Seleção de ovinos geneticamente resistentes ao scrapie

Abstract

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.

Report of outbreaks of classical scrapie in Dorper sheep and associated prion protein gene polymorphisms in affected flocks

“…At codon 171, considering the most relevant to susceptibility, approximately 90 % of sheep examined had genotype QR or QQ. This finding is consistent with data obtained by Ianella et al (2012) and Sotomaior et al (2012) who found that between 90 and 100 % of the Dorper sheep in Brazil presented these genotypes. When the sheep were classified into risk groups, approximately 69 % of animals in Dorper/White Dorper flocks from these three outbreaks belonged to moderate-to high-risk groups.…”

“…Since then, 16 cases of scrapie have been reported from 1978 to 2010 (Sotomaior et al 2012). Our previous work described a classical scrapie in Suffolk sheep where one animal presented clinical signs of infection (Andrade et al 2011).…”

Prion protein gene polymorphisms and accumulation of pathogenic prion protein (PrPSc) in a herd with previously confirmed scrapie cases

“…After this, other scrapie cases have been reported and published (http://www.oie.int; RIBEIRO et al, 2007;ANDRADE et al, 2011). Some of these cases were on the animals from Paraná State (SOTOMAIOR et al, 2012).…”