Tick-borne disease


Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. They are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. Because individual ticks can harbor more than one disease-causing agent, patients can be infected with more than one pathogen at the same time, compounding the difficulty in diagnosis and treatment. 16 tick-borne diseases of humans are known, of which four have been discovered since 2013.
As the incidence of tick-borne illnesses increases and the geographic areas in which they are found expand, health workers increasingly must be able to distinguish the diverse, and often overlapping, clinical presentations of these diseases. Several high-profile deaths have been caused by the tick–human transmission of disease, including the death of former Senator Kay Hagan in the United States in 2019 at the age of 66.

Diagnosis and treatment

In general, specific laboratory tests are not available to rapidly diagnose tick-borne diseases. Due to their seriousness, antibiotic treatment is often justified based on clinical presentation alone.

Exposure

Ticks tend to be more active during warmer months, though this varies by geographic region and climate. Areas with woods, bushes, high grass, or leaf litter are likely to have more ticks. Those bitten commonly experience symptoms such as body aches, fever, fatigue, joint pain, or rashes. People can limit their exposure to tick bites by wearing light-colored clothing, using insect repellent with 20%–30% DEET, tucking their pants legs into their socks, checking for ticks frequently, and washing and drying their clothing.

Assessing risk

For a person or companion animal to acquire a tick-borne disease requires that the individual gets bitten by a tick and that the tick feeds for a sufficient period of time. The feeding time required to transmit pathogens differs for different ticks and different pathogens. Transmission of the bacterium that causes Lyme disease is well understood to require a substantial feeding period.
For an individual to acquire infection, the feeding tick must also be infected. Not all ticks are infected. In most places in the US, 30-50% of deer ticks will be infected with Borrelia burgdorferi. Other pathogens are much more rare. Ticks can be tested for infection using a highly specific and sensitive qPCR procedure. Several commercial labs provide this service to individuals for a fee. The Laboratory of Medical Zoology, a nonprofit lab at the University of Massachusetts, provides a comprehensive TickReport for a variety of human pathogens and makes the data available to the public. Those wishing to know the incidence of tick-borne diseases in their town or state can search the LMZ surveillance database.

Examples

Major tick-borne diseases include:

Bacterial