At the southern doorstep to the United States along the Gulf of Mexico, similarly, scientists checked 3,000 birds at the border, reporting in 2015 that 3.6 percent were infested with ticks. That translated to 4 to 39 million neotropical ticks carried into the United States annually. Given that almost a third were infected with Rikettsia, a bacterium that causes spotted fever, this tick migration, the researchers wrote, poses “uncertain consequences for human and animal health.”
Migrating birds have long carried ticks—into Great Britain, where 8 percent arrive infested; onto the Isle of Capri, with one in twenty laden with ticks; and into Finland, where 25 million ticks are imported every year on the backs of 600 million migrating birds.
What scientists believe is different in the twenty-first century is the plethora of spirochetes and protozoans and viruses that they may carry with them. Moreover, these eight-legged menaces, and their unsavory cargo, may be able to survive and thrive in places they never could. “Considering an influx of 30–80 million passerines crossing the sea every spring,” wrote Gunnnar Hasle of Norway, “the limiting factor will not be the ticks’ dispersal ability, but the suitability of the area the ticks are released for the survival and reproduction of the ticks.” Chiefly, will it be warm enough? In many places, the answer is yes.
In the scheme of things, ticks are among the species that will benefit, and greatly, as climate changes. They are moving and populating, increasing their range and numbers in the United States, Canada, Western Europe, the Baltic States, Russia, and China. Mice spread them as they move north. Deer sustain and carry them. Birds import them. In each of those places, Lyme disease is proliferating. But what about South America? What about the place from which birds carry exotic species of ticks that are today being found on the boreal forest floor in the Yukon? Does Lyme disease live there, in the bellies of ticks, in mammals, in nature? The evidence, as scientists are fond of saying, is emerging.
It was not until 2013 that Ixodes ticks infected with a species in the Borrelia burgdorferi family were reported in South America, first in ticks harvested from cattle, deer, and vegetation in Uruguay. Then in 2014, two more South American countries joined the list. Scientists in Chile tested Ixodes stilesi ticks collected from the understory and from long-tailed rice rats and discovered a new branch in the Borrelia family tree, named Borellia chilensis, for its country of origin. Two months later came a report from Argentina, where the same bug was found in Ixodes pararicinus ticks. At that point, at least, researchers from the three countries reported optimistically, “there are no records of Ixodes ticks biting humans in the southern cone of South America.” We shall see.
Farther north, in the broad expanse of forest, coffee, cocoa, and coast that is Brazil, the first report had already turned up of what came to be called Lyme-like illness or Baggio-Yoshinari Syndrome, named for the scientists who identified it. In 1992, two tick-bitten brothers living in the State of São Paulo in the country’s southeast became the first victims of a disease that researchers, aware of an unfolding outbreak in the US Northeast, had been searching for since 1989. While the disease came with rashes and arthritis-like symptoms and bore some similarity to Lyme disease, its pathogen stubbornly refused to reveal itself. In 2007, a scientific article bore the intriguing title: “Description of Lyme disease-like syndrome in Brazil. Is it a new tick-borne disease or Lyme disease variation?” In 2010, a rather frustrated research group from São Paulo recounted, “In laboratorial terms, bacteria from the B. burgdorferi sensu lato complex”—the broad family of Lyme bugs—“were not isolated in biological fluids and tissues whatsoever.” By 2016, researchers knew only that sick patients harbored antibodies to Borrelia burgdorferi s. l., but that the pathogen could not be cultured and appeared in patient blood without the distinctive Borrelia flagellum. Then in 2017, there was a breakthrough. Using DNA testing, researchers found the genetic footprint of B. burgdorferi in four women from the southwestern state of Mato Grosso do Sul. One was ill with early Lyme-like illness, the others with advanced arthritic, cognitive, and psychological manifestations.
