Weak-born Piglets Research Articles

Premature farrowing and stillbirths in two organic sow farms due to riboflavin deficiency

BackgroundRiboflavin deficiency can lead to premature farrowing, stillborn piglets, weak-born piglets and neonatal death. Riboflavin (vitamin B2) is considered essential for reproductive function. The longer the period on riboflavin-deficient diets, the more severe the clinical signs become. Litter size as well as body size of piglets can also be considered risk factors that may contribute to the problem.Case presentationThis case report involved two organic farms of 320 (farm A) and 250 sows (farm B). Between 2019 and 2020, premature farrowing with weak-born or stillborn piglets and severe intra-litter mortality, ranging from 60 to 100% were observed. Investigations for infectious causes of reproductive disease, drinking water quality and general feed composition were performed, but showed no significant results. Feed composition was subsequently evaluated more in detail. Riboflavin levels were very low specifically 1.25 mg/kg of diet (3.75 mg/kg of diet is the NRC minimum recommended level). Riboflavin as a vitamin complex supplement (B complex) was administered to sows one month before the farrowing date and this led to a rapid improvement of the problem such that no stillbirth or intra-litter mortality was observed.ConclusionsThe clinical presentation, the low riboflavin levels in the feed below the recommended levels for gestating sows and the effectiveness of the riboflavin supplementation, led to an ex juvantibus diagnosis of this deficiency condition. This case report highlights that riboflavin deficiency during gestation should be considered in case of premature parturition and stillborn litters.

Porcine reproductive and respiratory syndrome virus induces tight junction barrier dysfunction and cell death in porcine glandular endometrial epithelial cells

Reproductive failure caused by porcine reproductive and respiratory syndrome virus (PRRSV) is characterized by embryonic death and weak-born piglets and is associated with placental cell apoptosis and impairment of endometrial integrity. Here, we aimed to determine whether endometrial epithelial barrier function and viability were altered following PRRSV type 1 or type 2 infection. PRRSV inoculation was examined at the apical or basolateral side of porcine glandular endometrial epithelial cell cultures isolated from 4- to 6-month-old PRRSV-free herd gilts (n = 7 pigs). On the apical side, four days postinfection (4 dpi) with type 2 PRRSV, transepithelial electrical resistance decreased by 31% ± 5%, and paracellular permeability to fluorescein isothiocyanate-dextran (4 kDa) increased by 10-fold as compared with the mock and type 1 infection. Real-time polymerase chain reaction results revealed that both PRRSV types upregulated the mRNA expression of the barrier builder tight junction protein (TJ) Cldn5, but downregulated pore-forming TJ Cldn7. Additionally, the expression of other TJ genes, i.e., Cldn3 and Cldn8, was differentially increased by PRRSV type 1 and that of zonula occludens-1 was increased by PRRSV type 2. MTT assays indicated an increase in porcine glandular endometrial epithelial cell culture at 2–6 dpi following type 2 infection. Analysis of apoptosis using Annexin/propidium iodide staining combined with flow cytometry showed that the percentage of viable cells decreased, accompanied by a significantly higher dead cell population following PRRSV type 2 infection at 2–4 dpi. PRRSV type 1 infection also induced dead cells (>4%) at 2 dpi; however, the cell population recovered at 4 dpi. In conclusion, PRRSV type 2 infection caused more severe TJ barrier dysfunction and reduced cell viability compared with PRRSV type 1 infection in the porcine endometrium. Impairment in the membrane integrity of the maternal glandular endometrium may be the underlying mechanism of PRRSV-induced reproductive failure in pregnant sows.

Heterologous Challenge with PRRSV-1 MLV in Pregnant Vaccinated Gilts: Potential Risk on Health and Immunity of Piglets.

