1
INTRODUCTION
Toxoplasma gondii is a protozoan able to infect all warm-blooded
animals, causing toxoplasmosis, and is widely distributed around the
world. In general, the infection is asymptomatic in immunocompetent
individuals but can be more severe in congenital transmission, specialy
when the infection happens in the first third of pregnancy, and in
immunodeficient people (Dubey et al., 2010; Cortés et al., 2019).
Humans often get infected by ingesting undercooked or raw meat
contaminated with tissue cysts with bradizoytes, or by accidentaly
ingesting food or water contaminated with oocysts from felids’ feces. In
some cases, tachyzoytes are viable in milk and are infectant for those
who drink it as well (Hill & Dubey, 2002; Cortés et al., 2019).
Researchers characterize T. gondii in three major clonal lineages
(Types I, II and III) related to high, medium and low mouse virulence.
The strains RH88, ME49 and VEG are important representants of Type I,
Type II and Type III, respectively. Nonetheless, recent literature
revealed huge genetic diversity among strains specially in South
America, Asia and Africa, where atypical are predominant. Atypical
strains are also related to high virulence, in some cases, can cause
congenital ocular toxoplasmosis and acute systemic toxoplasmosis even in
immunocompetent individuals (Howe & Sibley, 1995; Saeij et al., 2005;
Cortés et al., 2019). Mixed infections are rare, but may occur when more
than one strain of T. gondii are found simultaneously with
molecular assays in a host (Moreno et al., 2019).
Therefore, the combination of genes during sexual cycle in felids gut
led to more than 200 genotypes, which can be characterized by ToxoDB
database. Once, genotyping was performed by analysing only SAG2 marker,
which made it possible to classify the isolate as being part of one of
the three major lineages. Usually, more than 11 markers are used, and it
is not trustworthy to classify by using less than 5 (Ajzenberg et al.,
2004; Su et al., 2006; Rajendran et al., 2012; Shwab et al., 2014).
Free-range chickens are good bioindicators of soil contamination withT. gondii oocysts, and one of the most important source of
infections for humans, due to large consumption (Dubey, 2010; Dubey et
al., 2015). By studing T. gondii genotypes isolated from
chickens, it is possible to determine the frequence of specific strains
belonging to a determined genotype correlated with the locations where
they were identified from other hosts. In this sense, there are
systematic reviews regarding data of genetic characterization of this
parasite in felines and ruminants (Sharif et al., 2017; Amouei et al.,
2020), but not in chickens heretofore, what makes this work necessary.