Genetic Diversity of Toxoplasma Gondii in Cancer Patients

The global cancer burden is estimated to have risen to 18.1 million new cases and 9.6 million deaths in 2018. Patients with cancer have deficient cellular immunity and are potentially susceptible to opportunistic infections including Toxoplasma gondii (T. gondii). Few reports are available about toxoplasmosis in this group of patients. In recent years, it has emerged as an important life-threatening opportunistic pathogen in immunocompromised patients.

1. gondii is a ubiquitous obligate intracellular protozoan parasite that can infect virtually any nucleated vertebrate cell. T. gondii is one of the most successful parasites worldwide, with upwards of 30% of the human population infected.

While T. gondii infection in immunocompetent individuals is usually asymptomatic, it is more detrimental in immunocompromised individuals, such as those with HIV, patients receiving organ transplants or undergoing cancer treatment. A variety of malignancies, including lymphoma, leukemia, and myeloma, can reactivate toxoplasmosis. Moreover, T. gondii is incriminated to be responsible for the progression of malignant diseases.

Screening of toxoplasmosis in cancer patients is mandatory to guard against life-threatening disseminated disease. Diagnosis rely mainly on serology. A study in 2018 was performed to assess the prevalence of anti-T. gondii antibody among cancer patients in Cairo-Egypt. Among 180 cancer patients, a total of 110 patients (61.1%) were positive for anti-T. gondii antibodies. Till now there is no screening program in Egypt for toxoplasmosis in cancer patients although recently demonstrated to be at high risk for acquiring the infection with life-threatening sequelae.

Despite the significant improvements in serological methods, there are still unresolvable limitations such as inability of these methods to confirm the presence of parasite in immunocompromised patients. To overcome these limitations, different molecular methods including conventional PCR (cn PCR), nested PCR, real-time PCR (qPCR) and also loop-mediated isothermal amplification (LAMP) techniques have been developed to detect T. gondii DNA in biological samples.

As molecular diagnosis is not depending on the immunological condition of the host, it would be ideal for cancer patients. The ability of molecular methods to detect low amounts of parasites in fluids or tissues is a key issue, as Toxoplasma can circulate at low concentrations, or inconstantly.

1. gondii has been considered a single species in the genus Toxoplasma. Early studies on the parasite strains from North America and Europe identified limited genetic diversity, which were classified into three clonal lineages I, II, and III.

Genotyping of isolates from all continents revealed a complex population structure. Recent research supports the notion that T. gondii genotype may be associated with disease severity. The outcome of toxoplasmosis is related primarily to host and parasite genetics.

The first PCR technique for T. gondii detection was established by Burg and colleagues in which the 35-repeat B1 gene of T. gondii genome was amplified. Following it, several multi-copy targeting genes including 18S rRNA-, P30-,529-bp repeat fragment or the AF146527 element have been used for the detection of T. gondii in different biological samples.

In spite of the growing data concerning T. gondii genotypes and its role in epidemiological and biological studies,very few studies have been reported in Egypt until now. It is essential to genetically define and characterize T. gondii strains isolated from cancer patients to understand the population genetic structure, population biology, and pathogenesis of this important pathogen in our locality using the highly sensitive molecular techniques.

To the best of our knowledge, this is the first study in Egypt to reveal the population structure of T. gondii in patients with cancer.