TICK BORNE DISEASE PRIMER
TICKS
Ticks are parasites (aka "vectors") that transfer infective biological agents (bacteria, viruses, fungi, etc.) between hosts when feeding on their blood. Like other common blood-feeding "vectors" (mosquitoes, body lice and fleas) ticks are infected when they feed on animals ("reservoirs") that carry microorganisms in their blood. Known "reservoirs" of infective microorganisms are mice, chipmunks, woodchucks, and other small mammals.
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WORLDWIDE PROBLEM
Of all the pathogen-carrying "vectors", ticks are the main source of infections in humans and animals.
Worldwide there are over 900 different species of ticks. In the United States over 90 different species have been identified of which 2 (Ixodidae and Argasidae) are known to transmit diseases to humans. See the >>CDC ARTICLE for additional information.
TICKS ARE A THREAT TO PUBLIC HEALTH
According to the CDC the following ticks pose a significant threat to public health since they are responsible for transferring different pathogens to humans and animals:
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American Dog Tick is widely distributed east of the Rocky Mountains and in limited areas on the Pacific Coast. They transmit Tularemia and Rocky Mountain spotted fever. The highest risk of being bitten occurs during spring and summer. Dog ticks are sometimes called wood ticks. Adult females are most likely to bite humans.
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Blacklegged Tick is widely distributed in the northeastern and upper midwestern United States.
They transmit Lyme disease, anaplasmosis, babesiosis, bartonellosis, Powassan disease. The greatest risk of being bitten exists in the spring, summer, and fall. However, adults may be out searching for a host any time winter temperatures are above freezing. The nymph and adult females are most likely to bite humans and transmit disease. -
Brown Dog Tick is found worldwide. They transmit Rocky Mountain Spotted Fever (in the southwestern U.S. and along the U.S.-Mexico border). Dogs are the primary host for the brown dog tick in each of its life stages, but the tick may also bite humans or other mammals.
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Gulf Coast Tick is found in coastal areas of the U.S. along the Atlantic coast and the Gulf of Mexico.
They transmitRickettsia parkeri rickettsiosis, a form of spotted fever. The larvae and nymphs feed on birds and small rodents, while adult ticks feed on deer and other wildlife. Adult ticks have been associated with transmission of R. parkeri to humans. -
Lone Star Tick is widely distributed in the southeastern and eastern United States. They transmit
Ehrlichia chaffeensis and Ehrlichia ewingii (which cause humanehrlichiosis), tularemia, and STARI. A very aggressive tick that bites humans. The adult female is distinguished by a white dot or “lone star” on her back. Lone star tick saliva can be irritating; redness and discomfort at a bite site do not necessarily indicate an infection. The nymph and adult females most frequently bite humans and transmit disease. -
Rocky Mountain Wood Tick is found in the Rocky Mountain states and southwestern Canada from elevations of 4,000 to 10,500 feet. It transmits Rocky Mountain spotted fever, Colorado tick fever, and Tularemia. Adult ticks feed primarily on large mammals. Larvae and nymphs feed on small rodents. Adult ticks are primarily associated with pathogen transmission to humans.
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Western Blacklegged Tick is found along the Pacific coast of the U.S., particularly northern California. Transmits: Anaplasmosis and Lyme disease. Nymphs often feed on lizards, as well as other small animals. As a result, rates of infection are usually low (~1%) in adults. The stages most likely to bite humans are nymphs and adult females.
TICK BITES AND TICK DEVELOPMENT
Ticks develop in 4 stages over a 2-3 year life cycle: eggs, six-legged larvae, eight-legged nymphs, and adults. As larvae, nymphs, and adults the Tick's sole purpose in life is to seek out blood meals, molt into the next stage of development, and to reproduce the species. Note: Most Tick bites occur during the eight-legged nymph stage when the Tick is about the size of a poppy seed.
Both male and female ticks need blood to survive. During feeding, either tick can infect a host with pathogens, however, it's the female that is the aggressive and prolific feeder of the species. She stays attached longer, engorging herself on blood so she can molt into the next stage with the goal of becoming an adult so she can reproduce the species. As a larva, she feeds on small animals and larger hosts as a nymph and adult. She will die after her last meal but not before mating one time with a male tick, falling to the ground, and laying a nutrient rich egg cluster of 2,000 eggs. Unlike the female Tick, male Ticks can mate several times before they die.
QUESTING
Ticks are always looking for their next blood meal. They locate a host through a process call "questing" where they hang out in a suitable location (blades of grass, leaves, etc.) extending their 2 front legs to detect a passing animal. They have no eyes but can sense vibration, movement, body warmth / odor, and carbon dioxide through sensors called Haller's organs located on the tips of their front legs allowing the tick to sense a host from a distance.
Once a host is located, the Tick crawls onto the host and starts to crawl upwards towards the mammals head searching for a spot where the skin is thin so it can penetrate the skin to start the feeding process using a long barbed feeding tube called a "hypostome". It uses it's saliva as an anesthetic, lubricant, and adhesive to stay attached, undisturbed, for several hours to several days while it extracts nutrients from the host animal's blood. As it extracts nutrients it expels a lethal combination of waste water, pathogens, and saliva into the host's blood infecting the animal. Once the tick is engorged with nutrients it falls to the ground, molts, and transforms into the next stage of its life cycle.
Ticks have been infecting humans for thousands of years. The earliest evidence of tick borne disease was found in the mummified remains of a 5,300-year old iceman from the eastern Alps. Use MORE>> link to view article.
Prevent Tick Bites
