Marina Sibila

Control of Mycoplasma hyopneumoniae infections in pigs

Abstract Mycoplasma hyopneumoniae, the primary pathogen of enzootic pneumonia, occurs worldwide and causes major economic losses to the pig industry. The organism adheres to and damages the ciliated epithelium of the respiratory tract. Affected pigs show chronic coughing, are more susceptible to other respiratory infections and have a reduced performance. Control of the disease can be accomplished in a number of ways. First, management practices and housing conditions in the herd should be optimized. These include all-in/all-out production, limiting factors that may destabilize herd immunity, maintaining optimal stocking densities, prevention of other respiratory diseases, and optimal housing and climatic conditions. Strategic medication with antimicrobials active against M. hyopneumoniae and, preferably, also against major secondary bacteria may be useful during periods when the pigs are at risk for respiratory disease. Finally, commercial bacterins are widely used to control M. hyopneumoniae infections. The main effects of vaccination include less clinical symptoms, lung lesions and medication use, and improved performance. However, bacterins provide only partial protection and do not prevent colonization of the organism. Different vaccination strategies (timing of vaccination, vaccination of sows, vaccination combined with antimicrobial medication) can be used, depending on the type of herd, the production system and management practices, the infection pattern and the preferences of the pig producer. Research on new vaccines is actively occurring, including aerosol and feed-based vaccines as well as subunit and DNA vaccines. Eradication of the infection at herd level based on age-segregation and medication is possible, but there is a permanent risk for re-infections.

Porcine circovirus type 2 (PCV2) vaccination of conventional pigs prevents viremia against PCV2 isolates of different genotypes and geographic origins.

The efficacy of recently developed porcine circovirus type 2 (PCV2) vaccines has not been tested yet against PCV2 isolates of the two proposed genotypes. In the present work, the efficacy of a subunit vaccine containing PCV2 capsid protein was evaluated by using a challenge model with four different PCV2 isolates of different genotype and geographic origin. The vaccine prevented the development of viremia in all cases as well as significantly decreased nasal and faecal shedding of the virus. Also, the vaccine elicited PCV2-specific neutralizing antibodies to PCV2 even in the presence of maternally derived immunity.

Current perspectives on the diagnosis and epidemiology of Mycoplasma hyopneumoniae infection

Abstract Mycoplasma hyopneumoniae is the principal aetiological agent of enzootic pneumonia (EP), a chronic respiratory disease that affects mainly finishing pigs. Although major efforts to control M. hyopneumoniae infection and its detrimental effects have been made, significant economic losses in pig production worldwide due to EP continue. M. hyopneumoniae is typically introduced into pig herds by the purchase of subclinically infected animals or, less frequently, through airborne transmission over short distances. Once in the herd, M. hyopneumoniae may be transmitted by direct contact from infected sows to their offspring or between pen mates. The ‘gold standard’ technique used to diagnose M. hyopneumoniae infection, bacteriological culture, is laborious and is seldom used routinely. Enzyme-linked immunosorbent assay and polymerase chain reaction detection methods, in addition to post-mortem inspection in the form of abattoir surveillance or field necropsy, are the techniques most frequently used to investigate the potential involvement of M. hyopneumoniae in porcine respiratory disease. Such techniques have been used to monitor the incidence of M. hyopneumoniae infection in herds both clinically and subclinically affected by EP, in vaccinated and non-vaccinated herds and under different production and management conditions. Differences in the clinical course of EP at farm level and in the efficacy of M. hyopneumoniae vaccination suggest that the transmission and virulence characteristics of different field isolates of M. hyopneumoniae may vary. This paper reviews the current state of knowledge of the epidemiology of M. hyopneumoniae infection including its transmission, infection and seroconversion dynamics and also compares the various epidemiological tools used to monitor EP.

Retrospective study on swine Torque teno virus genogroups 1 and 2 infection from 1985 to 2005 in Spain

A retrospective study to detect evidence of swine Torque teno virus (TTV) genogroups 1 and 2 infection in sera of pigs from the Spanish livestock between years 1985 and 2005 was carried out by means of PCR. Also, the molecular evolution of TTV genogroups 1 and 2 during the 20-year period studied using a 250-base sequence of the non-coding region of the viral genome was assessed. Both TTV genogroup genomes were found in pig sera from the first year of study. Taking into account the whole study period, 113 out of 162 animals (69.8%) were infected with one or the other genogroup, while 38 out of 162 pigs (23.5%) were co-infected with both genogroups. Moreover, TTV genogroup 2 (90 out of 162, 55.6%) was significantly more prevalent than genogroup 1 (54 out of 162, 33.3%). The non-coding region of swine TTV genome sequenced showed its adequacy as a molecular marker in swine TTV. This study represents the earliest evidence of TTV infection in pigs to date, 14 years before the initial description of this virus. Moreover, this is also the earliest evidence of TTV infection in any species.

