The black-legged tick and two others - the lone star tick ( Amblyomma americanum) and the American dog tick ( Dermacentor variabilis) - are responsible for most cases of tick-borne illness in the United States. The same tick that causes Lyme disease in the eastern United States - the black-legged tick, Ixodes scapularis - can harbor six other pathogens. A handful of tick species are the most serious spreaders. Hard ticks can transmit an array of bacteria, viruses and parasites to human beings, causing a roster of diseases, both familiar-sounding and obscure: Lyme disease, Rocky Mountain spotted fever, Colorado tick fever, babesiosis, tularemia and more. There are hundreds of species in this family, scattered all over the world, and their origins are ancient, probably stretching back more than 150 million years. Though both types of arachnid can carry disease, hard ticks - the family Ixodidae - are by far the more serious vectors. Ticks come in two main varieties: hard ticks, which have visible mouthparts and a hard plate on their back, and soft ticks, which lack the hard plate and have mouthparts hidden on their undersides. “You can research the system for decades, and there’s still just so much to learn.” Ticks are expert spreaders of pathogens Teasing out all these factors is complicated, says Lucy Gilbert, an ecologist at the University of Glasgow in Scotland. All will have consequences for the number of ticks in a given area, as well as for the likelihood that a tick’s saliva will carry at least one of the 18 tick-borne pathogens identified in the US and the 27-plus known globally. Scientists are working to disentangle a patchwork of drivers - such as land development, climate change and the availability of blood to suck from an array of different critters, large and small. And that’s a lot more difficult than tricking ticks into grabbing onto flannel. It’s also important to predict where the blood-feasting arachnids will move to next. “We want to make sure that people are aware that there is a risk that maybe they didn’t have as they were growing up in these communities,” she says. In the United States, the annual number of cases of six tick-borne diseases has roughly doubled since 2004, with most of the increase dominated by Lyme disease cases.įrom a public health perspective, it’s important to know when ticks have spread to new places, says Rebecca Eisen, a research biologist focused on vector-borne bacterial diseases with the Centers for Disease Control and Prevention. That’s reason to worry, because ticks are prodigious vectors - they bring more types of pathogens over to people from animals than any other creature. Even when his tick count for the day is zero, “that’s a useful insight,” he says.Įlsewhere in North America and internationally, blanket-dragging tick biologists like him are uncovering an unsettling trend: Many tick species are expanding their ranges, swelling in number and picking up new pathogens that can deliver disease to people should a tick latch on and bite. He is curious to know what areas in California are high risk or low risk for tick-borne diseases. Salkeld tallies his haul as he walks and carefully places the ticks in vials for further examination back in his laboratory at Colorado State University. And luckily for the scientists who track them, they are easily fooled by wool fabric. Ticks are passive predators of blood - they wait for an unsuspecting mouse, deer or person to brush past the blade of grass they are clinging to. It’s his favorite spot to collect ticks.Īs he walks, he trails a white flannel blanket attached to a pole, and every 20 meters, he stops, scrutinizes the flannel and picks off any ticks that have latched on. On a warm spring day, disease ecologist Daniel Salkeld is hiking the hills of coastal scrub and chaparral of Marin County, north of San Francisco.
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