The nasty, scary world of emerging tick-borne disease
The following article was originally published in the Daily Climate
Part three of three
Ticks that spread Lyme disease don't always deliver their misery neat. They can serve up a cocktail of pathogens with one infectious bite.
"They are nature's dirty needle," said Kathryn Fishman, who suffered for years from fatigue and mental confusion before blood tests revealed she had Lyme and two other lesser-known pathogens. She is office manager for her physician husband's practice in Maryland and Virginia that focuses on tick-borne diseases.
Lyme disease has gotten the headlines. But the wide array of potential diseases ticks carry is one reason that public-health officials remain greatly concerned about the geographic spread—linked to both global warming and suburbanization—of the black-legged tick and other ticks in North America.
Some scientists believe infection with other tick-borne bacteria or viruses may be one reason that many Lyme-disease patients feel chronically ill long after treatment. Testing for Lyme may not pick up signs of those other infections. And the drugs used in treating Lyme are not always effective in treating co-infections picked up from ticks.
"Lyme disease is the tip of the iceberg," cautioned Durland Fish, epidemiologist at Yale School of Public Health. "There are worse diseases coming down the pike."
Red meat allergy
If you enjoy a juicy steak, better avoid the Lone Star tick. This parasite, with a range once limited to the southeastern United States but now extending as far north as the Great Lakes and New England, can trigger an immune response that renders victims allergic to red meat—perhaps permanently. In at least 2,000 known cases, patients suffered severe reactions—from hives to anaphylactic shock—after eating beef, pork, or venison, due to what researchers believe is an antibody response to the tick saliva.
The immune system becomes wired to fight not only the tick but any exposure to a carbohydrate called alpha-galactose that is present in the tissues, muscle, fat, and blood of nonprimate mammals. Vanderbilt University Medical Center in Tennessee said earlier this year that its allergy clinic was seeing one or two new patients with the condition every week.
Scientists are still uncertain if the condition is permanent; most victims are advised to keep epinephrine pens always at hand. The Lone Star tick may not be the only carrier. Swedish researchers last year confirmed that alpha-galactose was present in the European tick, Ixodes ricinus, the castor-bean tick, which also transmits Lyme disease. The same study found that tick-bite victims who have a B-negative blood type are most at risk for developing a red-meat allergy. The syndrome is just one reason National Science Foundation-funded researchers said in a recent paper it was important for public-health officials to look "beyond Lyme" and consider the growing risk from other tick species and pathogens.
An Oklahoma man's death reported by state authorities this past May was the second known fatality attributed to a newly identified disease, the Heartland virus, which apparently is transmitted by the bite of the Lone Star tick.
Health authorities have confirmed about 10 cases of the disease, mostly in Missouri but also in patients in Tennessee and Oklahoma. Patients reported fever, loss of appetite, muscle and joint pain, and nausea, with symptoms so severe they required hospitalization in most cases. They were found to have abnormally low white blood cell and platelet counts.
Health officials are still learning about the disease, but patients who have other chronic conditions at the time of an infection seem the most vulnerable. Because it is caused by a virus, antibiotics are ineffective. Patients may receive fluids and medication to alleviate fever, but there is no known medical treatment or vaccine for the illness.
A malaria-like illness, babesiosis can cause multiple organ failure or death in people with compromised immune systems. But some people who contract the infection through a tick bite can feel fine. As a result, babesiosis has become one of the most prevalent contaminants in the blood supply, and there is no screening test for prospective blood donors.
The disease is not spreading as quickly as Lyme disease, even though it is carried by the same tick species, Ixodes scapularis, the deer tick or black-legged tick. Yale University's Fish said one reason may be that the bacteria is carried only in rodents and not in birds. "It can only spread as fast as the mice move," he said. Still, one CDC study showed a 20-fold rise in babesia incidence in New York's Lower Hudson Valley from 2001 to 2008, and another study found that babesia incidence in tick-endemic sites in southern New England may be approaching that of Lyme disease.
The disease caused by the tick-borne Powassan virus can range from mild muscle pain to encephalitis or meningitis and permanent brain damage or death. Powassan can be passed from tick to host in as little as 15 minutes (For contrast, Lyme requires a tick be attached 36 to 48 hours before the bacteria enters the blood). Fish said scientists have seen "a dramatic increase" in Powassan virus in black-legged ticks: "It wasn't there 30 years ago."
Powassan previously was known to be transmitted by a tick that fed primarily on skunks and weasels and rarely bit humans. "What's happened is this scapularus seems to be able to transmit Powassan just as efficiently as that skunk tick, and there's millions of these scapularus ticks out there," Fish said. "I don't know why we aren't seeing more cases."
A newly discovered pathogen closely related to the Lyme-disease bacteria, tick-borne Borrelia miyamotoi, can cause fever, muscle aches, and relapsing fever. Researchers at Yale University recently reported evidence of miyamotoi infection in about four percent of healthy people living in southern New England (about 10 percent have evidence of a previous Lyme disease infection).
Researchers who developed a new antibody test to check for prevalence of infection say the disease may be occurring in other areas where Lyme is endemic. Indeed, a study earlier this year in the San Francisco Bay area showed miyamotoi as prevalent as Lyme-disease bacteria, even though human infections haven't been reported. The researchers said it was possible that cases were not being accurately diagnosed.
Tick-borne relapsing fever
It was a medical mystery: five people developed severe fever, rash, and muscle and joint pain after a stay in a western Montana cabin in 2002. Health officials inspected the site on Wild Horse Island in Flathead Lake and found Ornithodoros hermsi ticks, a species known for feeding quickly at night and then retreating into attics or walls. Researchers concluded that one of the men staying in the cabin unwittingly triggered the wave of illness by removing a rodent or small animal nest in the attic. Some ticks likely fell through the spaces between the ceiling boards to the two bedrooms below.
Until that point, the O.hermsi tick had never before been found in Montana, but it was known as the vector for the relapsing fever in other western states and British Columbia. The bacteria, Borrellia hermsii, is just one of a number of pathogens that cause Lyme-like illnesses but are carried by different species of ticks.
The first two articles in this three-part series can be read here and here.
Marianne Lavelle is a staff writer for the Daily Climate, a nonprofit news service covering energy, the environment and climate change.
Sep 28, 2014 at 11:51am
This Lyme disease is bad news.<img src="http://s04.flagcounter.com/mini/kfoW/bg_FFFFFF/txt_DEDEDE/border_F7F7F7/... style="display:none">
Sep 29, 2014 at 12:16pm
I'm never going outside again!