Diversity of African swine fever virus

An African swine fever virus is an heterogeneous population, consisting of clones having different biological characteristics in respect to hemadsorption, virulence, infectivity, plaque size, and antigenic determinants. The following observations were made: Nonhemadsorbing virus (NHV) have been segregated from field isolates from Haiti (HT-1) and a bone marrow- and buffy coat-passaged Portuguese isolate (L'60BM89BC1) and appear as a major, minor, or equal mixture with hemadsorbing viruses in the virus population. Biological characteristics of the virus inoculated into pigs often differed from viruses isolated later from the same pigs. Virulence and nonhemadsorbing characteristics of isolated clones were genetically stable. The lethal effect of 2 NHV clones of L'60BM89BC1 virus was dose-dependent; small doses of virus induced immunologic deaths or recoveries from the clinical disease in pigs, and large doses induced acute deaths. The NHV of Lisbon isolate of 1960 (L'60) and HT-1 isolate share the same antigenic determinants for inducing protection. Tengani isolate contained clones of distinctly different antigenic determinants, not shared by L'60 or HT-1 isolate that enabled it to overcome the protection induced by the other clones. Passaging of an African swine fever virus isolate in pigs or cell cultures may readily alter the proportions of the different clones in the population and thereby change its overall characteristics. A new virus population with atypical hemadsorption was found in HT-1 field isolate and L'60BM89BC1 virus.     

Abortion in sows experimentally infected with African swine fever virus: pathogenesis studies

Thirteen sows that were 38 to 92 days pregnant were experimentally infected with an African swine fever (ASF) virus strain of low virulence (Dominican Republic isolate). Seven of 11 sows that were not killed had aborted. The pathogenesis of the abortions was studied, using virus isolation, tissue immunofluoresence, and histopathologic techniques. African swine fever virus was recovered from 179 of 1,329 (13.5%) fetal tissues tested. The 3 fetal tissues most frequently yielding virus were the fetal placenta, amniotic fluid, and fetal heart blood. Virus was not recovered from fetal tissues obtained from 2 of the aborting sows. Direct immunofluorescent microscopy for ASF viral antigen was done on approximately 1,175 fetal tissues. Although brightly fluorescing cells were common in maternal tissues, specific immunofluorescence was present in only placental tissues from 2 sows. Microscopic lesions in fetal tissues were inconsistent and included mild focal placentitis, mild heptic degeneration and necrosis, and mild interstitial pneumonia. These changes were not considered to be sufficiently specific to have diagnostic significance. In marked contrast to these changes in the fetal tissues, maternal tissues had high titers of virus, with marked necrosis of lymphoid tissues, and contained many cells with ASF viral antigen. We conclude that specific diagnosis of abortion resulting from ASF infection should, therefore, be based on examination of maternal tissues, rather than fetal tissues. The pregnancy failure seems to result from the effects of the virus infection on the dam more so than from direct viral damage to the placenta or fetus.     

非洲猪瘟背景下的中国猪育种

2018年8月,沈阳发生我国第一起非洲猪瘟疫情,尔后在不到一年的时间内,非洲猪瘟疫情以星火燎原之势迅速传遍大江南北,由于猪场恐慌抛售或大量清场,导致我国生猪存栏量迅速下降,据官方统计,生猪的存栏量减少了1/3至1/2,有的地区甚至减少80%,大量猪场永远离开了养猪业。从我国暴发非洲猪瘟到现在已经两年,养猪行业发生了翻天覆地的变化。     

In vitro immune serum-mediated protection of pig monocytes against African swine fever virus

Serum samples from pigs that had recovered from infection with a Dominican Republic isolate of African swine fever virus (ASFV) were mixed with dilutions of the virus, then assayed in microcultures of normal pig mononuclear leukocytes to determine whether the samples contained antibodies that protected monocytes against the virus. Protection was determined by the difference in titer (log10) between virus mixed with healthy pig serum and virus mixed with immune pig serum, using 50% cytopathogenic effect end points; protection was expressed as an immune serum-protection index. After addition of virus-serum mixtures to mononuclear leukocyte microcultures, a time-dependent decrease in protective index and production of infectious virus (determined by use of yield reduction assays) were observed. Protective effects were associated with the immunoglobulin fraction of serum, were rapidly lost on dilution, and were independent of complement. Antibody was most protective for the homologous Dominican Republic isolate of ASFV, with decreased protection against Lisbon '60 ASFV, and no protection against foot-and-mouth disease virus or bluetongue virus. Low concentrations of protective antibody were found during the acute viremic phase in infected pigs; antibody increased to maximal concentrations as the viremia decreased.     

