Dark Banquet - Bill Schutt [86]
The black-legged tick, or deer tick (Ixodes scapularis), is responsible for the transmission of three human diseases, including Lyme disease. Two less frequently observed afflictions are babesiosis (a malaria-like infection that attacks red blood cells), and human granulocytic ehrlichiosis (a bacterial infection that is analogous to anaplasmosis—a form of “tick fever” in cattle). The primary reservoir for the Lyme disease bacterium, Borrelia burgdorferi, is the white-footed mouse (Peromyscus), which is apparently not sickened by the infection. Borrelia is transferred to the ticks when they obtain a blood meal from the mouse, and Lyme disease can result when the infected tick transfers the bacterium to other animals, like deer, dogs, and humans.
The American dog tick (sometimes called the wood tick), Dermacentor variabilis, is the primary vector for Rocky Mountain spotted fever, a potentially fatal disease caused by the bacterium Rickettsia rickettsii. Named for the area where the disease was first diagnosed, and for the characteristic spotted rash that occurs in places like the palms and soles of the feet, Rocky Mountain spotted fever begins with flulike symptoms that worsen as blood vessel linings are attacked and major organ systems suffer the consequences.
Finally, the Lone Star tick (Amblyomma americanum) is so named for the distinctive, roughly star-shaped silver marking on the dorsal surface of the female’s body (the male has white markings along the posterior edge of its body). The Lone Star is a major concern because it transmits a “Lyme disease–like illness.” This is no surprise to those who study ticks since the bacterium they transmit (Borrelia lonestari) is closely related to Borrelia burgdorferi, the spirochete that causes Lyme disease. Research on the Lone Star tick has been stepping up recently, mainly because of the way the tick is sweeping into the northeastern United States. In fact, in many places (like Long Island) it is swiftly replacing the black-legged tick as the species most commonly encountered by humans. A more aggressive predator than the black-legged tick, the Lone Star actively tracks its potential host rather than waiting for it to pass by.
According to entomologist Tamson Yeh, the Lone Star tick presents additional problems for both integrated-pest-control specialists and the public.
“In the past, tick-free zones could be set up in parks and playgrounds. We did this by cutting back on brush and building mulch or woodchip buffers between areas of woods and lawn. But since the Lone Star ticks are more mobile, they have no problem crossing these buffers.”
Interviewing Dr. Yeh at her office in Riverhead, New York, I also learned that while the black-legged tick is primarily a forest dweller, the Lone Star prefers its environments hot and dry with plenty of open spaces.
“Considering the changes in local moisture patterns, it’s a nobrainer that this particular tick is becoming prevalent in the northeastern United States.”
I shifted in my seat. “By changing moisture patterns, are you referring to global warming?” Considering the media bombardment surrounding this catch phrase, I felt slightly uncomfortable now that I’d finally used it in a complete sentence.
Dr. Yeh hesitated. “Yes, global warming is a consideration—but it’s more than that. When you cut down a wooded area and throw down a bunch of houses, lawns, and concrete, things are going to get hotter and drier. Humans are changing vegetation patterns, and the urban environments they’re creating are just what the Lone Star tick thrives in. Plus, more people equals more contact with ticks.”
Ticks exhibit significant variation in their hunting techniques and scientists have used these differences as a handy way to categorize them. The soft ticks (argasids or argasoids) are primarily “habitat ticks” that is, they encounter their hosts in nests, burrows, caves,