The Influence Of T Spiralis

Published Date: 02 Nov 2017

Following infection with T. spiralis, males showed a slight decrease in body mass on days 10 p.i., then presented weight gain at 20 and 30 days p.i. (Fig. 1) These findings also occurred in other laboratory rodents infected with nonfatal doses of T. spiralis (Auli M & Fernandez E 2005; Meagher S & Dudek SN 2002), and seemed to be consistent with the life cycle of the nematode parasite. Weight loss was probably caused by reduced appetite, diarrhea and dehydration in respond to the adult worms in intestine; weight gain may explained by the fact that worms were expelled from the intestine, and thereafter the hosts restored appetite and gut absorptive capacity (Gottstein B et al. 2009). Thus, we inferred that the greatest effects of T. spiralis infection on weight change were occurring during a period of 20 days p.i., and decreased after that. Although infected males were lighter than controls at the second time of mating (days 30 p.i.), the differences mainly because of a time cumulative effect. Our data indicated that a subclinical infection with T. spiralis did not have a significant effect on the male morphology, including clinical symptoms and mass changes.

We established that specific anti-Trichinella IgG antibodies were detected from 20 days p.i. (Fig. 2). Similar results were obtained by Dziemian and Machnicka (2000) in rats, who demonstrated specific IgG antibodies in serum appeared from 20 days p.i. Some recent studies reported that specific IgG antibodies were detected later in the chronic infection of BALB/c and ICR mice, from 40 �C 50 days p.i. till the end of experiment (Kolodziej-Sobocinska M et al. 2006; Reiterova K et al. 2009). It had been demonstrated that time of seroconversion after T. spiralis infection depended upon the infection dose and the individual immunity. The formation of specific anti-Trichinella IgG antibodies were characteristic of an adaptive immune response, and may persist in blood circulation for a long time (Gottstein B et al. 2009). We can expect that specific IgG antibodies are maintained for a long periods of time in mice with the subclinical T. spiralis infection. Indeed, the level of specific IgG antibodies had an increasing character toward our second mating procedure on 30 days p.i., and might be present during the succeeding 6 months (Reiterova K et al. 2009). The present study indicated that parasitic infection in male mice had a negative impact on the RRV of host, due to its chronic infection.

Our results showed, as expected (Klein SL et al. 1999), when T. spiralis infection reduces host��s RRV, a significant reduction in scent attractiveness will result. Based on the time females spent investigating the capillaries containing the urine of infected and control males, our data indicated that females found the urine odors of healthy control males more attractiveness than that of infected males (Fig. 3). In agreement with the present findings, previous studies demonstrated that female rodents can distinguish between, and avoid the odors of males immune responses were triggered by a wide range of pathogens (Kavaliers M et al. 2005) or non-replicated antigens (Gerlinskaya LA et al. 2012; Litvinova EA et al. 2005; Zala SM et al. 2004). Female rodents often selected males on the basis of chemical signals that provided by volatile pheromones, and major urinary proteins (MUPs) and MHC mediated or associated urine cues (Beauchamp GK & Yamazaki K 2003; Hurst JL & Beynon RJ 2004; Hurst JL et al. 2001). Through preferentially selecting pathogen-free males, females can potentially improve their fitness both directly by reducing contagion risk, and indirectly by enhancing offspring disease resistance (Kavaliers M et al. 2005).

When investigating which physiological changes best explained the influence of parasitic infection on female odor preferences, we found that a greater decline in scent attractiveness was explained by a greater reduction in concentration of urine proteins (Fig. 4). Some evidence existed that influence of immune activation on scent attractiveness was typically associated with a reduction in the androgen-dependent (regulated) urine protein secretions (Litvinova EA et al. 2005). Circulating testosterone level were often suppressed and corticosterone level were enhanced by immune activation (Boonekamp JJ et al. 2008; Moshkin M et al. 2002; Tumkiratiwong P et al. 2006), and productions of urine proteins may be down-regulated accordingly (Gerlinskaya LA et al. 2012; Litvinova EA et al. 2005). We presumed that reduced urine protein levels were positively associated with circulating testosterone levels, but their influence was yet to be further studied.

Although there was evidence that T. spiralis infection, and the subsequent long-lasting immune response they induce, affected female rodent odor preferences, few studies reported its impact on male host reproduction. In meadow voles, previous study suggested that infection with T. spiralis altered female odor preferences, however, there was no effect of infection status on mating preferences (Klein SL et al. 1999). The results were confirmed in our study, in which nematode infection reduced the attractiveness of male urine odors but had no significant effect on reproductive success under female choice constraint (Table 1). These findings supported our prediction that in response to reduced RRV, infected males increased their reproductive effort, having equivalent mating opportunities to health control mice.

Despite decreases in host��s RRV that occurred during T. spiralis infection, infected males showed no change in reproductive output except for differences in litter size and offspring mass. Following infection, the number of offspring per litter sired by infected males was not larger than that of controls as expected (Fig. 5, Fig. 6 a). The decreased fertility in male rodent hosts had been shown in previous studies. For instance, chronic parasite infections such as tapeworm (Taenia Taeniaeformis) reduced the number of pups sired (Lin YC et al. 1990), and in the case of nematode (Heligmosomoides polygyrus), the reproductive success of males on days 35 p.i. (Barthelemy M et al. 2004). One possible explanation for these findings was that hormone level changes induced by pathogenic infection may damage host reproductive ability (Barthelemy M et al. 2004; Tumkiratiwong P et al. 2006).

T. spiralis-infected males produced offspring of approximately 7% greater mass than offspring from control mice (Fig. 6 c). This may reflect an increased investment in the current reproductive output. Because decreased reproductive ability of infected males was confirmed, the increase in reproductive output observed here indicated an equivalent or greater increase in their reproductive effort. Another possible explanation for the greater body mass of offspring sired by infected males recorded here was the reproductive compensation (RC) hypothesis, which predicted that females may increase reproductive effort when they were constrained to mating with males they did not prefer (Gowaty PA et al. 2007). The negative impact on offspring fitness caused by constrained mate choice may be counteracted, through producing offspring of larger body mass, a potential measure of high fitness. Additional studies should evaluate the compensatory effect that enhanced offspring quality under the parasite-mediated sexual selection.

In conclusion, the influence of T. spiralis on the reproductive effort of male mice is considerable. Our results suggest that subclinical T. spiralis infection could trigger a humoral immunity response, and production of long-lasting parasite-specific IgG antibodies. Reduction in RRV caused by the indicated chronic infection may affect male reproductive effort in many aspects. We find that parasitic infection reduces the attractiveness of male scent, however, there are no significant effect on mating opportunities and reproductive success when females mating under constraints. Infected males sire less offspring with greater body mass, suggesting that when there are some negatively impacts on the reproductive ability upon T. spiralis infection, hosts may increase investment in reproductive effort in order to maximize their fitness.