Module 15-16

• Full-service virology laboratories provide viral culture and identification using cell cultures to support the growth of viruses from clinical specimens.
• Rapid tests that detect specific viruses can be used in medical facilities that do not provide full virology services.
• The viral titer is highest during the first 4 days after the onset of symptoms.
• Tissue culture or organ culture denotes the growth of tissues or an organ so that the architecture or function of the tissue or organ is preserved.
• Specimens should never be stored at -20° C because this temperature facilitates the formation of ice crystals, which disrupt the host cells and result in loss of viral viability.
• Most of the clinical workload focuses on the detection of HSV in genital specimens and respiratory viruses.
• In viral cultivation the most commonly used method for viral cultivation is cell culture.
• Cell Culture is technically used to indicate culture of cells in vitro; the cells are not organized into a tissue.
• Finite cell cultures are characterized by 75% of cells having the same karyotype as the original tissue.
• Embryonated eggs are rarely used
• In clinical virology, isolating viruses is still the gold standard against which all other methods are compared.
• Viral Cultivation involves providing living cells instead of chemical media for the cultivation of viruses in vitro.
• Primary cell cultures are obtained from tissue removed from an animal and are characterized by cells having the same karyotype and chromosome number as the original tissue.
• Animal inoculation is an expensive method used only in reference or research laboratories.
• Exceptions to early specimen collection are enterovirus, adenovirus and cytomegalovirus because of prolonged shedding of the virus.
• It is best to sample the infected site directly.
• It is best to sample the infected site directly exception is certain viral infections of the CNS when it may be recommended to culture the stool or throat instead of CSF (since virus is shed in stool or throat).
• Swabs should be cotton, rayon or Dacron on plastic shafts because wood is toxic to viruses.
• A shell vial is a small, round, flat - bottomed tube, generally with a screw cap.
• Continuous cell cultures are cell lines with less than 75% normal cells; more than 25% of the cells have an abnormal karyotype.
• Examples of immortal cell lines include HeLa (Henrietta Lacks), Hep - 2, KB, A-549 and Vero
• Electron microscopy has a greater magnification and can be used to detect virions.
• In many cases, virology results might be available before routine bacteriology culture results.
• The shell vial culture technique can more rapidly identify viruses than the traditional cell culture method.
• In general, direct detection methods are not as sensitive as culture methods but can offer quick results to allow for rapid therapy.
• EM makes use of negative staining technique in which specimens are placed on a carbon – coated grid and stained with K phosphotungstate or uranylacetate.
• The shell vial is incubated for 24 to 48 hours, after which the coverslip is removed and the IF technique performed.
• The shell vial is inoculated with the clinical sample and then centrifuged to promote viral absorption.
• Viral detection allows clinicians to make relevant decisions about therapy, infection control measures, and hospitalization.
• SVCE: A modification of this procedure is to use flat - bottomed microtiter plates.
• Examples of finite cell cultures include WI-38 MRC-5 and Human diploid fibroblasts
• Electron microscopy is useful to detect nonculturable viruses in stool filtrates such as the Norwalk viruses, Adenoviruses, and Coronaviruses.
• Cells are grown on a round coverslip in a shell vial.
• Diploid is the normal genetic makeup for eukaryotic cells.
• Although virus particles cannot be visualized, the CPE can be detected in cell scrapings from infected sites by bright field microscopy.
• Immortal cell lines are derived from malignant tissue or transformed/cancer cells; they are capable of infinite passage and are heteroploid, meaning that they have an abnormal and variable number of chromosomes that is not a multiple of the normal haploid number.
• Paired sera are recommended for serological detection with the first specimen collected when the clinical signs first appear and the second specimen collected 2 - 3 weeks later depending on the virus.
• Serologic assays measure the host response rather than directly detecting the virus.
• Ab level does not necessarily correlate with the acuteness or activity level of the infection, as this is also host-dependent.
• Paired sera (acute and convalescent) demonstrating seroconversion or a fourfold rise in titer are required to establish a diagnosis of recent infection.