Clinical uses of the diagnostic virology laboratory

Detection and identification of viruses by electron microscopy

Electron microscopy can aid in the rapid diagnosis of viral diseases, as it can be performed in a matter of hours, but on a routine basis it should be used in conjunction with other techniques. Initially, the specimen source and patient symptoms should be ascertained, as these will lend suggestions of possible agents while eliminating others; however, this information should not be allowed to prejudice observation in such a way as to cause oversight of an unlikely pathogen. Second, selection of the method of preparation should be based on sample consistency; extraction, debris clarification, concentration, tissue culture amplification, or embedment may be necessary. Finally, false-positive results must be avoided by differentiating viruses from cell organelles or debris, mycoplasmal or bacterial contamination, and bacteriophages.

Transport of viral specimens

The diagnosis of viral infections by culture relies on the collection of proper specimens, proper care to protect the virus in the specimens from environmental damage, and use of an adequate transport system to maintain virus activity. Collection of specimens with swabs that are toxic to either virus or cell culture should be avoided. A variety of transport media have been formulated, beginning with early bacteriological transport media. Certain swab-tube combinations have proven to be both effective and convenient. Of the liquid transport media, sucrose-based and broth-based media appear to be the most widely accepted and used. Studies on virus stability show that most viruses tested are sufficiently stable in transport media to withstand a transport time of 1 to 3 days. Some viruses may withstand longer transport times. In many cases, it is not necessary to store virus specimens in a refrigerator or send them to the laboratory on wet ice or frozen on dry ice. However, the specimen should not be exposed to environmental extremes. Modern viral transport media allow for more effective use of viral culture and culture enhancement techniques for the diagnosis of human viral infections.

Evaluation of five cell types for the isolation of herpes simplex virus

Five cells were evaluated in a comparative analysis for sensitivity, specificity, and rapidity in detecting the presence of herpes simplex virus HSV-1 and HSV-2. Included in this study were human embryonic kidney (HEK), rabbit kidney (RK), MRC-5, mink lung (ML), and Microtus agrestis (UMMA). A total of 274 specimens from genital, throat, skin, or other sources that were submitted for HSV isolation were used in the study. The sensitivity of the different cells was assessed by the total number of positive cultures detected by all the cells under evaluation. At 48 hr, HEK and RK detected 80% of the positives, ML detected 79%, MRC-5 detected 73%, and UMMA detected 60%. All cells tested were satisfactory; however, the choice of which cell to use for isolation of HSV depends upon the needs of the specific laboratory.

Diagnosis of oral herpes simplex virus infections: practical aspects of viral culture

Viral culture is a valuable aid in the diagnosis of herpes simplex virus infections of the oral cavity, but it is underutilized by members of the dental profession. This article outlines indications for culture, practical aspects of collection and transportation of specimens, reasons for false-negative and false-positive test results, and cost.