Overall annual incidence rose from 1.4 to 6.1 cases per million in the United States between 2000 and 2010 (Ismail 2017)
In endemic areas, the incidence rate is suggested to be more than 50 cases per 100,000 (Ismail 2017)
Age:
Median age is 51 years of age with greater than 95% of cases reported in Caucasian patients (Ismail 2017)
Gender:
Slight male to female predominance (Demma 2006)
Morbidity/Mortality: Case fatality rate is less than 1% (Ismail 2017)
Many patients will be either asymptomatic or manifest mild signs and symptoms
Hospitalization rates have been noted to be as high as 36% in epidemiological studies with a 7% ICU admission rate and mortality rate of 0.6% in those with severe symptoms (Dumler 2012)
Geography and Seasonality (Baker 2020): Upper Midwestern and Northeastern United States
Ten States account for over 90% of all reported cases (in order from highest concentration of cases): Minnesota, Wisconsin, Massachusetts, New York, Maine, Connecticut, New Jersey, Rhode Island, Vermont, and New Hampshire.
Seasonal distribution is concentrated in summer months corresponding to nymphal tick activity: June (23.4%), July (22.2%), August (12%), and May (10.4%).
Second smaller peak is noted in October and November when adult ticks are active
Poor Prognostic Factors:
Increased Age
Immunocompromised States
Delays in diagnosis and treatment
Pathogenesis (Biggs 2016):
After tick transmissibility, Anaplasma phagocytophilum has a predilection for granulocytes, specifically neutrophils
Once infected, the organism multiplies within cytoplasmic membrane-bound vacuoles forming clusters of bacterial called morulae
Infection elicits a systemic inflammatory response and alters the host’s neutrophil function leading to ineffective inflammatory regulation and microbicidal activity
History and Physical:
Symptoms (Ismail 2017, Biggs 2016):
Symptoms typically appear 5-14 days after bite of an infected tick
Rash is present in less than 10% of patients
Fever occurs in 92-100% of recognized cases of anaplasmosis along with other non-specific flu-like symptoms:
Headache
Malaise
Myalgias
Chills/Rigors
Arthralgias
Gastrointestinal symptoms are less frequently seen
Central Nervous System involvement is rare
Severe Manifestations: Most cases are self-limiting, but Anaplasmosis has been associated with the following severe disease manifestations:
ARDS
DIC
Rhabdomyolysis
Renal Failure
Pancreatitis
Hemophagocytic Syndromes
Opportunistic Viral and Fungal infection
Diagnosis:
Labs: Characteristic laboratory findings are seen in Anaplasmosis along fever and non-specific flu-like illness:
Leukopenia
Mild Anemia
Thrombocytopenia
Mild to Moderate Elevated Hepatic Transaminase
Increased Number of Immature Neutrophils
Blood Smear:
May see morulae within granulocytes with microscopic examination of blood smears but blood smear may be relatively insensitive and inconsistent and dependent on operator experience (Biggs 2016)
Observation of morulae is highly suggestive of infection
Confirmatory Testing (Ismail 2017):
Serological testing of IgM and IgG antibodies specific to A phagocytophilum using indirect immunofluorescence assay (IFA) is the gold standard.
RT-PCR assays are also available for diagnosis of A phagocytophilum and has become the test of choice due to rapid turnaround times and high specificity as well as sensitivity
Guest Post By:
Akash Ray, DO
PGY-2 Emergency Medicine Resident Inspira Medical Center
Vineland, NJ Twitter:@_kashray
References:
Biggs H et al. Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis – United States. MMWR Recomm Rep. 2016. PMID: 27172113
Todd S et al. No visible dental staining in children treated with doxycycline for suspected Rocky Mountain Spotted Fever. J Pediatr. 2015. PMID: 25794784
Volovitz B et al. Absence of tooth staining with doxycycline treatment in young children. Clin Pediatr (Phila). 2007. PMID: 17325084
Ismail N et al. Tick-Borne Emerging Infections: Ehrlichiosis and Anaplasmosis. Clin Lab Med. 2017. PMID: 28457353
Demma L et al. Human monocytic ehrlichiosis and human granulocytic anaplasmosis in the United States, 2001–2002. Ann N Y Acad Sci. 2006. PMID: 17114690
Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie)
