Effect of challenge dose and age in experimental infection of pigs with encephalomyocarditis virus

Two experiments were performed to compare the severity of encephalomyocarditis virus (EMCV) infection in pigs. The pigs were challenged with the Greek myocardial strain, at different ages and with different doses. In the first experiment, nineteen susceptible pigs, 40 days old, were divided into three groups and were experimentally infected with 10(6) TCID(50), 10(4) TCID(50) or 10(2) TCID(50) of the Greek EMCV strain. In the second experiment, 10 susceptible pigs, of either 20 or 105 days, were divided into two groups according to age and were experimentally infected with 10(6) TCID(50) of the Greek EMCV strain. In addition, five piglets, each one the same age as its experimental group, were used as uninfected controls. No clinical signs were observed after infection, except a transient temperature rise in some pigs. Another important observation was the difference in mortality between groups. The survival rate of the 40-day-old pigs was inversely related to the viral dose. In these pigs, a positive association between the viral dose and the severity of macroscopical and histopathological lesions of the heart was also evident. Viral isolations from various organs of the challenged 40-day-old pigs increased with the increasing dose level. When challenged with 10(6) TCID(50) of EMCV, there was no difference in the fatality rate of the 20- and 40-day-old pigs, but none of the 105-day-old pigs died. The severity of the macroscopical and the histopathological heart lesions was inversely related to the age of the pigs. Furthermore, viral isolations from the various organs were higher in 20- and 40-day-old pigs than in the older ones. In 40-day-old pigs, neutralizing antibodies linearly increased as the dose increased. These antibodies were consistently lower in 20-day-old pigs. Viraemia, and nasal and faecal excretions were detected in all groups and lasted 1-3 days, except for the 105-day-old pigs whose symptoms lasted for an additional day.     

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.     

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.     

猪脑心肌炎病毒感染对iNOS mRNA转录水平的影响

为研究iNOS在猪脑心肌炎病毒(EMCV)致病机制中的作用,本研究将猪源EMCV GXLC株人工感染小鼠、仔猪,观察临床症状和病理变化,检测心、脑组织中iNOS mRNA转录水平。试验结果表明,小鼠和仔猪感染EMCV后均出现明显的临床症状、剖检及组织病理学变化显示心、脑组织的病理炎症分值显著增加;心、脑组织中的iNOS mRNA转录水平显著上调,并且转录水平上调的峰值与感染小鼠、仔猪出现明显临床症状、严重病理损害及小鼠死亡高峰存在明显的时间相关性,与心、脑组织的病理炎症分值成线性正相关。表明组织中iNOS的过量表达与感染动物的发病和死亡密切相关,iNOS在EMCV致病机制中发挥重要作用。     

Characterization of encephalomyocarditis virus isolated from aborted swine fetuses.

Characteristics of 2 encephalomyocarditis virus (EMCV) isolates (MN-25 and MN-30) recovered from aborted swine fetuses were examined along with 2 other swine isolates (NVSL-MDV and NVSL-PR) and a reference ATCC strain (VR-129). All 5 EMCV isolates were found to be serologically related by cross testing, using serum neutralization and fluorescent antibody assays. Hemagglutination (HA) properties of the 5 isolates were compared, using 5 diluents. The MN-25 and NVSL-MDV strains had HA activity with guinea pig RBC in all 5 diluents, whereas MN-30, NVSL-PR, and VR-129 had HA activity only in KCl-borate buffer. The HA ability with RBC of various animal species was examined, using KCl-borate diluent. All virus isolates had high HA titer (1:512 to 1:2,048) with guinea pig, rat, and horse RBC and lower HA titer (1:16 to 1:64) with sheep RBC. The MN-25 and NVSL-MDV isolates agglutinated dogs RBC, whereas MN-30, NVSL-PR, and VR-129 strains did not. Viral replication was evident in 8 of 10 cell lines tested, although infectivity titers of each virus varied by cell line used. Plaque-forming ability was similar for all 5 isolates, but plaque size was different by virus and cell culture used. Virus isolates were found to be stable after being heated at 56 C and subjected to a wide range of pH. A viral polypeptide pattern difference for all 5 isolates was not found by use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transplacental BVD virus transmission after experimental inoculation of goats in different pregnancy stages

Eight groups of altogether 25 goats without neutralizing antibodies against BVD virus, were inoculated either intranasally or intranasally and subcutaneously with two different BVD virus isolates during different stages of gestation. In all 18 goats inoculated within the first 78 days of gestation an abortion and foetal death rate of approximately 100% occurred. Only one goat gave birth to a clinically healthy kid. The other seven goats which were inoculated after the 78th day of gestation showed also a high foetal death rate. Only two of them gave birth to clinically healthy kids. Neutralizing antibodies against BVD virus could be detected in blood samples drawn from 14 kids born at normal term including stillborn and non-viable offsprings. BVD virus was reisolated from different organs taken from seven foetuses. It was not possible to isolate BVD virus from any of the normal offsprings.     

