Zheng Heping/Yang Bin team of Southern Medical University developed a new method for syphilis detection based on Cas13a

Written by Wang Cong

EditorWang Duoyu

TypesettingShuichengwen

Syphilis, a chronic, systemic sexually transmitted disease caused by Treponema pallidum (TPA), is one of the most common sexually transmitted infections worldwide, with an estimated 6.
3 million infections each year
.
In fact, syphilis infection is easy to treat when caught early, but if it develops later, it can lead to serious long-term health problems, including organ damage and even death
.

Pregnant women infected with syphilis during pregnancy can transmit it to the fetus through the placenta, causing intrauterine infection of the fetus, resulting in congenital syphilis
.

It is also the second leading cause of stillbirth globally and can also have severe developmental consequences for full-term newborns
.
Laboratory testing is essential for the diagnosis of syphilis, but existing testing methods are difficult to balance sensitivity and specificity, and no single diagnostic test has sufficient sensitivity and specificity to identify various stages of syphilis
.
The incidence of syphilis declined in the 1980s and 1990s, in part because of the AIDS epidemic, which led to widespread popularization of safe sex in various countries
.

However, since the early 2000s, syphilis rates have rebounded sharply, surging by more than 300% in some countries
.

According to data from the China Center for Disease Control and Prevention, there will be more than 460,000 new cases of syphilis in China in 2020
.

Therefore, the development of highly sensitive and specific syphilis detection methods is particularly important
.
In 2017, Zhang Feng developed SHERLOCK, a highly sensitive and specific virus detection technology based on CRISPR-Cas13
.

Since then, pathogen detection technology based on the CRISPR-Cas system has developed rapidly and has been successfully applied to diagnose various pathogens, such as new coronavirus, Zika virus, Ebola virus, dengue virus, Lassa virus, human papilloma virus, and Plasmodium, Pseudomonas aeruginosa, etc.
, can also be genotyped and drug resistance monitored by distinguishing single nucleotide mutations (SNVs)
.
This provides exciting new ways to overcome the limitations of current syphilis testing
.
Recently, the team of Prof.
Heping Zheng and Prof.
Bin Yang from Dermatology Hospital of Southern Medical University published a research paper entitled: A suite of PCR-LwCas13a assays for detection and genotyping of Treponema pallidum in clinical samples in Nature Communications, a sub-journal of Nature
.
This study developed a combination of PCR and CRISPR-Cas13a for the detection of Treponema pallidum, which is robust and an order of magnitude more sensitive than PCR.
In addition, the method can be used for Treponema pallidum lineage identification and Identification of drug resistance genotyping
.

This has great potential and application value in improving the diagnosis and epidemiological surveillance of syphilis with CRISPR-based detection methods
.
The performance of commonly used assays for diagnosing syphilis varies widely by stage of infection and type of sample
.

To meet the need for improved syphilis diagnosis, the research team combined PCR technology with CRISPR-LwCas13a technology to achieve in vitro detection technology with high sensitivity and specificity for different templates
.
According to the tpp47 gene of Treponema pallidum (for diagnosis of Treponema pallidum), tp0548 gene (for pedigree identification), and 23S rRNA (for identification of macrolide resistance gene), the corresponding PCR amplification primers and crRNA were designed to achieve Detection, pedigree identification, and resistance genotyping of Treponema pallidum
.

The analytical sensitivity of PCR-LwCas13a detection is an order of magnitude higher than that of real-time PCR with equivalent specificity
.

When applied to a panel of 216 biological samples (including 135 clinically confirmed primary and secondary syphilis samples), the PCR-LwCas13a assay showed a clinical sensitivity of 93.
3% and a specificity of 100%, which was superior to Real-time PCR assay for tpp47 gene and rabbit infectivity assay (this is currently the most sensitive and reliable method for detecting Treponema pallidum)
.

In addition, the method was able to further differentiate Treponema pallidum lineages and identify macrolide resistance genetic markers
.
Collectively, these experimental results show that this CRISPR-Cas13a-based approach has great potential and application value in improving syphilis diagnosis and epidemiological surveillance
.

It is reported that the research team has applied for a patent for this detection method
.

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