Rosa Rosell

Porcine epidemic abortion and respiratory syndrome (mystery swine disease). Isolation in Spain of the causative agent and experimental reproduction of the disease

In March of 1991, a disease that affected pregnant sows and caused a high mortality in unweaned piglets was detected in Spain. Based on the clinical signs observed, mystery swine disease, which had been described recently in Germany, Holland and Belgium, was suspected. From the samples obtained from the affected farm, a filtrable agent (0.22 micron) was isolated on cell culture. It produced cytopathic effects, its replication was intracytoplasmic, it was sensitive to chloroform, and cross-reacted with a Lelystad reference serum. When inoculated into pregnant sows, the agent produced inappetence for 2-4 days, without hyperthermia. One of the sows aborted at 100 days of gestation; the two others had delayed parturitions (days 115 and 116). There was a mixture of healthy piglets, mummified fetuses, stillbirths and weak piglets. Microscopic examination of the lungs of healthy piglets killed at 8 and 12 days of life revealed the presence of interstitial pneumonia. The sera from the three sows at 39 days after infection cross-reacted with the Lelystad virus (titres > or = 1/640), whereas pre-inoculation sera did not recognize it (titres < or = 1/10). This is the first report from Spain of the isolation of an agent (antigenically related to the Lelystad virus), capable of reproducing the disease previously designated as mystery swine disease.

Interferon-gamma induction correlates with protection by DNA vaccine expressing E2 glycoprotein against classical swine fever virus infection in domestic pigs

Classical swine fever (CSF) is a highly contagious viral infection affecting domestic and wild pigs. For classical swine fever virus (CSFV), immunization with plasmids expressing different versions of glycoprotein E2 has proven an effective way to induce protection. Previously, we have also shown that immunization with DNA vaccine expressing glycoprotein E2 (DNA-E2) induced specific T helper cell responses in the absence of neutralizing antibodies. However, the role of T cell responses in protection against CSFV is largely unknown. Here we have extended these studies to deeply characterize the role of T cell responses by a DNA-E2 and their correlation with protection against CSFV infection. Thus, pigs vaccinated with the DNA vaccine induced a strong cellular immune response, characterized by the specific induction IFN-gamma expressing T cells after vaccination without any detectable levels of CSFV neutralizing antibodies. Constant levels of CSFV-specific IFN-gamma producing cells observed from the beginning of the infection until 7 days after challenge in vaccinated animals might contribute to early control of CSFV replication, at least until neutralizing antibodies are developed. Severe clinical signs of the disease, including high titers of viremia, pyrexia and virus spread to different organs, were recorded in the non-vaccinated challenged animals, in comparison to the vaccinated animals where only one animal showed mild clinical signs and a short peak of viremia. Lack of complete protection in this animal correlated with a delay on the induction of neutralizing antibodies, detectable only from day 11 post-CSFV challenge. Conversely, the rest of the pigs within the group developed neutralizing antibodies as early as at day two post-challenge, correlating with sterile protection. Finally, an inverse correlation seemed to exist between early induction of IFN-alpha and the protection observed, while IL-10 seemed to be differentially regulated in vaccinated and non-vaccinated animals. Our results support the relevance of the induction of a strong T cellular response to confer a solid protection upon DNA vaccination against CSFV. Further experiments are needed to be done in order to clarify the key cytokines playing a role in CSFV-protection and to obtain emergency vaccines capable to confer robust and fast protection.

Partial protection against classical swine fever virus elicited by dendrimeric vaccine-candidate peptides in domestic pigs.

We report the immunogenicity of three dendrimeric peptide vaccine candidates for classical swine fever virus (CSFV). Each dendrimeric construct contained four copies of a B-cell epitope from the E2 glycoprotein of CSFV [construct 1: E2 (694-712); 2: E2 (712-727); 3: E2 (829-842)] joined to a T-cell epitope from the NS3 protein (residues 1446-1460). Intramuscular immunization of domestic pigs with the different constructs significantly reduced the clinical score after lethal challenge with CSFV. In contrast, control pigs developed severe clinical signs of the disease. All pigs vaccinated with construct 1, containing a B-cell epitope from the E2 B-C domain, developed an antibody response that recognized not only the original dendrimeric immunogen but also its constituting E2 epitope in linear form, albeit no neutralizing antibodies were detected prior to viral challenge. Two of these pigs were partially protected, which associated with the induction of IFN-γ producing cells and of neutralizing antibodies upon challenge. Interestingly, the serological response elicited by construct 1 lacked antibodies to E2 A domain, used as infection markers. The dendrimeric approach could therefore provide a basis for the development of CSFV marker (DIVA) vaccines, and contribute to a better understanding of the immune responses against CSFV.

