Pathogenesis of in utero infection in porcine fetuses with porcine reproductive and respiratory syndrome virus.

Porcine fetuses were exposed in utero to porcine reproductive and respiratory syndrome virus (PRRSV) at stages of gestation ranging from 34 to 85 days and examined 17 to 31 days later to determine the effect of gestational age on fetal susceptibility. For each of the 8 litters tested during the study, all of the fetuses of 1 horn of the uterus were exposed to virus by intraamniotic injection; those of the other horn were exposed similarly to a sham inoculum that consisted of sterile cell culture medium. Viral infectivity titers associated with fetal tissues collected at necropsy indicated that, regardless of gestational age, the virus had replicated in fetuses exposed intraamniotically. In addition, virus had also spread and replicated in sham-inoculated littermates in 3 litters. On the basis of these findings it appears that there may be little or no temporal difference in fetal susceptibility to infection with PRRSV. If so, the lack of early fetal death as a commonly recognized feature of naturally occurring cases of PRRS may be due to a greater resistance of early gestational fetuses to the lethal effects of PRRSV, as suggested by this study, and/or a greater likelihood of transplacental infection during late gestation.     

In utero infection of swine fetuses with infectious bovine rhinotracheitis virus (bovine herpesvirus-1)

The pathogenesis of infectious bovine rhinotracheitis (IBR) virus (bovine herpesvirus-1) was studied in porcine fetuses after in utero inoculation. Laparotomies were performed on 8 seronegative pregnant sows at 34 to 86 days of gestation, and all fetuses in 1 uterine horn of each sow were exposed to IBR virus via inoculation into the amniotic sacs. Fetuses in the other horn served as controls. Clinical signs of infection were not observed in the sows, except for 2 sows that aborted at postinoculation days (PID) 11 and 15. Fetuses of the remaining 6 sows were collected at slaughter on PID 15 to 28. Fetuses were examined for gross abnormalities, presence of IBR virus in tissues, and the formation of neutralizing antibodies to IBR virus. Of 33 inoculated fetuses from 6 sows, 10 were mummified, 11 were hemorrhagic and/or edematous, and 12 were alive. Necrotic lesions were observed on the skin and in the liver of dead and live fetuses. Virus was recovered from 29 of 33 inoculated fetuses. Infectious bovine rhinotracheitis virus was isolated from fetal skin, liver, lungs, kidney, spleen, stomach contents, brain, amniotic fluid, and placenta. Virus was isolated from 4 of 11 fetuses recovered from 1 aborting sow. Antibodies to IBR virus were not detected in sera from the sows. However, antibodies were detected in 6 of 15 fetuses inoculated at 63 to 86 days of gestation and collected at slaughter at 86 to 112 days of gestation. The youngest fetus with detectable IBR antibody was estimated to be 74 days of gestation by measuring crown-rump length of the fetus.     

Prevalence and association of porcine circovirus type 2 (PCV2), porcine parvovirus (PPV) and porcine reproductive and respiratory syndrome virus (PRRSV) in aborted fetuses, mummified fetuses, stillborn and nonviable neonatal piglets

Porcine circovirus type 2 (PCV2) seems to cause reproductive failure in sows not only in experimental studies. A retrospective study was made with a total of 252 aborted fetuses, mummified fetuses, stillborn and nonviable neonatal piglets to determine the presence of PCV2, porcine parvovirus (PPV) and porcine respiratory and reproductive syndrome virus (PRRSV) by PCR. PCV2 was found in all stages of gestation in 27.1 percent of samples examined. A statistically significant association could be shown between the detection of PCV2 and PRRSV. However, no significant association was seen between the detection of PCV2 and PPV and between PPV and PRRSV.     

Pathogenesis of in utero infection: experimental infection of eight- and ten-week-old porcine fetuses with porcine parvovirus.

Selected numbers of fetuses in each of 4 pregnant gilts were exposed to a porcine parvovirus by injecting the virus into the allantoic fluid at gestation day 56 or 70. The fetuses were examined on postexposure day 7 or 14. When pregnancy was terminated, 2 of 15 exposed fetuses were dead. Several fetuses tested at post-exposure day 14 had hemagglutination-inhibiting antibodies to porcine parvovirus. Virus was detected most frequently and in highest concentration in the parenchymatous organs of thorax and abdomen of fetuses exposed on gestation day 56. A small amount of antigen was in neurons and capillary endothelium of cerebral and cerebellar cortexes.     

