Experimental production of congenital persistent swine fever infections: I. Clinical,pathological and virological observations

Twelve sows were inoculated with a low-virulent field strain of swine fever (SF) virus at 40, 65 and 90 days of pregnancy. Transplacental infection occurred in eight sows and these farrowed 88 piglets.Prenatal mortality was highest in litters from sows infected at 40 days after service, and postnatal death was most frequent in litters from sows infected at 65 days. Three sows gave birth to completely infected litters, whereas the five others farrowed litters in which uninfected piglets were found. The later the sows were infected during pregnancy, the more uninfected piglets were born. Twelve piglets recovered from the infection and the percentage of recoveries increased with the stage of pregnancy at which inoculation took place. Twenty-three piglets developed a persistent infection. The earlier infection occurred during pregnancy, the more persistent infections were produced. The persistently infected pigs developed a runting syndrome from about one week after weaning. The clinical signs were more severe in pigs from sows infected at 65 days of pregnancy than in pigs from sows infected at 40 days. A persistent viraemia was present in these pigs with titres ranging between 10^5.7 and 10^7.0 plaque forming units/ml of plasma. At autopsy the most pronounced lesions were an atrophy of the thymus, and swollen and pale lymph nodes. Virus antigen was present in lymphoidal, reticulo-endothelial and epithelial tissues.One persistently infected pig survived superinfection with a virulent strain of SF virus for 45 days.     

A congenital persistent swine fever infection. II. Immune response to swine fever virus and unrelated antigens

After the disappearance of maternal antibodies, no antibodies were detected in five pigs that were congenitally infected with the Bergen strain of swine fever virus. The pigs lived for 2–11 months. One pig showed low levels of precipitating antibody during the last month of its life. The pigs had a normal immune response to sheep red blood cells and to pig parvovirus. These observations suggest the presence of immunological tolerance to swine fever virus in these pigs.Cell mediated immunity, measured by phytohaemagglutinin lymphocyte stimulation, appeared to be normal.     

Effect of infections with swine fever virus on immune functions II. Lymphocyte response to mitogens and enumeration of lymphocyte subpopulations

Peripheral blood and spleen lymphocytes from pigs infected with a low-virulent strain of swine fever virus (SFV) were transiently hyporesponsive to the mitogenic action of PHA, PWM and Con A. The mitogenic reactivity of lymphocytes from lymph nodes from such pigs appeared to be enhanced rather than depressed at that time. In addition, hyperresponsiveness of peripheral blood lymphocytes (PBL) to these mitogens occurred in some pigs.PBL from pigs lethally infected with virulent SFV showed a persistent depression of the response to these mitogens, whereas lymphocytes from lymph nodes had a high responding capacity.A lymphocyte response to SFV antigens could not be demonstrated in infected pigs.These SFV infections did not markedly affect the percentage of lymphocytes in the blood and most lymphoid organs rosetting with sheep red blood cells. On the other hand, surface immunoglobulin-bearing lymphocytes were markedly increased in lymph nodes from pigs exposed to virulent SFV. The sum of both lymphocyte subpopulations in the lymph nodes from these pigs often considerably exceeded the 100% value, which strongly suggests the presence of cells bearing both surface immunoglobulin and receptors for dextran-treated sheep red blood cells.Possible correlations between these findings are discussed. The results suggest that infections with SFV induce systemic alterations in the process of lymphocyte recirculation in the pig.     

Effect of infections with swine fever virus on immune functions. III. Antibody response to lipopolysaccharide and sheep red blood cells

In order to determine the effect of infections with low-virulent swine fever virus (SFV) on antibody responses, pigs were administered lipopolysaccharide (LPS) or sheep red blood cells (SRBC), 2 days after infection. Infected pigs showed an enhanced primary response to LPS late during infection. The secondary response to LPS seemed to be unaffected. Both the primary and secondary antibody response to SRBC appeared to be enhanced rather than depressed in infected pigs. These in vivo findings suggest that pigs infected with low-virulent SFV do not develop a depression of B lymphocyte function.     

