Ehrlichiosis and Anaplasmosis
Several species in the genus Ehrlichia can cause disease in humans.
Human illness caused by the pathogen Ehrlichia chaffeensis is referred to as Human Monocytic Ehrlichiosis (HME).
It is transmitted by
Amblyomma americanum, also known as the lone star tick, which is one of the
most commonly encountered ticks in the southeastern United States.
Ticks become infected by feeding on white-tailed deer or other animals and can
transmit the disease to humans or dogs at a subsequent feeding. What was originally thought to be a second species of Ehrlichia was
recently reclassified as Anaplasma phagocytophilum, which causes Human Granulocytotropic Anaplasmosis (HGA)
in humans and is transmitted by Ixodes species ticks, such as
I. scapularis, the tick that transmits Lyme Disease.
Amblyomma americanum and Ixodes scapularis
Symptoms and Treatment
Some people infected with E. chaffeensis may have no symptoms, or have
symptoms so mild that they do not visit the doctor. For those who do become ill,
symptoms typically begin 5 to 10 days after a tick bite, and can initially
include fever, headache, fatigue, and muscle aches. Other signs include nausea,
vomiting, joint pain, diarrhea, and confusion. Adults with HME typically do not
develop a rash, though rash is reported in up to 60% of ill children.
People infected with A. phagocytophilum can have similar symptoms.
HME and HGA can be hard to diagnose because many of the symptoms look like those seen
for other diseases. It is important to tell the physician about any tick bites
that have occurred. Cases detected early in the course of disease can be treated
with antibiotics. Both diseases can cause severe illness with as many as half the patients
needing to be hospitalized. Approximately 2% to 3% of people who
become ill with HME die from the disease.
Research has shown that removing attached ticks within 24 hours of the bite
can greatly reduce the chance of infection. For this reason it is important to
check for ticks on a regular basis and to remove them right away.
HME and HGA in Florida
HME caused by E. chaffeensis is found primarily in the southeastern
part of the U.S. Cases are commonly reported from Missouri, Oklahoma, Tennessee,
Arkansas, and Maryland. In Florida, 71 cases were reported from 2000
through 2008. 16 cases of HGA were reported. The majority of HME
cases (70%) are reported as being acquired in Florida, primarily in the north
and central parts of the state. HGA is more likely to be acquired outside
Florida and is more prevalent in the northeast United States. In 2008, over half (52%) of the cases were male, and the most of were
also white (91%) and non-Hispanic
(86%). The number of cases increased
during the summer months, though cases are reported
in Florida year-round.
Prevention of Tick-borne Diseases
Centers for Disease
Control and Prevention (CDC) Human Ehrlichiosis
Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain
Spotted Fever, Ehrlichioses, and Anaplasmosis - United States. MMWR (1.1 MB PDF)