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Increasing population and the push for country homes bring many people into areas where once there was only wildlife. Now, parasites whose lives had alternated for eons between ticks and wildlife species are given a chance to experiment living in man and his pets. Vector ecologists throughout the country find themselves trying to learn a lot more about the tick species in their regions.
Tick bites range from completely unnoticed to irritating. Sometimes the anethesitic-like saliva causes "tick paralysis", and sometimes it carries a disease agent. All the diseases ticks pass on to man are actually zoonoses - diseases of wildlife that accidently find a way into human beings. In California, these diseases include Babesiosis, Ehrlichiosis, Rocky Mountain spotted fever, Tularemia and Lyme disease.
A tick passes through several stages: egg, larvae, nymph and adult. The larva is called a "seed tick" and measures about the size of a period. After hatching, at each stage it must find and attach to a favorite host, take a blood meal, and then drop off to the ground, digest the meal, molt and grow. Ticks tend to be rather host specific - they seek a blood meal from only one kind of host. Most complete their lives in two to three years, but some live for more than 20 years.
Ticks require high humidity and moderate temperatures. Young ticks live in the soil or vegetation at ground level. When ready to feed, they climb up on a blade of grass, leaf or small branch, wave their front legs with anchor-like claws, and wait for a potential host to pass by.
Heavy tick infestations alone are a common cause of suffering and death in wild amphibian, reptile, bird and mammal species. Among wildlife, ticks transmit a greater variety of infectious agents than any other group of arthropods. They include viruses, rickettsia, bacteria and protozoan parasites; only a tiny fraction of which have ever been found in man.
There are two main families: "soft ticks" (photo above), with soft, leathery bodies and mouth parts on the underside, and"hard ticks" (right), with a plate-like shield on the back and mouthparts on the forward edge of the body. Ranchers and veterinarians become familiar with the main groups: Otobius, Argus and Ornithodorus (soft ticks) and Ixodes, Dermacenter and Rhipicephalus (hard ticks). Ixodes scapularis is believed to be the main vector of human babesiosis, ehrlichiosis and Lyme disease in the eastern U. S., and Ixodes pacificus in California.
Ticks can be kept to low numbers on maintained property by keeping grasses cut low and shrubs trimmed close to the ground. But tick control in rural areas is not currently practical. The only way to completely avoid tick-borne diseases is to avoid the the places where ticks live. If this is not possible (or desirable), the risk of contracting an infection in endemic areas can be greatly reduced by using repellants on clothing, keeping pants legs tucked inside the tops of the socks, and routine frequent checking of the body so ticks can be removed before they become firmly attached.
Vector ecologists are now trying to identify the places or habitats where the risk of getting a tick-borne disease is especially high. Marin / Sonoma district personnel collaborate with research groups like those at the Veterinary School at the University of California at Davis and the Vector-Borne Disease Section of the California Department of Health Services to find out what percentage of local tick populations carry infectious agents, and describe the seasonal population trends of each of the different tick species.
Helpful references:
- Ticks Commonly Encountered In California University of California Davis.
- Safety Information on Lyme Disease University of California Davis, 1999.
- "Emergence of Tick-Borne Diseases", by Sam R. Telford III, Jacqueline E. Dawson and Karl C. Halupka. In: Science & Medicine, March/April 1997: pages 24-33.