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Infectious Disease
Introduction to Clinical Detection Techniques for Pathogens
Introduction to Pathogens

The first person in history to identify pathogens was the Hungarian obstetrician Ignaz Semmelweis in the 1840s. After discovering the existence of pathogens, Dr. Semmelweis saved many pregnant women by removing the pathogens with bleach. Later generations honored him as "the savior of mothers." A pathogen is any substance that can cause disease, generally referring to organisms and bio-like structures that can do so. Typically, the term "pathogen" is used to describe microorganisms or agents that are "contagious."

Classifications of Pathogens

Viroids: Single-Stranded Circular RNA Pathogens:
Viroids constitute pathogens that are smaller than viruses. Viroids lack the protein shell of a typical virus. They primarily dwell in angiosperms and their mechanism of transmission is through seeds or pollen.

Prions - Protein Pathogens:
Prions can cause infectious spongiform encephalopathy in mammals; well-known human afflictions include Alzheimer's disease and Parkinson's disease, while associated veterinary conditions include scrapie and mad cow disease.

About two million people die each year from tuberculosis, which is caused by a bacterium called Mycobacterium tuberculosis. In addition to tuberculosis, common conditions caused by bacterial pathogens also include pneumonia (caused by Streptococcus and Pseudomonas) and food poisoning (caused by Salmonella).

These include yeasts, molds, and mushrooms. Among them, the most well-known condition arising from fungal pathogens includes tinea pedis (commonly known as athlete's foot). This is a skin infection caused by fungi that are classified as dermatophytes.

Protozoa are primarily composed of single cells while a few are multicellular. Plasmodium (malarial parasites) are spread by mosquitoes, and victims of malaria can experience symptoms such as loss of consciousness, seizures, shock, kidney failure, difficulty breathing, or stroke. With more than two hundred million people infected worldwide each year, the corresponding death toll is about 600,000 individuals.

Viruses: the SARS-CoV-2 Virus Being an Example

Viruses constitute a non-cellular form of a bio-like structure composed of a nucleic acid molecule (DNA or RNA) and a protective shell (protein). The novel coronavirus SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) now stands as the most notorious viral pathogen. It belongs to the beta subfamily (betacoronavirus) of Coronavirinae. The novel coronavirus (SARS-CoV-2) is round, and constitutes a group of single-stranded positive-sense RNA viruses with mantles. The structure of SARS-CoV-2 from the inside out is: a positive stranded single stranded RNA with a virus shell mantle. The RNA genome of SARS-CoV-2 encodes four main structural proteins: spike proteins (S proteins), envelope proteins (E proteins), membrane proteins (M proteins), and nucleocapsid proteins (N proteins).

Together, these proteins make up the viral particle structure. In addition to the component of the main structural protein, the RNA genome of SARS-CoV-2 also contains fragments of an open reading frame (ORF1ab) for non-structural proteins.

SARS-CoV-2 meets the definition of a pathogen: it is a substance that can produce disease, namely causing COVID-19. The symptoms of COVID-19 are quite numerous, including fever, abnormalities in smell and taste, difficulty breathing, and so on; and severe cases lead to death. Most pathogens can be diagnosed by these symptoms. In addition, targeting pathogenic characteristics can also help us better understand the associated pathogens.

Pathogen Targeting and Detection Techniques

Through an understanding of the pathogen structures, detection methods can be developed that target these structures. At present, the detection technology using nucleic acid molecules as targets is polymerase chain reaction (PCR). Polymerase chain reaction is a molecular detection technique for nucleic acid amplification technologies (NAT) in vitro. The use of proteins as targets includes enzyme-linked immunosorbent assay (ELISA) and lateral flow immunoassay.

GB SARS-CoV-2 Real Time RT-PCR (4PCO052E) is a detection reagent that uses RNA in SARS-CoV-2 viral pathogens as the molecular detection target. It features qualitative detection of SARS-CoV-2 viruses using RNA polymerase chain reaction (PCR). Under the operation of professionals, the fluorescent signal released during the SARS-CoV-2 RNA amplification reaction can be used to understand the presence or absence of the genome of the SARS-CoV-2 virus. Since the mutation rates of different gene fragments is different, the probability of mutation causing undetectable results is reduced by detecting different fragments of RNA detection targets at the same time. GB SARS-CoV-2 Real Time RT-PCR (4PCO052E) products use two RNA fragments as detection targets, these being envelope proteins (E proteins) and open reading frame (ORF1ab) fragments of non-structural proteins, respectively. Simultaneous detection of two gene slices achieves the effect of accurate detection.

The main structural protein of SARS-CoV-2 can also be used as a detection target. Based on lateral flow immunoassay, GBC has developed products that use SARS-CoV-2 structural protein-nucleocapsid protein (N protein) antigens as the target of protein detection. These products include GB COVID-19 Ag Rapid Test (4LCO009E, Professional Use) and GB COVID-19 Ag Rapid Test (4LCO01AE, Home Use) . Nucleocapsid protein antigen is one of the main expressed structural proteins that can be detected one day before the onset of clinical symptoms and is an ideal target for early diagnostic detection of infection. 2, 3, 4

In summary, general users can operate a rapid screening based on lateral fluid immunoassay to initially detect the presence of pathogens. In addition to using lateral fluid immunoassay, professionals can also perform polymerase chain reaction (PCR) screening to assist the general population in identifying pathogens. Under the protection of multiple medical testing technologies for protein and genetic testing, we can go beyond observing symptoms to further identify pathogen types and then offer suitable medical treatment, helping us maintain health more accurately in real time.

1.Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. Introduction to Pathogens. Available from:
2.Diao B, Wen K, Zhang J, Chen J, Han C, Chen Y, Wang S, Deng G, Zhou H, Wu Y. Accuracy of a nucleocapsid protein antigen rapid test in the diagnosis of SARS-CoV-2 infection. Clin Microbiol Infect. 2021 Feb;27(2):289.e1-289.e4. doi: 10.1016/j.cmi.2020.09.057. Epub 2020 Oct 5. PMID: 33031947; PMCID: PMC7534827.
3.Wu F, Zhao S, Yu B, Chen Y, Wang W, Song Z, et al. A new coronavirus associated with human respiratory disease in China. Nature 2020;579:265e9.
4.Che X, Hao W, Wang Y, Di B, Yin K, Xu YC, et al. Nucleocapsid protein as early diagnostic marker for SARS. Emerg Infect Dis 2004;10:1947e9.