Tick-Borne Diseases : An Overview
A number of infectious diseases are transmitted by
ticks. As the incidence of tick-borne illnesses increases and the geographic
areas in which they are found expand, it becomes increasingly important
that health professionals be able to distinguish the diverse, and often
overlapping, clinical presentations of these diseases. This fact sheet
describes the major tick-associated diseases seen in the United States.
Tick-borne illnesses are caused by infection with
a variety of pathogens, including rickettsia and other types of bacteria,
viruses, and protozoa. Because ticks can harbor more than one disease-causing
agent, patients can be infected with more than one pathogen at the same
time, compounding the difficulty in diagnosis and treatment.
In general, specific laboratory tests are not available
to rapidly diagnose tick-borne diseases. Due to their seriousness, antibiotic
treatment is often justified based on clinical presentation alone. A description
of the major diseases transmitted by ticks follows.
Major Tick-Borne Diseases in the United States
(= I. dammini)
|Rocky Mountain Spotted Fever
|D. variabilis Amblyomma
|Colorado Tick Fever
Etiology: Borrelia burgdorferi
Lyme disease has become the most common tick-borne
disease in the U.S. More than 14,000 cases were reported to the Centers
for Disease Control and Prevention (CDC) in 1994, primarily in the Northeast
and Mid-Atlantic coastal states, and the north-central U.S. The Lyme disease
bacterium is transmitted primarily by the tiny deer tick, after it has
been attached to the host for more than 24 hours.
Signs and Symptoms:
More than half of the cases develop erythema migrans (EM) rash at the
site of the tick bite within 7 to 10 days. The rash expands, with an area
of central clearing. Accompanying constitutional symptoms may include
low-grade fever, headache, myalgia, arthralgia, and regional adenopathy.
The rash and early symptoms resolve within 3 to 4 weeks. Disseminated
disease may produce a recurrence of original symptoms and multiple secondary
Musculoskeletal symptoms may include recurring bouts
of asymmetric arthritis usually involving large joints, especially the
knee. The course of arthritis may be prolonged, but usually resolves in
3 to 4 years with or without treatment.
Early neurologic involvement includes cranial neuritis
(Bell's palsy), meningitis, and encephalitis. Chronic neurologic Lyme
includes subacute encephalopathy, axonal polyneuropathy, and less frequently,
leukoencephalopathy. Subacute encephalopathy is characterized by cognitive
deficits, mood and sleep disturbances. These symptoms may persist for
more than 10 years.
Cardiac symptoms such as an atrioventricular block,
which sometimes requires a pacemaker, occur in a small minority of patients.
Within 6 weeks, antibodies are usually detectable with an ELISA test.
Because this test is prone to false positives, CDC recommends confirmation
by a Western immunoblot. Nearly all patients with late Lyme disease are
seropositive. Although not always positive, the most specific test is
a culture of the organism from the EM lesion.
Early Lyme disease usually responds to several antibiotics, including
oral doxycycline and amoxicillin, often prescribed for 2 to 3 weeks. When
ehrlichiosis cannot be ruled out, treat with doxycycline, which is effective
against both diseases. Persistent symptoms may require a second course
of treatment. Neurologic involvement warrants 3 to 4 weeks of IV ceftriaxone
or penicillin G, as may arthritis and other symptoms of late-stage disease.
Chronic Lyme disease may not respond to antibiotic treatment. Prophylactic
treatment after a tick bite is not routinely recommended.
Rocky Mountain Spotted Fever
Etiology: Rickettsia rickettsiae
Most infections are acquired in the southeast and
west south-central regions of the country. A tick is most likely to transmit
the rickettsial agent after it has been attached to its human host for
at least 6-10 hours. More than 400 cases of Rocky Mountain Spotted Fever
(RMSF) were reported in 1994.