Infection, excretion and seroconversion dynamics of porcine circovirus type 2 (PCV2) in pigs from post-weaning multisystemic wasting syndrome (PMWS) affected farms in Spain and Denmark.

Longitudinal case-control studies were performed in post-weaning multisystemic wasting syndrome (PMWS) affected farms from Denmark and Spain using similar designs. Fourteen independent batches of 100-154 pigs per batch were monitored from birth to PMWS outbreak occurrence. Pigs displaying PMWS-like signs and matched healthy cohorts were euthanized during the clinical outbreak. PMWS was diagnosed according to internationally accepted criteria and pigs were classified as: (i) PMWS cases, (ii) wasted non-PMWS cases and (iii) healthy pigs. Porcine circovirus type 2 (PCV2) quantitative PCR (qPCR) and serology techniques were applied to analyse longitudinally collected sera and/or nasal and rectal swabs. Results showed that PCV2 load increased in parallel to waning maternal antibody levels, reaching the maximum viral load concurrent with development of clinical signs. PMWS affected pigs had higher PCV2 prevalence and/or viral load than healthy pigs in all collected samples at necropsy (p<0.0001-0.05) and even in sera and nasal swabs at the sampling prior to PMWS outbreak (p<0.01-0.05). Danish farms had a higher PCV2 prevalence in young piglets as well as an earlier PMWS presentation compared to Spanish farms. PMWS diagnoses were confirmed by laboratory tests in only half of pigs clinically suspected to suffer from PMWS. Positive and significant correlations were found among PCV2 viral loads present in sera, nasal swabs, rectal swabs and lymphoid tissues (R=0.289-0.827, p<0.0001-0.01), which indicates that nasal and rectal swabs were suitable indicators of PCV2 excretion. Sensitivity and/or specificity values observed from both tests used separately or combined suggested that qPCR and/or serology tests are not apparently able to substitute histopathology plus detection of PCV2 in tissues for the individual PMWS diagnosis within PMWS affected farms. However, qPCR appears to be a potential reliable technique to diagnose PMWS on a population basis.

Development of cell-mediated immunity to porcine circovirus type 2 (PCV2) in caesarean-derived, colostrum-deprived piglets.

Abstract The interaction between porcine circovirus type 2 (PCV2) and the pig immune system has been suggested to be a determinant event for the pathogenesis of postweaning multisystemic wasting syndrome (PMWS). To gain insight into the host immune mechanisms developed upon PCV2 infection, early innate and adaptive immune responses were examined in 1-week-old, caesarean-derived, colostrum-deprived piglets using a subclinical infection model of PCV2 in combination with lipopolysaccharide (LPS) as a potential immunostimulation factor. The use of LPS did not show any significant effect on the course of PCV2 infection, nor did in the evolution of the immunological parameters evaluated. Ex vivo responses were detected as early as 1 day post-infection (PI) and consisted of an elevation of the plasmatic levels of interleukin (IL)-8 in PCV2-inoculated pigs followed by an increase on plasmatic IFN-α at day 5 PI. Regarding IL-10, only one PCV2-inoculated pig was positive (day 7 PI); this pig was the only one in which viremia persisted until the end of the study. In vitro cytokine determination showed that, regardless of the treatment administrated to the pigs, an IL-10 release was observed when peripheral blood mononuclear cells (PBMC) cultures were stimulated with PCV2. Seroconvertion to PCV2 measured by an immunoperoxidase monolayer assay (IPMA) occurred between 7 and 14 days PI, whereas neutralizing antibodies (NA) did not appear until day 29 PI. PCV2 DNA was first detected in serum at day 7 PI, reaching the peak of viremia between days 14 and 21 PI, followed by a drop in viral load that was found coincident with the appearance of PCV2-specific IFN-γ-secreting cells (PCV2-IFN-γ-SC) and NA. Results from the present work suggest that viral clearance might be mediated by the development of PCV2-IFN-γ-SC in contribution to the PCV2-specific NA.

A genetically engineered chimeric vaccine against porcine circovirus type 2 (PCV2) improves clinical, pathological and virological outcomes in postweaning multisystemic wasting syndrome affected farms

The present study describes the effects of a commercially available genetically engineered chimeric vaccine against porcine circovirus type 2 (PCV2) on clinical, pathological and virological features in three multi-site farms suffering from postweaning multisystemic wasting syndrome (PMWS). The vaccine product was able to reduce clinical signs, PCV2 viral load in lymphoid organs and/or sera, and overall mortality in nurseries and fattening units. This is the first time in which is shown that a PCV2 vaccine is able to decrease specifically PMWS-associated mortality. Another novelty of this study is the assessment of PMWS-like histological lesions in a large number of vaccinated and non-vaccinated pigs under field conditions.

Genetic and immunobiological diversities of porcine reproductive and respiratory syndrome genotype I strains

Genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV) has been based on ORF5/GP5 and ORF7/N protein variations. Complete viral genome studies are limited and focused on a single or a few set of strains. Moreover, there is a general tendency to extrapolate results obtained from a single isolate to the overall PRRSV population. In the present study, six genotype-I isolates of PRRSV were sequenced from ORF1a to ORF7. Phylogenetic comparisons and the variability degree of known linear B-epitopes were done considering other available full-length genotype-I sequences. Cytokine induction of all strains was also evaluated in different cellular systems. Non structural protein 2 (nsp2) was the most variable part of the virus with 2 out of 6 strains harboring a 74 aa deletion. Deletions were also found in ORF3 and ORF4. Phylogenetic analyses showed that isolates could be grouped differently depending on the ORF examined and the highest similarity with the full genome cluster was found for the nsp9. Interestingly, most of predicted linear B-epitopes in the literature, particularly in nsp2 and GP4 regions, were found deleted or varied in some of our isolates. Moreover, 4 strains, those with deletions in nsp2, induced TNF-α and 3 induced IL-10. These results underline the high genetic diversity of PRRSV mainly in nsp1, nsp2 and ORFs 3 and 4. This variability also affects most of the known linear B-epitopes of the virus. Accordingly, different PRRSV strains might have substantially different immunobiological properties. These data can contribute to the understanding of PRRSV complexity.

Torque teno sus virus 1 and 2 viral loads in postweaning multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS) affected pigs

Torque teno viruses (TTV) are small, non-enveloped viruses with a circular single-stranded DNA genome, which are considered non-pathogenic. However, TTVs have been eventually linked to human diseases. TTVs infecting pigs, Torque teno sus virus 1 (TTSuV1) and 2 (TTSuV2), have been recently associated to porcine circovirus diseases (PCVD). To get more insights into such potential disease association, the aim of this study was to quantify TTSuV1 and TTSuV2 viral loads in serum of pigs affected by two PCVDs, postweaning multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS). Such study was carried out by means of a newly developed real-time quantitative PCR (qPCR) method. Both TTSuVs were highly prevalent among studied pigs. TTSuV2 viral loads were significantly higher in PMWS affected animals, further supporting the previously suggested association between TTSuV2 and PMWS. On the contrary, TTSuV1 prevalence and loads were not related with the studied PCVDs.

Differences in phagocytosis susceptibility in Haemophilus parasuis strains

Haemophilus parasuis is a colonizer of the upper respiratory tract of healthy pigs, but virulent strains can cause a systemic infection characterized by fibrinous polyserositis, commonly known as Glässer’s disease. The variability in virulence that is observed among H. parasuis strains is not completely understood, since the virulence mechanisms of H. parasuis are largely unknown. In the course of infection, H. parasuis has to survive the host pulmonary defences, which include alveolar macrophages, to produce disease. Using strains from different clinical backgrounds, we were able to detect clear differences in susceptibility to phagocytosis. Strains isolated from the nose of healthy animals were efficiently phagocytosed by porcine alveolar macrophages (PAM), while strains isolated from systemic lesions were resistant to this interaction. Phagocytosis of susceptible strains proceeded through mechanisms independent of a specific receptor, which involved actin filaments and microtubules. In all the systemic strains tested in this study, we observed a distinct capsule after interaction with PAM, indicating a role of this surface structure in phagocytosis resistance. However, additional mechanisms of resistance to phagocytosis should be explored, since we detected different effects of microtubule inhibition among systemic strains.