Anaplasmosis

Overview

Anaplasmosis is an infection caused by bacteria called Anaplasma phagocytophilum, which are spread to people through the bite of infected ticks, mainly the blacklegged (deer) tick. The bacteria infect certain white blood cells, leading to a flu-like illness that usually begins one to two weeks after a tick bite.

The disease occurs most often in regions where these ticks are common, particularly the upper Midwest and northeastern United States, and during the warmer months when ticks are active. The same ticks can also carry other infections, such as Lyme disease, so a person can occasionally have more than one tick-borne illness at the same time. Most cases respond well to prompt antibiotic treatment, but anaplasmosis can become serious if left untreated, especially in older adults or people with weakened immune systems.

Symptoms

Symptoms usually start about one to two weeks after a bite from an infected tick and resemble the flu:

• Fever and chills
• Severe headache
• Muscle aches
• Fatigue and feeling generally unwell
• Nausea, vomiting, or loss of appetite
• Cough in some cases

Unlike some other tick-borne illnesses, a rash is uncommon. If anaplasmosis is not treated, it can progress to more serious problems such as difficulty breathing, bleeding, organ failure, or, rarely, death. Seek prompt medical care for a high fever and severe illness after a recent tick bite or exposure to tick habitats.

Causes

Anaplasmosis is caused by the bacterium Anaplasma phagocytophilum. People become infected when bitten by a tick carrying the bacteria. Key points about how it spreads:

• Tick bite: The main route of infection is the bite of an infected blacklegged tick.
• Attachment time: Ticks generally need to be attached for a period of hours to transmit the bacteria, so prompt removal lowers the risk.
• Not spread person to person: Anaplasmosis is not passed directly from one person to another through casual contact.

Rarely, transmission has been linked to blood transfusion. The infection is not caught from pets, although pets can carry ticks into the home.

Risk Factors

• Spending time outdoors in wooded, brushy, or grassy areas where ticks live
• Living in or visiting regions where blacklegged ticks are common
• Outdoor activities such as hiking, camping, hunting, or gardening
• Warmer months when ticks are most active
• Older age and weakened immune systems, which raise the risk of severe illness

Diagnosis

Because early symptoms resemble many other illnesses, diagnosis relies on the combination of symptoms, recent tick exposure, and testing:

• Clinical assessment: A doctor considers anaplasmosis in someone with fever and flu-like symptoms after possible tick exposure.
• Blood tests: Routine blood work may show low white blood cell or platelet counts and abnormal liver tests, which support the diagnosis.
• Specific testing: Blood tests that detect the bacteria's genetic material or antibodies can confirm anaplasmosis.

Because treatment is most effective when started early, doctors often begin antibiotics based on clinical suspicion before test results return.

Treatment

Anaplasmosis usually responds well to antibiotics:

• Doxycycline: This antibiotic is the recommended treatment for adults and children of all ages and works best when started early.
• Early treatment: Starting antibiotics promptly, often based on symptoms and exposure history, leads to faster recovery and prevents complications.
• Supportive care: Rest, fluids, and fever-reducing measures help comfort during recovery.

Most people improve within a few days of starting treatment. Severe or advanced cases may require hospital care. Because the response to doxycycline is usually rapid, a slow recovery may prompt the doctor to look for another diagnosis or a co-occurring tick-borne infection.

Prevention

Preventing tick bites is the best way to avoid anaplasmosis:

• Use EPA-registered insect repellents on skin and treat clothing and gear with permethrin
• Wear long sleeves and pants and tuck pants into socks in tick habitats
• Stay on cleared trails and avoid tall grass and brush
• Check your body, children, and pets for ticks after being outdoors
• Remove attached ticks promptly with fine-tipped tweezers, grasping close to the skin
• Shower soon after coming indoors to wash off unattached ticks

When to See a Doctor

See a doctor promptly if you develop fever, chills, severe headache, or muscle aches after a tick bite or after spending time in areas where ticks are common, even if you do not recall a bite. Tell the doctor about any tick exposure so they can consider tick-borne illnesses. Seek urgent care if you have:

• A very high fever or severe, worsening illness
• Difficulty breathing
• Confusion or extreme weakness
• Unusual bleeding or bruising

Early treatment is important, particularly for older adults and people with weakened immune systems.

Related Topics

Frequently Asked Questions

References

1. Centers for Disease Control and Prevention (CDC). Anaplasmosis.
2. MedlinePlus, U.S. National Library of Medicine. Anaplasmosis.
3. Mayo Clinic. Ehrlichiosis and anaplasmosis.
4. National Institute of Allergy and Infectious Diseases (NIAID). Tickborne diseases.