Experimental production of congenital persistent swine fever infections: II. Effect on functions of the immune system

Twelve pregnant sows were infected at various stages of gestation with a low-virulent field strain of swine fever (SF) virus. The sows developed neutralizing antibody in serum, colostrum and milk.Only one pig had antibody to SF virus at birth. Twenty-three congenitally infected pigs developed a persistent viraemia. In the plasma samples of these pigs, neither antibodies nor virus-antibody complexes were detected after the disappearance of maternal antibodies.The persistently infected pigs showed a normal antibody response against sheep red blood cells, except in the terminal stage of disease. These observations indicate immunological tolerance to SF virus in these pigs. Immunological tolerance was also induced in pigs which had been infected in utero after the onset of immune competence.The lymphocyte response to phytohaemagglutinin seemed to be slightly depressed in the persistently infected pigs, whereas the response to pokeweed mitogen was comparable with that of control pigs.A clear, cell-mediated immune response to SF virus could not be demonstrated by the lymphocyte stimulation test.Three pigs that were born uninfected did not produce neutralizing antibody following natural exposure from in-contacts, whereas the littermates did. These pigs appeared to be sensitized when challenged with virulent SF virus.     

The influence of experimental Yersinia enterocolitica infection on the pregnancy course in sows--preliminary studies. III. Histopathological lesions

The aim of the study was to evaluate the anatomo- and histopathological lesions in internal organs of sows and their stillborn piglets after experimental Y. enterocolitica infection in different phases of pregnancy. Twelve pregnant sows were divided into 4 groups, infected per os on 33 (n = 3), 54 (n = 3) and 89 (n = 3) day of pregnancy with the pathogenic Y. enterocolitica strain isolated from the aborted swine fetus, and uninfected control group. Histopathological examinations of internal organs and intestine samples of stillborn piglets, slaughtered sows and samples of placentas were performed. Anatomo- and histopathological lesions were the most intense in the group of sows infected in the final phase of pregnancy, where the highest number of stillborn piglets was also found. Lesions of internal organs in stillborn piglets suggested a severe generalized bacterial infection. Although the analysis of experimental Y. enterocolitica infection of pregnant sows revealed that the most intense clinical, anatomopathological and histopathological abnormalities were recorded in the group of animals infected in the final phase of pregnancy. Infection in the first phase of pregnancy could have had an influence on the formation of the granulomatous inflammation. Differences in anatomopathological lesions between infected and control animals suggest that the period of pregnancy in which the infection appears could have had an influence on the course of yersiniosis in pigs.     

Strongyloides ransomi: prenatal and transmammary infection of pigs of sequential litters from dams experimentally exposed as weanlings.

Prenatal infection of pigs with Strongyloides ransomi occurred in 12% of 104 pigs and in 14% of 21 litters farrowed by 13 sows experimentally exposed to infective larvae as weanlings. Transmammary passage was observed in 38 of 39 litters studied. Milk samples obtained from 14 sows showed that larvae were usually shed in the colostrum within 24 hours after farrowing; however, larvae were recovered from samples of milk of sows up to 20 days after parturition. Larvae were recovered from milk samples obtained after each parturition up to the fourth. Prenatal infection in pigs was not detected after the 1st litter.     

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)     

Studies of transplacental and perinatal infection with two clones of a single Aujeszky's disease (pseudorabies) virus isolate

The effect of Aujeszky's disease virus (ADV) infection in the last third of gestation was studied using two clones from an ADV isolate. Twelve sows were infected with one or other clone at 85 +/- 1 days of gestation. The dose of infection was 5 X 10(6) TCID50 per sow. The clinical and serological responses to the infection were different. One clone, Ls-1, produces a severe and acute illness. The course of the disease went from 9 to 14 days while the other clone, Ls-2, caused a mild or silent infection and for a shorter time. Transplacental infection occurred in only one sow which had been infected with Ls-2. The litter consisted of 8 mummified fetuses. Sows infected with Ls-1 produced piglets or mummified fetuses that were virus-negative. Perinatal infection was found in litters from both groups. Colostrum-deprived piglets that did not have postpartum contact with the sow, produced specific antibodies, 2 out of 6 born to sows infected with Ls-1 and 1 out of 4 born to sows infected with Ls-2. The antibody titers in colostrum-fed piglets were related to the extent of clinical response of the sows to the infection. Litters born to sows infected with Ls-1 had mean SNT titers from 1/12 to 1/112 while litters born to sows infected with Ls-2 showed titers of 1/2 or less than 2.     