Entry of African swine fever virus into Vero cells and uncoating

African swine fever virus (ASFV) enters Vero cells by adsorptive endocytosis [Valdeira, M.L., Geraldes, A., 1985. Morphological study on the entry of African swine fever virus into cells, Biol. Cell. 55, 35–40]. Electron microscopy of a lysosomotropic drug-controlled penetration indicated that this step takes place in the endosomes, after fusion between the viral envelope and the limiting membrane of the endosome. Inhibition studies with colcemid, cytochalasin B, sodium azide, dinitrophenol, lysosomotropic weak bases, and the ionophore monensin, showed that the virus uptake is largely independent of cytoskeletal and lysosomal function, but dependent on oxidative phosphorylation. Some protease inhibitors inhibited viral replication at an early step, indicating that the initiation of infection depends on a viral proteolytic cleavage.     

Classical swine fever virus in plasma and peripheral blood mononuclear cells of acutely infected swine

The distribution of classical swine fever virus (CSFV) in plasma, monocytes, T and B lymphocytes in peripheral blood was monitored during experimentally induced acute classical swine fever infection in piglets. Six piglets were infected with 10(3.8) TCID50 of virus and blood samples taken up to 18 days post-inoculation (p.i.). Infectious virus was detected in monocytes, T and B lymphocytes to similar titres in five of the six infected piglets. Infectious virus was detected earlier in plasma than in any of the mononuclear cell subpopulations. No significant difference was observed in the period of time in which virus could be isolated from the three cell subpopulations. While a progressive lymphopenia developed, a marked B cell depletion was observed. However, B cells were apparently replaced by non-IgM-bearing mononuclear cells, as the proportion 'total lymphocyte/total leucocytes' remained unaltered throughout the experiment. Virus titres in plasma and peripheral blood mononuclear cells showed a tendency to increase as the disease progressed to its outcome.     

非洲猪瘟背景下猪育种策略探讨

非洲猪瘟给我国养猪业造成巨大损失,也沉重地打击了我国的猪育种工作,虽然目前非洲猪瘟已大大缓解,各核心育种场也逐渐恢复了育种工作,但非洲猪瘟并未消除,未来的育种工作将面临非洲猪瘟常态的挑战。在这样的背景下,我国的猪育种工作应做出针对性的改变,主要体现在：（1）建立严格的永久性的生物安全体系;（2）调整育种目标;（3）自动化、智能化、物联网技术的应用;（4）加快基因组选择技术应用;（5）建设高质量、高度生物安全的种公猪站;（6）利用冷冻精液技术。     

Coagulation changes in African swine fever virus infection

Pigs were infected with highly virulent (Tengani '62), with moderately virulent (DR '79) African swine fever (ASF) virus, or with virulent hog cholera (HC) virus. Changes in platelet counts, selected coagulation assays and concentrations of factor VIII-related antigen (VIIIR:Ag) were monitored. Permeability of aortic endothelium was studied after the injection of Evan's blue dye on various days after infection with DR '79 ASF virus. Virulent ASF virus caused prolongation of the activated partial thromboplastin time (APTT), 1-stage prothrombin time, and thrombin clotting time as early as postinoculation day (PID) 4. These changes became progressively more severe until death. Both virulent HC and DR'79 viruses induced an increase APPT and thrombin clotting time at PID 3 to 4, only occasionally did the prothrombin time increased significantly (P less than 0.01). The APPT began to decrease on PID 7 and 8, but only DR'79-infected pigs lived long enough to regain a normal APTT. Infection by ASF viruses caused acute thrombocytopenia after PID 6 and platelet counts of HC virus-infected pigs decreased progressively from the onset of fever to levels of 1 to 2 X 10(5)/mm3 at PID 6 to 7. All ASF virus-infected pigs had an increase in VIIIR:Ag beginning at PID 3, with maximum increases at PID 6 to 7. Hog cholera virus infection did not cause consistent changes in levels of VIIIR:Ag. Pigs infected with DR'79 virus did not have increased vascular permeability to Evan's blue dye during infection; however, there was markedly decreased staining of the aorta after pigs became thrombocytopenic.     

Detection of antibodies against African swine fever virus using infected monolayers and monoclonal antibodies

Three monoclonal antibodies, specific for porcine IgG, IgM and IgA, were used to develop isotype-specific immunoperoxidase monolayer assays for the detection of antibodies against African swine fever virus. A mixture of anti-IgM and anti-IgG monoclonal antibodies was used in an assay designed for screening sera. This test was compared with a commercially available ELISA by using experimental sera and field sera obtained after an outbreak of African swine fever on two farms in the Netherlands in 1986. Although the ELISA was less sensitive than the immunoperoxidase monolayer assay on sera taken early after infection, the tests were equally useful for screening purposes. The isotype-specific assays gave epizootiological information about the stage of infection on the two farms.     

Swine fever: classical swine fever and African swine fever.

