Questions and Answers
What is ehrlichiosis?
Ehrlichiosis is the general name used to describe several bacterial diseases that
affect animals and humans. These diseases are caused by the organisms in the
genus Ehrlichia. Worldwide, there are currently four ehrlichial
species that
are known to cause disease in humans.
How do people get ehrlichiosis?
In the United States, ehrlichiae are transmitted by the bite of an infected tick.
The lone star tick (Amblyomma americanum), the blacklegged tick (Ixodes
scapularis), and the western blacklegged tick (Ixodes pacificus) are
known vectors of ehrlichiosis in the United States. Ixodes ricinus is the primary
vector in Europe.
What are the symptoms of
ehrlichiosis?
The symptoms of ehrlichiosis may resemble
symptoms of various other infectious and non-infectious diseases. These
clinical features generally include fever, headache, fatigue, and muscle aches. Other signs and symptoms may
include nausea, vomiting, diarrhea, cough, joint pains, confusion, and occasionally rash.
Symptoms typically appear after an incubation period of 5-10 days following
the tick bite. It is possible that many individuals who become infected with ehrlichiae do not
become ill or they develop only very mild symptoms.
In the United States, where do
most cases of ehrlichiosis occur?
Most cases of ehrlichiosis are reported within the geographic distribution of the
vector ticks (see map below). Occasionally, cases are reported from areas outside the
distribution of the tick vector. In most instances, these cases have involved persons
who traveled to
areas where the diseases are endemic, and who had been bitten by an infected tick and
developed symptoms after returning home. Therefore, if you traveled to an
ehrlichiosis-endemic area 2 weeks prior to becoming ill, you should tell your doctor
where you traveled.
Figure
20. Areas where
human ehrlichiosis may occur based on approximate distribution of vector tick species
How is ehrlichiosis diagnosed?
A diagnosis of ehrlichiosis is based on a combination of clinical signs and
symptoms and confirmatory laboratory tests. Your doctor can send your blood sample to a
reference laboratory for testing. However, the availability of the different types of
laboratory tests varies considerably. Other laboratory findings indicative of ehrlichiosis
include low white blood cell count, low platelet count, and elevated liver enzymes.
How is ehrlichiosis treated?
Ehrlichiosis is treated with a tetracycline antibiotic, usually doxycycline.
Can a person get ehrlichiosis
more than once?
Very little is known about immunity to ehrlichial infections. Although it
has been proposed that infection with ehrlichiae confers long-term protection against
reinfection, there have been occassional reports of laboratory-confirmed
reinfection. Short-term protection has been described in animals
infected with some Ehrlichia species and this protection wanes after about
1 year.
Clearly, more studies are needed to determine the extent and duration of protection
against reinfection in humans.
How can ehrlichiosis be
prevented?
Limiting exposure to ticks reduces the likelihood of
infection in persons exposed to tick-infested habitats. Prompt careful inspection
of your body and
removal of crawling or attached ticks is an important method of preventing disease. It may
take 24–48 hours of attachment before microorganisms are transmitted from the tick to you.
It is unreasonable to assume that a
person can completely eliminate activities that may result in tick exposure. Therefore,
prevention measures should be aimed at personal protection:
- Wear light-colored clothing--
this will
allow you to see ticks that are crawling on your clothing.
- Tuck your pants legs into your socks so
that ticks cannot crawl up the inside of your pants legs.
- Apply repellants to discourage tick
attachment. Repellents containing permethrin can be sprayed on boots and clothing, and
will last for several days. Repellents containing DEET (n, n-diethyl-m-toluamide)
can be applied to the skin, but will last only a few hours before reapplication is
necessary. Use DEET with caution on children because adverse reactions have been reported.
- Conduct a body check upon return from
potentially tick-infested areas by searching your entire body for ticks. Use a hand-held
or full-length mirror to view all parts of your body. Promptly, remove any tick you find
on your body.
What is the best way to remove a
tick?
To remove attached ticks, use the following procedure:
1. Use fine-tipped tweezers or shield your fingers with a tissue, paper towel, or rubber
gloves.
2. Grasp the tick as close to the skin
surface as possible and pull upward with steady, even pressure. Do not twist or jerk the
tick; this may cause the mouthparts to break off and remain in the skin.
(If this happens, remove mouthparts with
tweezers. Consult your healthcare provider if infection occurs.)
Figure 21. Tick
removal
3. Do not squeeze, crush, or puncture
the body of the tick because its fluids (saliva, hemolymph, gut contents) may contain
infectious organisms.
4. Do not handle the tick with bare
hands because infectious agents may enter through mucous membranes or breaks in the skin. This
precaution is particularly directed to individuals who remove ticks from domestic animals
with unprotected fingers. Children, the elderly, and immunocompromised
persons may be at greater risk of infection and should avoid this
procedure.
5. After removing the tick, thoroughly
disinfect the bite site and wash your hands with soap and water.
6. You may wish to save the tick for identification
in case you become ill within 2 to 3 weeks. Your
doctor can use the information to assist in making an accurate diagnosis. Place the tick in a plastic
bag and put it in your freezer. Write the date of the bite on on a piece of paper with a
pencil and place it in the bag.
Note: Folklore remedies such as petroleum jelly or hot matches
do little to encourage a tick to detach from skin. In fact, they may make
matters worse by irritating the tick and stimulating it to release
additional saliva, increasing the chances of transmitting the pathogen. These methods of tick
removal should be avoided. In addition, a number of tick removal devices have been
marketed, but none are better than a plain set of fine tipped tweezers.
How can ticks be controlled?
Strategies to reduce vector tick densities through area-wide
application of acaricides (chemicals that will kill ticks and mites) and control of tick habitats (e.g., leaf litter and brush) have
been effective in small-scale trials. New methods under development include applying
acaricides to rodents and deer by using baited
tubes, boxes, and deer feeding stations in areas where these pathogens are endemic.
Biological control with fungi, parasitic nematodes, and parasitic wasps may
play important roles in integrated tick control efforts. Community-based integrated tick management strategies may prove to be an effective public
health response to reduce the incidence of tick-borne infections. However, limiting
exposure to ticks is presently the most effective method of prevention.
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