Serologic evidence of Toxoplasma gondii infection among cancer patients

To the Editor

I have read with interest the study by Imam et al on the serologic evidence of Toxoplasma gondii (T. gondii) infection among cancer patients.1 Based solely on enzyme-linked immunosorbent assay (ELIZA) test for anti-Toxoplasma IgG+IgM measurement, the authors found that the frequency of seropositivity for T. gondii infection in the studied cohort was 30.6%.1 Apart from 2 study limitations addressed by the authors, I presume that the following 4 points might be additionally contributory and could cast suspicions on the study results. First, the classical serologic diagnosis of T. gondii infection is often inconclusive in immuno-compromised individuals, including cancer patients. The altered immune response renders them unable to produce significant titers of anti-Toxoplasma antibodies.2 Second, there are many serologic tests for the diagnosis of T. gondii infection and variations in their performance do present. Hence, different estimations of seropositivity for T. gondii infection in a given population will be expected on employing different serologic tests. For instance, the pooled odds ratios (OR) of T. gondii infection in Chinese population with cancer were estimated to be 5.50 (95% CI 3.98-7.62) by using indirect hemagglutination assay method compared to 3.15 (95% CI 2.67-3.72) by using ELIZA method.3 Third, in the clinical practice, no single serologic test could precisely determine the estimate and time of T. gondii infection. The development of IgG avidity assays has noticeably facilitated timing and differentiation of primary and secondary T. gondii infections. Sequential (or combinatorial) use of high quality IgG, IgM, IgA, and IgG-avidity assays has been advocated.4 Finally, based on the noticeable inhibitory effect of T. gondii parasite on tumor cell proliferation, the frequency of low titer anti-Toxoplasma antibodies in cancer patients was noticed to be significantly higher than the frequency of low titer anti-Toxoplasma antibodies in normal people.5 In the light of the aforementioned points, DNA-based molecular techniques, particularly quantitative polymerase chain reaction (PCR) method with specific probes could be a better alternative than serologic tests in the surveillance, prevention, and control of T. gondii infection, particularly in immunocompromised patients.6

Reply from the Author

Thank you for your interest in our study. Paragraph 3 in the introduction of our paper states the following regarding the objective of our study (the purpose of the present study was to determine the frequency of serologic evidence of T. gondii infection).1 Our objective was not meant to establish a (serologic diagnosis) of T. gondii clinical disease. Our objective was to determine the frequency of exposure to T. gondii infection, as evidenced by serology (antibody detection tests).

Abdelmageed Imam

Parasitology Unit College of Medicine, Qassim University Qassim, Kingdom of Saudi Arabia