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- Lab diagnosis refers to the identification, examination & confirmation of pathogens in the lab.
- The diagnosis of virus infection can be established in several ways, often used together, namely:
- Detection of virus particles, viral antigens or viral nucleic acids in specimens taken from the appropriate site.
- Culture of infectious viruses from the appropriate sites.
- Serological tests to detect specific antiviral antibodies.
- Cytological or histological examination of cells from the site of infection in those viral infections in which a characteristics CPE is produced.
Clinical Specimens and Sample Collection
For diagnosis of coronavirus, the following specimens are taken:
- Respiratory materials including nasopharyngeal swabs, oropharyngeal swabs, sputum, etc.
- Rectal swab & stool
- Tissue from biopsies or autopsy including those from lungs
- Urine sample
- Serum for serological testing
Transportation and Storage of Specimens
• For storage: Specimens can be stored for 5 days at 4°c and for 6 days at -20°c.
• For transportation: Virus transport media(VTM) are used to transport a small volume of the fluid specimens, small tissues & scrapings & swabs specimens, especially when contaminated with microbial flora is expected.
• Some VTM are Hanks balanced salt solution, Stuart’s medium, Eagle’s tissue culture medium, etc.
Detection of Corona Virus
1. Isolation of Virus
The isolation and cultivation of coronavirus taken from specimens is an important step in the diagnosis of coronavirus. The novel coronavirus (SARS-CoV-2) is mainly cultivated in the Vero cell line which are one of the most common mammalian continuous cell lines used in the culture of SARS-CoV-2. It was extracted from the kidney of an African green monkey.
2. Serological Test
The serological test refers to the test involve virus detection, quantifying viral antigens & confirming the presence of the virus or specific antiviral antibodies. There are various types of serological test done for diagnosis of coronavirus:
Complement Fixation test
3. RNA Detection
As coronavirus is an RNA virus so performing Real-time Reverse transcription PCR (rRT-PCR) confirmed the coronavirus RNA in the respiratory secretions & even in the stool samples of patients.
The use of Real-time Reverse transcription (rRT-PCR) assays for the in-vitro qualitative detection of 2019-Novel coronavirus (SARS-CoV-2) in respiratory specimens and sera.
4. Electron Microscopy
Specimens collected from patients are observed under an electron microscope which shows petal-shaped projections that are widely spaced on the outer surface of the envelope etc, Which indicates the presence of coronavirus.