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Re-evaluating the sensitivity of the rabbit infectivity test for Treponema pallidum in modern era
Man-Li Tong1, Hui-Lin Zhang1, Xiao-Zhen Zhu1
1Clinical Laboratory, Zhongshan Hospital, Medical College of Xiamen University, Xiamen 361004, China.
Background:
The rabbit infectivity test (RIT) was previously described as a highly-sensitive method for clinically detecting Treponema pallidum. But our primary study indicated this result may have changed in current antibiotics era.
Methods:
By inoculating rabbits testis with cerebrospinal fluid (CSF) (n=63) and exudate from hard chancre lesions (n=13), we re-evaluated the sensitivity of RIT in modern era. All isolated T. pallidum strains from the RIT were performed for the strain type based on "CDC subtype/tp0548" method. Chi-square and Fisher's exact tests were used to determine the statistical significance of differences across data sets.
Results:
Result indicated that 2 of 63 CSF (2/63, 3.17%) and 5 of 13 lesion exudate samples (5/13, 38.47%) were positive in the RIT, with a much longer time to detection for CSF samples. Only 1 of 28 samples from patients who admitted treatment with antibiotics prior to clinical exam was positive in the RIT; while 6 of 48 patients, who admitted no recent exposure to antibiotics or was unclear about the medical history, were positive in RIT. DNA sequence analysis revealed 6 strains of 14d/f subtype and one strain of 14a/f subtype.
Conclusions:
In conclusions, RIT is no longer a highly sensitive method for detecting T. pallidum in clinical samples as before, and is not inadequately considered to be a reference method for measuring the sensitivity of other new methods, such as the PCR. These data represent the first reexamination of the sensitivity of RIT in the post-antibiotic era with a large clinical sample.
Insights
The rabbit infectivity test (RIT) is no longer a sensitive method for detecting Treponema pallidum in the current antibiotic era. This study re-evaluated RIT sensitivity using clinical samples, finding significantly reduced efficacy.
Area of Science:
- Infectious Diseases
- Microbiology
- Clinical Diagnostics
Background:
- The rabbit infectivity test (RIT) was historically considered highly sensitive for detecting Treponema pallidum.
- Recent changes in antibiotic usage may have impacted the efficacy of the RIT.
Purpose of the Study:
- To re-evaluate the sensitivity of the rabbit infectivity test (RIT) for detecting Treponema pallidum in the modern antibiotic era.
- To compare RIT sensitivity using cerebrospinal fluid (CSF) and lesion exudate samples.
Main Methods:
- Inoculation of rabbit testes with 63 CSF samples and 13 hard chancre lesion exudate samples.
- Strain typing of isolated T. pallidum using the "CDC subtype/tp0548" method.
- Statistical analysis using Chi-square and Fisher's exact tests.
Main Results:
- RIT detected T. pallidum in 3.17% of CSF samples and 38.47% of lesion exudate samples.
- Antibiotic exposure significantly reduced RIT sensitivity; only 1 of 28 pre-treated samples was positive compared to 6 of 48 untreated samples.
- DNA sequencing identified 6 strains of the 14d/f subtype and 1 strain of the 14a/f subtype.
Conclusions:
- The rabbit infectivity test (RIT) is no longer a highly sensitive method for detecting Treponema pallidum in clinical samples.
- RIT should not be considered a reference method for evaluating new diagnostic techniques like PCR.
- This study provides the first re-examination of RIT sensitivity in the post-antibiotic era using a substantial clinical sample size.