Pathologic consequences of a severe influenza outbreak (swine virus A/H1N1) under natural conditions in the non-immune sow at the beginning of pregnancy

Pathological consequences of a severe outbreak of swine influenza (H1N1 virus) in the non immune sow at the beginning of pregnancy, under natural conditions. A sudden acute outbreak of fever, depression, anorexia and coughing in a group of nulliparous sows from a herd that was currently under epidemiological investigation lead to build a particular disposal of observation. The clinical signs were daily recorded including rectal temperature. Blood was taken from the sows at the beginning of the troubles and 3 weeks later for the detection of Aujesky's disease, coronavirus TGE-like, Influenza viruses A/H1N1 and A/H3N2 and Mycoplasma hyopneumoniae. Viral detection was attempted from nasal swabs and aborted fetuses during the acute phase. The clinical study showed fever reaching near 41 degrees C on most of the pigs and lasting usually from 2 to 5 days. The diagnosis of Influenza (virus swine H1N1) was established both on serology (massive seroconversion) and on the detection of the virus from the nasal swabs and from an aborted fetus. The control of the lungs of sows "not in pig" and culled showed extended lesions of bronchopneumonia and Pasteurella multocida was found. The technical consequences of this severe outbreak of Influenza on reproduction were mainly important at the beginning of pregnancy. Over 13 sows inseminated less than 1 week before the outbreak, only 3 farrowed (respectively 5.5 and 12 piglets); 7 returned to oestrus and 3 "not a pig" at 21 days (echotomography) did not show signs of heat and were culled. Over 8 pregnant sows (1 month of pregnancy), 6 farrowed normal litters and total embryonic resorption occurred in 2 sows. Over 18 pregnant sows (more than 45 days gestation) one aborted.     

Preweaning mortality risks and recorded causes of death associated with production factors in swine breeding herds in Japan

Preweaning mortality risks, recorded death reasons and related factors for preweaning mortality were studied in 105 breeding herds. Preweaning mortality risk at the herd level was calculated as the difference between the number of pigs born alive in farrowed litters and the number of weaned pigs divided by the number of pigs born alive in litters that farrowed and weaned. The mean of annual preweaning mortality risk was 10.7%. In regression analysis, higher mortality risks were associated with higher parity at farrowing, greater numbers of pigs born alive, and longer lactation length. The period from July to September had a higher mortality risk than that from April to June. The means of cause-specific proportional mortality ratios (PMR) in trauma with low viability and scours were 80.4 and 6.2%, respectively. Sows with pig age 0-1 day during lactation had the highest daily PMR. Sows with pig age 0 to 7 days had higher PMR due to trauma and low variability than those with pig age 8 days older. Sows with pig age over 7 days had higher PMR due to scours than those with pig age 0-7 days. Careful management at farrowing and in early lactation on high parity sows with large litters should be considered to prevent piglets from death due to trauma and low viability, and appropriate herd health programs should be implemented for reducing preweaning mortality due to scours during late lactation.     

Plasma concentrations of steroid hormones in sows infected experimentally with Leptospira pomona or porcine enterovirus strain T1 in late gestation

Plasma levels of progesterone, corticosteroids and oestrone were determined during the late stages of pregnancy in four sows experimentally infected with Leptospira pomona and in a group of three sows in which fetuses were inoculated in utero with a strain of porcine enterovirus. Only one of the seven infected sows farrowed at full term. All fetuses were dead and delivery was prolonged in litters infected with the virus. In the sows with leptospirosis almost all piglets were expelled dead or in a weak condition. The amounts of progesterone in plasma were within the normal range and showed a decrease shortly before abortion similar to that observed before parturition in normal animals. The elevation in plasma corticosteroids at normal parturtion was not seen at abortion. An irregular pattern with rising levels of plasma oestrone was found in most sows. Peak levels of oestrone were usually reached close to the time of delivery, but occured earlier in most sows which aborted well before term. In conclusion differences were noted between the endocrine patterns in normal parturition and in abortion caused by infectious agents in sows.     

