Human (Granulocytic) Anaplasmosis (HGA ... - Allina Health

In 2010, there were 720 reported confirmed or probable cases of HGA in Minnesota (16.9
cases per 100,000 population), more than twice the number reported in 2009. 59% were in
males, the median age was 57 years, and the majority of cases were reported in May-July,
with a peak in June. 27% of patients were hospitalized (1-42 days) and there was one
reported death. 5% of HGA cases also had Lyme disease, and 1% also had confirmed or
probable babesiosis. The frequency of co-infection may be underestimated.
A disease related to HGA, called Human Monocytic Ehrlichiosis, is caused by Ehrlichia
chaffeensis. It is uncommon in Minnesota. It is found throughout much of the southeastern
and southcentral United States and is carried mainly by the Lone Star tick. However, a few
cases of Ehrlichia muris-like agent-related disease, carried by I. scapularis, have been reported
in Minnesota and Wisconsin since 2009. Ehrlichia ewingii, the agent of canine granulocytic
ehrlichiosis, may occasionally cause an ehrlichia-like illness in humans.
Anaplasma phagocytophilum (formerly known as Ehrlichia phagocytophilum) is the agent of
HGA. It has tropism for neutrophils (whereas E. chaffeensis has tropism for monocytes). The
incubation period is typically 7-10 days before development of overt symptoms, although onset
of illness may be 5-21 days after exposure. Disease transmission is usually from tick bite,
although other reported routes include blood inhalation/percutaneous blood exposure
following butchering of white-tailed deer, blood transfusion, and transplacental infection. Many
infections go undiagnosed because of the mild nonspecific symptomatology associated with
the majority of infections.
Symptoms typically include chills, fever, headache, myalgias and arthralgias. Less common
symptoms include nausea/anorexia and vomiting, weight loss, abdominal pain, cough,
diarrhea, and mental status changes. Rare patients will develop encephalitis, acute respiratory
distress syndrome, or shock-like illness with multiorgan involvement. Disease tends to be most
severe in elderly or immunocompromised individuals. The fatality rate is usually less than 1%,
although some sources state a 2-3% fatality rate, and may be associated with opportunistic
superimposed fungal or viral infection.
Laboratory Findings:
The majority of patients will have thrombocytopenia. Approximately 50% will have leukopenia.
Liver function tests (LFTs) may be elevated due to hepatocellular injury.
Pathology:
Intravacuolar bacterial microcolonies reside in neutrophils and may be seen by microscopic
evaluation when peripheral blood is smeared on a slide and stained by the Wright-Giemsa
method. These microcolonies resemble a mulberry and are therefore called morules or
morulae because the Latin word for mulberry is “morula.”
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