourteen other collaborators, including Schall, worked with Martinsen on the project, which included scanning blood samples from mule deer and elk — close cousins of white-tailed deer.
“Ellen is very generous in including us all in the paper,” Schall said. “She’d probably disagree with me, but I call it 99 percent Ellen’s work. She just loves going out and finding stuff.”
The malaria they’d discovered seemed confined to just the one target species, Martinsen said: “It doesn’t mean that the others don’t have it. It means we didn’t find it.”
But researchers have found disconcerting signs of malaria’s parasitic success elsewhere. Martinsen is charting the decline of the common loon — due, possibly, to a significant Plasmodium presence in their bloodstreams.
Scientists who track bobolinks from New England to breeding grounds in Bolivia have confirmed that bird as a malaria host.
Those creatures aren’t necessarily doomed by the parasite, Martinsen added. Most of the time, Plasmodium’s presence is held in check by an animal’s immune system.
Birds are most susceptible to dangerous levels of malaria in their systems during times of stress, which can include breeding and migration seasons, she said. And relatively isolated animals’ “naïve” immune systems — those that have never been exposed to a certain parasite — are particularly vulnerable.
Watch that mosquito
Thanks to anti-parasitic drugs and an energetic (if sometimes overly toxic) campaign against mosquitoes, the five or six species of Plasmodium that afflict humans were eradicated in the U.S. in the mid-1950s, according to the Centers for Disease Control and Prevention.
“Before then, every summer in Vermont, there were hundreds of cases,” Schall said.
Cases reported in the U.S. now stem from travelers who have been infected overseas, he continued. Those illnesses typically are diagnosed and treated quickly, before local Anopheles mosquitoes can spread the parasite further.
“I sit down in my back yard in Colchester, and I see Anopheles coming to me,” Schall said. “The vector is still here. And the human hosts are still here.”
Martinsen elaborated on her urgency to better understand malaria’s mobility: “The reintroduction of human malaria into the U.S. is always a threat.”
Although keenly aware of the threat, neither she nor Schall demonize the parasite.
“It’s such an amazingly diverse and successful group of parasites,” Martinsen said.
Schall holds a fascination for Plasmodium’s locomotion. “Under the microscope, you can see it sliding along like the Starship Enterprise,” he said, steering one hand gracefully through the air.
Plasmodium makes progress through a sea of red blood vessels with a mechanism similar to that of a small, primitive barge — the kind for which an operator at the front of the craft plants a pole in a pond-bottom and then “walks” the barge forward.
“It looks effortless,” Schall said. “But then, I think everything about Plasmodium is cool.”
As long as it keeps a healthy distance.
How do we know what’s an acceptable threshold of infection?
"I tend to take the perspective that every parasite is harmful," he said.
Schall turned to the subject of Plasmodium in lizards, which is his research specialty.
“These lizards were running around, courting, mating, laying eggs, eating bugs — but they were desperately ill,” he said. “These were some sick puppies; they have a short lifespan.
“Maybe they’d live longer if they didn’t have malaria,” Schall added. “We don't know."
It’s among the questions he’s hoping will infect more students.
Martinsen has that bug.
“The only continuity in all my studies is Plasmodium,” she said.
“And I’m a bird nut,” Martinsen added. “I live for birds. Who doesn’t live for birds? I had, like, 50 goldfinches at our bird feeder this morning.”
This story was originally published online Feb. 28, 2016. Contact Joel Banner Baird at 802-660-1843 or joelbaird@freepressmedia.com. Follow him on Twitter at www.twitter.com/vtgoingup.