Signs and Symptoms:
First symptoms appear 5-10 days after tick bite, including fever more
than 102°F, headache, and rash. Macular rash, present in 90 percent of
patients, begins on the wrists and ankles and spreads inward to trunk,
face, palms and soles. Skin lesions often become papular, petechial, or
purpuric. Other symptoms that may develop include abdominal pain, diarrhea,
conjunctivitis, confusion, meningismus, respiratory failure, renal dysfunction,
and myocarditis. Common abnormalities, not specific for RMSF, include
depressed leukocyte count, thrombocytopenia, elevated liver enzymes, and
hyponatremia. In fulminant cases, widespread vasculitis causes intravascular
coagulation and death.
Diagnosis must be made prior to laboratory confirmation, based on clinical
presentation and patient history. Serologic tests available to confirm
a diagnosis of RMSF include IHA, IFA, and latex agglutination. Antibodies
appear within 7-10 days of onset of illness and decline within 2 months.
The length of time required and the potential hazard to laboratory personnel
make culturing the organism impractical for clinical management.
Prompt treatment has reduced mortality from 25 percent to 5 percent. Tetracyclines
are recommended in adults with suspected RMSF. Chloramphenicol is the
preferred treatment in children under 8 years of age. Intravenous chloramphenicol
is recommended when central nervous system symptoms are present. Treatment
should continue for 5-7 days or at least 48 hours after resolution of
fever. Untreated patients can require weeks to months to recover. Survivors
develop permanent immunity against future attacks.
Etiology: Babesia microti in the Northeast
Babesia equi in West Coast states
This malaria-like illness is caused by a protozoan
parasite that invades erythrocytes. While babesiosis most often occurs
after a tick bite, the disease also has been transmitted through blood
transfusion. The same ticks responsible for Lyme disease, I. scapularis
and I. pacificus, are believed to transmit babesiosis. More than
450 cases have been reported since babesiosis first appeared in 1968,
most occurring in the Northeast during the summer months. Because many
infected persons have no symptoms, the incidence of babesiosis is unknown.
Most illness occurs in persons of advanced age or who have underlying
medical conditions (e.g., splenectomy). Since babesiosis is known to weaken
the immune system, co-infection with Lyme disease can result in severe
and prolonged illness. In spite of its ability to cause serious, and even
life-threatening disease, babesiosis is only occasionally fatal.
Signs and Symptoms:
One to 3 weeks after tick bite, malaise, loss of appetite, fatigue, and
dark urine are common. Initial symptoms are followed several days later
by fever, myalgia, headache, and drenching sweats. Illness can range from
a mild self-limited infection to severe hemolytic anemia, renal failure,
and severe hypertension. Decreased levels of blood platelets may necessitate
exchange blood transfusions.
Laboratory tests may identify liver and blood abnormalities (anemia, decreased
hemoglobin, hemoglobinuria). Most patients have thrombocytopenia. Wright's
or Giemsa-stained blood smears may reveal babesia organisms. An IFA test
confirms diagnosis, with titers for most acutely ill patients exceeding
1:1024. Elevated titers can persist for months after acute infection.
Most patients have a mild illness and recover without specific treatment.
A 7-day regimen of oral quinine plus oral or intravenous clindamycin is
recommended. Blood transfusions are given in severe cases. Fatigue and
low-grade fever may persist for weeks or months after treatment.
Etiology: Ehrlichia chafeensis
The latest tick-borne disease to emerge in the U.S.,
ehrlichiosis was first described in 1987. Much less common than either
Lyme disease or Rocky Mountain spotted fever, an average of 50 cases of
ehrlichiosis are reported each year. Because of the often mild and self-limited
symptoms, this rickettsial disease is likely to be underreported. Ehrlichiosis
has been reported in many areas, but most cases have occurred in the Southeast
and south-central U.S. Ehrlichia bacteria parasitize white blood cells,
causing illness that may range from mild to severe and even fatal. Most
patients, however, recover completely without treatment.
Signs and Symptoms:
Ehrlichiosis resembles Rocky Mountain spotted fever and cannot be reliably
distinguished from it on the basis of its clinical presentation. A rash
develops in only 20 percent of patients with ehrlichiosis and, unlike
the Rocky Mountain spotted fever rash, is rarely seen on palms and soles.
