HISTOPATHOLOGICAL OBSERVATIONS IN NEW AND CLASSIC MODELS OF EXPERIMENTAL SCHISTOSOMA-HAEMATOBIUM INFECTIONS

The authors present marsh rat Holochilus brasiliensis, jirds Meriones shawl and M. unguiculatus as new models of Schistosoma haematobium inf ection. Histological findings were compared with those of classic mode ls mouse Mns and hamster Mesocricetus. In new models, embryonated eggs were seen in the stool from 90 days post infestation (DPI) and active disease developed from 117 to 175 DPI. Seven out of Io rodents presen ted granulomatous and/or chronic cystitis, fibrosis, polyps and urothe lial changes: squamous metaplasia, precancerous dysplasia and squamous cell carcinoma of the urinary bladder. In the digestive tract of all new models, granulomas eroded the mucosa, formed inflammatory polyps, infiltrated the wall and accumulated into bilharziomas. In the liver, granulomatous hepatitis surrounded by bilharzial pigment deposit was a pparent. Pipe-stem fibrosis involved 4 rodents with precirrhotic chang es in 1 and portal hypertension in 2. One female Meriones suffered fro m granulomatous endometritis and salpingitis. All new models developed pulmonary granulomatosis with associated vascular lesions: giant cell arteritis in 1 rodent, thromboses in 3 and pulmonary hypertension in 4 others. In classic models, 1 Mus presented a squamous cell carcinoma of the urinary bladder while Mesocricetus displayed diverse lesions i n digestive and genital tracts, liver and lungs. All tissue lesions, r esembling those seen in humans in all points, were far more frequent a nd severe in new models than in classic ones. Those involving the urin ary bladder have never been reported in other models such as monkeys: Pan troglodytes, Cercopithecus aethiops and Cebus apella. A comparison was carried out between different models on the basis of experimental conditions: definitive hosts, number of cercariae used, type and dura tion of infection. This study clearly demonstrated that Holochilus bra siliensis, Meriones shawi and M. unguiculatus are perfectly adequate m odels in terms of laboratory facilities. They are helpful in investiga ting the pathogenic mechanism of some disorders in S. haematobium infe ction, particularly tumours of the urinary bladder, and this may enhan ce therapeutic assays.