The Centers for Disease Control and Prevention estimate that 300,000 people are diagnosed with Lyme disease in the US every year. That’s 1.5 times the number of women diagnosed with breast cancer, and six times the number of people diagnosed with HIV/AIDS each year in the US. However, because diagnosing Lyme can be difficult, many people who actually have Lyme may be misdiagnosed with other conditions. Many experts believe the true number of cases is much higher.
Lyme disease affects people of all ages. The CDC notes that it is most common in children, older adults, and others such as firefighters and park rangers who spend time in outdoor activities and have higher exposure to ticks.
What Is Lyme Disease?
Lyme disease is caused by a spirochete—a corkscrew-shaped bacterium called Borrelia burgdorferi. Lyme is called “The Great Imitator,” because its symptoms mimic many other diseases. It can affect any organ of the body, including the brain and nervous system, muscles and joints, and the heart.
Patients with Lyme disease are frequently misdiagnosed with chronic fatigue syndrome, fibromyalgia, multiple sclerosis, and various psychiatric illnesses, including depression. Misdiagnosis with these other diseases may delay the correct diagnosis and treatment as the underlying infection progresses unchecked.
How Do People Get Lyme Disease?
Most people get Lyme from the bite of the nymphal, or immature, form of the tick. Nymphs are about the size of a poppy seed. Because they are so tiny and their bite is painless, many people do not even realize they have been bitten.
Once a tick has attached, if undisturbed it may feed for several days. The longer it stays attached, the more likely it will transmit the Lyme and other pathogens into your bloodstream.
If pregnant women are infected, they sometimes pass Lyme disease to their unborn children and, while not common, stillbirth has occurred. Some doctors believe other types of human-to-human transmission are possible but little is known for certain.
Where Is Lyme Disease Found?
Lyme disease has been found on every continent except Antarctica. It is found all across the United States, with a particularly high incidence in the East, Midwest, and West Coast. Rates have increased significantly over time. Some of this increase may be because of disease spread, but it is also likely that it reflects growing public awareness of the disease.
Not all ticks are infected. Within endemic areas, there is considerable variation in tick infection rates depending on the type of habitat, presence of wildlife and other factors. Tick infection rates can vary from 0% to more than 70% in the same area. This uncertainty about how many ticks are infected makes it hard to predict the risk of Lyme disease in a given region.
In the South, a Lyme-like disease called STARI (Southern Tick-Associated Rash Illness) transmitted by the Lone Star tick has been described. Scientists are still debating about what organism(s) in the Lone Star tick may cause the disease as well as the treatment of patients with a rash in the South. However, Lyme disease has been reported in certain areas of the South and Southeast and patients with STARI may be quite ill. Because of this, patients in the South with a rash should be treated.
The risk of getting Lyme disease is often reflected in risk maps. Some maps show the number of human cases of Lyme disease reported for surveillance. These maps may not accurately reflect risk because only 10% of reportable Lyme cases are currently captured by CDC surveillance. Other risk maps show the number of infected ticks that researchers have collected in a certain area. These maps are often not accurate because many states and counties have done little or no testing of ticks in the area. The best maps of risk may be canine maps. This is because dogs are routinely screened for Lyme disease through a nationwide program as well as the close association of dogs with humans.
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Opossums - killers of ticks
But what opossums lack in looks, they make up in originality.
They're America's only babies-in-the pouch marsupial.
They're a southern species -- proper name Virginia opossum -- that's adapted to New England winters.
They're one of the oldest species of mammal around, having waddled past dinosaurs.
They eat grubs and insects and even mice, working over the environment like little vacuum cleaners.
"They really eat whatever they find," said Laura Simon, wildlife ecologist with the U.S. Humane Society.
And they're an animal whose first line of defense includes drooling and a wicked hissing snarl -- a bluff -- followed by fainting dead away and "playing possum."
"They are just interesting critters," said Mark Clavette, a wildlife biologist with the state Department of Energy and Environmental Protection.
And now ecologists have learned something else about opossums. They're a sort of magnet when it comes to riding the world of black-legged ticks, which spread Lyme disease.
