Diarreas de etiología vírica en el ganado porcinoaportaciones al diagnóstico y control

Resumen

Strict control of infectious diseases is a major pillar in the sanitary and welfare standards that current and next future policies demand in swine production. Enteric diseases are among the main hazards challenging pig health, especially in the early stages of production and among them, the relative importance of viral pathogens is gaining relevance in recent years, both associated to the emergence of new aetiological agents and the re-emergence of well-known pathogens, some of which exhibit new variants with higher virulence and/or transmissibility. The general objective of this Doctoral Thesis was to investigate the relevance of infections by different enteric viruses which have been suggested as aetiological agents of enteric disease on pig farms in Spain. The results of our research have been included in five peer-review articles answering questions about the prevalence of different enteric viruses in diarrhoea outbreaks (study 1: articles 1, 2 and 3), viral genetic characterization (study 2: articles 1, 2 and 3), the development of new diagnostic tools of interest for the control of these infections (study 3: article 4) and the characterization of the infection and cross-immunity associated with different variants of Porcine epidemic diarrhoea virus or PEDV (study 4: article 5). Study 1 investigated the prevalence of the five enteric coronaviruses described to date in the porcine host, rotaviruses of types A, B, C and H, as well as astroviruses, kobuviruses, toroviruses, orthoreviruses and mastadenoviruses in 206 outbreaks of enteric disease on Spanish swine farms. The detection of one or more of the investigated enteric viruses was very common with prevalence values ranging from 48.5% for astroviruses to 4.4% for orthoreoviruses. Particularly, PEDV was the only coronavirus detected, in almost 20 % of the outbreaks investigated, particularly in the fattening stage. Rotaviruses were detected in one out of four outbreaks investigated, mainly Rotavirus A (RVA) and to a lesser extent Rotavirus B (RVB) after weaning and Rotavirus C (RVC) in neonatal diarrhoea outbreaks. Rotavirus H (RVH) was identified for the first time in Europe, circulating on nine of the Spanish pig farms investigated. The molecular characterization of the main viruses involved in the etiology of swine enteric disease was the objective of study 2. The complete sequence of the protein S gene of all PEDV isolates was obtained, identifying the most widespread variants of this coronavirus in Spain, all of them included in the INDEL or G1b genogroup. Particularly, a recombinant variant (rPEDV-SeCoV) was identified as the predominant PEDV isolate in recent years in Spain. In addition, the complete genome sequences of PEDV (4), RVH (4), astrovirus (16), kobuvirus (3) and torovirus (1) isolates were obtained by high throughput sequencing techniques, allowing for the investigation of their relationships with isolates recovered in other geographical regions or in hosts other than swine. A rapid molecular diagnostic tool to discriminate between viable or infectious virus and non-viable virus, viability PCR, was optimized in study 3. This technique differentiated infectious and heat-inactivated virus in PEDV viral suspensions as well as in serum samples and can be use in the monitoring of potential sources of infection involved in the transmission of this coronavirus. Finally, in the fourth and last study, infection in weaned pigs by Swine enteric coronavirus (SeCoV) -a chimeric virus originating from a recombination event between Transmissible gastroenteritis virus (TGEV) or its mutant Porcine respiratory coronavirus (PRVC) and PEDV- and two variants of PEDV G1b genogroup, including the recombinant variant between PEDV and SeCoV or rPEDV-SeCoV, were characterized. The clinical signs and lesions were similar to previous reports of enteric coronavirus infections regardless of the inoculum and faecal excretion during the convalescence period was observed for the three investigated isolates. Protection against reinfection was complete after homologous challenge at 3 weeks, both in terms of clinical disease and viral shedding. In contrast, heterologous challenge was associated with a partial protection, with viral excretion in faeces or even diarrhoea and lesions in the small intestine. Overall, the results of this Doctoral Thesis allow us to conclude that there is a need for a continuous monitoring of the different viruses involved in the aetiology of enteric disease in swine as well as the convenience of new studies to investigate the clinical relevance of the infection by some of these viral agents.