Simple SummaryModified live virus (MLV) vaccines are considered as the key component to control the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV). The majority of pig farms apply the ‘mass’ vaccination strategy in breeding female animals. However, this PRRS MLV vaccination protocol involves the risk of inoculation of sows in the last stage of gestation, resulting in possible infection of the fetus as the virus can efficiently cross the placenta during the last period of pregnancy. Thus, we evaluated the ability of the vaccine virus to act as a pathogenic strain, to be transmitted to fetuses and to affect the health status of neonatal piglets. The results indicated that the study gilts transmitted the vaccine virus to their offspring, as well as that the PRRSV-infected piglets showed a poor clinical performance. Consequently, the pig farms that apply PRRS MLV vaccination in a routine blanket vaccination strategy must avoid inoculating pregnant gilts the last week before their parturition.The objective of the present study was to evaluate the potential risks of the four commercial PRRS-1 MLV vaccines in pregnant vaccinated gilts at the last stage of gestation under field conditions. The study was conducted at four pig farms, including 25 gilts from each farm (25 × 4 = 100 gilts), which were equally allocated to five different study groups. A PRRS-1 MLV vaccination was applied on the 100th day of their pregnancy with the different commercial vaccines that are available in the Greek market. The results indicated virus congenital infection and viremia in piglets (20/200 = 10% PRRSV infected piglets), and detection of PRRSV-specific antibodies (181/200 = 90.5% piglets found with PRRSV antibodies). The subsequent phylogenetic analyses revealed high percentages of similarity between the PRRSV-1 strain detected in infected litters and the PRRSV-1 vaccine strain to which the study gilts had been previously exposed to. Health status analyses of trial piglets resulted in differences between litters from vaccinated sows and litters from non-vaccinated sows at 110th day of gestation as regards the number of weak-born piglets, mummies, and piglets with splay-leg and/or respiratory symptoms. The current study’s results indicate several potential dangers of the PRRS MLV vaccination in late gestation.

Field infection of a gilt and its litter demonstrates vertical transmission and effect on reproductive failure caused by porcine circovirus type 3 (PCV3)

BackgroundPCV3 is a member of the Circovirus family, associated with disease and mortality in pigs. It is not clear whether PCV3 putatively causes clinical symptoms and disease. In the present case, we reported a gilt infected with PCV3 associated with reproductive failures, vertical transmission, tissue lesions, viral replication by in situ hybridization, and the hypothesis that some strains of PCV3 clade one are associated with reproductive failures at the field level.Case presentationIn May 2019, a pig farm in Colombia reported increased reproductive failures, and the presence of PCV3 in gilts and sows was established in a single form or coinfections, mainly with PCV2 and PPV7. Ten sows with a single infection with PCV3 were found, and one gilt with a pre-farrowing serum viral load above 103 was studied. This gilt was followed up during the pre-farrowing, farrowing period and on her litter for 6 weeks. During dystocic farrowing, a mummy and ten piglets were released, including two weak-born piglets. The highest viral loads for PCV3 were found in the mummy and the placenta. In the weak-born piglets, there were viral loads both in serum and in tissues, mainly in the mesenteric ganglia and lung. Replication of PCV3 in these tissues was demonstrated by in situ hybridizations. PCV3 was also found in the precolostrum sera of piglets and colostrum, showing vertical transmission. The viral load in piglets decreased gradually until week six of life. The viral genome’s complete sequencing was made from the mummy, and its analysis classified it as PCV3 clade one.ConclusionsThis report confirms that PCV3 can cause disease at the field level, and putatively, in this case, we find the generation of reproductive failures. The ability of PCV3 to cause disease as a putative pathogen may be associated with the viral load present in the pig and the strain that is affecting the farm. For this case, we found that viral loads above 103 (4.93 log genomic copies / mL) in the gilt were associated with clinical manifestation and that some PCV3 strains belonging to clade one are more associated with the reproductive presentation.

Vaccination of Sows against Porcine Circovirus Type 2 (PCV2) in a Subclinically Infected Herd Does Not Impact Reproductive Performance

Porcine circovirus type 2 (PCV2) vaccination in piglets has become one of the crucial and indisputable procedures in modern swine production. The role of PCV2 vaccination in breeding animals is less explored. In the present study, the evaluation of the impact of sow vaccination on reproductive parameters was performed in a high health status, PCV2 subclinically infected herd of 3200 sows. The comparison of the number of liveborn, stillborn, and weak born piglets between groups of sows vaccinated on 1 or 28 days after weaning, or nonvaccinated, did not show any statistically significant differences. Although in the tested farm the vaccination of sows appeared to have no effect on reproductive performance, the results should not be generalized. Careful and individualized analysis of diagnostic and production data is crucial in economizing infectious disease control programs in sow herds and pig populations.