Border Disease Virus among Chamois, Spain

Approximately 3,000 Pyrenean chamois (Rupicapra pyrenaica pyrenaica) died in northeastern Spain during 2005-2007. Border disease virus infection was identified by reverse transcription-PCR and sequencing analysis. These results implicate this virus as the primary cause of death, similar to findings in the previous epizootic in 2001.

Lack of transmission of porcine circovirus type 2 to weanling pigs by feeding them spray-dried porcine plasma.

An experiment was conducted to determine whether spray-dried porcine plasma containing 2·47 × 105 dna copies of porcine circovirus type 2 (pcv-2) could infect weanling pigs when fed to them. Five specific pathogen-free (spf) weanling pigs were fed ad libitum for 45 days a control diet and six pigs were fed a test diet containing 8 kg sdpp per 100 kg feed. The two groups were housed in separate biosecurity level-3 rooms. None of the pigs in either group developed any clinical signs or became pcv-2 viraemic or seroconverted.

Development and validation of a novel SYBR Green real-time RT-PCR assay for the detection of classical swine fever virus evaluated on different real-time PCR platforms.

Classical swine fever is a highly contagious viral disease that causes significant economic losses in pig production on a global scale. The rapid dissemination of the virus and the variability of the clinical signs merit the development of swift and accurate classical swine fever virus (CSFV) detection methods, which can assist in disease control. The development and evaluation of a novel quantitative real-time RT-PCR assay for CSFV detection, based on SYBR Green coupled to melting curve analysis, is described. The analytical and diagnostic performances of the method using two real-time PCR instruments were compared. The assay was specific and detected the major genotypes of CSFV. The limit of detection in cell culture medium and serum was 0.1 TCID50/reaction, while in tissue homogenate for both platforms, it was 1 TCID50/reaction. The limit of detection was 1, 10 and 10² gene copies/μL when nuclease-free water, serum and tissue homogenate, respectively, were used as sample matrices for both instruments. The analysis of 108 tissue homogenate and serum samples from animals infected with CSFV naturally and experimentally and non-infected animals showed that the assay provided a highly sensitive and specific method for classical swine fever.

Retrospective serological study on hepatitis E infection in pigs from 1985 to 1997 in Spain.

The objective of the present work was to ascertain the date in which hepatitis E virus (HEV) was introduced in the Spanish pig population. For this, a serological retrospective study was carried out using archived sera. A total of 2871 serum samples gathered between 1985 and 1997 and collected in 208 farms of Spain were tested for anti-HEV IgG by an in-house ELISA. Of the 2871 sera analyzed by ELISA, 1390 were positive for anti-HEV antibodies (48.4%, 95% CI: 46.9-49.9%) and that corresponded to 204/208 farms (98%, 95% CI: 96.1-99.9%) having at least one positive pig. Our results show that HEV was present and widespread in Spanish swine farms at least since 1985. Any significant changes in prevalence were detected from 1 year to another and therefore, HEV infection in swine should be considered endemic in Spain.

