Introduction
Infectious disease affects billions and is a worldwide concern. The current diagnostic tools are time-consuming, expensive, and require trained personnel. These methods are not useful for large-scale screening during outbreaks or epidemics. Developing diagnostic technology for accurate and rapid detection of infectious diseases can help curb and treat them.
What Are Infectious Diseases?
Infectious disease is an illness caused by bacteria, viruses, parasites, or fungi. The illness caused by infectious agents is often contagious. It can cause high rates of mortality and morbidity.
In recent years, pandemics of influenza such as Spanish flu, swine flu, and bird flu, outbreaks of Zika and Ebola, epidemics of MARS (Middle East respiratory syndrome) and SARS (severe acute respiratory syndrome), and COVID-19 (Coronavirus of 2019) have caused significant threats to human health. Some infectious diseases like viral hepatitis, HIV (human immunodeficiency virus), and tuberculosis persist until the infected person’s lifetime. Therefore, it significantly contributes to the global health burden.
Diagnosis and early treatment of infectious disease help to prevent its further spread. Conventional methods to diagnose infectious disease are directly isolating nucleic acids of infectious agents from biological samples and identifying them through polymerase chain reaction (PCR). Although PCR has several medical applications, it is expensive, highly sophisticated, and lacks standardization.
What Is CRISPR-Cas?
CRISPR-Cas (clustered regularly interspaced short palindromic repeats-associated protein) is a revolutionary gene editing technology with the potential to revolutionize the diagnosis and treatment of infectious diseases. It was recognized as a part of the bacterial immune system protecting against viral infections by storing the memory of previous infections through the viral DNA (deoxyribonucleic acid). Therefore, it helps the immune system to identify and eliminate the virus with subsequent infections.
It is used for deleting, modifying, or correcting specific DNA and RNA (ribonucleic acid) sequences of human infectious agents such as viruses, bacteria, fungi, or parasites. They have the potential to curb outbreaks and pandemics.
Cas proteins such as Cas3, Cas9, Cas12, Cas13, and Cas14 have been used to create sensitive and accurate tools for diagnosing. The various Cas proteins may mediate the cleavage of nucleic acid in different ways. Cas 9 works individually, but others form cleavage complexes consisting of multiple Cas proteins. Diagnostic tools with CRISPR technology have a tremendous opportunity to reshape epidemiological surveillance.
What Are the Applications of CRISPR Technology in Infectious Diseases?
CRISPR technology has enabled the development of rapid and accurate diagnostic tools that prevent and treat infectious diseases.
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Diagnostics for Infectious Disease: Rapid diagnostic tests enable early identification and treatment of disease, improving treatment outcomes and preventing further spread. An ideal diagnostic test must be sensitive, specific, easy to perform and interpret, and affordable. The virus or bacterial samples are amplified with recombinase polymerase amplification. The obtained DNA is mixed with the CRISPR/Cas system that identifies and cleaves sequences of interest.
Viral Disease
It is a living cell that hijacks intracellular processes to enable their replication.
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Tuberculosis is the leading cause of death. CRISPR-MTB (Mycobacterium tuberculosis complex) has been used in recent years for identifying the causative agent.
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HPV (Human Papilloma Virus) is responsible for cervical cancer in women. Many CRISPR-based systems like CARP (combination of PCR and CRISPR) and DETECTR (DNA endonuclease targeted CRISPR trans reporter). The DETECTR tool helps differentiate between various strains of HPV.
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Viral hepatitis B, D, and C affects millions worldwide and leads to significant mortality. Chronic hepatitis is asymptomatic until liver injury develops. CRISPR-cas 13a is successfully used for identifying hepatitis B DNA.
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Dengue fever affects many people, and their symptoms resemble hemorrhagic fever in Ebola. CRISPR-based tool, NASBACC (nucleic acid sequence-based amplification), can effectively detect outbreaks of dengue fever.
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Zika virus is known to cause neurological defects in newborns born to infected mothers. NASBACC is a sensitive and accurate tool to identify the virus. CRISPR-Cas 9 helps differentiate between several strains of Zika virus.
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Coronavirus infections like SARS, MERS, and COVID-19 have adversely affected human health and caused widespread deaths. CRISPR-based tools would have helped their rapid identification, diagnosis, and management. During the recent COVID-19 outbreak, a CRISPR tool called SHERLOCK could detect the disease 100 percent concordant to PCR.
Bacterial Disease
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CRISPR-Cas 9 combined with DNA mapping helps identify bacterial antibiotic resistance genes.
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CRISPR-Cas9 with DNA fluorescent in situ hybridization helps identify methicillin-resistant Staphylococcus aureus (MRSA).
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Understanding Host and Pathogen Interaction
It is vital to know the mechanism of bacteria, viruses, fungi, and parasites causing disease in humans to design treatments and vaccines. For example, CRISPR-Cas9 helps understand the mechanism of alpha-hemolysin, a virulence factor of Staphylococcus aureus, causing cytotoxicity.
2. Therapeutic Applications:
The primary goal of CRISPR-based infectious disease therapeutics is treating drug-resistant bacteria, such as antibiotic resistance. Persistent viral infections, such as HIV.
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Targeted Bacterial Resistance: The rationale for using CRISPR against resistant bacteria is to apply the bacteria’s defenses against them. The technology can help develop antimicrobials to eliminate pathogenic bacteria.
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Targeting Persistent Viral Infections: In some cases, during initial viral infection, the viral pathogen may integrate its genome with human chromosomal DNA. CRISPR-based tools help reduce or eliminate persistent infections.
3. CRISPR Vaccine
Traditionally, vaccines introduce viral and bacterial antigens into the host and generate an antibody response. However, designing the vaccine can be challenging due to variations in antibodies produced between individuals, and some viruses cause the generation of neutralizing antibodies in small quantities. In the CRISPR system, the host B cells are used for generating neutralizing antibodies. The CRISPR tools modify human B cells to produce HIV-1 specific neutralizing antibodies. It helped reduce viral load in infected patients.
What Are the Advantages and Disadvantages of CRISPR-Cas for Infectious Diseases?
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Advantages
It has several advantages over conventional diagnostics due to its high specificity, sensitivity, simplicity, rapidity, and low cost. Using CRISPR tools does not cause significant risks to patients that need to be addressed. The principal advantage of using CRISPR for gene editing is its accuracy and specificity for small sequences.
At present, the technology is primarily used for infectious diseases. In studies, CRISPR-Cas has shown high sensitivity and early diagnosis of Mycobacterium tuberculosis. It has also been proposed as a viable treatment option for viral diseases. The CRISPR-based tools can be easily modified to target novel pathogens and resistant pathways.
2. Disadvantages
There are obstacles to the therapeutic use of CRISPR-Cas due to its off-target concerns, delivery efficiency, or ethical considerations.
Conclusion
CRISPR technology has been regarded as an important discovery in genetic engineering. It could revolutionize the practices of clinical medicine. The technology can potentially be used for infectious disease identification and treatment because of its low cost, rapid diagnosis, and treatment of resistant bacterial strains. The technology is currently being studied for clinical application in infectious diseases.