Isolation of PCV3 from Perinatal and Reproductive Cases of PCV3-Associated Disease and In Vivo Characterization of PCV3 Replication in CD/CD Growing Pigs

Porcine circovirus 3 (PCV3) has been identified as a putative swine pathogen with a subset of infections resulting in stillborn and mummified fetuses, encephalitis and myocarditis in perinatal, and periarteritis in growing pigs. Three PCV3 isolates were isolated from weak-born piglets or elevated stillborn and mummified fetuses. Full-length genome sequences from different passages and isolates (PCV3a1 ISU27734, PCV3a2 ISU58312, PCV3c ISU44806) were determined using metagenomics sequencing. Virus production in cell culture was confirmed by qPCR, IFA, and in situ hybridization. In vivo replication of PCV3 was also demonstrated in CD/CD pigs (n = 8) under experimental conditions. Viremia, first detected at 7 dpi, was detected in all pigs by 28 dpi. IgM antibody response was detected between 7–14 dpi in 5/8 PCV3-inoculated pigs but no IgG seroconversion was detected throughout the study. Pigs presented histological lesion consistent with multi systemic inflammation characterized by myocarditis and systemic perivasculitis. Viral replication was confirmed in all tissues by in situ hybridization. Clinically, all animals were unremarkable throughout the study. Although the clinical relevance of PCV3 remains under debate, this is the first isolation of PCV3 from perinatal and reproductive cases of PCV3-associated disease and in vivo characterization of PCV3 infection in a CD/CD pig model.

Porcine circovirus type 3 detection in a Hungarian pig farm experiencing reproductive failures.

Porcine circovirus 3 (PCV3) infection has been reported in piglets and sows with porcine dermatitis and nephropathy syndrome, reproductive failure, and cardiac and multisystemic inflammation. Few studies linked PCV3 infection to increased incidence of abortion and weak-born piglets. This is the first report of a detection of PCV3 Hungarian strain in several organs of aborted and weak-born piglets, including the thymus, lymph node, placenta, spleen, kidney and the liver. The tissue tropism of PCV3 in affected litters was analysed using real-time quantitative PCR, and the result showed the highest load of viral DNA in the thymus and lymph nodes. The ORF2 of Hungarian PCV3 strains was 524 nucleotides in length, and the sequence identity to GenBank sequences ranged from 98.5 per cent to 99.2 per cent. The results suggest that PCV3 may have a relevant role in reproductive failure in gilts.

Maternal dietary supplementation with ferrous N-carbamylglycinate chelate affects sow reproductive performance and iron status of neonatal piglets

Iron-deficiency anemia is a public health concern that frequently occurs in pregnant mammals and neonatal offspring. Ferrous N-carbamylglycinate chelate (Fe-CGly) is a newly designed iron fortifier with proven effects in iron-deficient rats and weanling piglets. However, the effects of this new compound on pregnant mammals are unknown. Therefore, this experiment was conducted to evaluate the effects of Fe-CGly on sow reproductive performance and iron status of both sows and neonatal piglets. A total of 40 large-white sows after second parity were randomly assigned to two groups (n=20). They were receiving a diet including 80 mg Fe/kg as FeSO4 or Fe-CGly, respectively, from day 85 of gestation to parturition. The serum (day 110 of pregnancy) and placentas of sows were sampled. Litter size, mean weight of live born piglets, birth (live) litter weight, number of live born piglets, and the number of still-born piglets, mummies, and weak-born piglets were recorded. Once delivered, eight litters were randomly selected from the 20 litters per treatment, and one new-born male piglet (1.503±0.142 kg) from each selected litter was slaughtered within 3 h after birth from the selected litters, without colostrum ingestion. The serum, longissimus muscle, liver and kidneys of the piglets were collected. The iron status of the serum samples and the messenger RNA level of iron-related genes in the placenta, liver and kidney were analyzed. The results showed that litter weight of live born piglets was higher (P=0.030) in the Fe-CGly group (19.86 kg) than in the FeSO4 group (17.34 kg). Fe-CGly significantly increased placental iron concentration (P<0.05) of sows. It also significantly increased iron saturation and reduced the total iron-binding capacity of piglets (P<0.05) at birth. However, the results revealed that supplementation of Fe-CGly in sows reduced liver and kidney iron concentration of neonatal piglets (P<0.05), indicating decreased iron storage. In addition, the concentration of iron in the colostrum was not significantly changed. Therefore, the present results suggested that replacement of maternal FeSO4 supplement with Fe-CGly in the late-gestating period for sows could improve litter birth weight, probably via enhanced iron transportation in the placenta.

