Respiratory virus detection methods
There are many methods consist on the identifcation of the repiratory virus.
Viral respiratory infection can be caused by nemerous viruses:
- RSV A and RSV B (Respiratory Syncytial Virus).
- Parainfluenza Virus (types 1–4).
- Numerous Adenoviruses.
- Avian Influenza Virus (H5N1 and H7N9).
- Coronaviruses; including SARS (Severe Acute Respiratory Virus) and SARS-COV2 (The novel coronavirus which is responsible for COVID-19.
The above listed viruses causes different respiratory infection with symptoms from mild to severe, and thus form runny nose and sneezing to pharyngitis, laryngitis, bronchitis, or pneumonia.
The severity of disease varies depending on the level of immunity of the individual.
There are many methods for the diagnosis of the respiratory viruses; we can say that there is traditional methods and molecular methods.
The traditional methods are:
This method consist on:
- Isolation of the virus in cell cultures
- Incubation of specimen with these cell cultures in tubes.
- Placing the tubes in roller drum (Rotate for almost 10 days).
- Observing daily the cells under the microscopes, the damaged cells indicate the presence of the virus.
The inconvenient of this method is that not all viruses are culturable, and this method is not sensitive enough when antibodies in the specimen neutralize the virus.
Direct Fluorescent Antibody (FDA)
This methode consit on staining or the presence of virus-infected cells.
- collection of epithelial cells from a nasopharyngeal swab.
- fixing the epithelial cells to a glass microscope slide.
- Staining with individual antibodies labeled with a fluorescent tag.
- Viewing the slide with a fluorescent microscope.
Shell Vial Culture
This method consist on:
- Inoculation of an aliquot of the specimen onto a preformed cell monolayer in a small vial containing a mixture of two susceptible cells.
- Centrifugation to enhance virus attachment and entry.
- The centrifugation-assisted inoculation of the cells increases the amount of viral proteins produced.
- This allows staining to be performed at 24–48 h and thus providing a test result to be obtained significantly earlier than the 7–10 days necessary for traditional cell culture.
Enzyme-linked immunosorbent assays (ELISA)
The rapid enzyme-linked immunosorbent assays (ELISAs) consist on using a monoclonal conjugated antibody to an enzyme to quantify and detect the presence of a specific antigen in a sample.
The molecular methods are:
Nucleic Acid Amplification Tests (NAAT)
This technique started in the late 1980s, developped for the the first time for the influenza, In 1983; 1983 by Kary B. Mullis ( used a nucleic acid amplification method called Polymerase Chain Reaction (PCR).
Within a decade, NAATs were developed for all of the respiratory viruses.
The most used technique is PCR, but there are other techniques:
- Strand Displacement Amplification (SDA).
- Nucleic Acid–Sequence-Based Amplification (NASBA).
- Transcription-Mediated Amplification (TMA).
- Loop-Mediated Isothermal Amplification (LAMP).
These all NAATs techniques consist on:
- Extraction of the nucleic acid from the respiratory tract specimen.
- Copying the viral ribobucleic acid (RNA) into a complementary deoxyribonucleic acid (cDNA) by the enzyme Reverse transcriptase.
- Amplifying the cDNA by PCR using a virus-specific oligonucleotide primers.
- The result is a billion copies of DNA.
- These DNAs can then easily detected by different laboratory methods.
Molecular methods are more sensitive than traditional methods, they are also efficient and give results in a very short time.