Experimental in utero inoculation of late-term swine fetuses with porcine circovirus type 2.

All 37 fetuses of 3 laparotomized pregnant sows at 86, 92, and 93 days of gestation were inoculated intramuscularly through the uterine wall with porcine circovirus type 2 (PCV-2). The sows were allowed to farrow, and blood and tissue samples were collected from their piglets before and after suckling colostrum. Thirteen fetuses from 2 sows at 90 and 103 days of gestation were used as controls. Of the 37 PCV-2 inoculated fetuses, 24 were grossly normal and 13 were mummified, stillborn, or weak-born at farrowing. Infection with PCV-2 was demonstrated in various tissues of grossly normal and abnormal fetuses by virus isolation, polymerase chain reaction, and immunohistochemical methods. Antibodies specific to PCV-2 were also detected from the sera or thoracic fluids of abnormal fetuses and unsuckled normal pigs. No evidence of PCV-2 infection was found in any control fetuses. The present results confirm previous findings that PCV-2 can infect late-term swine fetuses and may cause reproductive abnormalities.     

Border disease: virus persistence, antibody response and transmission studies

Three groups of five and one group of four oestrus-synchronised sheep were inoculated with Border disease (BD) virus at 52 +/- 2 days after their first service. Transmission of virus to offspring as demonstrated by virus isolation, detection of viral antigen and, or antibody response occurred in 12 of 19 sheep and probably in four others which aborted or produced stillborn lambs. Both apparently normal and clinically affected animals excreted virus in saliva, urine and faeces, and excretion and contact transmission to sheep and pigs persisted for up to two and a half years. Most of the tissues of infected sheep contained virus titres between 10(3.5) and 10(5.5) TCID50 per g. The immune response in the lambs varied, in some it began before birth, in others a transient or low level response was observed in the first or second year, while others remained serologically negative for two and a half years.     

猪繁殖与呼吸综合征病毒与猪圆环病毒2型共感染猪组织中猪繁殖与呼吸综合征病毒抗原的分布

猪繁殖与呼吸综合征病毒(PRRSV)和猪圆环病毒2型(PCV2)同时感染猪50 d后,用免疫组化方法观察PRRSV抗原的分布.结果显示,单感染和共感染组在肺脏、脾脏、胸腺、扁桃体、颌下淋巴结、腹股沟淋巴结、肠系膜淋巴结、回肠和直肠中均可观察到PRRSV抗原阳性信号,且信号强度无显著差异;抗原信号的细胞分布范围也无差异,主要位于结缔组织的巨噬细胞、单核细胞、成纤维细胞、内皮细胞和淋巴细胞中.     

猪流行性腹泻病毒及其卵黄抗体研究进展

猪流行性腹泻病毒是引起仔猪病毒性腹泻甚至死亡的关键诱因,而安全高效的抗猪流行性腹泻病毒卵黄抗体具有降低仔猪腹泻率、死亡率等优点已应用于生猪养殖。本文总结了近年来猪流行性腹泻病毒的致病机理及其卵黄抗体的制备与应用效果的研究进展,为卵黄抗体在防治猪流行性腹泻上的应用提供理论基础和技术指导。     

The Effects of in utero Viral Infection on Embryonic, Fetal, and Neonatal Survival: A Comparison of SMEDI (Porcine Picorna) Viruses with Hog Cholera Vaccinal Virus

SMEDI and hog cholera viruses were shown to have marked effects upon the survival of the embryo (from conception to 30 days of gestation), the fetus (from 30 days of gestation until birth), and the neonatal pig (from birth until five days after birth). Embryonic infection was characterized by death and absorption of the embryo and in some instances the return to estrus after an irregular estrous cycle. Embryonic infection also may have been responsible for the development of some abnormal pigs. Fetal infection caused death with mummification of one or more fetuses and occasionally all fetuses in the uterus. Infection established in early gestation produced effects on the fetus which apparently persisted until after birth and varied from a persistent viremia (as in hog cholera infection) to an undefined lack of resistance in the newborn (as in SMEDI virus infection). Hog cholera vaccinal virus was the more virulent of the two virus types and reacted somewhat like rubella virus, in that infection apparently could be established in the fetus even in middle trimester of pregnancy, and possibly later. SMEDI viruses, in contrast, were less virulent and were most pathogenic when the dam was infected during the first 30 days of pregnancy. Immunity against either virus could be established in the nonpregnant gilt and was most effective in preventing intrauterine infections with that virus. However, with as many as 10 enteroviruses (five are known to cause intrauterine infection) it was believed that maintaining a closed breeding herd and introducing new stock into contact with the breeding herd at least 30 days before breeding time might be a safer means of control.     

