Estudo de Associação Genômica Ampla dos Níveis de Infestação por Rhipicephalus microplus e Infecção por Babesia bigemina e Babesia bovis em Bovinos da Raça Angus.
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Data
2021-12-20
Autores
David, Gabriela
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Universidade Estadual Paulista (Unesp)
Resumo
O Brasil está entre os principais produtores de carne. Animais taurinos são utilizados puros ou em cruzamentos em busca de maior produtividade e qualidade da carne e da carcaça. Entretanto, animais taurinos são mais suscetíveis à infestação por carrapatos. O Rhipicephalus microplus transmite os agentes patogênicos Anaplasma marginale, Babesia bigemina e Babesia bovis, que constituem a Tristeza Parasitária Bovina (TPB). Animais taurinos também são mais vulneráveis às infecções. Assim, além dos prejuízos causados, carrapato e babesiose bovina representam um entrave na intensificação da bovinocultura de corte. O presente estudo avaliou as características de níveis de infestação por R. microplus (Icar), por meio da contagem de carrapatos, infecção por B. bigemina (Ibig) e infecção B. bovis (Ibov), determinados por meio da técnica de Reação em Cadeia da Polimerase em Tempo Real (qPCR). Essas características são economicamente importantes e complexas e há dificuldade em selecionar animais resistentes pelo método BLUP tradicional. Foram estimados parâmetros genéticos e foi conduzido um estudo de associação genômica ampla (GWAS) para proporcionar maior entendimento da base genética dessas características, com o objetivo de auxiliar a seleção de animais resistentes. Foram realizadas análises para Icar (624 animais, n= 1246), Ibig (786 animais, n=1312) e Ibov (677 animais, n=980) utilizando 770 fêmeas genotipadas com painel de aproximadamente 150.000 marcadores do tipo SNP. Os componentes de variância foram obtidos por inferência bayesiana em um modelo tri-característica. A estimativa de herdabilidade para Icar foi de baixa magnitude (0,17), sugerindo que a seleção pelo fenótipo de contagem dos carrapatos trará respostas a longo prazo. Para Ibig e Ibov as estimativas foram próximas de zero, indicando maior influência ambiental. As repetibilidades de Icar (0,24), Ibig (0,12) e Ibov (0,12) também foram de baixa magnitude, evidenciando que as variações nos níveis de infestação e infecção podem ser atribuídas principalmente a fatores ambientais. As estimativas de correlações genética e fenotípica entre o Icar e níveis de infecção sugerem que não há relação entre níveis de infestação e infecção e a seleção para uma característica não afetaria significativamente a seleção para a outra, visto que, todas foram próximas de zero. A correlação genética entre Ibig e Ibov foi alta e negativa (-0,69). A correlação fenotípica também foi negativa (-0,10) e embora tenha apresentado valor de baixa magnitude, fortaleceu a associação inversa entre as características. Para o estudo de GWAS, foi empregado o método WssGBLUP, utilizando análises univariadas e realizando três iterações, as variâncias das soluções dos SNPs foram usadas como ponderadores. As 15 janelas com maior variação explicaram 30,84%, 54,30% e 47,63% da variância genética de Icar, Ibig e Ibov, respectivamente. Após análise funcional, diversos genes candidatos foram identificados nas 15 janelas de cada característica, contribuindo para a detecção de regiões promissoras para futuros estudos visando identificar genes diretamente envolvidos na resistência dos animais.
