4
DISCUSSION
Many genotypes were not defined because there were not enough markers in
the results. This is due to insufficient DNA in the samples, leading to
inconclusive RFLP genotyping. This explains why some studies realized
Nested-PCR before RFLP-PCR, to increase DNA of the samples.
This systematic study used papers From America 27/30 (Brazil 16/27)
majorly, and this was one of the reasons that the genetic
characteristics of T. gondii isolated from chickens around the
world is not conclusive yet. More genotyping studies must be performed
in order to increase data, especially in Europe (no data), Asia (1
article), Oceania (no data), Africa (2 articles with many inconclusive
genotypes) and North America (only USA has studies - 2).
Shwab et al. (2014) described that #1 (Type II clonal), #2 (Type III),
#3 (Type II variant) and #10 (Type I) are identified all over the
world. Genotypes #2 and #3 are most found in Africa, whereas genotypes
#9 (Chinese 1) and #10 are prevalent in Asia. The present study did
not find papers from Europe strains, however they described genotypes
#1, #2 and #3 as prevalent. ToxoDB #1, #2, #3, #4 and #5
dominate in North America, and the present study showed predominance of
#1 (31,4%) and #2 (34,3%) in USA.
Amouei et al. (2020) also had difficult to find studies regarding
genotyping of T. gondii isolates in Oceania, when studying
felids, they described only one study in which 8 isolates were genotyped
into 2 genotypes, and the majority of the strains (97,5%, n=7) were
genotype ToxoDB #3.
There are some strains of T. gondii which circulates in many species of
animals concomitantly. Melo et al. (2020) performed a study in Fernando
de Noronha Island, in Brazil, in which they isolated T. gondiigenotypes ToxoDB #146 from sheep and pigs. This strain was also
reported in chickens by Silva et al. (2010), in Brazil.
Besides, Pena et al. (2020) isolated ToxoDB #8 (Br III type) from giant
anteater (Myrmecophaga tridactyla ), which was also isolated in
chickens by Rocha et al. (2018), Feitosa et al. (2017) in Brazil and
Lindstrom et al. (2008) in Uganda. This find supports the theory
postulated by Pena et al. (2020) and Dubey et al. (2010) whom say that
giant anteater highly contributes to Brazil’s common lineages
circulation and that chickens are good bioindicators of T. gondiicontamination, respectively.
The systematic review demonstrated the presence of genotypes ToxoDB
#11, #162 and #206 in chickens (Table 2 ) and a Brazilian
study by Carneiro et al. (2013) identified such genotypes in cases of
congenital toxoplasmosis in humans, in the state of Minas Gerais,
corroborating the hypothesis that free-range chickens are sources of
contamination in humans and this affection may cause diseases. Such
study also showed that isolates #11 and #206 are highly virulent in
female mice of the BALB/c strain whereas isolate #162 shows
intermediate virulence.
North America and Europe have a predominance of archetypal strains of
type I, II and III, while South America has atypical strains without
genotype pattern prevail. This distribution of the diverse population
structure from T. gondii strains, is closely associated with
virulence patterns, and the severity of infections in humans (Xiao e
Yolken, 2015; Saraf et al., 2017). According to Shwab et al. (2016),
strains commonly found in Europe, North America, North Africa and Asia
are non-lethal to mice when used at low doses for infection, while those
prevalent in South America are highly virulent and lethal.