Saturday, August 13, 2011

General diagnosis of viruses (Part 1)

nullSpecimens collection and transport:
Collection and transport of an appropriate sample to the laboratory is a vital factor in successful diagnosis (Smith and Yassin, 2000).
Specimens collection
Collection of samples that contain the highest titer of virus is most desirable. Preservation of the viral titer and viral infectivity until cell cultures can be inoculated is essential. Body sites and collection methods vary according to the type of infection and viral etiology e.g. clinical samples collected from body sites such as skin and the genital tract, which is usually contaminated with microbial flora, are collected with
dacron or polyester swab and placed in viral transport medium (VTM) but CSF which is expected to be free of contamination, is collected in sterile containers (Leland and Ginocchio, 2007).
Table (2): shows Specimens useful for viral studies (Specter and Bendinelli, 2005).
Specimen type Disease category (example)
Nasopharyngeal swab or aspirate Respiratory tract infection, certain exanthemas, CNS infection (especially Enteroviruses).
Throat wash or swab Respiratory tract infection.
Sputum Respiratory infection (HSV, CMV).
Bronchoalveolar lavage Lower respiratory infection (CMV, Influenza virus, PIV).
Rectal swab or stool Gastroenteritis and Enteroviruses.
CSF Meningitis, encephalitis.
Brain biopsy Meningitis, encephalitis (HSV, Rabis virus).
Vesicle fluid or lesion scraping HSV, VZV.
Endocervical swab Genital infections (HSV).
Eye swab Ocular infections (Adenovirus, HSV).
Urine CMV, BK virus, Mumps virus.
Serum Antibody studies (most viruses).

Several VTM are commercially available. Most VTM consist of buffered isotonic solution with some types of protein as albumin, gelatin or serum to protect less stable viruses. Antibacterial and antifungal agents are added to prevent overgrowth of bacteria and fungi (Nauschuetz and Learmonth, 2007).
Ideally, all specimens collected for viral detection should be placed in ice and transported to the laboratory at once. If a delay is unavoidable, the specimen should be refrigerated not frozen until processing occurs. Every attempt should be made to process the specimen within 12 to 24 hours of collection. Under unusual circumstances, specimens may need to be held for days before processing. For storage up to 5 days, hold specimen at 4°C. Storage for 6 or more days should be at -70°C. Specimens for freezing should first be diluted in VTM. Significant loss of viral infectivity may occur during prolonged storage, especially for the more labile enveloped viruses (Forbes et al, 2007).

No comments: