Can sexual transmission support the enzootic cycle of Trypanosoma cruzi?

Abstract

Background: Trypanosoma cruzi circulates in sylvatic habitats, mainly through blood-feeding triatomines, although other routes also contribute to its dispersion. Sexual transmission of T. cruzi is an understudied topic, especially among wild mammals. Because of the difficulties inherent to field work, experimentally infected mice are frequently used to evaluate the transmission of T. cruzi.

Objective: This study aimed to evaluate the sexual transmission of T. cruzi in acutely infected mice.

Methods: Male and female mice in the acute phase of Chagas disease were mated with naïve partners. Then, parasitological tests, immunohistochemistry, serological assays, and polymerase chain reaction (PCR) assays were used to detect infection.

Findings: Parasitological analysis showed trypomastigotes in the blood of 20% of the naïve mice after mating with infected partners. Serological assays detected anti-T. cruzi antibodies in all naïve females mated with infected males and in 60% of naïve males mated with infected females. PCR showed T. cruzi nDNA bands for all naïve mice mated with infected partners. The possibility of sexual transmission was also confirmed by visualisation of amastigotes in the testes.

Main conclusions: Our results demonstrate that sexual transmission of T. cruzi is an ordinary event that may contribute to maintenance of the parasite's enzootic cycle.

Fig. 1. molecular demonstration of Trypanosoma cruzi infection in mice infected via sexual intercourse. The Tcz1/2 188-bp amplicon and catamers were detected with radiolabelled T. cruzi-specific nDNA probes. The top panel shows bands from intraperitoneally infected mice (odd numbers; males, 1-9; females, 11-19) before mating with uninfected animals. The bottom panel shows specific bands from mating partners after breeding (even numbers; females, 2-10; males, 12-20). Smears represent excess amplified product. NC: negative control; Tc: T. cruzi-positive control.

Fig. 2. vertical transmission of Trypanosoma cruzi after sexual transmission in mice. Southern blotting of the 188-bp Tcz-amplified nDNA sequence by hybridisation with a specific radiolabelled probe. Top lanes are the offspring born after mating of infected males with naïve uninfected females. The bottom lanes are the offspring born after mating of infected females with naïve uninfected males. Notice that 16 mice in the top lane and 14 in the bottom lane (total 30/70, 51%) did not have the 188-bp nDNA band, therefore, they are uninfected. NC: negative control; Tc: T. cruzi DNA (positive control).

Fig. 3. presence of Trypanosoma cruzi-specific IgG antibodies in the serum of sexually infected mice. Immunofluorescence of T. cruzi forms treated with mouse serum. The apple-green fluorescence was developed with a fluorescein-labelled secondary antibody against mouse anti-T. cruzi IgG. (A) Positive control, intraperitoneally infected mice. (B) Uninfected negative control. (C) Naïve male mice after mating with infected female mice. (D) Naïve female mice after mating with infected male mice.

Fig. 4. titration of anti-Trypanosoma cruzi antibodies. Antibody titres (IgG) in each group were determined by ELISA as the optical density at 490 nm (OD₄₉₀). Test and control serum assays were run in triplicate. One-way ANOVA was used for group analyses, and Tukey's test was used to compare the means and standard deviations of experimental data. A p value less than 0.05 was considered significant. NC: negative control; IP: intraperitoneally infected mice; SI: sexually infected mice; P: progeny; black triangles: antibody titres below the cut off; red triangles: antibody titres above the cut off.

Fig. 5. chagasic myocarditis in mice infected through the sexual route. (A) Negative control heart histology. (B) Histology of male mice infected through sexual intercourse. Notice the inflammatory lymphocyte infiltrates and lysis of target heart fibres. H&E stained sections, 400×.

Fig. 6. Trypanosoma cruzi forms in male sexual organs. Microphotographs showing (A) brownish immunoperoxidase-stained T. cruzi in the interstitial tissue of the epididymis, and (B) T. cruzi amastigotes nests in gonadal cells (circle). Inserts, negative control. Bars: 10 μM