Publicação
Resistance of Autochthonous Portuguese Cattle Breeds as a control strategy for Theileria annulata
| Resumo: | Parasitc diseases transmitted by ticks to animals have a major economic impact on livestock farms and animal welfare worldwide. The costs associated with these diseases are mainly related to the mortality and loss of productvity of livestock species, namely cattle, suffering from Anaplasmosis, Babesiosis and Theileriosis. Tropical Theileriosis is an endemic haemoparasitc disease caused by the protozoan parasite Theileria annulata, prevalent in Asia, the Middle East, Southern Europe, and North Africa. The transmission of this haemoprotozoan parasite by ticks of the genus Hyalomma (H. marginatum, H. anatolicum, H. lusitanicum, H. scupense and H. dromedarii) is widely described. In Portugal, transmission by the ticks H. lusitanicum and H. marginatum has been described. The prevalence of the disease reflects the geographical distribution of these ticks, being very common in countries bordering the Mediterranean Sea, which is why it is also called Mediterranean Theileriosis. In additon to its impact on productvity and mortality, Tropical Theileriosis is a disease that limits the implementation of Improvement Programs for different breeds. There is scientific evidence showing an increased risk of outbreaks of parasitic diseases in the coming years, associated with climate change, so their control is one of the most important global priorities for effective and efficient livestock management. Cell-based vaccines and chemical therapies are currently available to control Theileriosis, although these two approaches are not capable of eradicating the disease. In additon, vector control using acaricides has become unsustainable due to increasing resistance and concerns about food safety and the environment. New approaches to controlling the disease are therefore needed. This study aims to assess the resistance or tolerance of two autochthonous breeds of cattle to Theileria annulata. The use of resistant breeding animals could be a complementary and sustainable long-term approach to controlling Theileria annulata. Comparative studies carried out with Holstein (Bos taurus) and Sahiwal (Bos indicus originating from a T. annulata endemic area) cattle have shown that the Sahiwal breed is more resistant. However, the ability of indigenous Portuguese cattle breeds, namely the Alentejana and Mertolenga breeds, to resist or tolerate tropical Theileriosis is unknown, which is why this study was carried out. This thesis is structured in five chapters. Chapter I is a general review of the classification and biology, epidemiology, clinical signs, pathogenesis, diagnosis, and current control strategies for Theileriosis. It also includes a descripƟon of its economic impact on animal production and characterization of the genetic resistance of cattle to this disease. Chapter II is dedicated to studying the prevalence and risk factors for Theileria annulata infection in two autochthonous Portuguese cattle breeds. A sample of 843 animals was studied, 420 of which were Alentejana breed and 423 Mertolenga breed. The prevalence found was 10.8%, lower than that reported in previous studies (21.3%) in Portugal. In addition, there was a statistically significant difference between breeds and a greater likelihood of older animals being positive compared to younger ones (p < 0.05). Chapter III presents a Genome-Wide Association Study (GWAS) with the aim of identifying genomic variants associated with resistance to Theileria annulata infection. Thus, Single Nucleotide Polymorphisms (SNPs) were analyzed in the autochthonous Alentejana and Mertolenga cattle breeds. A total of 24 SNPs suggestive of significance (p ≤ 10-4) were identified for Alentejana and 20 SNPs for Mertolenga. The genomic regions around these SNPs were analyzed to identify genes and Quantitative Trait Loci (QTLs) already described. Regarding the Alentejana, the MAP3K1, CMTM7, SSFA2 and ATG13 genes are located close to suggestive SNPs and appear to be candidate genes for resistance to Tropical Theileriosis, due to their importance in regulatng the immune response or the impact on resistance to other diseases already described. On the other hand, in the Mertolenga, the UOX gene is also a candidate gene due to its apparent link to the pathogenesis of the disease. Chapter IV deals with a study assessing the Knowledge, Aƫtudes, and Practices of ticks and tick-borne diseases in animals of Alentejana and Mertolenga cattle breed. This study aims to help identify possible gaps in breeders' knowledge of the life cycle of this parasite, its distribution and seasonality, as well as resistance to acaricides and alternative control strategies. A KAP questionnaire was administered to 44 breeders of cattle of the autochthonous Portuguese breeds Alentejana (14) and Mertolenga (30). Most breeders showed that they had an average level of knowledge about ticks and tick-borne diseases. Furthermore, although few consider tick infestation to be a major animal health problem, the majority state that one of the main reasons for veterinary consulttions on their farm is to deworm their animals, with 92.9% of Alentejana breed cattle farmers and 96.7% of Mertolenga breed farmers reporting the use of acaricides as a strategy for controlling tick infestation. The final chapter (Chapter V – General Discussion and Conclusions) includes an overall conclusion to this work, emphasizing the most relevant and significant aspects. Thus, the studies presented aim to provide a more in-depth view of Tropical Theileriosis, its impact on cattle producƟon and contribute to the development of innovaƟve strategies for controlling the disease. |
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| Autores principais: | Valente, Diana Margarida da Silva |
