Serologic evidence of Toxoplasma gondii infection among cancer patients
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* Mahmood D. Al-Mendalawi

## A prospective study from Qassim region, Saudi Arabia

*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*

*   Copyright: © Saudi Medical Journal

This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## References

1.  Imam A, Al-Anzi FG, Al-Ghasham MA, Al-Suraikh MA, Al-Yahya AO, Rasheed Z (2017) Serologic evidence of Toxoplasma gondii infection among cancer patients. A prospective study from Qassim region, Saudi Arabia. Saudi Med J 38:319–321.
    
    [Abstract/FREE Full Text](http://smj.org.sa/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic21qIjtzOjU6InJlc2lkIjtzOjg6IjM4LzMvMzE5IjtzOjQ6ImF0b20iO3M6MTg6Ii9zbWovMzgvNi82NjkuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9) 

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6.  Robert-Gangneux F, Belaz S (2016) Molecular diagnosis of toxoplasmosis in immuno compromised patients. Curr Opin Infect Dis 29:330–339.
    
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