|May 31, 2017|
Lyme Isn't the Only Disease Ticks Are Spreading This Summer
|IT STARTED WITH vomiting and a fever. But a few days later, five-month-old Liam was in the emergency room, his tiny body gripped by hourly waves of seizures. X-rays and MRIs showed deep swelling in his brain. When an infectious disease specialist at Connecticut Children's Medical Center diagnosed Liam with Powassan virus in November, he became the first recorded case in state history. Doctors think Liam picked up the rare neurological disease from a tick his father brought back after a deer hunting trip.|
The toddler survived with some scar tissue---but not everyone who gets Powassan, POW for short, is so lucky. With no treatment available, half of all people who contract the virus suffer permanent brain damage; 10 percent die. And while POW is nowhere near as prevalent as that other tick-borne summer scourge---Lyme---it is starting to show up more often.
Scientists disagree if that's because doctor awareness and improved testing tools are just turning up more cases, or whether anthropogenic forces like climate change, reforestation, and suburban developments are driving up the likelihood that humans will come in contact with POW. But one thing's for sure: The only way to get those answers is to collect more data. Entomologists and virologists have been saying this for years. Yet current surveillance efforts are limited to counting cases only once they've reached hospital beds.
A Taste for Flesh
As far as emerging diseases go, Connecticut has had more than its fair share. Liam lives in the town of Griswold, just 30 miles down the road from Lyme, where in 1975 a mysterious outbreak of swollen knees, skin rashes, headaches, and severe fatigue swept through the town. Lyme disease has reached epidemic proportions in recent years; cases have tripled in the US over the last two decades as the tick that spreads the illness has expanded its territories from a few northern pockets into half of all US counties.
At some point along its manifest destiny tour, Ixodes scapularis, the blacklegged, or deer tick, seems to have picked up POW. Maybe it was in a skunk burrow or a badger den---historically, POW is carried around by a different kind of tick that prefers members of the weasel family. And unlike their weasel-loving brethren, deer ticks, in addition to their namesake host, have a real taste for human flesh.
This is one of the reasons Phil Armstrong, a virologist and medical entomologist with the Connecticut Agricultural Experiment Station, believes the risk for getting POW has increased over the last few decades. The research station, which has one of the country's longest-running tick-borne disease programs, has data going all the way back to the '70s.
Back then, scientists collected and screened thousands of ticks looking for Lyme and other diseases. Armstrong says none of them were carrying the POW virus. "If it was present then we would have detected it," he says. "Now we go to those same locations and 2 to 3 percent of the ticks have POW."
In another study, Connecticut researchers analyzed deer blood collected from animals that hunters had killed and brought in to DNR check stations, again going back to the '70s. They found the prevalence of deer antibodies to the POW virus had increased substantially over a 40 year period. "Deer are always heavily parasitized by the deer tick," says Armstrong. "But it's only recently that they're also getting exposed to this virus."
Scientists like Armstrong estimate that POW is only prevalent in about 4 percent of deer ticks, way lower than the 30 to 40 percent prevalence of Lyme disease. But here's the thing. Lyme disease, which is caused by a spiral-shaped bacterium, takes about 48 hours to transmit; if you find a tick on your body and remove it within a day or two, you can usually escape a Lyme infection. POW, on the other hand, goes from the tick's body, through its saliva, and into your bloodstream within a few minutes of a bite. So even though it's not in many ticks, if the right one gets you, there's not much you can do.
The most public health officials can do is recommend wearing long sleeves and pants when hiking, and using repellents on your skin, gear and clothing. That, and staying away from high-tick areas. Of course, that's easier said than done. Because most health agencies, including the Centers for Disease Control and Prevention, don't have great ideas about where and when disease-carrying ticks are going to be out in full force.
"It's very difficult to predict from year to year," says Marc Fischer, a medical officer with CDC's Division of Vector-Borne Diseases. "Changes in weather, temperature, humidity, in host species abundance, how many ticks are infected, where they are and how likely they are to bite humans, all these things are constantly changing and have to be factored in."
A model that can incorporate all those parameters could actually tell you something useful about disease risk when it comes to ticks. And that's exactly what Goudarz Molaei is building right now. Molaei runs the state of Connecticut's unique and long-running tick-testing program. Residents who get bitten send in their ticks and Molaei screens them for diseases like Lyme.
The problem is he can't screen for POW because of cuts to the state budget. He's working on trying to find other partners at academic institutions who might be able to change that. But for now, the only real data on POW in humans comes in from hospitals that are seeing patients with the most serious symptoms of the disease. They then pass samples on to state health departments and eventually the CDC, which records the cases. Molaei's screening protocol could help catch a diagnosis earlier, or provide information about how often people contract the virus but don't get the worst symptoms. But since he doesn't have the funds to test for POW, for now he's focusing on Lyme.
He's using 20 years worth of data---from weather patterns to rodent and deer populations to habitat changes and disease abundance---to make a Lyme disease risk map of Connecticut. For the first time, it would tell residents where tick-borne disease hot spots are, and help public health authorities focus their efforts. He's hoping to finish by this fall. And in the meantime he's taking a much more blunt approach; he's telling people they should all be on high alert. This spring, his mailbox has been inundated with ticks.
"Usually I can return test results to people in a few days," says Molaei. "This month it's been taking me more like two weeks because the number of submissions keeps going up." In spring of 2014, he says he would get maybe 50 ticks a month. Now, he's getting up to 200 ticks a day.
What changed? The weather. Two years of mild winters has tick populations booming. And Molaei expects to see more of the same, as climate change makes warmer winters in the northeastern US more common. Studies show that warmer-than-normal temperatures increase tick reproduction two to five times. As agricultural land increasingly turns back to forest and suburbs continue to encroach on these newly wild areas, people are also getting more and more opportunities to encounter ticks, and POW.
At least for now though, official numbers don't reflect these increasing risks. Fischer says that based on the national reporting system currently in place---where state authorities send any cases they think might be POW virus to CDC labs for testing---the disease doesn't appear to be on the rise. Or, if it is, it's happening very slowly, and could just be an artifact of better testing technologies and physician awareness. "It's very tough to tease out surveillance bias," he says. "Especially with so little data to work with."
Epidemiological data has historically been counted in numbers of sick people and dead bodies. But with technological advances in genetic sequencing, immunological screening, and computational biology, there's no reason to wait for hospital admissions to begin structuring a public health response. First-of-their-kind risk maps like the one Molaei is building can help officials understand the environmental and economic drivers of tick-borne disease, in close to real time. Connecticut may be in the best position to lead the way, given its 20-year headstart on data collection. But other states should take note. Because ticks aren't going anywhere, except almost everywhere.