A congenital persistent swine fever infection. I. Clinical and virological observations

A congenital swine fever infection is described. The infection is characterized by persistent viraemia, continuous virus excretion and late onset of disease, with death occurring 2–11 months after birth.A “carrier sow” from a field outbreak gave birth to one dead, one slightly abnormal and nine normal piglets, six of which were allowed to live. Disease symptoms were not observed before the age of 9–28 weeks (average 20 weeks) and the average survival time was over 6 months. Virus titres in blood plasma fluctuated between 10^5?0 and 10^6?9 plaque forming units/ml and virus was excreted throughout the lives of the pigs. Leucocyte counts showed normal to subnormal values, falling below 10 000/mm³ at about the onset of illness. Lesions characteristics of swine fever were not observed, but severe atrophy of the thymus was seen in all animals. Cryostat sections revealed the presence of viral antigen in lymphoidal, reticulo-endothelial and epithelial tissues. The difference between this persistent congenital infection and the chronic swine fever described by other authors, and the importance of “healthy” virus carriers for the epizootiology of the disease are discussed.     

Effect of infections with swine fever virus on immune functions I. Response of lymphocytes from blood and lymphoid organs from infected and normal pigs to anti-immunoglobulin serum and protein A

Pigs exposed to a low-virulent strain of swine fever virus (SFV) developed an inapparent infection. At times when a transient leucopenia occurred, the peripheral blood lymphocytes (PBL) were unresponsive to the mitogenic stimulus of anti-immunoglobulin serum (anti-Ig) and protein A.Pigs lethally infected with a virulent SFV showed leucopenia and unresponsiveness of PBL to anti-Ig and protein A from 2 days post infection until death.This suggests a defect in B lymphocyte function in pigs infected with SFV. The unresponsiveness to anti-Ig appeared not to be caused by a reduced ability of lymphocytes to redistribute their receptors into caps, the presence of suppressor cells or absence of surface immunoglobulin bearing lymphocytes in the peripheral blood. A direct action of the virus itself also seemed unlikely.Lymphocytes from spleen reacted as PBL. However, lymph node cells did not lose their capability to respond to anti-Ig.These data suggest that a change in the migration pattern of anti-Ig responsive lymphocytes could account for the observed unresponsiveness of PBL and spleen lymphocytes to anti-Ig.     

猪瘟免疫失败的原因分析

猪瘟是由猪瘟病毒属RNA病毒引起的急性、热性、败血性、具有高度传染性的疾病,急性以出血性败血症为特征,慢性以纤维素性坏死性肠炎为特征.猪瘟一旦发生,将给饲养者造成惨重的经济损失,应用猪瘟弱毒疫苗对猪进行免疫注射是防制猪瘟的有效方法之一,但由于种种因素影响,猪瘟免疫失败时有发生.     

持续定时免疫猪瘟疫苗应用效果研究

猪瘟(Classical swine fever,CSF)是由猪瘟病毒(Classical swine fever virus,CSFV)引起的严重危害养猪业的重大传染病。目前发现的CSFV毒株可分为3个基因型和11个基因亚型,但CSFV抗原性比较保守,只有一个血清型,不同基因型间有很好的抗原交叉,中和抗体水平可以直接反应疫苗免疫产生体液免疫力的高低。接种高效猪瘟细胞疫苗可以有效刺激机体产生体液免疫和细胞免疫,成为当前有效防控猪瘟的重要手段。     

Influence of the vaccination regime on the herd immune response for swine fever

Surveys in three areas with emergency vaccination programmes revealed that 86-94% of the pigs vaccinated in the initial mass campaign had developed an adequate antibody titre against swine fever as compared with 29-55% of the pigs involved in supplementary vaccination campaigns. The serological response of piglets born from immunised sows rose with the age of vaccination from 11% at 5-6 weeks to 42% at 7-8 weeks and 77% at 9-10 weeks. In piglets born from immunised sows, a 50% 'take' of the vaccine was not obtained before the age of 8-9 weeks. Re-vaccination of gilts born from immunised dams improved the immune status to almost the level observed after mass campaigns. To strengthen herd immunity in vaccination areas, the age of supplementary vaccination has been raised to 7-9 weeks, while breeding gilts are re-vaccinated when 6-7 months old.     

