Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
Ticks are small bloodsucking arthropods and are composed of two families, Ixodidae (hard ticks) and Argasidae (soft ticks), that each contain different genera and species of ticks.
Ticks are the leading carriers (vectors) of diseases to humans in the United States, second only to mosquitoes worldwide. It is not the tick bite but the toxins, secretions, or organisms in the tick's saliva transmitted through the bite that causes disease.
Ticks are arthropods, like spiders. There are more than 800 species of ticks throughout the world. Many organisms that bite humans for a blood meal are not ticks and should not be confused with ticks. Some common examples are bedbugs and fleas (both are insects, not arthropods). If it is possible to bring into the doctor's office what has caused a "bite," the physician may be able to determine what potential vector caused the "bite."
Two families of ticks, Ixodidae (hard ticks) and Argasidae (soft ticks), are important to humans because of the diseases or illnesses they can transmit or cause. Hard ticks have a tough back plate or scutum that defines their appearance. The hard ticks tend to attach and feed for hours to days. Disease transmission usually occurs near the end of a meal, as the tick becomes full of blood. Figure
1 shows several hard ticks and the various stages in their life cycle. The stages are part of the life cycle of ticks; the smallest stages, larva and nymph, are sometimes generally referred to as "seed ticks" because they resemble small plant seeds.
Figure 1: The life cycle of ticks. Source: CDC
Soft ticks have more rounded bodies and do not have the hard scutum found in hard ticks. These ticks usually feed for less than one hour. Disease transmission from these ticks can occur in less than a minute. The bite of some of these ticks produces intensely painful reactions. Ticks can transmit disease to many hosts; some
diseases cause economic harm such as Texas fever (bovine babesiosis) in cattle that can kill up to 90% of yearling cows. Figure 2 shows the body of a soft tick; there is no hard scutum, only the soft body. The adult soft ticks are about the same size as adult hard ticks (see Figures 1
Medical Authors: Barbara K. Hecht,
PhD, Frederick Hecht, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
Ticks carry the bacteria that cause Lyme disease. People
contract Lyme disease by being bitten by these ticks.
In order to investigate whether specific human behavior increases the risk of
tick exposure, researchers from the University of California at Berkeley took to
the woods. They found that sitting on a log carried with it the greatest risk of
picking up a tick. If you sit on a log (at least in Northern California) for
only five minutes, you have a 30% chance of getting a tick on you! Gathering wood
was also cited as a risky activity as well as leaning up against a tree.
Comment: Aside from issuing a press release (below) about this study,
it was also published in the current issue of the Journal of Medical Entomology.
In case you aren't familiar with this journal, it is chock-full of everything
you might want to know (or not know) about the dangers that mosquitoes, cat
fleas, ticks, flies, scorpions, mange mites and other insects pose to you. We
don't recommend it for bedtime reading.