Investigation of T-cell responses and viral mRNA persistence in lymph nodes of pigs infected with porcine rubulavirus

Selected lymphocyte subpopulations were studied and the distribution of viral mRNA were investigated during acute and persistent porcine rubulavirus (PoRV-LPMV) infection in Vietnamese pot-bellied pigs. Six pigs infected with PoRV-LPMV at 17 days of age exhibited clinical signs 7-10 days post-inoculation (pi). One infected piglet died 11 days pi while the other five recovered around day 13 pi and survived until euthanasia on day 277 pi. Increased numbers of CD8+, CD4+ and CD2+ T cells were detected during the acute phase of infection while CD8+ cells were elevated throughout the infection, including during the persistent stage. Specific antibodies against the haemagglutinin-neuraminidase protein of PoRV-LPMV were detected during persistent infection. Although infectious virus could not be recovered from tissues from any of the infected pigs at necropsy 277 days pi, PoRV-LPMV mRNA was detected in lymph nodes, pancreas and central nervous system using a nested polymerase chain reaction technique. Continued lymphocyte interaction with viral RNA may be an important factor in promoting cellular and humoral responses during persistent PoRV-LPMV infection.     

Experimental in utero infection of pig foetuses with porcine parvovirus (PPV).

Pig foetuses of various gestational ages were exposed to experimental infection with porcine parvovirus (PPV) in utero. Inoculation of 40-, 50- and 60-day-old foetuses with PPV caused foetal death and mummification and spread of the infection to non-inoculated foetuses. Inoculation at 80 and 100 days gestation caused pathological lesions of various degrees whereas spread of infection occurred only sporadically. Serological examinations of foetuses of different ages suggest that immunocompetence for PPV develops before 70 days gestation. The present results strongly indicate that intrauterine spread of PPV is a route of transmission of this virus between pig foetuses.     

Detection of porcine reproductive and respiratory syndrome virus, porcine circovirus type 2, swine influenza virus and Aujeszky's disease virus in cases of porcine proliferative and necrotizing pneumonia (PNP) in Spain

Proliferative and necrotizing pneumonia (PNP) is a severe form of interstitial pneumonia characterised by hypertrophy and proliferation of pneumocytes type 2 and presence of necrotic cells within alveoli lumen. Many viral agents have been linked to PNP aetiology, with especial emphasis on porcine reproductive and respiratory syndrome virus (PRRSV). To gain knowledge on PNP causality, a retrospective study on 74 PNP cases from postweaning pigs from Spain was carried out. Coupled with histopathological examinations, the presence of porcine circovirus type 2 (PCV2) by in situ hybridization (ISH), and PRRSV, swine influenza virus (SIV) and Aujeszky's disease virus (ADV) by immunohistochemical (IHC) methods, were investigated. PCV2 was the most prevalent viral agent in PNP cases (85.1%) followed by PRRSV (44.6%); 39.1% of PNP cases showed PCV2 as the solely detected agent, while only 4.1% had PRRSV as the unique pathogen. SIV and ADV were very sporadically detected in PNP cases, and always in co-infection with PCV2. Therefore, present data indicate that PCV2 is the most important aetiological agent in PNP cases from Spain and that PRRSV is not essential for the development of PNP. Taking into account the presented results and available literature, we suggest that PCV2 is possibly the main contributor to PNP cases in Europe while PRRSV could play a similar role in North America.     

Pathogenesis of porcine reproductive and respiratory syndrome virus infection in mid-gestation sows and fetuses.