| Assunto: | Bovine Parasite Alentejana Mertolenga SNP QTL genetics |
| Ano: | 2024 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Trás-os-Montes e Alto Douro |
| Idioma: | inglês |
| Origem: | Repositório da UTAD |
| Resumo: | Parasitc diseases transmitted by ticks to animals have a major economic impact on livestock farms and animal welfare worldwide. The costs associated with these diseases are mainly related to the mortality and loss of productvity of livestock species, namely cattle, suffering from Anaplasmosis, Babesiosis and Theileriosis. Tropical Theileriosis is an endemic haemoparasitc disease caused by the protozoan parasite Theileria annulata, prevalent in Asia, the Middle East, Southern Europe, and North Africa. The transmission of this haemoprotozoan parasite by ticks of the genus Hyalomma (H. marginatum, H. anatolicum, H. lusitanicum, H. scupense and H. dromedarii) is widely described. In Portugal, transmission by the ticks H. lusitanicum and H. marginatum has been described. The prevalence of the disease reflects the geographical distribution of these ticks, being very common in countries bordering the Mediterranean Sea, which is why it is also called Mediterranean Theileriosis. In additon to its impact on productvity and mortality, Tropical Theileriosis is a disease that limits the implementation of Improvement Programs for different breeds. There is scientific evidence showing an increased risk of outbreaks of parasitic diseases in the coming years, associated with climate change, so their control is one of the most important global priorities for effective and efficient livestock management. Cell-based vaccines and chemical therapies are currently available to control Theileriosis, although these two approaches are not capable of eradicating the disease. In additon, vector control using acaricides has become unsustainable due to increasing resistance and concerns about food safety and the environment. New approaches to controlling the disease are therefore needed. This study aims to assess the resistance or tolerance of two autochthonous breeds of cattle to Theileria annulata. The use of resistant breeding animals could be a complementary and sustainable long-term approach to controlling Theileria annulata. Comparative studies carried out with Holstein (Bos taurus) and Sahiwal (Bos indicus originating from a T. annulata endemic area) cattle have shown that the Sahiwal breed is more resistant. However, the ability of indigenous Portuguese cattle breeds, namely the Alentejana and Mertolenga breeds, to resist or tolerate tropical Theileriosis is unknown, which is why this study was carried out. This thesis is structured in five chapters. Chapter I is a general review of the classification and biology, epidemiology, clinical signs, pathogenesis, diagnosis, and current control strategies for Theileriosis. It also includes a descripƟon of its economic impact on animal production and characterization of the genetic resistance of cattle to this disease. Chapter II is dedicated to studying the prevalence and risk factors for Theileria annulata infection in two autochthonous Portuguese cattle breeds. A sample of 843 animals was studied, 420 of which were Alentejana breed and 423 Mertolenga breed. The prevalence found was 10.8%, lower than that reported in previous studies (21.3%) in Portugal. In addition, there was a statistically significant difference between breeds and a greater likelihood of older animals being positive compared to younger ones (p < 0.05). Chapter III presents a Genome-Wide Association Study (GWAS) with the aim of identifying genomic variants associated with resistance to Theileria annulata infection. Thus, Single Nucleotide Polymorphisms (SNPs) were analyzed in the autochthonous Alentejana and Mertolenga cattle breeds. A total of 24 SNPs suggestive of significance (p ≤ 10-4) were identified for Alentejana and 20 SNPs for Mertolenga. The genomic regions around these SNPs were analyzed to identify genes and Quantitative Trait Loci (QTLs) already described. Regarding the Alentejana, the MAP3K1, CMTM7, SSFA2 and ATG13 genes are located close to suggestive SNPs and appear to be candidate genes for resistance to Tropical Theileriosis, due to their importance in regulatng the immune response or the impact on resistance to other diseases already described. On the other hand, in the Mertolenga, the UOX gene is also a candidate gene due to its apparent link to the pathogenesis of the disease. Chapter IV deals with a study assessing the Knowledge, Aƫtudes, and Practices of ticks and tick-borne diseases in animals of Alentejana and Mertolenga cattle breed. This study aims to help identify possible gaps in breeders' knowledge of the life cycle of this parasite, its distribution and seasonality, as well as resistance to acaricides and alternative control strategies. A KAP questionnaire was administered to 44 breeders of cattle of the autochthonous Portuguese breeds Alentejana (14) and Mertolenga (30). Most breeders showed that they had an average level of knowledge about ticks and tick-borne diseases. Furthermore, although few consider tick infestation to be a major animal health problem, the majority state that one of the main reasons for veterinary consulttions on their farm is to deworm their animals, with 92.9% of Alentejana breed cattle farmers and 96.7% of Mertolenga breed farmers reporting the use of acaricides as a strategy for controlling tick infestation. The final chapter (Chapter V – General Discussion and Conclusions) includes an overall conclusion to this work, emphasizing the most relevant and significant aspects. Thus, the studies presented aim to provide a more in-depth view of Tropical Theileriosis, its impact on cattle producƟon and contribute to the development of innovaƟve strategies for controlling the disease. |
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