What was ultimately named Brazilian borreliosis was different from the North American version of Lyme disease, which itself differed from Europe’s Lyme borreliosis—a function of varying species and strains. Brazil’s disease is different in other ways too. The prime “reservoir” from which ticks are infected is not a tiny mouse or assorted other mammals but a 100- to 150-pound rodent called a capybara that likes to swim, has coarse reddish fur and a broad blunt snout, and was spotted on the fifth hole of the Olympic Golf Course in Rio de Janeiro in 2016. Further, it remains unclear which tick family is the prime vector—Ixodes, Amblyomma, or Rhipicephalus. In that respect, Brazilians share a problem with residents of the American South, whose Lyme-like illness is delivered by Amblyomma, or lone star ticks, and is called Southern tick-associated rash illness. The pathogen that causes it, its relationship to Lyme disease, and the possible role of Ixodes ticks are still unknown. Clearly, we don’t have this whole thing figured out.
Beyond the role of birds and ticks and assorted hairy mammals, South America’s experience with tick-borne disease is instructive in another way. As in North America, the malady “was reported to cause neurological, cardiac, ophthalmic, muscle, and joint alterations in humans,” and it responded well, early on, to antibiotics. But relapses there were common and harsh, described in the Brazilian Journal of Microbiology in 2017 as “symptom recurrence, severe reactive manifestations such as autoimmunity, and”—in a statement reminiscent of the early days of Lyme disease in the United States, “the need for prolonged treatment.” Will Brazilian doctors someday be censured for treating patients with additional courses of antibiotics, which they presumably are finding helpful, just as American and European doctors?
In São Paulo, where two young boys became the first Lyme-like cases in 1992, a plague hit in 1918. In the course of ten weeks, 100,000 of 500,000 residents were stricken with influenza. More than 5,000 died. Lyme and tick-borne disease surely do not work that way. We can all be grateful for that. But their slow and even spread, their complex ecology, and their broad array of symptoms has made them a more difficult target. Brazil, which is almost the size of the United States, is yet another new frontier.
Shorter, Earlier Journeys
Charles Francis has charted the ebb and flow of birds in Canada for fifteen years as manager of bird population monitoring for the Canadian Wildlife Service. He has used marine radar to gauge the densities and flight patterns of migrating birds over the Great Lakes. He has studied threats to birdlife as large as habitat loss and as specific as wind turbines. It was Francis who, in chapter 1, was on a team that pulled the tail feathers from migrating gray-cheeked thrushes to learn that they were en route to the taiga and boreal forest of the southern Canadian Arctic; the molecular composition of those feathers signaled to scientists that the birds had been born there. Francis and his colleagues had found, moreover, that the thrushes sometimes carried ticks to these far-flung places, supporting the hypothesis that Ixodes ticks may just be spreading north on the backs of birds.
That climate is changing fundamentally—and that it is changing nature—is a guiding principal of Charles Francis’ work as Canada’s bird manager-in-chief. And he worries and wonders. What of those birds that forget or fail to migrate—the ones still around at Christmastime when they would normally be in Mexico? Will an altered migratory clock leave them enough to eat in their springtime homes? Will they survive?
In 2005, Pete Marra, head of the Smithsonian Migratory Bird Center in Washington, DC, devised a way to measure the effect of weather on birds migrating along the Atlantic flyway. Made possible by the dogged work of avid American and Canadian bird monitors, Marra, Francis, and other researchers scoured the diligently kept records from 1961 to 2000 of birds captured and tagged as they migrated from a birding station in Louisiana in the southern United States to two stations about 1,500 miles north in Pennsylvania and far southern Ontario
. Other researchers had already tied climate warming to all manner of changes for birds: earlier breeding and extensions in range, to name two. In one study, researchers had found a mismatch between the hatching of baby birds at Vic-le-Fesq, thirty miles north of the Mediterranean in France, and the availability of food. As a paper published in the journal Science put it, adult birds were pushed “beyond their apparent sustainable limit,” trying to feed babies that arrived before caterpillars were ready.
Marra et al. added to that body of knowledge. For every 1 degree Celsius increase in spring temperature, they observed, birds arrived a day earlier on their annual migration north. Further, these avian migrants had not left their tropical homes earlier but rather made the made the trek through eastern North America faster in warmer years. The study made the case: shifts in temperature meant changes in migration, suggesting what future wholesale changes in climate might do and, in other places, already had done. In the United Kingdom, three studies showed migrating birds arriving up to two weeks earlier in a twenty- to thirty-year period. Two dozen studies in Europe and Asia demonstrated that migrating birds arrived 3.7 days earlier on average with every passing decade. In the Southern Hemisphere, meantime, the inverse has unfolded. Hampered by a shortage of sea ice in East Antarctica, penguins and petrels have delayed breeding cycles that had been set in ice, if not stone, for generations: they arrived at breeding grounds nine days later, on average, and laid their eggs two days later than in the early 1950s.