Schmallenberg Virus Circulation in High Mountain Ecosystem, Spain

To the Editor: Schmallenberg virus (SBV) is an emerging vector-borne virus mainly associated with Culicoides spp. midges (1,2). Factors affecting the density and distribution of vectors may help determine the prevalence of SBV infection in particular areas. Altitude could be one limiting factor for virus transmission; however, little information is available regarding SBV in high-altitude regions. During December 29, 2012–February 21, 2013, morphologic anomalies were identified in 4 stillborn calves from different farms in northeastern Spain, and infection with SBV was suspected. The cases were clustered in the Ripolles and Garrotxa regions of Catalonia and appeared in beef cattle herds that spent the grazing season (May–November) in the alpine meadows (>2,000 m altitude) of the National Game Reserve of Freser-Setcases in the Eastern Pyrenees Mountains. The calves had severe arthrogryposis, ankylosis of several joints, abnormal curvature of the vertebral column, and severe muscle atrophy. Malformations of the central nervous system included bilateral hydrocephalus, cerebellar hypoplasia, and micromyelia, characterized by the presence of few neurons in the ventral horns and moderate to severe bilateral reduction of white matter in the ventral and lateral funiculi. SBV infection was confirmed by real-time reverse transcription qualitative PCR (RT-qPCR) (1,3) or serologic testing in 3 of the 4 calves and all 4 of the mothers (Table). Serum samples were tested by using a commercial indirect ELISA (ID.vet; Innovative Diagnostics, Montpellier, France) and a virus neutralization test using the BH80/11–4 isolate (provided by the Friedrich-Loeffler-Institut, Isle of Riems, Germany) (4). Consistent results were obtained from both of these techniques, and the proportions of calves positive by ELISA and RT-qPCR were similar to those found in previous studies (5). Table Results of serologic and molecular analyses of SBV in sympatric wild and domestic ruminants, Eastern Pyrenees, Spain, 2010–2013* The neurologic and musculoskeletal lesions found in the calves indicated that fetal infection probably occurred at 5–6 months’ gestation (6). Gestation started in mid-April to mid-May; therefore, maternal infection most probably occurred in late summer 2012 (September–October), when cows were grazing in the alpine meadows. We then performed a serologic study in domestic and sympatric wild ruminants from the National Game Reserve of Freser-Setcases, which comprises 20,200 ha of alpine and subalpine ecosystems. We analyzed serum samples from 355 wild ruminants hunted during August 2010–May 2013; species sampled included Pyrenean chamois (Rupicapra pyrenaica), European mouflon (Ovis aries musimon), and roe deer (Capreolus capreolus). We also analyzed samples from fetuses of these species obtained in April 2013 (Table), as well as animals from 8 cow herds and 4 sheep–goat mixed herds; a mean of 14 samples were collected per herd during 2 sampling periods (Table). Two of the mixed sheep–goat herds were sampled during both sampling periods. All serum samples underwent ELISA testing; positive results were confirmed by virus neutralization (4). Domestic ruminants sampled during October–November 2011 were seronegative, whereas all farms sampled during November 2012–April 2013 had infected animals (Table). High mean seroprevalence was found in cow herds; 105 (86.8% [95% CI 80.7%–92.8%]) of 121 herds tested were infected. Seroprevalance was lower but still high for mixed sheep–goat herds; 16 (41% [95% CI 25.6%–56.5%]) of 39 herds were infected. The earliest evidence of SBV in the study area came from a seropositive Pyrenean chamois hunted on September 3, 2012; this date coincides with the estimated months when cows that delivered stillborn calves were infected. For wild ungulates tested from September 2012 onwards, overall SBV seroprevalence was statistically higher (χ2 33.47, 2 d.f., p<0.0001) in roe deer (4/5, 80% [95% CI 44.9%–100%]) than in Pyrenean chamois (8/105, 7.6% [95% CI 2.5%–12.7%]) and mouflon (0/23). Differences in seroprevalence for summer through autumn 2012 compared with spring 2013 in Pyrenean chamois were not significant (Table). Roe deer seroprevalence was similar to the 88.9% reported in Belgium in December 2011, which contrasted with the lower seroprevalence observed in red deer, 54.6%, for the same month in the same study (7). Differences in seroprevalence between wild host species might be related to differences in exposure to SBV vectors depending on habitat selection, vector feeding habits, or host-specific factors; altitude might be an additional factor affecting exposure (8). Thus, the lower altitude habitat selection of roe deer and the housing of domestic ruminants in valley areas could explain the higher seroprevalence observed in these species compared with that in Pyrenean chamois and mouflon. All fetuses of wild ruminants had negative serologic test results for SBV, and no gross lesions indicating infection were observed (Table). However, the potential reproductive disorders that SBV infection can cause in these species are unknown. Our findings support the hypothesis that SBV can circulate in alpine meadows at >2,000 m altitude and confirm the appearance of SBV in late summer and autumn 2012 in the high mountain ecosystem of the Eastern Pyrenees in Spain. A variety of domestic and wild ruminants showed susceptibility to SBV infection, but differences in seroprevalence suggest different roles for sympatric ruminants in SBV epidemiology. The role of vector species in the transmission of SBV in alpine ecosystems should be analyzed.