Two experiments were undertaken to evaluate whether porcine reproductive and respiratory syndrome (PRRS) virus was able to cross the placenta and infect midgestation fetuses following intranasal inoculation of sows and whether PRRS virus directly infected fetuses following in utero inoculation. In experiment 1, eight sows between 45 and 50 days of gestation were intranasally inoculated with PRRS virus (ATCC VR-2332), and four control sows were inoculated with uninfected cell culture lysate. Virus inoculated sows were viremic on postinoculation (PI) days 1, 3, 5, 7 and 9, shed virus in their feces and nasal secretions, and became leukopenic. Sixty-nine of 71 fetuses from principal sows euthanized on PI day 7, 14 or 21 were alive at necropsy and no virus was isolated from any of the fetuses. Two principal sows that farrowed 65 and 67 days PI delivered 25 live piglets and three stillborn fetuses. The PRRS virus was isolated from two live piglets in one litter. In experiment 2, laparotomies were performed on five sows between 40 and 45 days of gestation and fetuses were inoculated in utero with either PRRS virus alone, PRRS virus plus a swine serum containing PRRS antibodies, or uninfected cell culture lysate. Three sows were euthanized on PI day 4 and two sows on PI day 11. Viral replication occurred in fetuses inoculated with virus alone and was enhanced in fetuses inoculated with virus plus antibody. No virus was isolated from control fetuses.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of long-term antibody responses to two inactivated bovine viral diarrhoea virus (BVDV) vaccines

The aim of the present study was to determine the serological response of heifers after vaccination with two inactivated bovine viral diarrhoea virus (BVDV) vaccines by means of various ELISA tests. Three dairy farms were selected from the Galicia region of Spain. In each herd, a batch of heifers to be vaccinated for the first time was selected and followed for 15 months. Heifers from farm 1 (n = 25) were vaccinated with Vaccine A, whereas heifers from farm 2 (n = 16) were vaccinated with Vaccine B. Heifers from farm 3 (n = 17), where no BVDV vaccines were used, acted as controls. Blood samples were analyzed periodically for BVDV antibodies, using five commercial ELISAs, based on BVDV p80 antigen or whole virus.At the end of the study, none of the animals vaccinated with Vaccine A seroconverted according to p80 antibody status, whereas up to 80% tested positive by ELISA against whole virus antigen. For the animals vaccinated with Vaccine B, 2/16 animals seroconverted according to p80 antibody ELISAs, whereas all had seroconverted according to the ELISA against whole virus antigen. In most cases, based on the use of ELISAs to detect specific antibodies against the p80 protein, at 15 months post-vaccination with inactivated BVDV vaccines the responses did not seem to interfere with detection of antibody to BVDV infection. However, the finding of a small proportion of vaccinated animals seropositive against BVDV p80 antigen suggests that antibodies that interfere with diagnosis of BVDV infection within the herd could exist, even when using p80 ELISAs.     

猪病毒性腹泻(PED)疫苗免疫后母猪乳汁中PEDV IgA消长动态

为了解猪病毒性腹泻(PED)疫苗免疫后母猪乳汁中IgA抗体消长规律,筛选100头妊娠母猪,平均分为5组(4个试验组和1个对照组),采用猪流行性腹泻病毒(PEDV)-猪传染性胃肠炎病毒(TGEV)-猪轮状病毒(PoRV)三联弱毒疫苗(PTR)和PEDV-TGEV二联灭活疫苗(PT)进行不同的免疫。其中,试验Ⅰ组产前40d和产前20d免疫PTR,试验Ⅱ组产前40d和产前20d免疫PT,试验Ⅲ组产前40d免疫PTR和产前20d免疫PT,试验Ⅳ组产前40d免疫PT和产前20d免疫PTR,对照组产前40d和产前20d注射生理盐水。通过PEDV IgA抗体检测试剂盒分别检测母猪分娩后0,1,2,3,5,7,10,14d各组乳汁中特异性PEDV IgA抗体水平。结果显示,试验组IgA水平明显高于对照组,其中试验Ⅰ、Ⅱ组与试验Ⅲ、Ⅳ组间差异极显著(P<0.01),而试验Ⅰ、Ⅱ组间以及试验Ⅲ、Ⅳ组间差异不显著(P<0.05)。结果表明,产前40d和产前20d交替使用PTR和PT的抗体滴度明显优于单一接种PTR或PT的抗体滴度。其中只注射PTR母猪分娩后10d乳汁对仔猪没有保护力,注射PT母猪分娩后7d乳汁对仔猪没有保护力。通过本试验基本上了解了PEDV母源抗体消长规律,为今后规模化猪场制定免疫程序提供理论支持。