But Is This New?
In Canada, John D. Scott and his colleagues were busy from the mid-1990s through the 2010s identifying ticks pulled from migrating birds. In 2005, he reported the first instance of an Ixodes auritulus, or avian coastal tick, infected with the Lyme disease pathogen on Vancouver Island, British Columbia; it had hitched a ride on an American robin, originating somewhere in Central America. At Watson Lake, which is above the 60th parallel north in the chilly Yukon Territory, he found three new species on long-distance flyers: Ixodes brunneus, Ixodes muris, and in 2012, another Ixodes auritulus that had never been seen so far north. He also identified the first lone star stick, Amblyomma americanum, from a Yukon migrant in 2010, and in 2015, two other types of Amblyomma tick on migrating veeries. Scott’s report included this observation, fascinating if one appreciates the power of a pair of wings on a two-ounce frame: “Veeries could theoretically transport A. dissimile [an Amblyomma tick] from as far south as southeastern Brazil, a distance of over 7,500 km.” That is roughly 4,600 miles.
Scientists still do not know precisely what all this adds up to. The lone star tick, among the new species found by Scott, cannot overwinter in Canada, he said; it’s just too cold—for now—for their larvae to survive. An American study, recall from chapter 8, predicted significant northward movement of the lone star tick, from the American Southeast to huge stretches of the Great Plains and Midwest. Will it move farther north still?
While large questions remain, scientists are confident of this: Ixodes scapularis ticks, laden with Lyme, will pour into Canada on birds from the United States, where Lyme disease is well established, a phenomenon playing out south-to-north in other countries around the world. Those birds will fly the Atlantic flyway from the US Northeast to the Atlantic provinces. They will take the Mississippi flyway from the US Midwest to western Ontario and points west. To a lesser extent, they will cross the border from western areas of Pennsylvania, New Jersey, and New York and into eastern Ontario and Quebec. In 2013, government researchers released a study of what it called a current and anticipated tick “invasion,” a word it used thirty times. In southern Quebec, the stage was set in 2004 by a cluster of ticks, new to the region and the country, which by 2009 had reached a critical mass, what researchers called, “the establishment of efficient B. burgdorferi transmission cycle.”
That study gave the country five years from the seeding of new tick populations to the point at which “significant Lyme disease risk emerges.” “Different parts of Canada will receive ticks carried by migratory birds from different parts of the USA,” the study predicted. Other countries, too, may see ticks take root that formerly could not survive. For now, for example, the Ornate cow tick, which carries pathogens that cause spotted fever and tick-borne encephalitis, cannot overwinter in Norway. It is nonetheless a champion survivor, able to live for months under water and “to overcome years of unfavorable conditions,” according to a 2015 report in the journal Parasites & Vectors. The report designated four of five Scandinavian countries (Denmark excluded) as places where the tick was “anticipated-absent.” In other words, this “vector on the rise,” as the tick was called, is not there now. But it’s likely coming.
Scott, the scientist who has done more than most anyone to document sightings of ticks from faraway places, thinks these arthropods—whether exotic hitchhikers from South America or run-of-the-mill ticks from the neighbor down south—have likely been carried into Canada for thousands of years. He disputes assertions that a warming climate is creating new places for more ticks, including the indigenous Ixodes scapularis tick, the primary carrier in North America of Lyme disease. In Canada in 1911, two researchers named Nuttall and Warburton reported the first Ixodes scapularis tick on a person in Bracebridge, Ontario, 200 miles north of where the ticks were said to have emerged nearly a century later. The ticks have always been there, he maintains, and his argument makes a certain amount of sense: ticks adapt. They have a kind of antifreeze compound in their bodies that allows them to withstand intense cold. The climate has changed in Canada, sure, but what’s a degree Celsius of warming to a tick?