The impact of CSFV on the immune response to control infection.

The severity of the acute form of CSF is responsible for the high mortality rate and has been the subject of many studies. Nevertheless, some animals are likely to develop a mild, chronic, or unapparent form of the disease. Paradoxically, this clinical form of the disease has not been well studied, especially regarding its pathogenesis. In this study, we investigated the infection in domestic pigs that is caused by the CSFV Cat01 strain, which is responsible for the 2001-2002 CSFV outbreak in Catalonia, Spain, and which caused mild and nonspecific clinical signs compared to the infection that is caused by another CSFV strain that is responsible for inducing severe clinical symptoms of disease. We assessed the impact of the CSFV infection in the immune system of domestic pigs, mainly on the kinetics of different cytokines, such as IFN-α (innate immunity) and IFN-γ (adaptive immune response), during the first weeks after infection. In addition, we evaluated the impact on the induction of the humoral response and its relation to the course of infection and the RNA CSFV viral load. The IFN-α levels in the serum samples from the pigs that developed a milder form of the CSF disease (infected with Cat01 strain) were lower than those that were detected in the pig with severe clinical CSF signs (Margarita strain). After infection with Cat01 strain, the IFN-γ levels in response to CSFV were detected in addition to the humoral response. Interestingly, in the serum samples of these animals, we detected the lowest load of CSFV RNA. Similarly, the lowest viral load levels were detected in the tonsils of these pigs. Both the T cells and the humoral response that were generated in most of the pigs that were infected with strain Cat01 may be related to the protection in the symptom progression of CSF against this viral strain. These results explain the antiviral role of IFN-γ in the absence of an antibody response. Likewise, these results corroborate the relevance and relationship that exists between the intensity of the T cell response and the protection against CSFV replication. Additionally, these results also explain how the failure to induce optimal levels of humoral and cellular responses after CSFV infection promotes the spread and persistence of the virus.

Postnatal Persistent Infection with Classical Swine Fever Virus and Its Immunological Implications

It is well established that trans-placental transmission of classical swine fever virus (CSFV) during mid-gestation can lead to persistently infected offspring. The aim of the present study was to evaluate the ability of CSFV to induce viral persistence upon early postnatal infection. Two litters of 10 piglets each were infected intranasally on the day of birth with low and moderate virulence CSFV isolates, respectively. During six weeks after postnatal infection, most of the piglets remained clinically healthy, despite persistent high virus titres in the serum. Importantly, these animals were unable to mount any detectable humoral and cellular immune response. At necropsy, the most prominent gross pathological lesion was a severe thymus atrophy. Four weeks after infection, PBMCs from the persistently infected seronegative piglets were unresponsive to both, specific CSFV and non-specific PHA stimulation in terms of IFN-γ-producing cells. These results suggested the development of a state of immunosuppression in these postnatally persistently infected pigs. However, IL-10 was undetectable in the sera of the persistently infected animals. Interestingly, CSFV-stimulated PBMCs from the persistently infected piglets produced IL-10. Nevertheless, despite the addition of the anti-IL-10 antibody in the PBMC culture from persistently infected piglets, the response of the IFN-γ producing cells was not restored. Therefore, other factors than IL-10 may be involved in the general suppression of the T-cell responses upon CSFV and mitogen activation. Interestingly, bone marrow immature granulocytes were increased and targeted by the virus in persistently infected piglets. Taken together, we provided the first data demonstrating the feasibility of CSFV in generating a postnatal persistent disease, which has not been shown for other members of the Pestivirus genus yet. Since serological methods are routinely used in CSFV surveillance, persistently infected pigs might go unnoticed. In addition to the epidemiological and economic significance of persistent CSFV infection, this model could be useful for understanding the mechanisms of viral persistence.