Application of RGB trichrome staining to the study of human parasites

Abstract

Human parasitic infections are major contributors to global disease load, compromising the human life and resulting in considerable morbidity and mortality worldwide. However, many parasitic diseases have been neglected and little investigated in western medicine. Although recently developed molecular techniques have revolutionized the taxonomy of parasites and the parasitic disease diagnosis, histopathology still remains a powerfull tool for the analysis of parasitic diseases, allowing direct observation of the parasite thus providing information about the morphological features of the parasite ifself, and revealing tissue alterations at the parasite-host interface. The recently developed RGB trichrome (acronym for the primary dye components, picrosirius Red, fast Green, and alcian Blue) stains the main components of the extracellular matrix, specifically collagens and proteoglycans. We have applied the RGB tricrome staining to human tissues infected by the main three classes of human parasites: Protozoa (Leishmania donovanii and Toxoplasma gondii), helminths (Trichinella spiralis, Enterobius vermicularis, Dirofilaria spp. and Echinococcus granulosus) and ectoparasites (Demodex folliculorum and Demodex brevis). Trichrome stain results in detailed staining of the parasite microanatomical structure, and highlights host tissue alterations such as granulomatous inflammation, immune cell infiltrate, or increased amount of collagen as a sign of parasite-induced fibrosis. Yet, the use of RGB trichrome, as a complement of hematoxylin and eosin staining, provides additional valuable information to assess parasitic infection histopathology.