Pathological and immunohistochemical assessment of the impact of three different strains of swine enteric coronaviruses in the intestinal barrier

Swine enteric coronaviruses, such as porcine epidemic diarrhea virus (PEDV) or transmissible gastroenteritis virus (TGEV), have risen concern for the porcine industry and research community due to the increase in their virulence, their potential recombination capacity and the emergence of new variants. This in vivo study aims to compare the impact of three different strains of swine enteric coronaviruses [(two G1b (S-INDEL) PEDV strains and a recombinant TGEV-PEDV or Swine enteric coronavirus (SeCoV)] in the intestine of 3-weeks-old infected piglets, focusing on the pathology and main components of the intestinal barrier, including the number of goblet cells, and the expression of IgA as well as FoxP3, a regulatory T cell marker. Severity of lesions was evidenced in the three infected groups and was highly correlated with the viral load in feces and the frequency of viral antigen-positive cells. Furthermore, higher cellular death together with an increase in the expression of the FoxP3 marker was detected in the duodenum and jejunum of infected animals at 3 days post-infection. Our results highlight a recruitment of FoxP3+ cells in the small intestine of infected animals which may represent a response to the tissue damage caused by viral replication and cell death. Further studies should be addressed to determine the potential role of these cells during swine enteric coronavirus infections.

The jigsaw of PRRSV virulence

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of the, probably, most economically important disease for the pig industry worldwide. This disease, characterised by producing reproductive failure in sows and respiratory problems in growing pigs, appeared in the late 1980s in the United States and Canada. Since its appearance, strains capable of producing higher mortality rates as well as greater severity in clinical signs and lesions than classical strains have been identified. However, since the first reports of these "virulent" PRRSV outbreaks, no homogeneity and consensus in their description have been established. Moreover, to the authors' knowledge, there is no published information related to the criteria that a PRRSV strain should fulfil to be considered as a "virulent" strain. In this review, we revise the terminology used and gather the information related to the main characteristics and differences in clinical signs, lesions, viral replication and tropism as well as immunological parameters between virulent and classical PRRSV strains and propose a first approximation to the criteria to define a virulent PRRSV strain.

Prevalence of mycoplasma-like lung lesions in pigs from commercial farms from Spain and Portugal

Background

Mycoplasma hyopneumoniae causes a chronic respiratory disease that produces important economic losses due to poor productive performance, increased mortality and costs for several control strategies. The prevalence of mycoplasma-like lesions (MLL) at abattoir has been widely studied in different countries, making use of different scoring systems. However, most of them are difficult to apply in abattoirs with high number of pigs sacrificed per hour. For that reason, it is necessary to adapt the scoring system to the reality of the modern abattoir, even if there is a loss of accuracy. Our purpose was to investigate the prevalence and severity of MLL at abattoirs in Spain and Portugal using a 0 to 5 scoring system adapted to abattoirs with high number of sacrificed pigs per hour and to highlight the histopathological diagnosis as confirmatory method to identify patterns of pneumonia correlated to gross lesions.

Results

Cranioventral pulmonary consolidation, a typical MLL, was the most frequent lung lesion (30.97 %) detected at the abattoir, followed by dorsocaudal infarcts with pleurisy (12.51 %) and pleurisy alone (6.26 %). The average score for all examined lungs at abattoir was 1.99 out of 5 points. The histopathological study revealed that the 78.17 % of the randomly selected lungs with MLL presented microscopic lesions compatible with M. hyopneumoniae infection. Most bronchointerstitial and interstitial pneumonia lesions had a chronic course while most suppurative and fibrinous bronchopneumonia lesions had an acute course and a higher degree of severity. The combination of microscopic lesions more frequently observed was bronchointerstitial pneumonia + interstitial pneumonia + suppurative bronchopneumonia.

Conclusions

The prevalence of MLL at abattoir was 30.97 %, however, after microscopic examination the real prevalence of lungs with lesions compatible with M. hyopneumoniae infection was reduced up to 24.21 %. The six more prevalent combinations of lesions in the microscopic study involved the 66.13 % of examined lungs, and in all of them, microscopic lesions characteristic of M. hyopneumoniae infection were found, what supports the importance of M. hyopneumoniae as a primary pathogen in cases of PRDC.

Activation of pro- and anti-inflammatory responses in lung tissue injury during the acute phase of PRRSV-1 infection with the virulent strain Lena

•

Lena virulent strain caused an increase in sera levels of IFN-γ and IL-6.

•

Lung viral load and PRRSV-N-protein⁺ cells were inversely correlated with CD163⁺ macrophages in the lung.

•

CD14⁺ cells infiltrated interstitium to possibly replenish macrophages subsets.

•

Lena-induced microscopic lung injury was linked to an increase of iNOS⁺ cells.

•

The increase of CD200R1⁺ and FoxP3⁺ cells was associated with the course of lung injury.

Porcine reproductive and respiratory syndrome virus (PRRSV) plays a key role in porcine respiratory disease complex modulating the host immune response and favouring secondary bacterial infections. Pulmonary alveolar macrophages (PAMs) are the main cells supporting PRRSV replication, with CD163 as the essential receptor for viral infection. Although interstitial pneumonia is by far the representative lung lesion, suppurative bronchopneumonia is described for PRRSV virulent strains. This research explores the role of several immune markers potentially involved in the regulation of the inflammatory response and sensitisation of lung to secondary bacterial infections by PRRSV-1 strains of different virulence. Conventional pigs were intranasally inoculated with the virulent subtype 3 Lena strain or the low virulent subtype 1 3249 strain and euthanised at 1, 3, 6 and 8 dpi. Lena-infected pigs exhibited more severe clinical signs, macroscopic lung score and viraemia associated with an increase of IL-6 and IFN-γ in sera compared to 3249-infected pigs. Extensive areas of lung consolidation corresponding with suppurative bronchopneumonia were observed in Lena-infected pigs. Lung viral load and PRRSV-N-protein⁺ cells were always higher in Lena-infected animals. PRRSV-N-protein⁺ cells were linked to a marked drop of CD163⁺ macrophages. The number of CD14⁺ and iNOS⁺ cells gradually increased along PRRSV-1 infection, being more evident in Lena-infected pigs. The frequency of CD200R1⁺ and FoxP3⁺ cells peaked late in both PRRSV-1 strains, with a strong correlation between CD200R1⁺ cells and lung injury in Lena-infected pigs. These results highlight the role of molecules involved in the earlier and higher extent of lung lesions in piglets infected with the virulent Lena strain, pointing out the activation of routes potentially involved in the restraint of the local inflammatory response.