Tick-borne diseases outside usual borders.

• Position: Pathogens

As summer approaches, people in the Northeast and Midwest look forward to spending more time outdoors--which also means plotting ways to avoid the disease carrying black-legged deer tick. However, those living outside of these areas also may want to take precautions. Black-legged ticks are growing in number rapidly, expanding geographically, and carrying pathogens that can lead to ailments like Lyme disease and babesiosis into places where they were relatively unknown.

Disease ecologist Maria Wasser of Columbia University, New York, is tracking the spread and emergence of tick-borne pathogens, including a malaria-like parasite called Babesia microti, which causes babesiosis--a malaria-like malady-when transmitted to humans. An increasing number of ticks are infected with Babesia and Wasser's team is exploring evidence that the trend is connected to the rapid spread of Borrelia burgdorferi, the bacterium that causes Lyme disease.

"We found that these two pathogens co-occur in ticks more frequently than expected, resulting in enhanced human exposure to multiple infections," says Wasser, associate professor in the Department of Ecology, Evolution and Environmental Biology. "Multiple infections lead to more severe symptoms and can make diagnosis more muddled and difficult."

About 1,000 new cases of babesiosis are reported each year, while Lyme disease infects about 30,000 people annually. The two diseases share some of the same symptoms, including a flu-like illness, but babesiosis, which can cause certain types of anemia, potentially is fatal in people with suppressed immune systems. It also can be transmitted via blood...