A systematic review of Toxoplasma gondii genotypes in Gallus gallus domesticus worldwide: The focus is Brazil

Abstract

Toxoplasma gondii was initially classified in three main lineages related to its virulence: Types I, II and III. The recombination of genes during sexual cycle in felids gut led to more than 200 genotypes, found in ToxoDB database, using 11 RFLP markers. Free-range chickens are good bioindicators of soil contamination with T. gondii oocysts. In this sense, there are systematic reviews regarding data of genetic characterization of this parasite in felines and ruminants, but not in chickens heretofore, what makes this work necessary. A systematic review in the literature was performed with papers published prior to September 21st, 2020. The main inclusion criteria was the presence of T. gondii genotypes, isolated strictly from free-range chickens, in experimental works. Initially, a total of 1,343 studies related to the terms were identified on databases and 30 studies were selected to be systematically reviewed. A total of 561 isolates of T. gondii from 6,356 free-range chickens were analyzed for genotyping, revealing 190 genotypes. ToxoDB #59 and #2 were the most frequent in America, #1 was the most frequent in Africa and 3 atypical isolates from genotype ToxoDB #9 were found in Asia. There is not data from Europe and Oceania. The majority of studies were Brazilian (16/30). A total of 68 RFLP genotypes were recognized among the 561 isolates’ DNAs analyzed from the 30 studies. Some studies show new genotypes never described before, which reinforces the idea that some years from now, even more new genotypes will be isolated, due to progressive genetic recombination. The large amount of undefined genotypes makes it necessary to perform Nested PCR technique when genotyping. Moreover, the lack of data in Continents such as Europe, Asia and Oceania makes it necessary to perform new isolating and genotyping studies in these places.