الفهرس 
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Abstract
Toxoplasmosis is a common parasite infection that frequently goes undetected in immunocompetent people. The immune system can be tricked by this parasitic obligate intracellular protozoan, though it primarily lives in the muscles, retina, and brain. When the immune system is compromised, latent cysts could reactivate as in HIV patients, patients with malignancies and organ transplant recipients. Cyst reactivation can lead to ocular, cerebral or disseminated toxoplasmosis. Diagnosis is routinely made by serologic detection of specific antibodies. However, definitive diagnosis is attained by the recognition of parasites in blood, cerebrospinal fluid or bronchoalveolar lavage fluid by PCR which is the most sensitive method. The present study aimed to detect the presence of Toxoplasma gondii in patients with lymphadenopathy and to identify the prevailing associated genotypes.
Blood samples were collected from 100 patients with lymphadenopathy attending outpatient clinics of Medical Research Institute, Alexandria university. The sample collection extended from September 2020 to December 2021. One part of each blood sample was used for serological detection of anti-Toxoplasma IgG and IgM. The second part of the blood sample was stored at -20o C till used for DNA extraction and PCR amplification of Toxoplasma GRA7 & RE genes and identification of the prevailing associated genotypes.
Patients’ age ranged from 5 to 76 years with a mean of 44.5± 14.2 years. Females constituted 73% of cases and 56% of the patients were rural. The most common cause of lymphadenopathy was metastasis (53%) followed by inflammatory causes (23%). Less common causes were Lymphoma (15%), and Idiopathic (9%).
Toxoplasma seropositive rates were 33% in patients with lymphadenopathy. Both anti-Toxoplasma IgG and IgM were detected in 5%, while 28% of patients had IgG antibodies with no detectable IgM. The highest seropositivity was among patients with inflammatory causes (60.9%), followed by metastatic causes 30.1% and the least seropositivity was detected in lymphoma patients (20%). The association between serologically confirmed T. gondii infection and demographic factors, risk factors was studied. It was observed that T. gondii infection rates were comparable among the studied age groups. As regard gender, males had slightly higher rate than females (40.7% versus 30.1%). For residence, rural residence was associated with slightly higher rate than urban residence (37% versus 28.3%). On the contrary, patients reporting contact with cats had slightly lower rate of infection (28.6% versus 33.7%). Other risk factors such as consumption of undercooked meat and hand washing also had no effect on seropositivity rates. Statistical analysis showed that none of these parameters were significantly associated with T. gondii infection. On the other hand, a statistically significant association was found between not washing vegetables and Toxoplasma infection (66.7% versus 29.7%).
Molecular detection of T. gondii was performed on the 33 serologically positive samples. Positive PCR results were obtained in 66.7% (22 out of 33) using RE primers, compared to 90.9% (30 out of 33) using GRA7 primers. Concomitant results were detected among 21 positive and 2 negative cases using both genes. However, 9 cases were positive using GRA7 while negative by RE gene. Also, one case was positive using RE gene and negative by GRA7 gene.
Although GRA7 gene detected more cases (30 cases) compared to RE gene (22 cases), no statistically significant difference was detected (p= 0.534).
GRA7 gene was used to recognize the prevailing genotypes of T. gondii using sequencing technique. Among the 30 PCR positive cases, successful results were obtained for 14 cases. 64.3% of cases were Type I (9/14) while the rest were atypical strains (5/14). Results showed that 71.4% of patients with inflammatory causes were infected by Type I compared to 57.1% among patients with cancer. Atypical strains were more detected among cancer patients than patients with inflammatory causes, although the difference was not statistically significant.