Diseases > Ticks

The topic of tick-borne disease is complex, and presentation of information pertaining to it requires the use of technical terms. These terms are depicted in bold type and are explained in a glossary.

Ticks are vectors of a wide range of disease agents worldwide, including viruses, bacteria, and protozoa. In North America, the role of ticks as vectors of two bacterial diseases, Lyme disease and Rocky Mountain spotted fever, is well documented. More recently, ticks have been implicated as vectors of additional diseases in North America, including anaplasmosis, babesiosis, and ehrlichiosis. Ticks also are involved in tick paralysis, a condition caused by a toxin or toxins in the saliva of ticks.

Every tick-borne disease is a zoonosis. This means that the disease agents exist year after year in a non-human animal reservoir, including a variety of small and large wild mammals. Ticks also can be part of the reservoir for disease agents. For example, certain disease agents can pass from infected female ticks into their eggs (transovariole transmission) and so hatching larvae may be infected. Also, most tick-borne disease agents can pass during a molt into the next life cycle stage, that is, from infected larvae to nymphs and infected nymphs to adults (transstadial transmission). Together, these two types of transmission help to explain the role of ticks as vectors and as part of the reservoir of disease agents.

There currently are no vaccines against disease agents transmitted by ticks available to the public, but early antibiotic therapy is effective against the disease agents transmitted in Indiana. You are encouraged to learn more about tick biology (see E-243-W "The Biology and Medical Importance of Ticks in Indiana" (PDF 757KB)) and tick-borne diseases (see E-244-W "Lyme Disease" (PDF 834KB)). This will enable you to make more informed decisions about health risks and how to protect yourself and your family. The ticks covered here are the so-called "hard ticks" (family Ixodidae), the type of ticks that are most frequently encountered by the public.

What Makes Ticks Effective Vectors?

Several factors determine the ability of a tick to transmit disease agents. First, a tick must be a competent vector. "Vector competence" refers to the ability of a tick to acquire a disease agent from an infected vertebrate and to then transmit it to a susceptible vertebrate animal during the taking of a subsequent blood meal. The potential vector must be a hospitable host in which the disease agent completes essential development and multiplies.

Second, a tick species must possess "vector capacity," which is determined by a number of factors such as vector competence, population density, host preferences, and feeding behavior. Some specific factors that contribute to the vector capacity of ticks include:

• All species feed on blood in each of three life cycle stages: larva, nymph, and adult.
• Adults, and to a lesser extent nymphs, attach and suck blood for up to several days. This increases the chance of acquiring a disease agent and increases the possibility of transmitting it to a susceptible host during a subsequent feeding.
• Ticks are competent hosts for a wide variety of viruses, bacteria, and protozoa, a wider variety than any other arthropod, including mosquitoes.
• Ticks are capable of transovariole and transstadial transmission of certain disease agents.
• Ticks have a very high reproductive rate and often exist in very high population densities. This increases the chance of a vertebrate host to come in contact with an infected tick.
• Ticks have relatively few natural enemies that contribute to their control.

What Should I Know About Tick Control?

Several species of ticks are vectors of disease agents in Indiana and can exist in large numbers some years in certain habitats including in and around residential developments adjacent to hardwood forests. Property owners can eliminate or at least cut back unwanted vegetation around yards, especially along the edge of woods and along paths in woods leading into the yard. Removal of leaf litter and use of woodchips or gravel as mulch along the edge of woods can help reduce the number of ticks in this area.

If warranted by the presence of large numbers of ticks, professional pest control companies can apply a registered chemical to control them. Homeowners planning to attempt tick control on their property should read E-71-W "Ticks - Biology and Their Control" (PDF 732KB) and be sure to follow directions and precautions on the label of the product used.

What Should I Know About Tick Repellents?

Tick repellents appear to act by masking odor cues given off by a person that attract ticks or by direct repellency to female ticks seeking a blood meal. Repellent products containing DEET are recommended by the Centers for Disease Control and Prevention (CDC). The CDC also recommends treating clothing with permethrin, which both repells and kills ticks. Various other compounds such as citronella, garlic, and vitamin B are purported to be repellents, but research does not support this. Readers interested in detailed information regarding the effectiveness and proper use of tick repellents and permethrin are directed to the CDC Web site listed below.

What Diseases Are Transmitted or Potentially Transmitted by Ticks in Indiana?

Ticks are involved in the transmission of several disease agents, including some about which details pertaining to the disease agent, vectors, and reservoir animals are still being documented. The disease links at the top of this page provide specific information pertaining to tick-borne diseases in Indiana. The key points are presented in "bullets" for quick reference. Additional information on tick biology and tick-borne diseases can be found in the websites listed at the bottom of this page.

It is important for the reader to know that the majority of patients infected with a tick-borne disease in Indiana will experience no symptoms or only mild, flu-like symptoms, but disease can be severe or fatal, especially in patients with a weakened immune system. People experiencing symptoms presented below who may have been exposed to tick bites are strongly encouraged to see a physician. Accurate diagnosis and early treatment with an appropriate antibiotic prescribed by a physician is extremely important. Tick-borne diseases in Indiana typically are successfully treated during the initial, acute infection whereas chronic disease is more difficult to treat and may not respond to treatment at all.

Where Can I Find More Information on Ticks and Tick-borne Diseases?

There are numerous sources of information pertaining to ticks and tick-borne diseases including Purdue University Cooperative Extension publications E-71-W "Ticks - Biology and their control" (PDF 732KB), E-243-W "The Biology and Medical Importance of Ticks in Indiana " (PDF 757KB), and E-244-W "Lyme Disease" (PDF 834KB), which focus on ticks and tick-borne diseases in Indiana. Numerous Web sites provide detailed information on tick biology, tick-borne diseases, and control. The following Web sites are recommended as accurate and current sources of information.

• Purdue Cooperative Extension Service
• Centers for Disease Control and Prevention
• Indiana State Department of Health
• Minnesota Department of Health
• Mayo Clinic

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