A number of ticks in the United States spread pathogens that the CDC considers potential bioterrorism weapons. The family to which I. scapularis belongs, Ixodidae, carries many of the microbes included on the CDC's Select Biological Agents and Toxins list. Among the diseases caused worldwide by these organisms are Rocky Mountain spotted fever, tularemia, Crimean-Congo hemorrhagic fever and tick-borne encephalitic diseases.
Ticks spread disease by taking blood from an infected animal and then feasting on another animal. They need the blood to grow from egg to adult, and the adult female needs the blood to nourish her eggs.
In the case of Lyme disease-carrying deer ticks, the larvae feed on infected white-footed mice and other small mammals that harbor the pathogens. The tick develops into a nymph, which carries the Lyme disease-producing bacteria to people, pets and other animal species.
The tick's olfactory system, or what we call our noses, is in its feet. These organs recognize carbon dioxide, which animals, including people, emit when they exhale. Ticks lie in wait until they receive the carbon dioxide signal that a meal is nearby. Then they leap, sink their mouths into flesh, and gorge themselves while at the same time spreading insidious diseases.
Ticks feed on a diverse group of hosts including people, pets, livestock, reptiles and birds. Most of these are susceptible to the pathogens carried by one type of tick or another. Ticks have unique ways of interacting with both host and the disease-causing microbes they carry, Hill said. A host is the animal from which the tick sucks blood.
"Ticks stay on their host for a long time, and they've developed a complicated mechanism to avoid being detected," said Hill, an entomology assistant professor. "Ticks can increase the blood supply to the area where they're feeding. They release pain inhibitors so the host can'
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Contact: Susan A. Steeves
ssteeves@purdue.edu
765-496-7481
Purdue University
2-Sep-2004