Anaplasmosis is a bacterium transmitted to humans and animals by tick bites primarily from the blacklegged tick (Ixodes scapularis) in the northeastern and upper midwestern U.S. and the western blacklegged tick (Ixodes pacificus) along the Pacific coast. Formerly known as Human Granulocytic Ehrlichiosis (HGE), this disease is caused by Anaplasma phagacytophilium. In humans it is known as Human Granulocytic Anaplasmosis (HGA). This pathogen may also pose a risk to human health through blood transfusions.
The tick, Ixodes spinipalpis was found to be a competent vector of Anaplasmosis from Colorado rodents including the Mexican woodrat, or pack rat. Companion Animal Parasite Council prevalence maps also display growing incidence of Anaplasmosis in dogs within Colorado.
Hunters are at risk through close contact with animals where they may have greater exposure to ticks, as well as through contact with blood while field dressing or butchering deer, elk, bison, pronghorn antelope, and bighorn sheep. Cattle, sheep and goats can also carry Anaplasmosis, so it is advised for those processing meat from both wild animals and domestic livestock to wear gloves while preparing carcasses. Healthy looking animals can be reservoirs of this disease. Horses are also at risk of contracting this illness.
Symptoms of Anaplasmosis typically begin within 1-2 weeks after the bite of an infected tick. A tick bite is usually painless, and some patients who develop Anaplasmosis do not remember being bitten. The following is a list of symptoms commonly seen with this disease. The symptoms vary from patient to patient and can be difficult to distinguish from other diseases. The clinical presentation for Anaplasmosis can resemble other tick-borne diseases, such as Rocky Mountain spotted fever and Ehrlichiosis. Presentation of Anaplasmosis may also be complicated by co-infection with Lyme disease.
Symptoms may include:
- Severe Headache
- Severe Muscle aches
- Gastrointestinal Symptoms (nausea, vomiting, diarrhea, loss of appetite)
- Rash (rare cases, may also indicate co-infection with Lyme or Rocky Mountain Spotted Fever)
Anaplasmosis can be a serious illness that can be fatal if not treated correctly, even in previously healthy people. Severe clinical presentations may include difficulty breathing, hemorrhage, renal failure or neurological problems. Patients who are treated early may recover quickly on oral antibiotics, while those who experience a more severe course may require intravenous antibiotics, prolonged hospitalization or intensive care. This disease has resulted in death in some cases. Anaplasmosis is a disease that may also present as a co-infection with Lyme disease as greater numbers of ticks are being found carrying both bacteria.
Healthcare providers must use their judgment to treat patients based on clinical suspicion alone! Diagnostic tests based on the detection of antibodies will frequently appear negative in the first 7-10 days of illness. Information such as recent tick bites, exposure to tick habitats, contact with wild game or livestock carcasses, or history of recent travel to areas where Anaplasmosis is endemic can be helpful in making the diagnosis. Routine blood tests, such as a complete blood cell count or a chemistry panel may also be helpful. Low platelet count (thrombocytopenia), low white blood cell count (leukopenia), or elevated liver enzyme levels are helpful predictors of Anaplasmosis, but may not be present in all patients.
The diagnosis of Anaplasmosis must be made based on clinical signs and symptoms, and can later be confirmed using specialized confirmatory laboratory tests. Treatment should never be delayed pending the receipt of laboratory test results, or be withheld on the basis of an initial negative laboratory result.
During the acute phase of illness, a sample of whole blood can be tested by polymerase chain reaction (PCR) assay to determine if a patient has Anaplasmosis. Although a positive PCR result is helpful, a negative result does not rule out the diagnosis. Treatment should not be withheld due to a negative result!
During the first week of illness a microscopic examination of blood smears (known as a peripheral blood smear) may reveal morulae (microcolonies of anaplasma) in the cytoplasm of white blood cells in up to 20% of patients. During A. phagocytophilum infection, morulae are most frequently observed in granulocytes. However, the observance of morulae in a particular cell type cannot conclusively identify the infecting species. Culture isolation of A. phagocytophilum is only available at specialized laboratories; routine hospital blood cultures cannot detect the organism.
When a person develops Anaplasmosis, their immune system produces antibodies to A. phagocytophilum, with detectable antibody titers usually observed by 7-10 days after illness onset. It is important to note that a negative test during the first week of illness does not rule out Anaplasmosis as a cause of illness.
The gold standard serologic test for diagnosis of Anaplasmosis is the indirect immunofluorescence assay (IFA) using A. phagocytophilum antigen, performed on paired serum samples to demonstrate a significant (four-fold) rise in antibody titers. The first sample should be taken as early in the disease as possible, preferably in the first week of symptoms, and the second sample should be taken 2 to 4 weeks later.
Doxycycline is the first line treatment for adults and children of all ages and should be initiated immediately whenever Anaplasmosis is suspected.
Doxycycline is most effective at preventing severe complications from developing if it is started early in the course of disease. Therefore, treatment must be based on clinical suspicion alone.