Human Monocytic Ehrlichiosis

What is Ehrlichiosis?

Most cases of ehrlichiosis in the United States are due to human monocytic ehrlichiosis (HME), a tick-borne infection caused by the bacterium, Ehrlichia chaffeensis, although there have also been rare reports of ehrlichiosis due to infection with Ehrlichia ewingii.

Ehrlichiosis in New York City

A person can develop ehrlichiosis if they are bitten by a tick that is infected with E. chaffeensis. It is transmitted by the lone star tick, Amblyomma americanum. Lone star ticks may become infected with E. chaffeensis when feeding on mice or deer and elk. The tick must be attached at least 12-24 hours to transmit the bacteria that cause ehrlichiosis. Not all ticks carry these bacteria. Most patients become infected during the spring and summer in endemic areas, when smaller nymphal ticks are in greatest abundance. Ehrlichiosis cannot be spread from person-to-person. While the lone star tick is not known to be established in NYC, more surveillance is needed to determine whether the tick may be moving into parts of NYC. In New York State, most cases occur in Westchester County, the lower Hudson Valley, and Long Island. The number of cases reported on NYC has ranged from 1 to 20 per year. For more information on the number of NYC residents reported to have ehrlichiosis, please visit Epi Query.

How can ehrlichiosis be prevented?

For more information on ticks and preventing tick bites, including the use of repellents, go to Ticks and Tick Prevention.

How should a tick be removed?

For guidance on the appropriate way to remove a tick, please go to Ticks and Tick Prevention.

For more information

For the most up to date information visit the CDC's ehrlichiosis webpage.

For more information about preventing tick bites, see How to Prevent Tick Bites brochure
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Information for Professionals

For more clinical, diagnostic and treatment information please visit Compendiums and Diagnostic and Treatment Guidelines.

Last updated March 2011