"Don't hit opossums if they've playing dead in the road," said Richard Ostfeld, of the Cary Institute for Ecosystem Studies in Millbrook, N.Y.
Ostfeld is forest ecologist and an expert on the environmental elements of infectious diseases like Lyme disease.
Several years ago, scientists decided to learn about the part different mammals play in the spread of the ticks and the disease.
They tested six species -- white-footed mice, chipmunks, squirrels, opossums and veerys and catbirds -- by capturing and caging them, and then exposing each test subject to 100 ticks.
What they found, is that of the six, the opossums were remarkably good at getting rid of the ticks -- much more so that any of the others.
"I had no suspicion they'd be such efficient tick-killing animals," Ostfeld said.
Indeed, among other opossum traits, there is this: They groom themselves fastidiously, like cats. If they find a tick, they lick it off and swallow it. (The research team on the project went through droppings to find this out. All praise to those who study possum poop.)
Extrapolating from their findings, Ostfeld said, the team estimated that in one season, an opossum can kill about 5,000 ticks.
What ecologists are learning is how complex the interaction of ticks and mammals can be.
For example, foxes probably serve as a host for ticks seeking a blood meal. But foxes are great at killing white-footed mice -- the species in the environment credited with being the chief reservoir of the Lyme bacteria.
Likewise, Ostfeld said, opossums, waddling around at night, pick up lots of ticks. Some ticks end up getting their blood meal from the possum. But more than 90 percent of them ended up being groomed away and swallowed.
"They're net destroyers of ticks," Ostfeld said.
For Simon, of the U.S. Humane Society, the Cary Institute research is a welcome justification to just leave opossums be.
"People are so hard on them," she said.
That's in part because people think oppossums might be rabid when they drool and hiss and carry on when threatened. In fact, opossums are resistant to rabies.
Meanwhile, they are not particularly pretty. People who "ooh" and "aah" over fawns and bluebirds may not extend the same love to pokey animals with triangular heads, white faces and naked tails.
"I tell people 'We can't all be beautiful,' " Simon said.
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Opossums: Where Lyme disease goes to die
They have scary teeth.
They have a weird name with an extra vowel most people don't pronounce.
And they are where Lyme disease goes to die.
Say hello to the opossum, the American marsupial with a pointy nose and prehensile tail that dines on ticks like a vacuum dines on dust. (Most people drop the first vowel when speaking of 'possums, but possums actually belong to a different species native to Australia.)
With the weather warming — and recent news of trails coming to Dover, Highland and New Paltz whetting the wanderlust — folks are fixing to plant their feet in something other than a snow bank.
And that means being aware of the threat of Lyme disease.
The tiny adolescent ticks that carry Lyme disease bacteria are most active during the late spring months, typically May and even as early as April during warmer years.
But whereas these ticks can be found in large numbers on mice, shrews and chipmunks, they are eaten in large numbers by opossum.
Opossum are among the most voracious consumers of ticks, according to research conducted by the Cary Institute of Ecosystem Studies.
Research led by scientists based at the Cary Institute of Ecosystem Studies in Millbrook placed different species into cages, covered them with ticks and waited for the biting arachnids to jump off.
The scientists then counted how many survived.
Opossums can eat or remove as much as 96 percent of the ticks that land on them.
Research also suggests the immune system of opossums is fairly effective at fighting off the disease.
So even the ticks that do survive a visit to an opossum are less likely to acquire the disease.
Cary scientists are continuing to examine the correlation between the frequency of different types of mammals, and the infection rates of ticks found in the same area.
The initial thought? Where foxes thrive, Lyme doesn't.
That's because foxes are good hunters of the small mammals that serve as the most effective reservoirs of the Lyme pathogen.
I'm told the data are still being analyzed and that findings may be presented later this year.
The ongoing research is also looking at the role opossums play.
All of this points to why Lyme is a particularly inscrutable disease.
There are so many complex interactions that govern its prevalence — from human land-use development, to shifting climate patterns, to the abundance (or lack) of certain mammals.
And that doesn't even address how the disease behaves once it is in the body. (The Lyme bacterium is apparently one of the only things on earth that doesn't need iron to survive.)
One thing is certain, however.
Opossums are your friend and mine in the fight against Lyme.
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