Transplacental infection following exposure of gilts to porcine reproductive and respiratory syndrome virus at the onset of gestation

Twenty-five gilts without measurable porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) serum antibody titres were used for this experiment. All of them were randomly assigned to one of the treatment groups at the time of artificial insemination. Twelve gilts were exposed to PRRSV, of these, six were slaughtered on day 10 after exposure and constituted group A. The remaining six were slaughtered on day 20 after infection and constituted group C. Thirteen gilts were used as controls, six of these were slaughtered on day 10 after treatment and constituted group B. The remaining seven were slaughtered on day 20 after treatment and constituted group D. The infected gilts were inoculated with PRRSV intranasally and intravenously in the ear vein. They were observed for clinical signs of infection and the effects on conception and fertilization rates were studied, while the gilts and their embryos were tested for PRRSV and homologous antibodies. The infected animals developed signs of PRRS associated with anorexia and slight pyrexia. Infection was verified by reisolation of the virus from serum and other tissue samples and also by seroconversion. Ten out of 12 infected gilts and 10 out of 13 controls were pregnant at the time of slaughter and the ratio of embryos to corpora lutea was the same in both, infected and control groups (0.75). Therefore, infection with PRRSV at the onset of gestation did not appear to interfere with conception and fertilization rates and subsequent pregnancy. The PRRSV was not isolated from any of the embryos collected at day 10 postexposure, but was present in 20-day-old embryos of group C gilts. In this group, 60% of litters were infected prenatally, with 16% of embryos infected. The proportion of dead embryos was three times greater than in control group D (35.4% and 9.8%, respectively). The results of this report indicate that exposure of susceptible gilts to PRRSV at the onset of gestation has no significant effect on conception and fertilization rates. However, although infection does not appear to have any effect on the embryos before implantation, it can result in transplacental infection and embryo death.     

Experimental infection in pigs with encephalomyocarditis virus

Non-suppurative myocarditis in pigs that were experimentally infected with encephalomyocarditis (EMC) virus is reported. Two of the four pigs that were infected with the virus died suddenly from myocardial failure, and all four had gross and microscopic changes consistent with EMC infection. This confirms the pathogenic potential of some strains of EMC virus for young pigs.     

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.     

Intratracheal inoculation as an efficient route of experimental infection with maedi-visna virus

Maedi-visna virus (MVV) spreads horizontally via the respiratory route. In order to establish an experimental mucosal infection route, we compared intranasal and intratracheal inoculation using the infectious MVV molecular clone KV1772-kv72/67. For intranasal infection 0.5 x 10(3)-0.5 x 10(7) TCID50 of virus was sprayed into the nostrils of the sheep. For the intratracheal infection 10(0)-10(6) TCID50 of virus was injected into the trachea. Successful infection was indicated by development of MVV specific antibodies and virus isolation over a period of 6 months. In the intranasal infection, only the sheep receiving the highest dose i.e., 0.5 x 10(7) TCID50, became infected, suggesting that intranasal application was not an efficient mode of infection. In the intratracheal infection, the sheep infectious dose 50% was 10(1) TCID50 and virus could be isolated from the central nervous system 4 months post infection with 10(4) TCID50. Therefore it is concluded that intratracheal infection is a very efficient route for experimental inoculation with MVV.     

Transplacental infection in mice inoculated with Getah virus

Transplacental transmission was demonstrated in pregnant mice subcutaneously inoculated with Getah virus. Viremia was shown in the infected dams, and high-titered virus was detected in the placenta and later in the fetus, suggesting virus invasion of the fetus through hematogenous infection of the placenta. High-titered virus was shown in the fetal brain and muscle and in the brain of the young dying soon after birth. Intrauterine infection resulted in a reduction of the litter size, number of young born alive and survival rate to 1 week of age. These results were further corroborated by necropsy performed several days after virus inoculation. The stage of gestation at the time of virus inoculation greatly influenced these results. Dams inoculated at 12 days of gestation delivered all dead babies, whereas virus inoculation at 5 days of gestation had no effect on the number of young born alive. The dams inoculated at 8 days of gestation had reduced litter sizes and those inoculated at 16 days of gestation produced slightly fewer live babies. Gestational stage at the time of virus inoculation also influenced viral growth in fetuses and placentas. The infection rate was low in dams inoculated at 5 days of gestation, high in dams inoculated at 8 or 16 days of gestation and 100% in dams inoculated at 12 days of gestation. High-titered virus was shown in placentas and fetuses of the dams inoculated at 8, 12 or 16 days of gestation. These results suggest that Getah virus may readily cross the placental barrier through hematogenous infection of the placenta in mice.     

