Epidemiology of Ocular Toxoplasmosis in Eye Banks from São Paulo State, Brazil

Author(s)

Ana Beatriz Melles Cassinelli

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina Veterinária e Zootecnia (FMVZ/SBD)
• Defense date: 2021-10-22

Examining board members

Hilda Fátima de Jesus Pena; Daniela Pontes Chiebáo; Arlei Marcili; Herbert Sousa Soares; Sérgio Netto Vitaliano

• Advisor: Hilda Fátima de Jesus Pena; João Marcello Fórtes Furtado

Abstract

Toxoplasma gondii is an obligate intracellular parasite widely spread around the world. It is estimated that one third of the world population is chronically infected by this coccidia. In Brazil, this prevalence is estimated at 70% in some regions of the country. Despite having a high prevalence, the primary infection by T. gondii ends up going unnoticed in immunocompetent patients, with subclinical conditions or with symptoms similar to those in a flu. In immunocompromised patients and pregnant women, recent infections deserve great attention, as the clinical course of the disease is more severe and can lead to the development of irreversible sequelae or even death. One of the most common manifestations of systemic infection by T. gondii is the ocular form, affecting mainly the retina and choroid. The isolation of T. gondii from human samples is essential to verify whether or not there is a correlation between the phenotypic expression of the disease and the parasite lineage. In Brazil, there are few reports of isolations obtained from human samples. The aim of this study was to determine the epidemiology of ocular toxoplasmosis in eye banks in the cities of Ribeirão Preto (BORP) and São José do Rio Preto (BOSJRP), from São Paulo State. A total of 395 eyes from 201 donors were received. Of these samples, 289 were captured by BORP, while 106 were captured by BOSJRP. Among the BORP donors, 42/148 (28.3%) had both tissues (eyes and blood) available for research and 5.4% (8/148) of the donors had lesions compatible with ocular toxoplasmosis (OT). Three of them had bilateral lesions and five had unilateral lesions. Among the 53 BOSJRP donors, 86.8% (46/53) had both tissues available for research and no ocular tissue sample had lesions compatible with OT. Of the total 88 sera analyzed, 70.5% (62/88) had only IgG antibodies against T. gondii, 6.8% (6/88) were positive for both antibodies (IgG and IgM) against T. gondii and 22.7% (20/88) were considered seronegative. All eyes with lesions potentially caused by T. gondii were submitted to a bioassay in mice to isolate the parasite. At the end of the bioassay period, no mouse showed antibodies against T. gondii in the Modified Agglutination Test (MAT) and no cysts were found in tissues analyzed during necropsy. In cPCR, the amplification of the fragments of B1 gene and the repetitive region of the REP-529 genome was observed in a sample, designated as PS-TgOTBrSP1 which did not show macroscopic lesion. In addition to this positive sample, eight others showed amplification for selected markers in real-time PCR, therefore, 2.3% (9/395) of the eyes were diagnosed as positive for T. gondii. The remaining samples, including all eleven samples with macroscopic lesions, were diagnosed as negative. The PS-TgOTBrSP1 sample was identified as non-archetype through the analysis of 15 microsatellite markers and an incomplete, non-archetype genotype was obtained through PCR-RFLP. The MS genotype of T. gondii from the PS- TgOTBrSP1 sample is a unique genotype, which contributes to corroborate that T. gondii has a low circulation of classical clonal strains and has a wide genetic variability in Brazil. Although it was only possible to examine a small number of samples in this study, the data herein obtained also contributes to validate findings from other groups showing that 50-80% of the adult population has antibodies against T. gondii in Brazil. (AU)

• FAPESP's process: 17/18084-7 - Serological profile of antibodies and isolation of Toxoplasma gondii from eyes donated to the bank of eyes of the Medical School of Ribeirão Preto
• Grantee: Ana Beatriz Melles Cassinelli
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)