African swine fever and classical swine fever: a review of the pathogenesis

This paper describes major pathogenetic mechanisms of African and Classical Swine Fever virus infections. The interactions between both viruses and the monocyte-macrophage-system result in the release of mediator molecules, which are important for the further progression of the diseases. The causes of the thrombocytopenia and the mechanisms of the haemorrhages, which are characteristic in both infections, are described. Apoptotic cell death is regarded as the predominant cause of lymphopenia in both virus infections.     

牛病毒性腹泻病毒感染对猪瘟免疫的影响

猪瘟病毒（CSFV）与同属的牛病毒性腹泻病病毒（BVDV）同源性较高,抗原性上有交叉。本次调查对368份猪瘟免疫猪血清样本进行BVDV抗原检测,其中7份呈阳性,阳性率1.90%。对7份BVDV阳性血清采用ELISA和IHA两种方法检测猪瘟（CSFV）抗体水平,抗体合格率偏低,两者的结果符合率为71%。研究表明：BVDV在一定程度上干扰了猪瘟疫苗的免疫效果,影响抗体水平。     

Monte Carlo simulation of classical swine fever epidemics and control. II. Validation of the model

A stochastic and spatial simulation model was developed to simulate the spread of classical swine fever virus among herds in a certain area. A model is a simplification of a real system. The mechanisms and parameters are often not exactly known. Validation is necessary to gain insight into model behaviour and to identify risk factors with great impact on the response variables. Several risk factors such as incubation period, number of daily farm contacts, probability of detection, probability of infection after contact, probability of local spread and time from infection to infectivity were considered in the model as probability distributions in order to take the stochastic component of disease dynamics into account. In order to estimate the effects of the risk factors on the response variables mean size and duration of epidemics, a sensitivity analysis was performed. A fractional factorial design with two-level factors (2(7-2) design) was developed to gain the maximum strength with minimum demand on the calculating capacity. The main factors were unconfounded with any other main factor and also unconfounded with two-factor interactions. Apart from the time from infection to infectivity, all risk factors had a significant effect on the mean size and duration of epidemics (p<0.05). Eight two-factor interactions had a significant influence as well (p<0.05). Mainly, two-factor interactions with probability of detection were significant thus emphasising the impact of a rapid detection of outbreaks. The reaction of the simulation responses to changing of the parameter values was consistent with the expected reaction.     

复方中草药止泻散对猪免疫功能的影响

复方中草药制剂止泻散,通过临床实验已经证明其对仔猪黄白痢具有良好的防治效果,为了从其对猪体免疫力的影响方面探讨作用机理,给试验猪灌服不同浓度的止泻散煎剂（0.5g/ml、1．0g／ml、1.5g／m）,观察用药后不同时间（0、3、7、10、14、20d）猪的T淋巴细胞百分率的变化情况。     

泉州市洛江区猪瘟抗体水平检测效果分析

结合实验室每年的检测工作,2013-2014年对洛江区辖区内20个生猪规模养殖场和89个散养户的856份猪血清进行猪瘟疫苗免疫抗体检测。结果表明:洛江区猪瘟疫苗免疫抗体合格率呈现上升趋势,规模场猪瘟疫苗免疫抗体合格率明显高于散养户,免疫2次的抗体合格率明显高于1次。抗体检测工作的开展,对制定科学合理的免疫程序,有效防控猪瘟疫情的发生发挥了积极的作用。     

Effect of husbandry methods on seropositivity to African swine fever virus in Sardinian swine herds

Multiple logistic regression was used on serological data collected in the context of the Sardinian African swine fever (ASF) eradication program from pig farms in the province of Nuoro, Sardinia. The monthly percentage of ASFV-positive herds decreased significantly from October 1994 through March 1996 (P < 0.001). The farm-level risk of seropositivity to African swine fever virus (ASFV) was higher in free-range farms than in partial-confinement farms (odds ratios (OR) varied between 4.9 in October 1994, and 5.7 in March 1996, P < 0.001). The risk of infection for total-confinement farms was one-fifth of the risk for partial-confinement farms in October 1994 (OR = 0.2, P < 0.001), whereas in March 1996, the estimated OR was 0.57 and not significant (upper confidence limit = 1.1). The maintenance of ASFV in Sardinia was primarily associated with free-range pig farms. The natural logarithm of the number of pigs tested per visit in a farm was positively associated with the risk of herd seropositivity (OR = 2.6, P < 0.001).