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Ehrlichiosis
What bacteria cause ehrlichiosis?
- Bacteria from the Ehrlichia genus
- There are three types of ehrlichioses that have been identified
that infect people:
- Human Monocytic Ehrlichiosis (HME) is caused by Ehrlichia
chaffeensis (see picture below)
- Human Granulocytic Ehrlichiosis (HGE) is caused by Anaplasma
phagocytophila, and is referred to as the “HGE agent”
(see picture below); it is closely related to both Ehrlichia
phagocytophila and Ehrlichia equi
- Ehrlichia ewingii is a third type of ehrlichiosis that
has recently been identified in Missouri
- Ehrlichiosis is a tick-borne,
zoonotic disease
- Ehrlichiosis is seen across the United States
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A magnified picture of Ehrlichia chaffeensis
bacteria
(from the CDC website)
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A magnified picture of HGE agent
(from the CDC website)
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How is ehrlichiosis spread?
- Animals and ticks maintain Ehrlichia infection in a natural
cycle
- The animals serve as reservoirs,
from which a tick can become infected when taking a blood meal;
likewise, an infected tick can transmit the bacteria to an animal
or person when taking blood
- Ehrlichiosis is NOT spread person-to-person
- E. chaffeensis (HME) is transmitted to humans by the lone star
tick (Amblyomma americanum)
A female lone star tick
(from the CDC website)
- Animals such as dogs, deer, and goats are common natural hosts
(or reservoirs) for E. chaffeensis (which causes HME)
- HGE agent is transmitted to humans by black-legged ticks (Ixodes
scapularis in the eastern US and Ixodes pacificus in the western
US)
A female black-legged tick
(from the CDC website)
- Deer, wild rodents, and elk are common natural hosts (or reservoirs)
for the HGE agent
- Most ehrlichial infections in dogs are due to Ehrlichia canis.
However, canine infections due to E. ewingii, E. equi, E. risticii,
E. chaffeensis, and E. platys have also been reported. Such infections
are rare in cats.
What are the symptoms of ehrlichiosis in humans?
- The symptoms of HME and HGE are the same and usually occur
within 5 to 10 days following a bite from an infected tick
- Non-specific symptoms include
- Fever
- Muscle aches
- Weakness
- Joint pain
- Headaches
- Some patients may also experience confusion, nausea, vomiting,
and joint pain
- A rash is NOT common
- Illness is usually mild, but occasionally may be life-threatening,
especially if untreated
- Antibiotics are the treatment of choice
Who is most at risk for ehrlichiosis?
- People who spend time outdoors in tick-infested areas during
the tick active season (April to October); this includes parks
within cities and urban areas
- Recreational risks have also been identified, such as golfing
and hiking
How can ehrlichiosis be prevented?
- Limit exposures to ticks by staying away from tick habitats,
if possible
- When in grassy or wooded areas:
- Check frequently for tick attachment
- Wear light-colored clothing to spot ticks easier
- Tuck pants into socks and shirts into pants
- Consider the use of repellents (containing 20-30% DEET [N,N-diethyl-m-toluamide]
for adults and less than 10%- 15% for children; follow all label
directions)
- At the end of the day, do a thorough body check to detect all
attached ticks; check all pets as well
- If a tick is removed within 36 hours of attachment, the risk
of ehrlichial infection is very small
- Minimize tick habitat around your home by removing leaf litter
and brush
- Consider using tick products on pets; consult with your veterinarian
before using any tick product on an animal
- There is no vaccine against ehrlichiosis, so avoiding ticks
is the best prevention
Links
CDC
website on ehrlichiosis
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