VIRAL AND RICKETTSIAL DISEASES 
Diagnosis of viral and rickettsial diseases in the lab- 
oratory may be attempted by three general pro- 
cedures. 
1. Isolation and identification of the inciting 
agents; 
2. Demonstration of a rise in titer of specific 
antibodies during the course of the illness; 
3. Examination of the infected tissues for 
pathologic alterations. 
It is rarely possible or necessary to use all three 
procedures in diagnostic work. A decision as to which 
procedure should be followed is dictated by the 
nature of the infection, the stage of the illness when 
the patient is first seen, and the amount of informa- 
tion the methods will yield in relation to the time, 
effort, and expense involved. 
Direct microscopic methods are rarely used and are 
of limited usefulness except in rabies diagnosis and 
a few other special cases. Aside from immunofluo- 
rescence, microscopy is usually confirmed by some 
other procedure such as serology or isolation of the 
agent. 
Serologic tests have far greater usefulness in the 
diagnostic laboratory than either of the other ap- 
proaches. Serologic methods generally yield informa- 
tion more rapidly and less expensively than isolation 
and identification of an agent, but they do not give 
the same degree of assurance of etiologic involve- 
ment. In fatal infections, when there has been in- 
sufficient time for specific antibody development, 
isolation of the causative agent is the only means of 
diagnosis. When the virus exists in many antigenic 
types, as in the Coxsackie group, it is essential to 
isolate the virus from clinical material. Serologic 
tests are possible only for those diseases whose 
causative agents have been isolated and from which 
satisfactory antigens can be produced. Obviously, 
some exception must be made for those diseases in 
which a biologically nonspecific phenomenon can be 
useful in suggesting a diagnosis, as in the Weil-Felix 
reaction for certain rickettsioses, and the heterophile 
test for infectious mononucleosis. Serologic methods 
alone with contribute little to establishing the etiology 
of diseases of unknown causation. 
The types of specimens that may be submitted for 
laboratory examination in viral and rickettsial dis- 
eases are more varied than in any other type of in- 
fection. Depending on the disease, the specimens in- 
clude: nasal swabs, throat swabs, swabs of oral 
lesions, saliva, sputum, nasopharyngeal swabs, nose 
and throat washings, stool or rectal swabs, cerebro- 
spinal fluid, vesicle fluid, pleural effusion fluid, bubo 
aspiration fluid, muscle biopsy, crusts, scrapings 
from fever sores, postmortem tissue and paired sera. 
In interpreting isolation results, it should be remem- 
bered that the mere presence of a virus in excreta 
does not necessarily establish the etiological relation- 
ship of the agent to the disease. Inapparent and 
mixed infections, particularly with enteroviruses, are 
common and the etiologically unrelated virus may 
even give rise to antibody formation which coin- 
cides with the timetable of the disease. 
1. Preparation and Shipment of Diagnostic Speci- 
mens 
a. Type of Specimen to be Collected 
(1) Virus isolation. Materials for isolation 
must be freshly obtained and, if pos- 
sible, collected with aseptic precau- 
tions. Source of materials depends on 
the type of clinical disease (that is, 
throat swabs or throat washings in 
respiratory infections, etc.). Usual 
materials include blood, throat wash- 
ings, sputum, feces, effusion fluid, tis- 
sue biopsies, autopsy tissue, or lesion 
scrapings. No preservative or fixative 
should be added. After collection, blood 
for virus isolation should be frozen 
without further treatment. 
(2) Serological tests. Serum should be 
obtained from clotted blood collected 
and kept under sterile conditions. No 
preservative need be added. Separating 
the serum from the clot at the source 
prevents hemolysis which interferes 
with some tests. At least 10 ml. of 
blood (5 ml. of serum) and preferably 
20 ml. of blood should be collected 
for serological tests to permit a multi- 
plicity of tests, confirmation, or repeti- 
tion of equivocal results when neces- 
sary. 
b. Time to Collect Specimens 
( 1 ) Virus isolation. The time in the course 
of the clinical disease that specimens 
are collected is of utmost importance. 
In general, for isolation techniques 
the earlier in the acute stage the speci- 
men is taken, the better the chance for 
successful isolation. The specimen 
should certainly be taken while the 
patient is still acutely ill and febrile. 
(2) Serological tests. Except in outbreaks 
of encephalitis, serum specimens must 
be paired since only a rise in specific 
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