Reproduction of postweaning multisystemic wasting syndrome in pigs by prenatal porcine circovirus 2 infection and postnatal porcine parvovirus infection or immunostimulation

Postweaning multisystemic wasting syndrome (PMWS) was reproduced in prenatally porcine circovirus 2 (PCV2)-infected pigs by either postnatal infection with porcine parvovirus (PPV) or by immunostimulation. Twenty-four randomly selected piglets from 3 sows, which had been experimentally infected during gestation with PCV2, were randomly divided into 3 groups; group 1 (prenatal PCV2 infection, with postnatal PPV infection), group 2 (prenatal PCV2 infection, with postnatal keyhole limpet hemocyanin, emulsified in incomplete Freund's adjuvant [KLH/ICFA] injection), and group 3 (prenatal PCV2 infection only). Twenty-four randomly selected piglets from 3 uninfected sows were randomly divided into 3 groups; group 4 (no prenatal infection, with postnatal PCV2 and PPV infection), group 5 (no prenatal infection, with postnatal PCV2 infection), and group 6 (negative control pigs). Body weight in negative control pigs (group 6) was increased significantly compared with pigs in groups 1, 2, and 4 at 49, 52, 56, 59, and 63 days of age. The granulomatous inflammatory reaction and lymphoid depletion that are typical lesions in pigs with PMWS were observed in the lymph node of piglets in groups 1, 2, and 4 at 63 days of age. Pigs in group 3 had significantly fewer PCV2-positive cells than those from groups 1, 2, 4, or 5. When the prenatally PCV2-infected pigs were infected with PPV or injected with immunostimulant in the postnatal period, they developed PMWS. Thus, factors that potentiate the progression of prenatal PCV2 infection to PMWS are postnatal infection with PPV or immune stimulation.     

Natural transmission of group A rotavirus within a pig population

Five litters of piglets born within two days of each other, together with their dams, were investigated for faecal excretion of group A rotavirus antigen from birth to two months old. All the 50 piglets in these litters became infected with the virus between 19 and 35 days old. Rotavirus excretion was first seen in one litter which was housed with other litters not included in this study. Two days later, piglets of the second litter in another farrowing room began to excrete rotavirus, and then infection spread to the other three litters in the same room. Within each of these litters, one or two piglets were infected early and thereafter infection spread to other piglets. It took four to 10 days for rotavirus to infect every piglet within a litter, and 16 days in total before all piglets in the five litters were infected. No rotavirus antigen was demonstrated in faeces from sows during the investigation period.     

Effect of season and outdoor climate on litter size at birth in purebred landrace and yorkshire sows in Thailand

The objective of the present study was to retrospectively investigate causes of variation on litter size at birth (total number of piglets born per litter (TB) and number of piglets born alive per litter (BA)) of Landrace (L) and Yorkshire (Y) sows in swine nucleus herds in Thailand. The data included sows farrowed during a four-year period from January 1998 to December 2001. The analyzed data set included observations on 8020 litters from 2199 L sows and 6919 litters from 1680 Y sows. Analysis of variance (ANOVA) was applied for statistical analyses using General Linear Mixed Model (MIXED) procedure of SAS. No breed difference was found for both TB and BA. Farrowing months significantly influenced TB and BA (P<0.001). Sows farrowed in August and September had a lower BA than sows farrowed from November to June (P<0.05). Effect of farrowing months on both TB and BA was more pronounced in primiparous compared with multiparous sows. Average minimum daily temperature during gestation negatively correlated with both TB and BA, average maximum daily temperature during gestation negatively correlated with BA and average daily humidity during gestation negatively correlated with both TB and BA. The correlations were stronger in L than in Y sows.     

Prevalence of Streptococcus suis types 1 and 2 in domestic pigs in Australia and New Zealand

Using an indirect fluorescent antibody test, 54 per cent of 734 palatine tonsils of conventional pigs slaughtered in Australia and New Zealand were found to be infected with Streptococcus suis type 1 and 73 per cent of 959 were infected with S suis type 2. Variations in the prevalence of infection in pigs from different herds were thought to be due to differences in the sample sizes rather than to real differences in the prevalence between herds. The prevalence of infection with S suis was similar in pigs of either sex and in different age groups. Streptococcus suis type 2 was detected in the blood of 3 per cent of apparently normal pigs slaughtered at a meat processing plant. The presence of this organism in edible tissue may pose a health risk to consumers and meat-workers. Both S suis types 1 and 2 were detected in the vaginas and uteri of slaughtered pigs and the female reproductive tract could be another site for the carriage of infection. Piglets from sows with vaginas infected with S suis type 2 became infected earlier than piglets from sows with uninfected vaginas. No infected male reproductive tracts were detected and venereal transmission of S suis therefore appears unlikely. Three specific pathogen free herds were found to be free from infection with both S suis types 1 and 2. It is concluded that hysterectomy derived piglets are delivered free from infection, whereas some piglets born to sows with uterine and vaginal infections are either born infected or become infected at, or soon after, birth.     

