Page 225 - Review of Medical Microbiology and Immunology ( PDFDrive )

mebooksfree.com
mebooksfree.com
mebooksfree.com

mebooksfree.com
mebooksfree.com
mebooksfree.com
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com convalescent serum samples is the most common way the mebooksfree.com
mebooksfree.com
PART II Clinical Bacteriology
214
A fourfold or greater rise in titer between the acute and
Typhus
There are several forms of typhus, namely, louse-borne epi-
laboratory diagnosis is made. This is usually a retrospective
demic typhus caused by R. prowazekii, flea-borne endemic
diagnosis, because the convalescent sample is obtained
typhus caused by Rickettsia typhi, chigger-borne scrub
2 weeks after the acute sample. If the clinical picture is typi-
typhus caused by O. tsutsugamushi, and several other quite
rare forms. Cases of flea-borne endemic typhus, also called
as presumptive evidence. If the test is available, a diagnosis
murine typhus, occur in small numbers in the southern
can be made during the acute phase of the disease by
regions of California and Texas. The following description
immunofluorescence assay on tissue obtained from the site
is limited to epidemic typhus, the most important of the cal, a single acute-phase titer of 1:128 or greater is accepted
mebooksfree.com mebooksfree.com mebooksfree.com saccharide found in P. vulgaris OX-2, OX-19, and OX-K. mebooksfree.com
mebooksfree.com
of the petechial rash.
mebooksfree.com
typhus group of diseases.
The Weil-Felix test is based on the cross-reaction of an
Typhus begins with the sudden onset of chills, fever,
antigen present in many rickettsiae with the O antigen poly-
headache, and other influenzalike symptoms approxi-
mately 1 to 3 weeks after the louse bite occurs. Between the
The test measures the presence of antirickettsial antibodies
fifth and ninth days after the onset of symptoms, a maculo-
in the patient’s serum by their ability to agglutinate Proteus
papular rash begins on the trunk and spreads peripherally.
bacteria. The specific rickettsial organism can be identified
The rash becomes petechial and spreads over the entire
by the agglutination observed with one or another of these
body but spares the face, palms, and soles. Signs of severe
three different strains of P. vulgaris. However, as mentioned,
meningoencephalitis, including delirium and coma, begin
this test is no longer used in the United States.
with the rash and continue into the second and third weeks.
In untreated cases, death occurs from peripheral vascular
collapse or from bacterial pneumonia.
Epidemic typhus is transmitted from person to person by Treatment
The treatment of choice for all rickettsial diseases is
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com Prevention of many of these diseases is based on reducing mebooksfree.com
the human body louse, Pediculus. When a bacteremic patient
mebooksfree.com
doxycycline.
is bitten, the organism is ingested by the louse and multiplies
in the gut epithelium. It is excreted in the feces of the louse
Prevention
during the act of biting the next person and autoinoculated by
the person while scratching the bite. The infected louse dies
exposure to the arthropod vector by wearing protective
after a few weeks, and there is no louse-to-louse transmission;
clothing and using insect repellent. Frequent examination
therefore, human infection is an obligatory stage in the cycle.
of the skin for ticks is important in preventing Rocky
Epidemic typhus is associated with wars and poverty; at pres-
Mountain spotted fever; the tick must be attached for sev-
ent it is found in developing countries in Africa and South
eral hours to transmit the disease. There is no vaccine
America but not in the United States.
A recurrent form of epidemic typhus is called Brill-
otics are not recommended in the asymptomatic person
Zinsser disease. The signs and symptoms are similar to
bitten by a tick.
those of epidemic typhus but are less severe, of shorter against Rocky Mountain spotted fever. Prophylactic antibi-
Prevention of typhus is based on personal hygiene and
duration, and rarely fatal. Recurrences can appear as long
mebooksfree.com mebooksfree.com mebooksfree.com military during wartime but is not available to civilians in mebooksfree.com
mebooksfree.com
mebooksfree.com
“delousing” with DDT. A typhus vaccine containing formalin-
as 50 years later and can be precipitated by another inter-
killed R. prowazekii organisms is effective and useful in the
current disease. In the United States, the disease is seen in
older people who had epidemic typhus during World War II
the United States.
in Europe. Brill-Zinsser disease is epidemiologically inter-
esting; persistently infected patients can serve as a source of
the organism should a louse bite occur.
COXIELLA BURNETII
Laboratory Diagnosis
Disease
Laboratory diagnosis of rickettsial diseases is based on
serologic analysis rather than isolation of the organism.
cause of this disease was a question mark (i.e., was
Although rickettsiae can be grown in cell culture or embry-
unknown) when the disease was first described in Australia
onated eggs, this is a hazardous procedure that is not avail- Coxiella burnetii causes Q fever. Q stands for “Query”; the
in 1937.
mebooksfree.com mebooksfree.com mebooksfree.com Coxiella burnetii has a sporelike stage that is highly resistant mebooksfree.com
mebooksfree.com
mebooksfree.com
able in the standard clinical laboratory.
Of the serologic tests, the indirect immunofluorescence
Important Properties
and enzyme-linked immunosorbent assay (ELISA) tests are
most often used. The Weil-Felix test is of historic interest
to drying, which enhances its ability to cause infection. It
but is no longer performed because its specificity and sen-
also has a very low ID estimated to be approximately one
sitivity are too low. The basis of the Weil-Felix test is
50
organism.
described later.
mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com