Porcine circovirus type 2 associated reproductive failure in a specific pathogen free (SPF) piglet producing herd in Norway: a case report

BackgroundSince 1999, scientists have published evidence of transplacental infection by porcine circovirus type 2 (PCV2) and reproductive failure in pigs. Affected herds have frequently been start-up herds, either naïve or with a high proportion of PCV2 susceptible gilts. Here, delayed farrowing in non-vaccinated gilts was observed in a commercial specific pathogen free (SPF) herd. Mummified fetuses and stillborn piglets recovered from these gilts were PCV2 positive.Case presentationThe case herd was a self-recruiting, piglet producing unit of 240 sows. After detecting livestock associated methicillin resistant Staphylococcus aureus (LA-MRSA, CC398), stamping out was imposed by the authorities. An SPF herd was re-established and all dams were vaccinated against PCV2 until the farmer decided to exclude this vaccine. The first non-vaccinated batch consisted of 76% gilts. Here, one gilt showed signs of impending farrowing. This gilt was slaughtered three to four weeks after the expected farrowing date without having expelled any uterine contents. In the subsequent batch consisting of 79% gilts, three gilts showed similar clinical signs. Delayed farrowing was observed in two of these gilts and the uterine contents from the third gilt were recovered at the abattoir. Mummified fetuses and stillborn piglets were recovered from all three gilts. High levels of PCV2 DNA (>107 viral genomic copies/ 500 ng tissue) were found in myocardial samples by real-time PCR analysis. One myocardial sample submitted for immunohistochemical (IHC) analysis showed moderate amounts of PCV2 antigen. In the subsequent batch consisting of 77% gilts, several weak-born piglets were seen across different litters.ConclusionsThis case report describes an apparent link between in utero PCV2 infection, pre partum nest-building behaviour, mammary development and delayed farrowing. To date, no reports have described imminent signs of farrowing and delayed farrowing as clinical signs in conjunction with transplacental PCV2 infection in Norway. Reinitiation of PCV2 vaccination was strongly advised in this herd due to recent depopulation and repopulation and the high proportion of gilts. Vaccination was effective because no further cases have occurred since.

Farm characteristics and management routines related to neonatal porcine diarrhoea: a survey among Swedish piglet producers.

BackgroundIn recent years reports from a number of countries, including Sweden, describe problems with diarrhoea in newborn piglets despite the use of previously effective preventive measures. This seemingly altered disease pattern of neonatal porcine diarrhoea (NPD) warrants investigations on the magnitude and manifestation of the problem. The aim of the present study was to investigate the herd-level prevalence of NPD in Sweden and to describe disease characteristics and intervention strategies used in affected herds. To obtain this information a questionnaire was developed and sent out to 170 randomly selected herds. The presence of NPD in the herds was specified as “Yes”, “No” or “Occasional cases” during the preceding year.ResultsA response rate of 58% (98/170) was achieved. The total prevalence of farmer experienced NPD, including occasional cases was 79.6% (95% CI 70.6–86.4%). Most herds (85%; 83/98) employed maternal vaccination against enterotoxigenic Escherichia coli (ETEC). The most common treatment regimens used in affected herds included antimicrobials only (43%; 18/42) or antimicrobials in combination with supplementary fluids (33%; 14/42). Trimethoprim in combination with a sulphonamide was the drug of choice in 57% (24/42) of the affected herds whereas the remaining herds used a broad range of other antimicrobials (neomycin, amoxicillin, fluoroquinolones, penicillin, and tylosin). Furthermore, the risk of experiencing NPD was found to be higher in herds with >200 sows (OR = 4.0) compared to herds with <200 sows and in herds where more ambitious efforts (such as providing supplemental colostrum or practicing split-suckling) were made to save weak-born piglets (OR = 4.4).ConclusionsThe results of the present study indicate that Swedish farmers commonly experience NPD in their herds, often despite vaccination against ETEC. Considering the extent of this problem and its contribution to antimicrobial usage, improving alternative control strategies for NPD needs to be prioritized.Electronic supplementary materialThe online version of this article (doi:10.1186/s13028-016-0261-0) contains supplementary material, which is available to authorized users.