太湖猪高产综合技术研究试验

本文系对103头360窝太湖猪的繁殖性能进行系统研究。结果是60头母猪在6个繁殖周期中共繁殖360窝,平均繁殖周期158.33天,年产仔2.31胎。窝产仔16.35头,活仔15.10头,35日龄断奶育成14.44头,窝重83.48公斤。每头母猪年产仔37.69头,年产活仔34.81头,年提供断奶仔猪33.29头。其中窝产仔达到18头以上,出现1胎或连续4胎高产的母猪69头,占试验母猪群66.99％。     

Ivermectin for the control of swine scabies: relative values of prefarrowing treatment of sows and weaning treatment of pigs

Ivermectin given in a single subcutaneous dose (300 micrograms/kg of body weight) was tested for activity against swine scabies (Sarcoptes scabiei). Efficacy was determined by recoveries of mites from ear scrapings and by observations of clinical signs. Treatment of infected sows 8 to 37 days before farrowing eliminated scabies from the sows and prevented its transmission to their offspring. Pigs farrowed by ivermectin-treated sows remained noninfected throughout the study regardless of whether they were treated with ivermectin at weaning. Placebo-treated sows remained infected and transmitted scabies to their offspring. Ivermectin treatment of pigs at weaning eliminated the infection, whereas placebo treatment did not. The placebo-treated pigs remained infected while in the nursery, but ivermectin treatment eliminated the infection when they were moved to the growing and finishing floor at 12 weeks of age. It appears that an effective control program for swine scabies using ivermectin could be based on a single treatment of the sows before farrowing. Any infection (epizootic) appearing in growing pigs could be controlled by a single treatment of all in-contact pigs.     

猪瘟病毒持续感染对母猪繁殖性能及仔猪猪瘟疫苗免疫效力的影响

利用来源于同一猪场的2头猪瘟病毒(HCV)持续感染的带毒母猪及所产35头仔猪(包括13头死胎)和6头阴性对照猪,观察母猪的胎儿发育成活状况、仔猪HCV带毒率及HCV垂直传播对仔猪猪瘟兔化弱毒疫苗(HCLV)免疫效力的干扰作用,同时进行水平传播试验和观察HCV持续感染对母猪繁殖功能的影响。结果表明：HCV持续感染对其中1头母猪的胎儿发育和成活有明显影响,而对另1头母猪的胎儿发育没有明显影响;HCV持续感染母猪可经过胎盘垂直传播病毒给仔猪,传播率达45％～86％;吃初乳和接种HCLV不能阻止带毒仔猪的死亡,9头带毒仔猪在45d内死亡4头;免疫HCLV不能使带毒仔猪产生免疫保护力。5头猪在强毒攻击后死亡4头;HCV垂直传播的带毒猪可发生水平传播,并引起3／4感染猪死亡;HCV持续感染可引起母猪生殖系统病理变化。导致繁殖障碍。     

Experimental reproduction of swine infertility and respiratory syndrome in pregnant sows.

The purpose of this study was to experimentally reproduce swine infertility and respiratory syndrome (SIRS). Six multiparous sows were intranasally inoculated at 93 days of gestation with lung homogenates from clinically affected pigs, and 3 additional sows were similarly inoculated with a virus isolated in cell culture from the lung homogenate (SIRS virus, isolate ATCC VR-2332). Inoculated sows developed transient anorexia, farrowed up to 7 days prematurely, and delivered a mean of 5.8 live pigs and 6.0 dead fetuses/litter. Clinical signs of disease were not observed in 3 sham-inoculated control sows that delivered a mean of 12.7 live pigs and 0.3 stillborn fetuses/litter. The SIRS virus was isolated from 50 of 76 live-born and stillborn fetuses from the 9 infected litters. Virus was not isolated from 26 autolyzed fetuses or 15 control pigs. Six of 9 inoculated sows developed neutralizing antibodies to SIRS virus. The reproductive effects found in these experiments were identical to those found in field cases. On the basis of our findings, virus isolate ATCC VR-2332 causes the reproductive failure associated with SIRS.     

Ovarian hemangioma in swine

Eighteen (3.9%) ovarian hemangiomas were diagnosed in a survey of reproductive disorders in 460 sows from two to eight years of age during a three-year study. Ovarian hemangiomas only were observed in sows aged over 30 months, and no such neoplasms were found in 42 gilts. The incidence of ovarian hemangioma was highest at five to eight years of age. Of the 18 sows with ovarian hemangioma, one was purebred and 17 were crossbred pigs; of these, twelve had farrowed 12 to 15 litters, four had farrowed six to 11 litters and two had farrowed three litters. All 18 sows with ovarian hemangioma had one or more clinical signs related to reproductive disorders including small litter size, agalactia, fertilization failure, fetal death, silent estrus, anestrus, abortion, and stillbirth. The pathological features of the neoplasms in sows were similar to those described previously in swine and in man. Spontaneous ovarian hemangioma might provide a model for investigation of the etiology and pathogenesis of ovarian hemangioma in man.     

