ABSTRACT The Western-blotting technique was applied to identify antigenic fractions of excretory-secretory Toxocara canis antigen recognized by IgG antibodies throughout an experimental infection in mice challenged by different inocula. Mice were inoculated with 5, 50 and 500 embryonated eggs and serum samples were collected 15, 30, 60, 90 and 120 days post-infection. Serum samples were analyzed using an excretory-secretory Toxocara antigen. Antibodies recognized antigenic fractions from 30 to 90 kDa. The protein fraction of 30-35 kDa was the most frequently recognized regardless of the size of inoculum and the stage of infection represented by the different collection times, but the antigenic recognition was more evident in groups infected with 50 and 500 eggs. This study presents an antigenic panel of the excretory-secretory antigen of T. canis and suggests that the 30-35 kDa antigenic fraction is a promising marker of the infection and should be further explored in future studies on experimental toxocariasis.

BALB/c mice were inoculated with 5-500 Toxocara canis infective eggs, and bled at 15-120 days post infection (dpi) to evaluate the dynamics of IgG antibody response and larvae distribution. Positive results were observed in all occasions for every inoculum, and a direct proportional relationship between antibody detection and the parasitic load was observed. In samples collected at 60 dpi, detection of IgG was more intense, especially with the 50 and 500 egg doses; also, a correlation between antibody level and egg count was observed with these two inocula. At 120 dpi, a decrease in antibody titer was observed for all groups; and at the end of the experiment, larvae were recovered from carcass, liver and brain. In the liver, larvae were only found in mice inoculated with 500 T. canis eggs. In carcasses, these were recovered in all groups, and the group inoculated with 50 eggs showed the highest percentage of larvae in the brain.

INTRODUÇÃO: Toxoplasmose é geralmente uma infecção benigna, exceto nos eventos de doença ocular, congênito e do sistema nervoso central, e particularmente quando o paciente é imunocomprometido. O tratamento consiste de drogas que frequentemente causam efeitos adversos, então novas drogas, mais efetivas são necessárias. Neste estudo, a possível atividade de artesunato, uma droga usada com sucesso no tratamento da malária, sobre o crescimento de Toxoplasma gondii em cultura celular é avaliado e comparado à ação de drogas que já estão sendo utilizadas contra este parasita. MÉTODOS: Células LLC-MK2 foram cultivadas em meio RPMI, mantidas em garrafas plásticas descartáveis e incubados a 36ºC com 5% CO2. Taquizoítos da cepa RH foram usados. As seguintes drogas foram testadas: artesunato, cotrimoxazol, pentamidina, pirimetamina, quinino e trimetoprima. Os efeitos dessas drogas sobre taquizoítos foram analisados por análise regressiva não linear com o software Prism 3.0. RESULTADOS: Artesunato mostrou uma concentração inibitória media (IC50) de 0,075µM e uma toxicidade sobre células LLC MK2 de 2,003µM. Pirimetamina foi efetiva a uma IC50 de 0,482µM e uma toxicidade de 11,178µM. Trimetoprima sozinha foi efetiva contra o parasita in vitro. Cotrimoxazol também foi efetivo contra o parasita, mas a concentrações mais altas que aquelas observadas para artesunato e pirimetamina. Pentamidina e quinino não tiveram efeitos inibitórios sobre os taquizoítos. CONCLUSÕES: Provou-se que artesunato in vitro pode ser uma alternativa útil para o tratamento da toxoplasmose, implicando um subsequente efeito in vivo e sugerindo o mecanismo desta droga contra o parasita.

INTRODUCTION: Toxoplasmosis is usually a benign infection, except in the event of ocular, central nervous system (CNS), or congenital disease and particularly when the patient is immunocompromised. Treatment consists of drugs that frequently cause adverse effects; thus, newer, more effective drugs are needed. In this study, the possible activity of artesunate, a drug successfully being used for the treatment of malaria, on Toxoplasma gondii growth in cell culture is evaluated and compared with the action of drugs that are already being used against this parasite. METHODS: LLC-MK2 cells were cultivated in RPMI medium, kept in disposable plastic bottles, and incubated at 36ºC with 5% CO2. Tachyzoites of the RH strain were used. The following drugs were tested: artesunate, cotrimoxazole, pentamidine, pyrimethamine, quinine, and trimethoprim. The effects of these drugs on tachyzoites and LLC-MK2 cells were analyzed using nonlinear regression analysis with Prism 3.0 software. RESULTS: Artesunate showed a mean tachyzoite inhibitory concentration (IC50) of 0.075µM and an LLC MK2 toxicity of 2.003µM. Pyrimethamine was effective at an IC50 of 0.482µM and a toxicity of 11.178µM. Trimethoprim alone was effective against the in vitro parasite. Cotrimoxazole also was effective against the parasite but at higher concentrations than those observed for artesunate and pyrimethamine. Pentamidine and quinine had no inhibitory effect over tachyzoites. CONCLUSIONS: Artesunate is proven in vitro to be a useful alternative for the treatment of toxoplasmosis, implying a subsequent in vivo effect and suggesting the mechanism of this drug against the parasite.