Evidence for the involvement of the optic nerve as a migration route for larvae in ocular toxocariasis of Mongolian gerbils.

Although Toxocara canis, an important pathogen of ocular disease, tends to migrate to the eye, the precise migratory route has yet to be determined experimentally. Mongolian gerbils, Meriones unguiculatus, known as a useful animal model for human toxocariasis, were used to investigate the migration route toward the eyes. Infective larvae of T. canis were directly inoculated into the intracranial region. Haemorrhagic lesions or larvae were observed in 56.3% of cases. Histopathologically, a larva was observed in the optic nerve of gerbils 6 days after inoculation, and two larvae were found in the optic chiasma in the gerbils having a haemorrhage in the retina 9 days after inoculation. These results indicate that T. canis migrates from the brain to the eye through the optic nerve. Considering these data and previous studies showing that the ocular changes appear as early as 3 days of infection in the oral-administrated gerbils, there are two phases in the migration to the retina: a haematogenous early phase and an optic nerve route late phase.

New animal model for human ocular toxocariasis: ophthalmoscopic observation.

BACKGROUND/AIMS: Although human ocular toxocariasis causes severe vision defect, little is known about its aetiology, diagnosis, and treatment. To develop a new animal model for human ocular toxocariasis, ophthalmological findings of fundi in Mongolian gerbils, Meriones unguiculatus, and BALB/c mice were investigated following infection with Toxocara canis. METHODS: Using an ophthalmoscope, which was specifically developed to observe the fundi of small animals, ocular changes of fundi of 20 gerbils and 11 mice were monitored after oral infection with embryonated eggs of T canis. RESULTS: Vitreous, choroidal, and retinal haemorrhages were consistently observed in Mongolian gerbils, but rarely in mice. Severe exudative lesions and vasculitis were often present in gerbils but not in mice. Migrating larvae were also frequently observed in gerbils. CONCLUSION: Mongolian gerbils are more appropriate animal model for human ocular toxocariasis than previously used experimental animal such as mice, guinea pigs, rabbits, and monkeys because of its high susceptibility of ocular infection.

The occurrence of Sphaerospora renicola K-stages in the choroidal rete mirabile of the common carp.

It is known from earlier studies that the so-called K-protozoa, the late presporogonic stages of Sphaerospora renicola, a parasite causing renal sphaerosporosis in common carp (Cyprinus carpio), accumulate in the swimbladder wall and give rise to the disease called myxosporean swimbladder inflammation. The present study indicates that in the case of intensive infection these parasites also occur in the rete mirabile of the choroid of the eye, causing haemorrhages and necrosis. The results suggest that the K-stages of S. renicola are located in the blood path just like the early presporogonic C-stages; however, as they get stuck in organs rich in capillaries, it is difficult to demonstrate them from the blood of the common carp.