AreToxoplasma-infected subjects more attractive, symmetrical, or healthier than non-infected ones? Evidence from subjective and objective measurements

Abstract

Background Parasites are among the main factors that negatively impact the health and reproductive success of organisms. However, if parasites diminish a host’s health and attractiveness to such an extent that finding a mate becomes almost impossible, the parasite would decrease its odds of reproducing and passing to the next generation. There is evidence that Toxoplasma gondii (T. gondii) manipulates phenotypic characteristics of its intermediate hosts to increase its spread. However, whether T. gondii manipulates phenotypic characteristics in humans remains poorly studied. Therefore, the present research had two main aims: (1) To compare traits associated with health and parasite resistance in Toxoplasma-infected and non-infected subjects. (2) To investigate whether other people perceive differences in attractiveness and health between Toxoplasma-infected and non-infected subjects of both sexes. Methods For the first aim, Toxoplasma-infected (n = 35) and non-infected subjects (n = 178) were compared for self-perceived attractiveness, number of sexual partners, number of minor ailments, body mass index, mate value, handgrip strength, facial fluctuating asymmetry, and facial width-to-height ratio. For the second aim, an independent group of 205 raters (59 men and 146 women) evaluated the attractiveness and perceived health of facial pictures of Toxoplasma-infected and non-infected subjects. Results First, we found that infected men had lower facial fluctuating asymmetry whereas infected women had lower body mass, lower body mass index, a tendency for lower facial fluctuating asymmetry, higher self-perceived attractiveness, and a higher number of sexual partners than non-infected ones. Then, we found that infected men and women were rated as more attractive and healthier than non-infected ones. Conclusions Our results suggest that some sexually transmitted parasites, such as T. gondii, may produce changes in the appearance and behavior of the human host, either as a by-product of the infection or as the result of the manipulation of the parasite to increase its spread to new hosts. Taken together, these results lay the foundation for future research on the manipulation of the human host by sexually transmitted pathogens and parasites.

Toxoplasma gondii infection and testosterone alteration: A systematic review and meta-analyses

“…On the other hand, recent evidence revealed that T . gondii infection augments sexual behavior and attractiveness in humans [ 61 ] and experimentally infected rodents [ 5 ]. In this regard, Borráz-León et al [ 61 ] assessed several factors related to attractiveness among T .…”

“…They also assessed the attractiveness and perceived health of facial pictures of T . gondii -infected and non-infected subjects by an independent group of raters and found that both infected women and men were rated as more attractive and healthier than non-infected individuals [ 61 ]. Increased testosterone could enhance sexual behavior and attractiveness in infected subjects and could increase mating opportunity and transmission of T .…”

“…Testosterone plays an important role in sexual behavior and mating success [57][58][59][60]. On the other hand, recent evidence revealed that T. gondii infection augments sexual behavior and attractiveness in humans [61] and experimentally infected rodents [5]. In this regard, Borra ´z-Leo ´n et al [61] assessed several factors related to attractiveness among T. gondii-infected and non -infected individuals.…”

Coevolutionary Stability of Host-Symbiont Systems with Mixed-mode Transmission

“…On the other hand, infections make patients sexually more attractive. Since they have more sexual partners, their reproductive success may increase (Borráz-León et al 2022)…”

Definitions of parasitism, considering its potentially opposing effects at different levels of hierarchical organization

“…– of reducing its longevity (Yule et al ., 2013 ). Toxoplasma gondii , a widespread infection in rodents and humans, increase predation pressure (Berdoy et al ., 1995 ) and traffic accidents (Gohardehi et al ., 2018 ) of infected hosts while, on the other hand, makes them sexually more attractive potentially increasing their reproductive success (Dass et al ., 2011 ; Borráz-León et al ., 2022 ). We cannot quantify the combined fitness effects of reduced lifespan and (presumably) increased reproductive success of infected hosts; however, host adaptations to combat Toxoplasma infections indicate that it is unfavourable at the lineage level.…”