“Climate change doesn’t have one iota of effect on it. To me it’s just a bunch of baloney,” Scott told me more than once. “Birds are dropping these ticks all over the place. It’s been going on here in Canada for the last 10,000 years since the last Ice Age.” When Scott contracted Lyme disease thirty years ago, his hometown of Fergus, Ontario, where he believes he was infected, supposedly had no infected ticks. Government officials insisted into the late 1990s that the only place to get Lyme disease was in Long Point, Ontario. Climate change and ticks? A fad to get research grants, by Scott’s way of thinking.
I have spoken with other scientists like him who believe we may simply be finding ticks because we have a reason to look. Indeed, historical data is scant, as I covered earlier. But what little there is points to more ticks in more places. The better question may be, perhaps, are we finding more ticks with more disease? That is a trend Scott does embrace. In 2006, 13 percent of adult Ixodes scapularis ticks across Ontario were infected with the Lyme disease spirochete. A decade later, Scott reported an infection rate of 73 percent in the adult ticks on Corkscrew Island in sprawling Lake of the Woods in southern Ontario. He attributes some of the huge increase in infected ticks to the technology used to detect the pathogen. But still. “What was once considered by some researchers as a hostile environment for I. scapularis has turned out to be one of the most hyperendemic areas for Lyme disease in Canada,” he and his colleagues wrote in that report in 2016.
In the 2000s, researchers ventured to Gull Island, off the coast of Newfoundland, where they checked seabirds for ticks, finding, not surprisingly, that ten of sixty-one Ixodes ticks were infected with the pathogen that causes Lyme disease. What was surprising was that the Lyme pathogen found was not the common North American species. While this species, Borellia garinii, had been known to exist in Europe, Asia, even Alaska, it had never been seen on the continent’s east side. I wrote earlier about a Canadian woman, Sue Faber, and her young daughter, who were both infected with European strains of Lyme disease that standard tests did not catch. They are harbingers perhaps. In 2014, a report from Canada’s National Collaborating Centre for Infectious Disease said attention should be paid to the Gull Island findings: “This could introduce B. garinii into Canadian mammalian populations, and cause Lyme borreliosis in North America with significantly divergent symptoms.”
Here, then, is a new wrinkle in th
e avian importation picture. While the general trend of ticks and disease is northward, this pathogen has the potential to be carried east and south too, a newcomer to Canada and, potentially, the United States, courtesy of the wings of a few million migrating birds.
CHAPTER 11:
A Lyme-Free World
* * *
From late 2015 through 2016, a mosquito-borne virus named for the Zika Forest in Uganda was linked to 2,336 cases of Brazilian babies born with horrifically undersized heads, a condition called microcephaly. As reports accumulated, the threat of the Zika virus nearly shut down the 2016 Summer Olympics in Rio de Janeiro. Then the virus showed up on the shores of Florida. The US government response to the Zika threat was swift. By September of that year, Congress approved, and the president signed into law, a $1.1 billion commitment to fight the mosquito-borne threat. Just three months later, the US Centers for Disease Control and Prevention awarded $184 million in grants for Zika monitoring, prevention, and research. That same year, in sorry contrast, the CDC awarded $2.7 million in grants to control Lyme disease, the second-leading infectious disease in America.
Zach Adelman is a forty-something mosquito researcher at Texas A&M University who had been very busy in the months after Zika exploded into the New World’s consciousness. Adelman’s lab was flush with funding from the US government, and it was developing a method, not of any small consequence, to defuse the power of disease-carrying Aedes aegypti mosquitoes. The breakthrough would not only curb the threat of Zika but potentially of other devastating mosquito-borne diseases, like dengue fever and malaria. When I spoke to him in the spring of 2017, Adelman and his colleagues were on their way to genetically engineering mosquitoes that would, if scientific and ethical hurdles were cleared, produce male-only offspring. Within a few years perhaps, a nuisance bug that had caused millions of deaths over thousands of years could, when and where necessary, be vanquished. Zika, discovered in a rhesus monkey in Africa in 1947, was merely the latest addition to A. aegypti’s extensive and lethal cargo. Its power to inflict misery was predicted to grow as climate change ushered in new pathogens and expanded the insect’s geography. If anything, the grants aimed at the mosquitoes were inadequate and overdue, given the global implications of this ubiquitous bug.
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