Murine models of vaginal trichomonad infections

Abstract

Trichomonas vaginalis and Tritrichomonas foetus cause common sexually transmitted infections in humans and cattle, respectively. Mouse models of trichomoniasis are important for pathogenic and therapeutic studies. Here, we compared murine genital infections with T. vaginalis and T. foetus. Persistent vaginal infection with T. foetus was established with 100 parasites but T. vaginalis infection required doses of 10(6), perhaps because of greater susceptibility to killing by mouse vaginal polymorphonuclear leukocytes. Infection with T. vaginalis persisted longest after combined treatment of mice with estrogen and dexamethasone, whereas infection was only short-lived when mice were given estrogen or dexamethasone alone, co-infected with Lactobacillus acidophilus, and/or pretreated with antibiotics. Infection rates were similar with metronidazole-resistant (MR) and metronidazole-sensitive (MS) T. vaginalis. High dose but not low dose metronidazole treatment controlled infection with MS better than MR T. vaginalis. These murine models will be valuable for investigating the pathogenesis and treatment of trichomoniasis.

Figure 1.

Vaginal infection with Tritrichomonas foetus. Five mice per group were infected intravaginally with T. foetus D1 strain at Days 0 and 1. (A) Hemocytometer counts of trichomonads. (B) Vaginal T. foetus cultures. All mice were persistently infected with T. foetus even at the lowest challenge dose (10²) for at least 34 days post challenge. Solid boxes indicate that all mice in all groups were positive. There was no difference among challenge dose groups in the number of trichomonads in vaginal secretions (P > 0.05).

Figure 2.

Vaginal infection with Trichomonas vaginalis. Five mice per group were infected intravaginally with different strains of T. vaginalis at Days 0 and 1 and then cultured for T. vaginalis. Strain of T. vaginalis 12047 infected the most mice for the longest duration, although the infection rates were not significantly different among groups (P > 0.05).

Figure 3.

Effect of treatments with single agents—estradiol, dexamethasone, Lactobacillus acidophilus, or antibiotics (ATB) to sustain Trichomonas vaginalis infection. Five mice per group were infected intravaginally with T. vaginalis 12047 strain at Days 0 and 1 and then cultured for T. vaginalis. (A) Mice received estradiol (500 μg/dose) at Days −9 and −2, Lactobacillus acidophilus intravaginally at Days −7 and −6, or ATBs (vancomycin, streptomycin, and trimethoprim) daily from Days −2 to 7 days. (B) Mice received dexamethasone daily from Days −4 to +6. Control mice did not receive any treatment (no pretreatment). No single treatment increased infection rates significantly as compared with control mice (P > 0.05).

Figure 4.

Combination treatment consisting of estradiol, dexamethasone (Dx) and antibiotics (ATB) to increase Trichomonas vaginalis infection. Five mice per group were infected intravaginally with T. vaginalis 12047 strain at Days 0 and 1 and then cultured for T. vaginalis. (A) Dexamethasone plus ATB was compared with a combination of estradiol, dexamethasone, and ATB. (B) Estradiol plus dexamethasone compared with a combination of estradiol, dexamethasone, and ATB. Mice received estradiol (500 μg/dose) at Days −9 and −2, and/or ATBs vancomycin, streptomycin, and trimethoprim daily from Days −2 to +7, and/or dexamethasone daily from Days −4 to +6. Control mice did not receive any treatment (no pretreatment). Pretreatment of mice with estradiol and dexamethasone (with or without ATB) resulted in more mice infected for a prolonged time than treatment with dexamethasone plus ATB or no treatment. “a” indicates P < 0.05 compared with control group.

Figure 5.

Infectivity of different strains of metronidazole resistant (MR) or metronidazole sensitive (MS) strains of Trichomonas vaginalis in estradiol and dexamethasone pretreated mice. Five mice per group were infected intravaginally with different strains of T. vaginalis at Days 0 and 1 and then cultured for T. vaginalis. Mice received estradiol (50 μg/dose) at Days −9 and −2 and dexamethasone daily from Days −4 to +6. MR T. vaginalis strain B7268 and MS strain 12047 infected more mice than the other strains for up to at least 7 days post challenge, although only strain B7268 was significantly different from the other strains. Different letters indicate significantly different results. (P < 0.05).

Figure 6.

Effect of oral metronidazole treatment of Trichomonas vaginalis infection in estradiol and dexamethasone pretreated mice. Five mice per group were infected intravaginally with T. vaginalis metronidazole resistant (MR) strain B7268 and metronidazole sensitive (MS) strain 12047 at Days 0 and 1 and then cultured for T. vaginalis. Mice received estradiol (50 μg/dose) at Days −9 and −2 and dexamethasone daily from Days −4 to +6. They were treated with metronidazole (2–50 mg/kg) 5 times twice daily at Days +2, 3, and 4 (see arrows). Doses of 50 mg/kg of metronidazole eliminated infection of T. vaginalis MS strain 12047 with a significantly lower percentage of infected mice at 5 and 7 days post challenge (“a” = significantly lower than controls. P < 0.05). Other doses of metronidazole were not significantly different from the untreated controls and no treatments reduced MR strain B7268 infection rates in comparison with untreated controls (P > 0.05).