Sunday, August 14, 2011

Gastrointestinal Viral Infections:Enteroviruses

• Collection of specimens and Virus isolation
Isolation of Enteroviruses from specimens using appropriate cultured cell lines is often possible within 2-3 days and remains a very sensitive method for detecting these viruses. The best specimens for isolation of virus are stool specimens or rectal swabs, throat swabs or washings, and cerebrospinal fluid. Throat swabs or washings and cerebrospinal fluid are most likely to yield virus isolates if they are obtained early in the acute phase of the illness. For cases of acute hemorrhagic conjunctivitis, the best specimens are conjunctival swabs (Shulman et al., 1997).
There is no single cell line capable of growing all human Enteroviruses. There is several tissue lines (PMK, RD, and HEP2) support growth of many Enteroviruses (Huang et al., 2002). CPE begins as focal pyknotic changes with individual cell rounding which then rapidly progresses across the cell monolayer. It is defined within 4 days. Shell vial is also excellent choice for culture of Enterovirus (Lipson et al., 2001).
In routine diagnostic testing, all Enterovirus growth in cell culture is detected by its CPE and confirmed by neutralization with type-specific antisera. As there are many different known Enteroviruses, it would be impractical to attempt neutralization using all possible reference antisera individually. Type-specific antisera are therefore combined in pools in which Ab to any type is present in only eight pools (A - H). The typical neutralization test consists of mixing of an unknown virus with an antiserum pool then the virus antiserum mixture is inoculated on susceptible cell culture, which is then observed for several days. A separate virus antiserum mixture is made for each of the available antiserum pools. The pool that neutralizes the unknown isolate identifies the virus e.g. If only E and F neutralize the unknown virus, it is identified as echovirus 18, because only antisera to this virus are found in both of these pools and not in the others (Mahy and Meulen, 2005).
• Serologic diagnosis
The serological diagnosis is often feasible. Antibody titers are compared in paired sera, the first sample being collected in the acute phase and the second 1-14 days later. ELISA or RIA may be used as well as neutralization or in some cases, HI such methods can be used to assay for IgM specifically, and thus identify acute infection (Minor, 2005).
• Molecular detection
The major advantage of PCR is that rapid detection of Enteroviruses is possible, even with very small amounts of clinical specimens such as spinal fluid. It is also possible to detect Enteroviruses that do not readily grow in cell culture (Muir et al., 1999). RT-PCR and nucleic acid amplification tests that detect a common sequence present in all Enteroviruses have excellent sensitivity, superior to standard culture (Landry et al., 2003).

No comments: