Seeking to solve the Lyme disease puzzle
- 18 April 2012
- From the section US & Canada
Lyme disease remains a mysterious ailment, even as the ticks that carry the illness continue to spread across the United States. But a new study could help determine why some people get sick.
While on a camping trip in Virginia last spring, I was bitten by an Ixodes scapularis, more commonly known as a deer tick. I'm still not sure where the parasite lodged itself, but I think it must have crawled into my hair and fastened on to my scalp.
More revolting still, it probably remained there, gorging itself on my blood for at least 36 hours - the average time experts believe it takes to infect a human with the bacteria that causes Lyme disease.
A couple of weeks later I had all the symptoms: chronic fatigue, agonising headaches, back and muscle pain, and the classic red-ringed rash that is often the hallmark of Lyme disease. My doctor immediately prescribed a month-long course of antibiotics.
If the disease is caught early, most experts say such treatment will solve the problem completely. It did for me.
But about 20% of patients report lingering or recurring symptoms even after taking antibiotics. The condition is often referred to as chronic Lyme disease or more formally, Post-Treatment Lyme Disease Syndrome (PTLDS).
PTLDS is hugely controversial because nobody knows what causes it. The Centers for Disease Control and Prevention says it's generally thought to be the result of damage to tissues or the immune system.
But it could also be that the antibiotics haven't eliminated all the infecting bacteria - and current tests on humans can't prove it one way or another.
That's why a team of researchers at the National Institute of Allergy and Infectious Diseases (NIAID) is testing a new approach.
They're in the middle of a clinical trial that allows uninfected ticks to feed on humans who have been treated for Lyme disease. Researchers will then test the ticks for the bacteria that causes the disease.
The process is called xenodiagnosis. It's been successful in identifying Lyme disease in animals, but this is the first time it's being tried on humans.
"It's very important because it could open many new avenues of research and provide a new tool for the study of Lyme disease," says Dr Adriana Marques, who's in charge of the trial.
"Right now we need hard evidence that persistence of infection plays any role in PLDS symptoms," she says.
Turning the tables on the ticks certainly has its appeal. Dr Marques says a number of people have come forward to volunteer, even though it means being bitten by up to 30 ticks at a time.
The ticks are placed on the patient's skin under a small container or filter paper held in place with a dressing. After four to five days they are removed and tested. The trial is set to continue for another three years, but Dr Marques hopes the study may start yielding information sooner.
That will be welcome news for the roughly 30,000 people who are diagnosed with Lyme disease every year. The CDC says it's now one of the top five infectious diseases in North America.
First identified 30 years ago in Lyme, Connecticut, the disease has since spread to several other states.
A new map that tracks tick populations has shown that for the first time, most of Wisconsin, a large area in northern Minnesota, a small portion of northern Illinois and parts of southern Virginia are among those at risk.
"In the space of six years, infected areas have grown and are growing," says Dr Maria Diuk-Wasser, assistant professor at the Yale School of Public Health and the lead author of the study.
Taste for human blood
Rather than rely on reports of human infection which can be geographically inaccurate or misdiagnosed, she and her team spent several years hunting down the ticks themselves.
They made their way across 37 states dragging a 10 sq ft (1m sq) of corduroy cloth to snag the insects.
"This is not purely a human health problem - it's an environmental problem," says Dr Diuk-Wasser. "Deer have become overpopulated because they have no natural predators."
Ticks need blood to thrive. They have their first meal as larva, feasting on mice which may be infected with Lyme disease. That begins the life-cycle of the disease.
As they grow into nymphs, or non-adult ticks, they need larger mammals - usually deer, but increasingly human.
Despite the spread of deer ticks, incidence of Lyme disease itself appears to have stabilised, says Dr Phillip Baker, Executive Director of the American Lyme Disease Association.
"Over the last 10 years the figures show that the reported rate of infection has remained roughly the same - it's not increasing to epidemic proportions," he says.
"And the evidence suggests it's a limited infection in humans that can be easily treated with antibiotics," he says. "It's not a life-threatening disease."
In the absence of any preventative vaccine and in light of the ongoing controversy over treatment and cure, it seems the best defence against Lyme disease is to avoid being bitten.
Spring and early summer are the most dangerous times of the year and the unseasonably warm weather across the region is even more likely to lure people outdoors and into the paths of nymphs looking for their next meal.
Perhaps I'll delay this year's camping trip.