Pathological diagnosis of porcine circovirus-2 associated reproductive failure in pigs of Mizoram

Porcine circovirus type 2 is the primary causative agent of porcine circovirus associated disease which is characterised by acute systemic illness of the dam, abortion, mummified foetus, stillborn piglets or weak born piglets. The present study was conducted to investigate and better understand the presence of PCV-2 in the pig population in Mizoram. Detailed pathological examination on 18 aborted cases, 9 stillbirth cases and 5 neonatal cases revealed a significant gross lesions and histopathological findings. Based on Polymerase Chain Reaction analysis, 18.7% (6 out of 32 tissue samples collected from aborted, stillborn and weak born piglets) were found to be positive for the presence of PCV2.

Reproductive performance of sows with and without PRRS modified live virus vaccination in PRRS-virus-seropositive herds.

Porcine reproductive and respiratory syndrome (PRRS) virus infection causes reproductive failures including return to oestrus, abortion, mummified foetuses, stillborn, and weak-born piglets. The objective of the present study was to investigate reproductive performance of sows in PRRS-virus-seropositive herds with and without PRRS modified live virus (PRRS-MLV) vaccination. The study was conducted in 20 PRRS-virus-seropositive commercial swine herds in Thailand. The data included 211,009 mating and 180,935 farrowing records. The analysed variables included farrowing rate (FR), return rate (RR), abortion rate (AR), total number of piglets born per litter (TB), number of piglets born alive per litter (BA), percentage of stillborn (SB), percentage of mummified foetuses (MM), and number of piglets weaned per litter (WP). The results revealed that FR in non-vaccinated sows was lower than that in vaccinated sows (85.0 vs 89.7%, respectively, P < 0.001), and RR in non-vaccinated sows was higher than that in vaccinated sows (6.9 vs 3.7%, respectively, P < 0.001). AR did not differ significantly between non-vaccinated and vaccinated sows (1.6 and 2.0%, respectively, P = 0.964). TB (11.2 and 11.5, respectively, P < 0.001), BA (10.0 and 10.6, respectively, P < 0.001), and WP (9.2 and 9.6, respectively, P < 0.001) in non-vaccinated sows were lower than those in vaccinated sows. SB (6.9 and 5.1%, respectively, P < 0.001) and MM (3.2 and 2.2%, respectively, P < 0.001) in PRRS-MLV-vaccinated sows were higher than those in non-vaccinated sows. The improvement in sow reproductive performance in PRRS-MLV-vaccinated herds was most pronounced in gilts and primiparous sows.

Pathogenesis and prevention of placental and transplacental porcine reproductive and respiratory syndrome virus infection

Porcine reproductive and respiratory syndrome virus (PRRSV)-induced reproductive problems are characterized by embryonic death, late-term abortions, early farrowing and increase in number of dead and mummified fetuses, and weak-born piglets. The virus recovery from fetal tissues illustrates transplacental infection, but despite many studies on the subject, the means by which PRRSV spreads from mother to fetus and the exact pathophysiological basis of the virus-induced reproductive failure remain unexplained. Recent findings from our group indicate that the endometrium and placenta are involved in the PRRSV passage from mother to fetus and that virus replication in the endometrial/placental tissues can be the actual reason for fetal death. The main purpose of this review is to clarify the role that PRRSV replication and PRRSV-induced changes in the endometrium/placenta play in the pathogenesis of PRRSV-induced reproductive failure in pregnant sows. In addition, strategies to control placental and transplacental PRRSV infection are discussed.

Infektionsbedingte Fruchtbarkeitsstörungen in schweizerischen Schweinezuchtbetrieben am Ende der «Postweaning Multisystemic Wasting Syndrome» (PMWS)-Epizootie

Porcine Circovirus type 2 (PCV2) is able to induce reproductive failures. 286 fetuses from 113 sows of 59 farms with increased reproductive disorders which included abortions, mummies, stillborn and weak born piglets were studied six years after the beginning of the epizooty of postweaning multisystemic wasting syndrome (PMWS) in Switzerland. 14 % of the cases were bacterial infections based on histological signs of inflammation and pathogen isolation. 12 % further cases showed inflammatory reactions by histology without pathogen identification. PCV2 was identified in only 4 % of cases by immunohistochemistry (IHC). Thus, PCV2 infections are of minor importance in respect to pig reproductive failures in Switzerland. Porcine parvovirus (PPV) infections were found in 3 % of the cases and seem to occur more infrequently compared to former findings. Hitherto, Enteroviruses/Teschovirus were marginally studied in etiologically undefined cases with a prevalence of 11 %. To our knowledge this is the first identification of Enteroviruses/Teschovirus in fetal tissue from reproductive failures in Switzerland. The etiology remained unclear in more than 50 % of all cases in spite of modern diagnostic methods.