Most frequent symptoms are headache and high fever, which usually develop
within 7-11 days after the tick bite. Other common symptoms are chills,
nausea, vomiting, anorexia, and muscle ache. Patients may also develop
cough, diarrhea, and swollen lymph glands. The symptoms last 1-2 weeks,
and recovery generally occurs without long-lasting problems. However,
complications have occurred in some people, including blood and kidney
abnormalities, respiratory failure, and meningitis. A particularly severe
form of disease, human granulocytic ehrlichiosis (HGE), can cause overwhelming
infection, toxic shock, and death. Prompt recognition and proper treatment
of ehrlichiosis is critical to avoid serious complications.
Diagnosis is made on a clinical basis. Certain laboratory tests are most
likely to detect abnormalities in the first 5 to 7 days of infection.
These abnormalities are not specific for ehrlichiosis and may include
leukopenia, thrombocytopenia, and elevated liver enzymes. Mulberry-like
bodies called morulae can sometimes be seen in the cytoplasm of white
blood cells by light or electron microscopy. Serologic tests, useful only
to confirm past infection, include IFA and ELISA. Patients seroconvert
in 4 weeks. A four-fold rise in antibody between the acute and convalescent
stage verifies diagnosis.
Unlike Lyme disease, ehrlichiosis does not respond to amoxicillin, and
misdiagnosis and incorrect treatment have led to overwhelming infection
and fatalities. Prompt treatment with tetracycline or doxycycline for
10-14 days is effective. Like other rickettsial diseases, chloramphenicol
can be used when tetracyclines are contraindicated. Convalescence can
Tick-Borne Relapsing Fever
Etiology: Borrelia hermsii in mountainous regions
Borrelia turicatae in semi-arid plains
An uncommon disease, relapsing fever is the only tick-borne
illness transmitted by the soft tick, Ornithodoros, found mainly
in remote mountainous settings. The true incidence of relapsing fever
is unknown due to a lack of surveillance and frequent misdiagnosis. Epidemics
have been traced to vacation cabins infested with rodents. The number
of cases peaks in the summer months. Ornithodoros ticks feed at night
for only 5-20 minutes and their bites usually go unnoticed.
Signs and Symptoms:
A 2-3 inch itchy black scab may develop at the site of the tick bite.
Incubation is usually 7 days, at which time the patient abruptly develops
high fever, chills, headache, tachycardia, muscle and joint pain, and
abdominal pain. Neurologic involvement occurs in only 5-10 percent of
cases. Rash is seen in less than half of cases, as fever wanes. Untreated,
the fever breaks within 6 days and the patient experiences drenching sweats.
Fever returns 8 days later, and subsequent episodes are milder. On average,
a patient experiences 3-5 recurrences of the illness. Infants and the
elderly may become severely ill and require hospitalization, but deaths
Common abnormalities include leukocytosis, increased erythrocyte sedimentation
rate, and thrombocytopenia. A rapid and specific diagnosis is made by
observing the bacteria in a sample of blood under the microscope. Organisms
are most likely to be seen in blood drawn during a febrile episode. Serologic
tests are not standardized and cross-react with B. burgdorferi (the agent
that causes Lyme disease). Western immunoblot confirms the diagnosis.
Either tetracycline or erythromycin for 5-10 days is effective. Rare treatment
failures have occurred using doxycycline. Severely ill patients may require
intravenous antibiotic treatment and hospitalization. A Jarisch-Herxheimer
reaction occurs in one-third of patients treated with antibiotics. Severity
of this reaction can be reduced by giving meptazinol or anti-pyretic or
Colorado Tick Fever
Colorado Tick Fever (CTF), also known as "mountain
fever," is a viral illness transmitted by the Rocky Mountain wood
tick, D. andersoni. CTF has also been transmitted by blood transfusions.
Between 200-300 cases are reported annually in the U.S., but the actual
incidence of the disease is likely to be much higher. Most cases occur
in mountainous regions of the western states. Once infected, a person
develops long-lasting immunity. A rare disease caused by another tick-borne
virus, Powassan encephalitis, causes similar symptoms but more often leaves
survivors with neurologic impairments.
