A susceptibilidade dos ovinos ao scrapie está relacionada a polimorfismos do gene da proteína priônica celular (PRNP). Polimorfismos nos códons 136 (alanina, A/ valina, V), 154 (arginina, R/ histidina, H) e 171 (glutamina, Q/ arginina, R/ histidina, H) são os principais determinantes de susceptibilidade/resistência ao scrapie clássico. Eles são combinados em 4 principais variantes do alelo ancestral ARQ: VRQ, AHQ, ARH e ARR. Programas de melhoramento genético na União Europeia e Estados Unidos têm utilizado como estratégia selecionar o alelo resistente ARR, diminuindo a frequência do alelo susceptível VRQ em populações de ovinos. No Brasil, há poucos dados de genotipagem do gene PRNP e, até o momento, nenhum tipo de controle baseado em cruzamentos direcionados foi implementado. Esta revisão focará aspectos importantes como epidemiologia e resistência genética, como ferramenta de programas de controle de scrapie. Palavras-chaves:Genotipagem; Ovinos; Polimorfismo; Proteína priônica celular; Scrapie AbstractSelective breeding for scrapie resistance in sheep. It is well known that the susceptibility of sheep to scrapie is determined by the host's prion protein gene (PRNP). PRNP polymorphisms at codons 136 (alanine, A/ valine, V), 154 (histidine, H/arginine, R) and 171 (glutamine, Q/histidine, H/arginine, R) are the main determinants of sheep susceptibility/resistance to classical scrapie. There are four major variants of the wild-type ARQ allele: VRQ, AHQ, ARH and ARR. Breeding programs have been developed in the European Union and the USA to increase the frequency of the resistant ARR allele while decreasing the frequency of the susceptible VRQ allele in sheep populations. In Brazil, little PRNP genotyping data are available for sheep, and thus far, no controlled breeding scheme for scrapie has been implemented. This review will focus on important epidemiological aspects of scrapie and the use of genetic resistance as a tool in breeding programs to control the disease.

Fibrosarcoma is characterized as an invasive nodular tumor of mesodermal origin, with elongated normochromatic nuclei. The histopathologic analysis using specific staining techniques is efficient in detailing the neoplastic architecture and the relations with surrounding tissues. In the present study, the canine skin fibrosarcoma was histologically characterized using Hematoxilin-Eosin stain, Mallory’s Trichrome stain and Shorr’s Trichrome stain as routine staining for conjunctive tissue, Toluidine Blue to highlight the mitosis and Picrosirius-Hematoxilin Trichrome to characterize the collagen type. It was concluded that the Picrosirius stain characterized the existing collagen type as type I and III; the Toluidine Blue staining highlighted the mitoses together with Shorr’s staining, as this one also provided a marking for the conjunctive tissue and the formed bands. The Mallory’s staining technique highlighted the conjunctive tissue and the bands that are spread; the Hematoxilin-Eosin stain highlighted with emphasis the neoplastic cells.