Porcine reproductive and respiratory syndrome virus (PRRSV) causes apoptosis during its replication in fetal implantation sites

Reproductive failure due to porcine reproductive and respiratory syndrome virus (PRRSV) is characterized by late-term abortions, early farrowing and an increase of dead and mummified fetuses and weak-born piglets. The mechanism of PRRSV-induced reproductive failure is poorly understood. Human pregnancies, complicated by some pathogens leading to reproductive disorders exhibit increased apoptosis in the fetal membranes. Because PRRSV-target cells are present in endometrium/fetal placentas from healthy sows and PRRSV-infected macrophages in other organs die by apoptosis, we hypothesized that PRRSV can replicate and induce apoptosis in the fetal implantation sites at the last stage of gestation. In the present study, identification, localization and quantification of the PRRSV-positive and apoptotic cells were performed in the fetal implantation sites. Three dams were inoculated intranasally with 10 5 TCID 50 PRRSV 07V063 at 90 days of gestation and sampled at 10 days post-inoculation. Two non-inoculated dams that were euthanized at 100 days of gestation served as control animals. Inoculation of the dams resulted in a viremia that lasted until the end of the study. Transplacental PRRSV spread was detected in all inoculated dams. Using immunofluorescence staining, single PRRSV-positive cells were found in the endometrial connective tissues adjacent to both PRRSV-positive and PRRSV-negative fetuses. In the fetal placental mesenchyme of the PRRSV-positive fetuses, infected cells were more abundant and spread focally. Double staining showed that all PRRSV-positive cells in the fetal implantation sites were positive for sialoadhesin and CD163. Apoptotic cells (TUNEL+) were detected in endometrium and fetal placentas of both non- and PRRSV-inoculated dams. The number of apoptotic cells was significantly higher in PRRSV-positive endometrium/fetal placentas. PRRSV caused apoptosis in infected cells since 20–61% of PRRSV-positive cells were apoptotic and in surrounding cells since 43–91% of the apoptotic cells were virus-negative. The main conclusion obtained from the present study is that PRRSV replicates in the fetal implantation sites and causes apoptosis in infected macrophages and surrounding cells at the last stage of gestation. The possible mode of PRRSV replication in the fetal implantation sites and the events that might contribute to the reproductive disorders are discussed.

Morphological Changes in the Lungs of Meconium-Stained Piglets

Meconium staining of the skin is a common event associated with fetal hypoxia, stillbirths, weak-born piglets, and neonatal mortality. Aspiration of meconium leads to meconium aspiration syndrome (MAS). This study was undertaken to assess the relationship between the degree of meconium staining of the skin at birth, meconium aspiration, and pulmonary changes in porcine neonates. A total of 353 farrowing sows and 3,693 born piglets were monitored during parturition and for 15 days after delivery. Umbilical cords were classified as normal or ruptured. Meconium staining in the skin was graded as nonstained, mildly, moderately, and severely stained. Mortality from birth to 15 days of age was 8.4%. The lungs from 60 meconium-stained piglets and 60 lungs from nonstained piglets were collected and microscopically examined for meconium aspiration and inflammation. Rupture of the umbilical cord was significantly higher (P < 0.01) in meconium-stained piglets. Microscopically, 32% and 40% of the lungs had evidence of meconium for the stained and nonstained groups, respectively. The microscopic grade of meconium aspiration and inflammatory cells was not different between nonstained and meconium-stained piglets. Aspiration of meconium induced a granulomatous response in the lungs. It was concluded that the grade of meconium staining is a good indicator of fetal hypoxia, but not a good predictor for meconium aspiration and MAS in piglets.

