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Q Q fever FEVER
Q (or Query) fever is a disease that is caused by the bacterium
Coxiella burnetii. The bacterium is passed to humans by con-
tact with infected animals such as sheep, cattle, and goats,
which are the main reservoirs of the microorganism. The dis-
ease, which was first described in Australia in 1935, can have
a short-term (acute) stage and, in some people, a much longer,
chronic stage.
The bacterium that causes Q fever is a rickettsia. Other
rickettsia are responsible for Rocky Mountain Spotted Fever
and trench fever, as examples. Coxiella burnettiand the other
rickettsia are Gram-negative organisms, which need to infect
host cells in order to grow and divide. Outside of the host the
bacteriacan survive, but do not replicate. Q fever differs from
the other rickettsial diseases in that it is caused by the inhala-
tion of the bacteria, not by the bite of a tick.
Groups most at risk to acquire Q fever are those who are
around animals. These include veterinarians, sheep, cattle and
dairy farmers, and workers in processing plants.
The bacteria are excreted into the environment in the
milk, urine, and feces of the animals. Also, bacteria can be
present in the amniotic fluid and the placenta in the birthing
process. The latter is particularly relevant, as humans tend to
be near the animals during birth, and so the chances of trans-
fer of the bacterium from animal to human are great.
In addition, the microorganismsare hardy and can
endure environmental stress. The chances for human infection
are also increased because of the persistence of the bacteria in
the environment outside of the animal host. Coxiella burnetii
are very hardy bacteria, being resistant to antibacterial com-
pounds, and to environmental stresses such as heat and lack of
moisture. When present in a dry area, such as in hay or the
dust of a barnyard, the organisms can be easily inhaled.
The entry of only a few live bacteria or even one living
bacterium is required to cause an infection in humans. The
environmental hardiness and low number of microbesrequired for an infection has made Coxiella burnetiia poten-
tial agent of bioterrorism.
Of those who become infected, only about half display
symptoms. When symptoms of Q fever appear, they can
include the sudden development of a high fever, severe
headache, nausea, vomiting, abdominal pain, and an overall
feeling of illness. Pneumoniaand liver damage can develop in
some people. Usually the symptoms pass in several months.
However, the establishment of a chronic disease can occur,
and is fatal in over 60 per cent of cases. The chronic form may
not develop immediately after the transient disease. In fact,
cases have been documented where the lapse between the ini-
tial disease and the chromic form was several decades. The
chronic disease can lead to heart valve damage.
Why some people display symptoms of infection while
others do not is still not resolved. Neither are the reasons why
the disease is self-limiting within a short time in some people
but develops into a lengthy, debilitating, and potentially lethal
disease in other people.
Coxiella burnetiihas two different forms, which have
differing surface chemistries. These are called phase I and
phase II. The phase I form is associated more with the chronic
Q fever than is phase II.
Diagnosis of Q fever is most reliably obtained by the
detection of antibodies to the infecting bacterium. Following
diagnosis, treatment consists of antibiotic therapy. The antibi-
oticsthat have achieved the most success are fluoroquinolone,
rifampin, and trimethoprim-sulfamethoxazole. In the chronic
form of Q fever, the antibiotics may need to be administered
for several years. If the disease has damaged body parts, such
as heart valve, then treatment may also involve the replace-
ment of the damaged tissues.
Vaccinationagainst Q fever is not yet a standard option.
Avaccineis available in Australia and parts of Europe, but has
not yet been approved in North America.
Prevention of the transmission of the bacterium to
humans involves the wearing of masks when around domesticwomi_Q 5/7/03 8:08 AM Page 471