If a tick carrying the bacterium that causes ehrlichiosis has been feeding on you for at least 24 hours, the following flu-like signs and symptoms may appear — usually within seven to 14 days of the bite:

• Mild fever
• Headache
• Chills
• Muscle aches
• Nausea
• Vomiting
• Diarrhea
• Fatigue
• Loss of appetite
• Joint pain
• Confusion
• Rash
• Cough

Some people infected with ehrlichiosis may have symptoms so mild that they never seek medical attention, and the body fights off the illness on its own. But untreated ehrlichiosis with persistent symptoms can result in an illness serious enough to require hospitalization.

Ehrlichiosis is caused by ehrlichia bacteria and is transmitted primarily by the Lone Star tick.

Ticks feed on blood, latching onto a host and feeding until they're swollen to many times their normal size. During feeding, ticks that carry disease-producing bacteria can transmit the bacteria to a healthy host. Or they may pick up bacteria themselves if the host, such as a white-tailed deer or a coyote, is infected.

Usually, to get ehrlichiosis, you must be bitten by an infected tick. The bacteria enter your skin through the bite and eventually make their way into your bloodstream.

Before bacteria can be transmitted, a tick must be attached and feeding for at least 24 hours. An attached tick with a swollen appearance may have been feeding long enough to have transmitted bacteria. Removing ticks as soon as possible may prevent infection.

It's also possible that ehrlichiosis may be transmitted through blood transfusions, from mother to fetus, and through direct contact with an infected, slaughtered animal.

Ehrlichiosis spreads when an infected tick, primarily the Lone Star tick, bites you and feeds on you for 24 hours or longer. The following factors may increase your risk of getting tick-borne infections:

• Being outdoors in warm weather. Most cases of ehrlichiosis occur in the spring and summer months when populations of the Lone Star tick are at their peak, and people are outside more often.
• Living in or visiting an area with a high tick population. You are at greater risk if you are in an area with a high Lone Star tick population. In the United States, Lone Star ticks are most common in southeastern, eastern and south-central states.
• Being male. Ehrlichiosis infections are more common in males, possibly because of increased time outdoors for work and recreation.

Without prompt treatment, ehrlichiosis can have serious effects on an otherwise healthy adult or child.

People with weakened immune systems are at an even higher risk of more-serious and potentially life-threatening consequences. Serious complications of untreated infection include:

• Kidney failure
• Respiratory failure
• Heart failure
• Seizures
• Coma