Anaplasmosis
The case
A 55-year-old man with non-insulin dependent diabetes, hypertension, and hyperlipidemia presents to the Emergency Department with 1 day of severe retro-orbital headache followed by fever, chills, drenching sweats, generalized myalgias, and cough. At one point, he remarks "my hair hurts."
He works as a logger in northern Wisconsin and states he frequently removes attached ticks from his skin despite wearing long sleeves and pants while working.
Initial vitals are as follows: T 102 F, HR 117, BP 126/79, RR 20, SpO2 96% on room air.
Physical exam demonstrates an ill-appearing man who is alert and fully oriented. He is diaphoretic. He has no nuchal rigidity and a non-focal neurologic exam. No respiratory distress. Lungs are clear to auscultation. Abdomen is soft and non-tender.
Laboratory evaluation demonstrates total white blood cell count 2.5, hemoglobin 9.8, platelet count 80, AST 276, ALT 213, and creatinine 1.8. Chest x-ray shows no focal opacity. Non-contrast head CT shows no acute abnormality.
The brush up
Frequently associated with the tick vector Ixodes scapularis (deer/black-legged tick), Anaplasma phagocytophilum is the causative organism in human granulocyte anaplasmosis (HGA).
There are also rare reports of human-to-human transmission from blood exposure. Infection is similar to that of, but much more common than, human monocytic ehrlichiosis (HME).
Most patients become symptomatic within 2 weeks after a tick bite. Fever, headache, malaise, and myalgias are common presenting symptoms. While the gold standard diagnostic test is ehrlichial culture, this is extremely time-consuming. A quicker and more reasonable diagnostic approach involves serology, peripheral blood smear/buffy coat, and PCR analyses. The majority of patients will have leukopenia, thrombocytopenia, and transaminitis. White blood cell staining will show morulae, or clusters of intracellular bacteria within vacuoles.
All symptomatic patients should be treated with antibiotics, the drug of choice being doxycycline (100 mg BID x 10 days or 3-5 days after defervescence, whichever is longer). Consider rifampin (300 mg BID x 7-10 days) in pregnant women and young children. Unlike Lyme disease, prophylactic antibiotics after a tick bite is not recommended to prevent HME and HGA.
There are myriad potential complications including opportunistic infections, seizures, coma, and organ failure. While mortality data in previously healthy patients is limited and highly variable, infection in transplant patients and co-infection with HIV can be life-threatening. Delay in antibiotic therapy (> 24 hours after hospital admission) has been associated with increased risk of transfer to the intensive care unit, need for mechanical ventilation, increased hospital length-of-stay, and longer illness course.
The conclusion
The patient was started on intravenous doxycycline and admitted to the hospital. Tickborne PCR panel testing was positive for HGA only. His fever resolved and his symptoms improved significantly within 3 days. He was subsequently discharged home to complete a 10-day course of doxycycline.
References
Chapman AS, et al. Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever, ehrlichioses, and anaplasmosis--United States: a practical guide for physicians and other healthcare and public health professionals. MMWR Recomm Rep 2006 Mar 31;55(RR-4):1-27.
Hamburg BJ, et al. The importance of early treatment with doxycycline in human ehrlichiosis. Medicine (Baltimore) 2008 Mar;87(2):53-60.
Sexton DJ and McClain MT. Human ehrlichiosis and anaplasmosis. In: UpToDate, Mitty J (Ed), UpToDate, Waltham, MA, 2017.
CDC - Anaplasmosis. http://www.cdc.gov/anaplasmosis/index.html. June 23, 2016.