Because of the clinical and pathologic similarity to common endemic diseases, introduction of CSFV or ASFV strains of moderate to low virulence represents the greatest risk to North American swine herds. Producers, veterinarians, and diagnosticians should increase their awareness of these devastating diseases and request specific diagnostic testing whenever they are suspected. Production practices that improve biosecurity will reduce the risk of introduction of CSF and ASF and limit the spread if an incursion occurs. Additional resources. The following Web sites contain excellent color photographs that will assist producers and practitioners in identifying clinical signs and gross lesions associated with CSFV and ASFV: http://www.vet.uga.edu/vpp/gray_book/FAD and http://www.pighealth.com. The latter Web site and the OIE Web site (http://www.oie.int) offer updated information on current worldwide epizootics of ASF and CSF and other swine diseases. Details of biosecurity procedures can be found at http://www.agebb.missouri.edu; see publication G2340.     

对非洲猪瘟后生猪复养工作的探讨

文章就生猪复养的历史背景、生猪复养技术指南,中国防控非洲猪瘟模式,国家恢复生猪生产政策,补齐基层防疫服务短板等生猪复养工作,结合湖南省洞口县生猪复养工作实践,进行了理论和实际的探讨。提出建立县级生猪复养工作专家组,加强生猪复养技术培训和技术服务,对规模化猪场生猪复养技术进行分级指导,建立县级车辆清洗消毒中心出台扶持母猪生产奖补政策的的建议,供同行参考。     

Neutralization of African swine fever virus by sera from African swine fever-resistant pigs

Sera from African swine fever-resistant pigs with infection-inhibitory activity decreased virus replication in infected porcine buffy coat cultures. This same effect was observed even after virus was adsorbed. The infection-inhibition was not reversed by removing the immune serum from the assay cultures. Reduction of African swine fever virus replication by immune sera was demonstrated by fluorescent focus assay on MS cell line cultures. Virus-neutralization tests showed a persistent fraction of non-neutralized virus, which was not demonstrable by infection-inhibition tests. One hypothesis for explaining this difference is proposed.     

非洲猪瘟病毒入胞过程相关蛋白及分子机制的研究进展

非洲猪瘟病毒(ASFV)是非洲猪瘟(ASF)的病原,可引发家猪和野猪急性、传染性出血死亡,目前尚无有效的疫苗和抗病毒药物。ASFV是囊膜病毒,其囊膜蛋白的结构和功能可能是影响病毒入侵和细胞嗜性的重要因素。病毒入胞是病毒感染细胞的第一步,通常是通过细胞表面特定的分子与病毒蛋白相结合吸附于宿主细胞表面,对ASFV入胞过程的病毒蛋白或宿主因子为靶点或可有效抑制ASFV的复制。本文从ASFV入胞过程中起重要作用的囊膜蛋白出发,对ASFV的入胞分子机制进行综述,为ASFV入胞深入研究以及治疗性药物和疫苗的研发提供参考。     

Pathogenesis of African swine fever virus in Ornithodoros ticks

African swine fever virus (ASFV) is the only known DNA arbovirus and the sole member of the family Asfarviridae. It causes a lethal, hemorrhagic disease in domestic pigs. ASFV is enzootic in sub-Saharan Africa and is maintained in a sylvatic cycle by infecting both wild members of the Suidae (e.g. warthogs) and the argasid tick Ornithodoros porcinus porcinus. The pathogenesis of ASFV in O. porcinus porcinus ticks is characterized by a low infectious dose, lifelong infection, efficient transmission to both pigs and ticks, and low mortality until after the first oviposition. ASFV pathogenesis in warthogs is characterized by an inapparent infection with transient, low viremic titers. Thus O. porcinus porcinus ticks probably constitute the most important natural vector of ASFV, although both the mammalian and tick hosts are probably required for the maintenance of ASFV in the sylvatic cycle. The mechanism of ASFV transmission from the sylvatic cycle to domestic pigs is probably through infected ticks feeding on pigs. In addition to O. porcinus porcinus, a number of North American, Central American and Caribbean species of Ornithodoros have been shown to be potential vectors of ASFV.     

非洲猪瘟常态下猪场建设的12345

首例非洲猪瘟在我国暴发至今两年来,严重影响了我国生猪产业以往的正常周期运行规律,迫使大家对非洲猪瘟的防控和整个养猪生产模式进行多方面探讨,实践表明,猪场的建设对完善生物安全体系,防控非洲猪瘟疫情起到重要作用.     

Cytopathogenic effect of African swine fever virus for pig monocytes: characterization and use in microassay

A microculture assay is described for the titration of African swine fever virus (ASFV) using swine monocytes contained in mononuclear leucocyte (MNL) microcultures. Titration endpoints were determined by observing cytopathogenic effects (CPE) of ASFV infected monocytes with an inverted microscope at 40 X magnification. CPE was a late event following the detection of ASFV antigens in monocytes by radioimmune assay, immunofluorescence and hemadsorption. It began with the detachment, enlargement and rounding of monocytes which progressively formed into grape-like clusters of 3-20 or more cells which eventually lysed. The characteristic CPE was produced in monocyte microcultures by virulent, moderately virulent, Vero cell adapted, and nonhemadsorbing ASFV strains. The sensitivity and reproducibility of the CPE microassay was similar to that of the hemadsorption microassay.