[Granulomas caused by animal parasites]

Numerous animal parasites, protozoan, metazoan and in particular helminths, may cause a varied range of granulomatous lesions in man. Study of two examples, the leishmaniasis granuloma and the schistomiasis granuloma, would appear to indicate that reactions between the host and the parasite at various stages of its development are dependent upon facilitation or rejection phenomena in which both humoral and cellular mechanisms are involved. The appearance of the granuloma thus depends upon the reactional possibilities of the host. The lesions seen in these granulomas may be related to a certain number of basic processes: phenomenon of necrosis, of fibrosis, specific or non-specific reactions and allergic reactions which are processes also seen under other aetiological circumstances. Certain of them, in particular giant cell or epithelio-giant cell reactions and the tissue eosinophilia associated with helminthic infestations, the role of which is not clearly known, are suggestive of a parasitic aetiology but are in no way pathognomonic. Thee demonstration and identification of the parasite, sometimes difficult or even impossible, should take into account the geographical and epidemiological context, as well as the localisation of the lesions, and often require the pathologist to study serial sections, with special stains. The timely aid of the parasitologist or immunologist is often essential to the aetiological diagnosis of the granuloma.