Brazil is among the main beef producers. Taurine animals are used pure or in crossbreeding in search of greater productivity and quality of meat and carcass. However, Bos taurus taurus animals are more susceptible to tick infestation. Rhipicephalus microplus transmits the pathogens Anaplasma marginale, Babesia bigemina, and Babesia bovis, which constitute Bovine Parasiti Sadness (BPS). Taurine animals are also more vulnerable to infections. Thus, in addition to the damage caused, ticks and bovine babesiosis represent an obstacle in the intensification of beef cattle breeding. The present study evaluated the characteristics of Rhipicephalus microplus infestation level (IT), determined by tick counts, and infection levels by B. bigemina (Ibig) and Babesia bovis (Ibov), determined using the Real-Time Polymerase Chain Reaction (qPCR) technique. These traits are economically important and complex, and there is difficulty in selecting more resistant animals by the traditional method. Genetic parameters were estimated and a genome-wide association study (GWAS) was conducted to provide a further understanding of the genetic basis of these traits to aid in the selection of resistant animals. Analyses were performed for IT (624 animals, n= 1246), Ibig (786 animals, n=1312), and Ibov (677 animals, n=980) using 770 females genotyped with a panel of approximately 150,000 SNP markers. Variance components were obtained by Bayesian inference in a tri-characteristic model. The heritability estimate for IT was of low magnitude (0.17), suggesting that selection by phenotype will bring long-term responses. For Ibig and Ibov the estimates were close to zero, indicating greater environmental influence. The repeatabilities for IT (0.24), Ibig (0.12), and Ibov (0.12) were also of low magnitude, showing that the variations in the levels of infestation and infection can be attributed mainly to environmental factors. The correlation estimates between infestation and infection levels suggest that there is no relationship between them, and selection for one trait would not significantly affect selection for the other, since they were all close to zero. The genetic correlation between Ibig and Ibov was high and negative (-0.69), the phenotypic correlation was also negative (-0.10) and although it presented a low magnitude value, it strengthened the inverse association between the characteristics. For the GWAS, the WssGBLUP method was employed, using univariate analysis and performing three iterations, the variances of the SNP solutions were used as weights. The 15 windows with the highest variance explained 30.84%, 54.30%, and 47.63% of the genetic variance of IT, Ibig, and Ibov, respectively. After functional analysis, several candidate genes were identified in the 15 windows of each trait. Thus, contributing to the detection of promising regions for future studies aiming to identify genes directly involved in the resistance of animals.
Brazil is among the main beef producers. Taurine animals are used pure or in crossbreeding in search of greater productivity and quality of meat and carcass. However, Bos taurus taurus animals are more susceptible to tick infestation. Rhipicephalus microplus transmits the pathogens Anaplasma marginale, Babesia bigemina, and Babesia bovis, which constitute Bovine Parasiti Sadness (BPS). Taurine animals are also more vulnerable to infections. Thus, in addition to the damage caused, ticks and bovine babesiosis represent an obstacle in the intensification of beef cattle breeding. The present study evaluated the characteristics of Rhipicephalus microplus infestation level (IT), determined by tick counts, and infection levels by B. bigemina (Ibig) and Babesia bovis (Ibov), determined using the Real-Time Polymerase Chain Reaction (qPCR) technique. These traits are economically important and complex, and there is difficulty in selecting more resistant animals by the traditional method. Genetic parameters were estimated and a genome-wide association study (GWAS) was conducted to provide a further understanding of the genetic basis of these traits to aid in the selection of resistant animals. Analyses were performed for IT (624 animals, n= 1246), Ibig (786 animals, n=1312), and Ibov (677 animals, n=980) using 770 females genotyped with a panel of approximately 150,000 SNP markers. Variance components were obtained by Bayesian inference in a tri-characteristic model. The heritability estimate for IT was of low magnitude (0.17), suggesting that selection by phenotype will bring long-term responses. For Ibig and Ibov the estimates were close to zero, indicating greater environmental influence. The repeatabilities for IT (0.24), Ibig (0.12), and Ibov (0.12) were also of low magnitude, showing that the variations in the levels of infestation and infection can be attributed mainly to environmental factors. The correlation estimates between infestation and infection levels suggest that there is no relationship between them, and selection for one trait would not significantly affect selection for the other, since they were all close to zero. The genetic correlation between Ibig and Ibov was high and negative (-0.69), the phenotypic correlation was also negative (-0.10) and although it presented a low magnitude value, it strengthened the inverse association between the characteristics. For the GWAS, the WssGBLUP method was employed, using univariate analysis and performing three iterations, the variances of the SNP solutions were used as weights. The 15 windows with the highest variance explained 30.84%, 54.30%, and 47.63% of the genetic variance of IT, Ibig, and Ibov, respectively. After functional analysis, several candidate genes were identified in the 15 windows of each trait. Thus, contributing to the detection of promising regions for future studies aiming to identify genes directly involved in the resistance of animals.
Descrição
Palavras-chave
Babesiose bovina, Carrapato, Genética quantitativa, Genômica, Genética animal, GWAS, Bovine babesiosis, Tick, Quantitative genetics, Genomics