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The main pathogens causing the greatest reproductive losses worldwide and in our\ncountry are the protozoan parasite N. caninum (phylum Apicomplexa) and the bovine viral diarrhea virus (BVDV, genus Pestivirus, family Flaviviridae).\nN. caninum is a causative agent of bovine abortions and neonatal mo...
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| Formato: | Tesis doctoral acceptedVersion |
| Lenguaje: | Español |
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Universidad de Buenos Aires. Facultad de Ciencias Veterinarias
2024
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| Acceso en línea: | http://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=avaposgra&cl=CL1&d=HWA_7383 https://repositoriouba.sisbi.uba.ar/gsdl/collect/avaposgra/index/assoc/HWA_7383.dir/7383.PDF |
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| Sumario: | The main pathogens causing the greatest reproductive losses worldwide and in our\ncountry are the protozoan parasite N. caninum (phylum Apicomplexa) and the bovine viral diarrhea virus (BVDV, genus Pestivirus, family Flaviviridae).\nN. caninum is a causative agent of bovine abortions and neonatal mortality worldwide. This parasite has a wide range of intermediate hosts (such as cattle), and its sexual cycle occurs exclusively in canines. In cattle, transmission can be vertical or horizontal. Vertical\ntransmission occurs in both acutely and chronically infected cattle. There is little information about the immune response required to prevent endogenous transplacental transmission,\nparticularly from chronically infected cattle to their offspring in a natural environment. BVDV\ncan cause a variety of symptoms in cattle with complex pathogenicity. Maternal infection\nduring gestation results in fetal infection, which can lead to embryonic death, teratogenic effects, or the birth of persistently infected calves (PI). PI animals shed BVDV in their excretions and secretions throughout their lives and are the main route of virus transmission. BVDV infections cause significant economic losses due to various clinical manifestations such as abortion, birth of animals with malformations, immunosuppression,\netc., and are the subject of several mitigation and eradication plans worldwide. Different control measures have been used, including segregation of PI animals and vaccination in\nhigh prevalence areas.\nWhile there is information about the epidemiology of these two pathogens in some areas of our country, the dairy basin of the Lerma Valley in the Province of Salta (CVLSa) has never been studied. This region is the largest producer of bovine milk in the Northwest\nof Argentina (NOA). Between 2003 and 2011, the national cattle stock decreased by 22%,\nbut in Salta, it increased by 79%. To assess the current status of neosporosis and BVDV in the CVLSa, a surveillance was designed comprising the evaluation of serum samples\nfrom 40 cattle per farm in 16 farms, and the determination of serum antibodies against N.caninum in the dogs that were in those farms. For the serological analysis for N. caninum an indirect ELISA developed in our laboratory "Ya neospora" was used and subsequently, the same ELISA with an urea washing step was employed to determine antibody avidity\nand discriminate chronic from acute infections. Nested PCR was performed on samples from aborted fetuses. Canine sera were analyzed by indirect immunofluorescence. For the diagnosis of BVDV, a commercial indirect ELISA was used to measure antibodies against\nthe non-structural protein NS3. The results were confirmed by Western Blot. A nested RTPCR was applied for the identification of persistently infected (PI) cattle. The epidemiological study of N. caninum and BVDV in the Lerma Valley of Salta (CVLSa) showed that antibodies against N. caninum were found in all farms. The seroprevalence at the herd level: 43.7% of the farms had seroprevalences higher than\n40%. A positive association was found between seroprevalence and the presence of acute\ninfections. Moreover, at least one seropositive dog was detected in each of the analyzed farms (6/16). BVDV also showed a high seroprevalence, 50% of the establishments had\nvalues greater than 70% for while 81.2% of the establishments had at least 1 animal with persistent infection. From isolates obtained from PI cattle, a high homology (>85%) with\nthe genotype BVDV-1b was identified. The association between the type of service using bulls and the percentage of abortions was significant (p<0.01).\nThis thesis represents the first report on the circulation of N. caninum and BVDV in the CVLSa. Additionally, our study delved into the immune response profile to N. caninum. Nonaborting seropositive mothers with chronic infection were studied in 3 farms. Serum\nsamples were collected from 75 pregnant cows and heifers, along with their colostrumdeprived calves. Different ELISAs (IgM, IgG1, IgG2, IFN-) were applied, along with the analysis of the presence of bovine leukemia virus and BVDV. Cows with chronic infection\nand no abortion showed higher titers of anti- N. caninum IgG1 antibodies than IgG2 and\nthe presence of IFN- (p<0.001), whereas the opposite profile was related to vertical transmission. These results allow for an improved immunological characterization when\nconducting prevalence studies. A field trial for the control of BVDV infections based on diagnosis and vaccination was carried out, due to the high prevalence found, as proof-of-concept. Two farms with a total\nof 1220 cattle (749 for farm 1,309 for farm 2, and 90 calves) were selected. The\nseroprevalence to BVDV was above 60% and the presence of PI cattle was higher than 2%. Serology was determined using commercial kits, while the presence of PI cattle was\ndetected by an in-house nested RT-PCR and using a commercial ELISA that detects NS3 antigen. An inactivated combined commercial vaccine containing the BVDV 1a-Strain Singer "Complex Intensivo" was used, and vaccine-induced immunity was determined by\nviral seroneutralization using the vaccine strain. The study established a chronological\norder of activities consisting of a) sampling all cattle (sera), b) serological analysis and\ndetection of viral genome for identification of PI cattle, c) re-sampling for confirmation and\nsegregation of PI cattle, d) vaccination against BVDV with a second dose after 21 days, e)\nannual vaccination and diagnostics.\nThe seroneutralizing titers induced by vaccination increased significantly (p<0.05) in all\nevaluated animals between 0- and 90-days post-vaccination. Additionally, there was a decrease in the percentage of abortions (from 2019 to 2021) and an increase in the conception rate. These farms did not have BVDV circulation or PI animals during the following 2 years. This is the first work that identified the impact of BVDV and N. caninum infections in the CVLSa. Overall, our results suggest that an immunological profile combining an N. caninum IgG1/IgG2 antibody ratio >1 with high systemic levels of IFN- is associated with\na lower risk of transplacental infection in cows with chronic infection. It is essential to consider that these immunological parameters can be easily evaluated by conducting\nELISAs with field samples, which is crucial when working in field trials. We also demonstrated for the first time in Argentina and under field conditions, that it is possible to control infections caused by BVDV using currently available diagnostic tools and a\ncommercial vaccine.\n |
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