Ticked off: America’s quiet epidemic of tickborne diseases

John Ross, MD, FIDSA

Contributing Editor

For most of us, springtime marks the return of life to a dreary landscape, bringing birdsong, trees in bud, and daffodils in bloom. But if you work for the Centers for Disease Control and Prevention (CDC), the coming of spring means the return of nasty diseases spread by ticks and mosquitoes.

The killjoys at CDC celebrated the end of winter with a bummer of a paper showing that infections spread by ticks doubled in the United States from 2004 to 2016. (Tick populations have exploded in recent decades, perhaps due to climate change and loss of biodiversity.)

Lyme disease

The most common infection spread by ticks in the US is Lyme disease. There were 19,804 confirmed cases of Lyme in 2004, compared to 36,429 in 2016. Because of incomplete testing and reporting, these numbers are almost certainly an underestimate. There may be as many as 329,000 cases of Lyme disease in the United States every year. New England, the mid-Atlantic states, and Minnesota and Wisconsin account for 95% of reported cases.

While Lyme disease may lead to fever, rash, meningitis, Bell’s palsy, and arthritis, it rarely kills. More worrisome are surges in deadly diseases spread by ticks, such as Rocky Mountain spotted fever, anaplasmosis, ehrlichiosis, and babesiosis.

Other serious tickborne illnesses

Rocky Mountain spotted fever (RMSF) is a misnomer. Although it occurs throughout much of the United States, including the Rocky Mountains, it is most common in southern Appalachia and the Ozarks; 60% of cases are diagnosed in North Carolina, Tennessee, Arkansas, Missouri, and Oklahoma. Reported cases of RMSF rose from 1,713 in 2004 to 4,269 in 2016. Patients with RMSF have high fever, headache, belly pain, and a rash with pinpoint red dots or red splotches. The rash may not be present early in the disease. Even with treatment, RMSF is fatal in up to 4% of cases.

Anaplasmosis and ehrlichiosis resemble RMSF, except that rash is less prominent (and is rare in anaplasmosis). Anaplasmosis is lethal in 0.5% of cases, while ehrlichiosis kills 1% to 2% of patients. Cases of these two diseases rose from 875 in 2004 to 5,750 in 2016. Anaplasmosis is most common in New York, New Jersey, New England, Minnesota, and Wisconsin, while ehrlichiosis abounds in the southeastern and south central United States.

Babesiosis is a tickborne disease that mimics malaria, leading to hectic fevers, headache, body aches, anemia, and liver and kidney damage. Cases rose from 1,128 in 2011, the first year it was a reportable disease, to 1,910 in 2016. In the US, it is most common in coastal New England and parts of New York, New Jersey, Wisconsin, and Minnesota.

As if that wasn’t enough to worry about, we are still discovering new infections spread by ticks, including Bourbon virus, which killed a man in Bourbon County, Kansas, in 2014, and Heartland virus, first diagnosed in two Missouri farmers in 2009.

Infections spread by mosquitoes

If infections spread by ticks have increased steadily, infections spread by mosquitoes tend to have more of a waxing and waning pattern. West Nile virus, which first came to the United States in 1999, has flared up multiple times in the continental US since then. Other exotic viruses, such as Zika, dengue, and chikungunya, have caused major outbreaks in Puerto Rico, American Samoa, and the US Virgin Islands, with occasional spillover into the continental US.

How to protect against ticks and mosquitoes

  • Avoid walking in scrubby areas with shrubs, bushes, high grass, and leaf litter, where ticks abound.
  • When walking in the woods, stick to the center of cleared trails.
  • Tick repellents containing picaridin, IR3535, or at least 20% DEET will provide several hours of protection to exposed skin. Clothing and camping gear can be treated with sprays containing 0.5% permethrin.
  • The Environmental Protection Agency (EPA) has a search tool to help you find safe and effective mosquito and tick repellents.
  • Looking at your body in a full-length mirror and taking a bath or shower soon after you come inside will help you to identify and remove ticks.
  • Ticks like to hide in protected areas. When checking their kids out for ticks, parents should pay special attention to the scalp and ears, the shoulder blades, the waist, belly button, and behind the knees and between the legs.
  • Ticks are vulnerable to heat and dehydration. Washing your clothes in hot water, or putting them in the dryer on high heat, should kill ticks hiding in them.

What to do if you find a tick on your skin

  • If you find any ticks attached to your body, use fine-tipped (jeweler’s) tweezers to remove them. Grasp them next to the skin and apply steady, gentle pressure. Do not yank or twist the tick, as this may cause its mouth parts to break off and stay embedded in your skin. Do not apply nail polish or petroleum jelly to the tick, or try to burn it off!
  • Clean the bite site afterward with soap and water, iodine, or rubbing alcohol.
  • If you develop a rash at the bite site or feel ill, see your doctor.

Follow me on Twitter @JohnRossMD

Related Information: Harvard Health Letter


  1. sanjit

    thank for your articles full on scientific information about about mosquitoes harmness

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