Experimental toxocariosis in BALB/c mice: effect of the inoculation dose on brain and eye involvement

Ocular toxocarosis (OT) is a well-established disease. However, our understanding of the migratory route, time and circumstances that produce ocular invasion are not clear. To improve our knowledge of factors related to ocular invasion, BALB/c mice were inoculated with simple doses (SD) of 6, 12, 50, 100, 200 and 1000 embryonated eggs (EE) and multiple doses (MD) of 200 and 1000 EE. Brains and eyes were studied for the presence of larvae in animals sacrificed on days 3, 5, 7, 9, 11, 13, 15, 17, 19, 40, 80 and 120 in SD and on days 28, 30, 32, 34, 36, 38, 40, 42, 46, 87 and 127 in MD. The humoral immune responses were studied by ELISA using excretory-secretory antigen. Due to the considerable number of days tested, results showed are based on one set of experiments. However, each point studied represents the result obtained from a group of five mice. We have shown that the eye involvement with Toxocara canis larvae is a phenomenon mainly produced once larvae have reached the brain. There is a direct relationship between the parasitic load and the number of ocular larvae. Moreover, the arrival of larvae to the eye is an independent event, unrelated to the kind of administered dose (SD, MD), although the number of the brain larvae was higher in the cases of MD. High levels of specific antibodies were observed but they did not prevent the arrival of the larvae to the brain and the eye.