Maternally-derived antibodies to porcine parvovirus and their effect on active antibody production after vaccination with an inactivated oil-emulsion vaccine

Two sows which had been vaccinated with an oil-emulsion porcine parvovirus vaccine, and had developed high haemagglutination-inhibiting antibody levels to the virus, farrowed three successive litters each, a total of 74 piglets. Serum samples from these piglets were tested for haemagglutination-inhibiting antibody at birth, three and 17 days after birth, and at monthly intervals thereafter to study the decline of maternally-derived antibody. Regression curves were constructed from the data to show the projected pathway (mean and 95 per cent tolerance limits) of the decline of maternally-derived antibody. Approximately half the pigs still had positive titres of up to 1/160 at six months old, and traces of antibody were detected in a few pigs at nine months. Thus, even at the onset of breeding some gilts can have maternally-derived antibody which may interfere with their ability to develop active immunity to porcine parvovirus. From the same litters three groups of 12 pigs were selected randomly and were vaccinated with a single dose of the oil-emulsion vaccine at 70 days, 130 days or 190 days respectively. Despite the presence of moderate to high titres of maternally-derived antibody, especially in the younger pigs, all of those vaccinated showed strong and long lasting antibody responses to the vaccine. High serum antibody titres at the time of vaccination seemed to depress the response to the vaccine slightly but the effect was not statistically significant. These results have important implications for prevention of reproductive failure induced by porcine parvovirus.     

Induction of lactogenic immunity to transmissible gastroenteritis virus of swine using an attenuated coronavirus mutant able to survive in the physicochemical environment of the digestive tract.

A transmissible gastroenteritis (TGE) coronavirus mutant (188-SG), selected as attenuated and resistant to acidity and proteases of the digestive tract of adult pigs, was used as vaccine ("Nouzilly strain") in sows to protect suckling piglets against a challenge exposure carried out with a highly virulent TGEV strain. The pregnant sows were immunized once (42-49 days before farrowing) or twice (42-49 and 7-15 days before farrowing) by the oral, intramuscular or conjunctival route with the 188-SG strain. Sows exposed to virulent TGEV in the field and experimentally infected sows (two oral inoculations during pregnancy) were used as positive controls leading to high protection. The neutralizing antibody response to vaccination and/or infection was studied in serum and milk. No protection against mortality was observed in the litters of (1) the nine seronegative, susceptible sows, with piglet mortality of 65/70, (2) the seven once orally vaccinated sows, with mortality of 44/54, (3) the seven sows vaccinated twice by the conjunctival route, with mortality of 55/76. Moderate protection was observed in (1) the eight sows vaccinated intramuscularly twice with piglet mortality of 36/90, (2) the seven orally and intramuscularly vaccinated sows with piglet mortality of 31/51. In of 3 contrast, improved protection was observed in (1) the 10 sows vaccinated twice orally, with piglet mortality of 23/95, (2) the four naturally infected sows with piglet mortality of 6/41, (3) the six sows experimentally infected with virulent TGEV with piglet mortality of 1/59. No correlation was found between neutralizing antibodies titers in serum and milk and protection rate of the piglets. The results indicate that relative protective lactogenic immunity against TGEV is induced only by repeated ingestion of the attenuated 188-SG strain of TGEV.     

不同年龄猪群中猪瘟抗体监测及免疫效果分析

为制订合理的猪瘟免疫程序,本研究采用正向间接血凝试验(IHA)对某规模化猪场进行猪瘟免疫监测和分析。结果表明:猪瘟母源抗体的合格率、抗体效价平均值均存在随着仔猪日龄的增长而呈逐渐下降的趋势;35 d～40 d仔猪母源抗体的合格率达78.79%、抗体平均效价为5.97 Log2;仔猪35 d～40 d实施猪瘟首免,其一免抗体合格率和抗体效价均比20 d首免有所提高;同一窝仔猪的猪瘟母源抗体,有11%窝次的猪差距在3个～8个滴度;母猪猪瘟免疫抗体的合格率,一胎母猪稍低,其它经产母猪基本接近;猪瘟抗体效价的平均值随胎龄增加而升高,并且抗体的离散度则随胎龄增加而缩小。因此,在母猪实施与仔猪同时免疫的猪场,40日龄左右是较佳的首免日期。