Lactobacillus rhamnosus reduces parasite load on Toxocara canis experimental infection in mice, but has no effect on the parasite in vitro.

Human toxocariasis is a neglected global parasitic zoonosis. The efficacy of drug treatment for this disease has been hindered by the biological complexity of the main etiological agent, the nematode Toxocara canis. Experimental studies have shown the potential of probiotics to promote a reduction in the parasite load of T. canis larvae. This study aimed to evaluate the effect of probiotic Lactobacillus rhamnosus ATCC 7469 on the parasite load of BALB/c mice with acute toxocariasis and evaluate the direct effect of this probiotic on T. canis larvae in vitro. In vivo administration of probiotics reduced the parasite load of T. canis larvae by 53.3% (p = 0.0018) during the early stage of infection in mice. However, when analyzed in vitro, it was observed that the probiotic did not present a deleterious effect on the larvae, as approximately 90% of these remained viable. These results demonstrate the potential of the probiotic L. rhamnosus in the reduction of T. canis larvae in BALB/c mice and suggest it could be used as an alternative means for the controlling of visceral toxocariasis. However, further studies are required to elucidate the mechanisms of action promoted by this probiotic.

Transmammary infection in BALB/c mice with chronic toxocariasis.

Human toxocariasis is a neglected public health problem. Infection of humans generally results from the accidental ingestion of embryonated Toxocara canis eggs, but it is important to broaden knowledge about other forms of transmission. This study aimed to demonstrate the prevalence of transmammary transmission in mice with chronic toxocariasis. BALB/c mice in groups 1 (G1) and 3 (G3) were inoculated with 1200 T. canis eggs 60days before mating, whereas those of group 2 (G2) were not infected. After delivery, the G1 neonates were transferred to G2 females to be nursed, and vice versa. Thus, the mice generated by G2 females and breastfed by G1 females could be infected only during lactation. In the G3 group, offspring were not exchanged. The search for T. canis larvae in the bodies of the lactating females and their offspring was performed after weaning and at 60days old, respectively. The frequency of transmammary infection in the mice generated by G2 uninfected females and breastfed by G1 infected females was 19.8%, which was similar to that observed (19.6%) in the mice bred and fed by G3 females. The frequency of infection in the mice generated by G1 females and breastfed by G2 females was only 4.2%, which was lower than that of G1 (p=0.0064) and G3 (p=0.0062) groups. Transmammary infection by mice with chronic toxocariasis was found to be more prevalent than congenital infection.

Evaluation of the initial and chronic phases of toxocariasis after consumption of liver treated by freezing or cooling.

Human toxocariasis is a neglected parasitic zoonosis of worldwide distribution. The consumption of raw or undercooked meat and offal from paratenic hosts of the Toxocara canis nematode can cause infection in humans, but there have been a lack of studies examining specific prophylactic measures to combat this mode of transmission. The aim of this study was to evaluate the establishment of infection by T. canis larvae at the initial and chronic phases of visceral toxocariasis after the consumption of mouse liver subjected to cold treatment. This study was divided into two stages using groups (G) of five donor mice inoculated with 2,000 eggs of T. canis. Two days post-inoculation, the livers of donor mice in G1 and G2 were kept at -20 °C and between 0 and 4 °C, respectively, for 10 days. In the first stage of the study, the livers of mice from G1, G2, and G3 (control) were subjected to a tissue digestion technique and found to be positive for infection. In the second stage, which evaluated infection in mice that had consumed livers from donor mice, receiver mice of G4 and G7 were fed with livers of donor mice from G1 (freezing), receiver mice of G5 and G8 were fed with livers of donor mice from G2 (cooling), and receiver mice of G6 and G9 with livers from G3 (control). Then, the tissue digestion technique was performed for recovering larvae from organs and carcasses of mice, at 2 days (G4, G5, and G6) and 60 days after liver consumption (G7, G8, and G9). It was observed that freezing inhibited the viability of 100 % of the larvae, while cooling promoted 87.7 and 95.7 % reductions in the intensity of infection at 2 and 60 days after liver consumption, respectively. Under the studied conditions, cold treatment shows great potential to help control this parasitosis, both in the initial and chronic phases of toxocariasis.

Evaluation of the immunosuppressive effect of cyclophosphamide and dexamethasone in mice with visceral toxocariasis.

Visceral toxocariasis is a serious public health problem with a cosmopolitan distribution. Children are susceptible due to their immature immune system and high risks of infection. Nevertheless, the few completed studies about immunosuppression have had controversial results. To evaluate the effect of two immunosuppressive drugs on the larval burden of Toxocara canis, four groups of ten Swiss strain mice each were inoculated on day 0 with 1,200 embryonated T. canis eggs. Fifteen days before the experimental infection, group 1 (control) was treated via intraperitoneal injection (IP) with sterile distilled water and groups 2 and 3 were treated with dexamethasone (DEX) at 1 and 5 mg/kg/day, respectively. Additionally, group 4 was treated IP with cyclophosphamide (CY) at 50 mg/kg at two times per week for 2 weeks. Sixty days following infection, the mice were euthanised to recover the larvae by means of the tissue digestion technique. The levels of antibodies detected by indirect ELISA were not associated with the larval burden. Administration of CY (50 mg/kg) and DEX (5 mg/kg) resulted in an increase of the larval burden of 162.1% and 50.8%, respectively, in relation to the control group. These two treatments, especially CY (50 mg/kg), promoted immunosuppression and the establishment of a significant larval burden, supporting its further utilisation in studies related to immunosuppression in visceral toxocariasis.