Anaplasmosis: Reporting and Surveillance

DHS surveillance resources

• Case Reporting and Investigation Protocol (previously called EpiNet)—Anaplasmosis, P-01951 (PDF)
• Wisconsin case report form for mail or fax—Tickborne Rickettsial Disease Case Report, F-00336 (PDF)
• Preparation and response—Vectorborne Disease Toolkit, P-01109 (PDF)

Provider resources

• Clinical signs and symptoms from the CDC (Centers for Disease Control and Prevention)—Clinical Signs and Symptoms of Anaplasmosis
• Guidance on laboratory testing and clinical diagnosis from the CDC—Clinical Testing and Diagnosis for Anaplasmosis
• A practical guide for health care and public health professionals from the CDC—Diagnosis and Management of Tickborne Rickettsial Diseases (PDF)
• A fact sheet comparing common rickettsial disease diagnostic testing methods from the CDC —Rickettsial Disease Diagnostic Testing and Interpretation (PDF)

Anaplasma and Ehrlichia infections can have similar signs and symptoms. In parts of Wisconsin, the two agents also can overlap geographically. Diagnostic tests are needed to identify the specific agent causing the illness. Most patients being tested for Anaplasma also should be tested for Ehrlichia. Providers should order a panel that includes testing for both Ehrlichia and Anaplasma.

Several different lab tests are used to aid in the diagnosis of anaplasmosis.

Polymerase chain reaction (PCR)

PCR is the preferred diagnostic test because it is highly sensitive and specific during the acute disease phase. PCR testing should be performed using whole blood collected upon the initial physician's visit, before starting antibiotics.

A positive PCR result is confirmation of A. phagocytophilum infection. It is important to note that a negative result does not rule out infection, and treatment should not be withheld due to a negative result.

Serologic testing (IFA/EIA)

Serologic testing is less specific than the PCR test and cross-reactivity often occurs among the Anaplasma and Ehrlichia agents. Serologic confirmation of Anaplasma phagocytophilum or Ehrlichia species infection requires demonstration of at least a fourfold change (e.g., 1:64 to 1:256, or 1:128 to 1:512) in immunoglobulin G (IgG) specific antibody titer between paired acute and convalescent sera tested by indirect immunofluorescence assay (IFA).

Collect the acute sample during the first week of illness. Collect the convalescent sample two to four weeks later.

A single positive IgG titer can indicate a current or past infection.

Immunoglobulin M (IgM) antibody test aren’t as reliable as IgG tests. IgM tests are less specific, so they are more likely to produce false positive results. IgM antibodies can persist for a long period of time, so positive IgM titers may not indicate acute infection. Single IgM antibody tests shouldn’t be used for diagnosis.

Serologic tests based on enzyme immunoassay (EIA) only provide a positive or negative result. They can’t be used to measure changes in antibody titers between paired sera.

Cross-reactivity between Anaplasma phagocytophilum and Ehrlichia species often occurs with serologic testing. Therefore, the agent demonstrating at least a fourfold higher titer is most likely causing the illness. The infecting agent cannot be determined if there’s less than a fourfold difference in titer.

Smear/Morulae

Early in illness, a blood smear might reveal morulae in the cytoplasm of granulocytes. This evidence can support a diagnosis of anaplasmosis. However, don’t rely solely on this test since it’s relatively insensitive. If a lab routinely performs only peripheral blood smears, the Division of Public Health recommends a PCR or an IFA test to accompany a blood smear for more definitive results.

Other tests

Immunohistochemistry (IHC) detection and cell culture are confirmatory tests. However, it’s rare to see these types of positive test results.

In addition to a positive lab result, a patient should also have a clinically compatible illness. Most patients with anaplasmosis will exhibit fever, sweats, or chills and at least one of the following:

• Severe headache
• Body aches
• Fatigue
• Gastrointestinal symptoms (nausea, vomiting, diarrhea) in about 20% of cases
• Leukopenia (low white blood cell count)
• Thrombocytopenia (low platelet count)
• Elevated liver enzymes

Treatment should be initiated as soon as anaplasmosis is clinically suspected. Treatment for anaplasmosis should not be delayed while waiting for lab results. Treatment should not be withheld based on an initial negative lab result. Treatment decisions should be based on clinically compatible signs and symptoms and an assessment of the patient’s likelihood of tick exposure. Delaying treatment can lead to serious illness.

Anaplasmosis can be treated with antibiotics. Doxycycline is the antibiotic of choice for adults and children of all ages. Most people treated with oral antibiotics during the early stages of anaplasmosis fully recover. Some patients may continue to have headache, weakness, and malaise for weeks after receiving treatment.

*Patients with suspected anaplasmosis should be treated with doxycycline for 10–14 days to cover for possible co-infection with Borrelia burgdorferi (Lyme disease).

Antibiotic treatment following a tick bite isn’t recommended to prevent anaplasmosis. There’s no evidence this practice is effective, and it may only delay onset of disease.