As if the threat of Lyme disease weren’t enough, a new study finds that a deer tick carrying the potentially debilitating illness has a good chance of toting some other malady, too — and that may be especially true if the tick hails from the suburbs.
One-third of ticks infected with Lyme disease in Dutchess County, a Hudson Valley area with high rates of tick-borne illness, were also infected with another pathogen, according to research conducted by scientists at Bard College, Sarah Lawrence College and the Cary Institute of Ecosystem Studies. The researchers collected thousands of deer, or blacklegged, ticks, from more than 150 sites in Dutchess County.
Doctors, patients and scientists have long known about the chance of getting multiple infections from a single tick, and the threat of co-infections has been part of a decades-old controversy over how to test for and treat tick-borne illness.
New to this study, said co-author Felicia Keesing, is that the small mammals the ticks feed on also carry multiple infections. This means that the tick isn’t getting different infections from multiple sources — it’s getting two and sometimes three infections from the same mouse or chipmunk.
Researchers at the three Hudson Valley institutions found higher levels of co-infections in Dutchess County ticks than would occur by chance. That was particularly true for the bacteria that causes Lyme and the protozoan that causes babesiosis, which causes flu-like symptoms and can be life-threatening to people with weakened immune systems. About 7 percent of the ticks in the study carried the pathogens for both those diseases.
Researchers also looked at the likelihood that a tick would carry both the bacteria for Lyme disease and for anaplasmosis, another emerging tick-borne illness that can be fatal if not treated correctly, even in otherwise healthy people. Ticks were not more likely to be co-infected with bacteria for those two illnesses, they found.
But rates of triple infection with the agents of Lyme, babesiosis, and anaplasmosis were about twice as likely as chance would predict.
The seemingly high rates of multiple infections in ticks made more sense to scientists once they realized the bugs could ingest several pathogens in a single, small-mammal meal.
‘’It’s not a coincidence that the co-infection rate is so high,’’ Keesing said.
The study may offer a cautionary tale about development that reduces the types of animals thriving in a region, she said. Ticks resort to feeding exclusively on small mammals when there aren’t larger animals, like raccoons or deer, to feast upon. Mice and chipmunks are more able to prosper in densely populated areas, like suburbia, than larger mammals are.
‘‘That means that when we have habitats with lots of small mammals in them, our rates of co-infection should be higher,’’ Keesing said. ‘‘When we lose competitors or when we reduce diversity, it’s the small mammals that thrive.’’
It also means the relatively high rate of tick co-infections found by the Hudson Valley researchers might not be seen in regions in which Lyme disease is just emerging, like the Adirondacks.
The Trudeau Institute in Saranac Lake is embarking on its own research on rates of disease in ticks, in conjunction with the state Health Department. Timothy Sellati, an immunologist at Trudeau, praised the Hudson Valley study for considering both the ticks and their mammal hosts.
‘’It looks at both of them in the same environment, and that’s the only way to get a definitive answer to this question of co-infection,’’ Sellati said.
Additional research is needed to understand the effects on patients of contracting more than one infection simultaneously from a tick bite, according to Bryon Backenson, who heads the Health Department’s Investigations and Vector Surveillance programs.
The bottom line for people sickened by a tick bite — especially in a more densely populated area — is that treatment for one disease may not cure them, Keesing said. Patients must be aware that their chance for co-infection is higher than their doctors may realize, she said.
That’s a precaution a well-organized group of patients who have suffered from lingering symptoms following tick bites have long advocated.
‘’If you have a different species (of bacteria) or any of the co-infections, there’s a lot that can be missed,’’ said Holly Ahern, a microbiologist at SUNY Adirondack and patient advocate.
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Beware of ticks
To prevent infection, avoid tick bites, and take these precautions when outdoors, especially in wooded areas.
Wear light-colored clothes that cover arms and legs, so ticks can be spotted.
Use insect repellents with DEET or Permethrin, according to instructions.
Shower or bathe soon after coming indoors.
Check your body for ticks and remove them immediately.
If you find a tick:
Remove it with fine-tipped tweezers. Grab close to the skin and pull upward.
If a rash or other symptoms develop, seek medical help.
Sources: Bryon Backenson/New York State Department of Health, U.S. Centers for Disease Control and Prevention
At a glance
Cases of tick-borne disease statewide*
Lyme disease: 5,887
*For 2012, the latest data available
Source: New York State Department of Health