Signs and Symptoms:
Three to 6 days after infection, symptoms begin abruptly with fever, chills,
severe headache, photophobia, abdominal pain, nausea, and muscle aches.
Symptoms last for up to 7-10 days and may recur several days later. The
second bout of illness typically lasts only 2-4 days. While the convalescent
period can be prolonged, especially in adults over age 30, prognosis is
generally excellent. Rare complications include meningitis, encephalitis,
and fatal hemorrhage. A transient macular or petechial rash is seen in
only a small percentage of patients, but may appear anywhere on the body
during the course of illness.
Serologic tests, including complement fixation, neutralizing antibody
determination, and IFA are available to confirm diagnosis. Less commonly,
the virus itself may be cultured from blood. Because it may take several
weeks to develop antibodies, blood samples should be taken during both
the acute illness and post-convalescent periods.
There is no specific treatment. Therapy is limited to supportive care.
Recovered patients should not donate blood for at least 6 months.
Etiology: Francisella tularensis
Tularemia, also called "Rabbit Fever" or
"Deer-Fly Fever," is an infection that causes two forms of disease,
a mild illness and a more severe one. While tularemia can be contracted
by handling tissues of infected animals, especially by hunters who skin
wild rabbits, more than half of all cases result from tick bites. Approximately
150-300 cases are reported each year, mostly from Arkansas, Missouri,
and Oklahoma. Recovered patients usually develop long-lasting immunity,
however cases of re-infection have been reported.
Signs and Symptoms:
A sore or ulcer develops within 24-48 hours at the site of tick bite,
usually on lower extremities or trunk. Lymph glands become swollen and
painful. The disease may be mild and self-limited, with fever abating
within 4 weeks. A more fulminant disease leads to fever with chills, headache,
abdominal pain, and severe prostration.
There is no rapid diagnostic test for tularemia. A serum agglutination
test can detect antibodies 10-14 days after onset of illness. Titer peaks
in 4-6 weeks. Pre- and post-convalescent blood samples showing a four-fold
rise in antibody confirms infection.
Streptomycin or gentamycin are effective. Tetracycline or chloramphenicol
are alternatives, but relapses can occur if taken for less than 14 days.
Considerable improvement is seen within 48 hours after treatment.
This rare disease is the only tick-borne illness that
is not caused by an infectious organism. The illness is caused by a neurotoxin
produced in the tick's salivary gland. After prolonged attachment, the
engorged tick transmits the toxin to its human host. The incidence of
tick paralysis is unknown.
Signs and Symptoms:
The toxin causes symptoms within 2-7 days, beginning with weakness in
both legs that progresses to paralysis. The paralysis ascends upward to
trunk, arms, and head within hours and may lead to respiratory failure
and death. The disease can present as acute ataxia without muscle weakness.
Diagnosis is based on symptoms and upon finding an embedded tick, usually
on the scalp.
Removal of the embedded tick usually results in resolution of symptoms
within several hours to days. If the tick is not removed, the toxin can
be fatal, with reported mortality rates of 10-12 percent.
No vaccine is currently available for any tick-borne
disease. Individuals should therefore take precautions when entering tick-infested
areas, particularly in the spring and summer months. Preventive measures
include avoiding trails that are overgrown with bushy vegetation, wearing
light-colored clothes that allow one to see the ticks more easily, and
wearing long pants and closed-toe shoes. Tick repellents containing DEET
(N,N, diethyl-m-toluamide) are effective and can be applied to skin or
clothing. Although highly effective, severe reactions have occurred in
some people who use DEET-containing products. Young children may be especially
vulnerable to these adverse effects. Permethrin, which can only be applied
to clothing, kills ticks on contact.
If an embedded tick is found, it should be removed
promptly with tweezers, grasping the tick close to the skin and pulling
with steady pressure upward, in a direction perpendicular to the skin.
Engorged ticks should be handled only with gloves or other barrier and
saved for identification by the physician.
Source: National Institute of Allergy and Infectious Diseases, National Institutes of Health, June 1996