DNA Vaccination of Pigs with Plasmids Expressing the Nucleoprotein of PRRS Virus

Porcine reproductive and respiratory syndrome (PRRS) is an economically significant viral disease common in swine producing countries all over the world. The clinical parameters comprise late term abortions, stillborn, mummified and weak born piglets and interstitial pneumonia in neonatal and young pigs. In order to develop rational, efficient and safe ways to control the further spreading of the disease, the ability of the individual PRRS virus (PRRSV) proteins to induce protective immune responses must be elucidated. The aim of this project is to optimise DNA immunisation of pigs in order to use this vaccination technique to test the immunological abilities of the individual PRRSV proteins. For this the immunodominant nucleocapsid protein (N) from PRRSV has been used as model protein. We have compared two different DNA immunisation techniques (intradermal/intramuscular (ID/IM) injection and GeneGun immunisation), and tested the importance of the chosen administration route for GeneGun immunisation, comparing skin and mucosa as immunisation sites. The efficacy of three related plasmid vectors containing various amounts of immunostimulating CpG-sequences has also been investigated. Furthermore, the influence of the vaccinations on post challenge virus specific antibody titers has been followed. DNA immunisation with both techniques generated high N-specific antibody titers. However, the antibody response in the GeneGun immunised pigs arose earlier and resulted in higher titers than in the ID/IM immunised pigs. As administration route the tongue mucosa was observed to be of lower importance, while immunisation on the epidermis of the ear was very efficient. No significant difference in stimulation of the immune response was observed between the three vectors. Post PRRSV challenge control pigs showed a normal anti-viral antibody response, while the vaccinated pigs showed a more rapid anamnestic response with very high anti-viral antibody titers. We therefore conclude that the DNA immunisation technique has been well adapted for use in pigs and we now have a useful model to test the immunological abilities of the remaining PRRSV proteins.

In utero infection by porcine reproductive and respiratory syndrome virus is sufficient to increase susceptibility of piglets to challenge by Streptococcus suis type II.

Porcine reproductive and respiratory syndrome (PRRS) consistently elevates the frequency of disease and mortality in young pigs. Many different secondary bacterial diseases occur in PRRS virus (PRRSV)-infected pigs. However, to date, establishing a reproducible experimental model of PRRSV infection in weaned pigs, with subsequent clinical disease following secondary bacterial challenge, has been difficult. PRRSV is frequently isolated during outbreaks from weak-born piglets affected by secondary bacterial diseases. This study was performed to investigate the potential role of intrauterine PRRSV infection on piglet susceptibility to secondary bacterial infection. PRRSV-free pregnant sows were intranasally infected at 98 days of gestation with PRRSV strain SD 23983. All piglets born to the PRRSV-infected sows were viremic. Piglets were removed from the sows at birth and deprived of colostrum. Piglets from PRRSV-infected and noninfected sows were randomly assigned to Streptococcus suis challenge or control subgroups. At 5 days of age, piglets were challenged intranasally with strain MN 87555 of S. suis type II. Total and differential leukocyte counts were performed on blood samples collected at 3 days of age. The numbers of leukocytes, lymphocytes, and monocytes were significantly reduced in the PRRSV-infected piglets. Lesions were observed in bone marrow, brain, lung, heart, spleen, lymph node, tonsil, and thymus of PRRSV-infected piglets. Thymus/body weight ratios of in utero PRRSV-infected piglets were significantly reduced compared to those of non-PRRSV-infected piglets, and thymic lesions were characterized by severe cortical depletion of thymocytes. Lesions were not observed in piglets born to PRRSV-free sows. Overall, 20 out of 22 piglets in the PRRSV-S. suis dual-infection group died within 1 week after challenge with S. suis (10 of 11 in each of two trials). This contrasts with 1 of 18 piglets in the PRRSV-infection-only group and 5 of 23 piglets in the S. suis-challenge-only group (1 of 12 in trial 1 and 4 of 11 in trial 2). No piglets died in the uninfected control groups. Most of the piglets in the PRRSV-S. suis dual-infection group developed suppurative meningitis. S. suis type II was recovered from their brains and joints. These results indicate that in utero infection by PRRSV makes piglets more susceptible to infection and disease following challenge by S. suis type II. In utero infection by PRRSV may provide a useful model to study the interaction between PRRSV and bacterial coinfections in piglets.