Testicular changes observed in boars following experimental inoculation with pseudorabies (Aujeszky''s) virus.

Four boars were inoculated intranasally with pseudorabies virus to determine if microscopic testicular changes occurred as a result of infection. Testicular biopsies and semen samples were taken at two, four and six weeks postinoculation and the boars were castrated immediately after the last sample collection. Testicular samples and semen were cultured to determine if the virus was present. Pseudorabies virus was not isolated from the semen or testicular tissue. Virus was isolated from trigeminal ganglia at necropsy and from nasal swabs taken one day after castration. Consequently, a time of high risk for shed of the virus from clinically normal carrier animals is immediately following castration. Gross changes were not observed in testicular tissues and microscopic changes in the testicles were the result of biopsy. Lesions consistent with pseudorabies virus infection were observed in the central nervous system of all inoculated boars. Temporary lowered fertility may result from the effects of elevated body temperature on spermatogenesis during acute clinical disease. However, it appears that the strain of pseudorabies virus used, lacked the ability to infect and/or replicate in the boars' reproductive tracts.     

Porcine fetuses with pulmonary hypoplasia resulting from experimental swine influenza virus infection

Porcine fetuses between 51 and 57 days of gestation were inoculated intraallantoically with swine influenza virus and examined 3, 7, 13, 28 and 58 days after inoculation. At 3 and 7 days, severe epithelial necrosis was seen in most bronchial buds and there was moderate epithelial necrosis in more fully differentiated major bronchi. As a result of the epithelial injury, bronchial buds did not develop further and the surrounding mesoderm failed to differentiate. By 28 days, the lungs of inoculated fetuses were about one-half the size of the normal control lungs. Microscopically, the lungs of the inoculated fetuses were composed of major bronchi surrounded by multiple islands of cartilage, medium to large arteries and a few small, incompletely developed lobules. Influenza virus was isolated most consistently and in greatest quantity from the lung, trachea and chorion of inoculated fetuses. Influenza viral antigen was shown in the epithelium of bronchial buds, bronchi and the trachea by direct fluorescent antibody staining. Hemagglutination inhibiting antibodies to influenza virus were first found in the serum of an inoculated fetus at 13 days and in the sera of all inoculated fetuses at 28 and 58 days.     

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)     

Longevity of protective immunity to experimental bovine herpesvirus-1 infection following inoculation with a combination modified-live virus vaccine in beef calves

OBJECTIVE: To determine whether a combination viral vaccine containing modified-live bovine herpesvirus-1 (BHV-1) would protect calves from infection with a recent field isolate of BHV-1. DESIGN: Randomized controlled trial. ANIMALS: Sixty 4- to 6-month-old beef calves. PROCEDURE: Calves were inoculated with a placebo 42 and 20 days prior to challenge (group 1; n = 10) or with the combination vaccine 42 and 20 days prior to challenge (group 2; 10), 146 and 126 days prior to challenge (group 3; 10), 117 and 96 days prior to challenge (group 4; 10), 86 and 65 days prior to challenge (group 5; 10), or 126 days prior to challenge (group 6; 10). All calves were challenged with BHV-1 via aerosol. Clinical signs, immune responses, and nasal shedding of virus were monitored for 14 days after challenge. RESULTS: Vaccination elicited increases in BHV-1-specific IgG antibody titers. Challenge with BHV-1 resulted in mild respiratory tract disease in all groups, but vaccinated calves had less severe signs of clinical disease. Extent and duration of nasal BHV-1 shedding following challenge was significantly lower in vaccinated calves than in control calves. In calves that received 2 doses of the vaccine, the degree of protection varied with the interval between the last vaccination and challenge, as evidenced by increases in risk of clinical signs and extent and duration of viral shedding. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that this combination vaccine provided protection from infection with virulent BHV-1 and significantly reduced nasal shedding of the virus for at least 126 days after vaccination.     

The experimental infection of piglets with a porcine reovirus.

A strain (Quebec) of reovirus isolated from the faeces of a pig with dysentery was neutralised by reovirus type 1 antiserum. Four of eight hysterectomy-produced, colostrum-deprived (HPCD) piglets dosed orally with the third cell culture passage of the virus developed diarrhoea and showed focal areas of villous atrophy in the small intestine. The virus was isolated from the intestinal tract of all eight specific pathogen free piglets, but not from three control animals. Nine germ-free piglets dosed orally with the eight cell culture passage of the virus showed neither clinical signs nor lesions, but virus was recovered from their intestinal tracts for 14 days after infection. No virus was isolated from four control germ-free piglets.