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.     

非洲猪瘟病毒VP73结构蛋白表达及鉴定

根据GenBank登录的非洲猪瘟病毒(ASFV) VP73基因序列,人工合成VP73主要抗原表位区基因片段,克隆至pUC57载体中.设计1对引物,PCR扩增获得429 bp的VP73基因片段;将VP73基因片段使用EcoRI和SalI酶切后亚克隆至表达载体pGEX-KG,经PCR、酶切、测序鉴定挑选阳性克隆,转化至表达菌株BL21 (DM3)中,进行体外诱导表达,SDS-PAGE和Western blot分析蛋白表达及其活性.结果显示,成功构建表达重组载体pGEX-KG-VP73,对该重组载体进行诱导,有效表达了41 ku重组蛋白,表达量约占菌体总蛋白的17％,Western blot分析证实该蛋白具有良好反应原性.     

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.     

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.     

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 African swine fever virus antibodies by immunoblotting assay.

An immunoblotting assay has been adapted to detect antibodies against African swine fever virus. The electrophoretic transfer of proteins and the immunoreaction conditions were optimized, using 4 mA/cm2 of current intensity and 10 micrograms of soluble cytoplasmic antigen of infected cells per strip. Filters of polyvinylidene difluoride showed the highest capacity for protein absorption, but nitrocellulose filters showed lower backgrounds. The specificity and the pattern of the proteins induced by African swine fever virus that react with the antisera were determined in immunoblotting assay, IP30 being the most reactive protein.     

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.     

非洲猪瘟病毒p72蛋白杆状病毒表达系统的构建及其抗原性分析

为研究真核表达非洲猪瘟病毒(ASFV)主要结构蛋白p72,本研究从含ASFV p72基因全序列的重组质粒pGEX-6p-p72中扩增出1 941 bp的p72全长基因,将其插入于pFastBac HTa杆状病毒载体中,构建了重组质粒pFastBac HTa-p72,转化至感受态细胞DH10Bac中,获得重组杆粒rBacmid-p72。再将其转染至sf9昆虫细胞,获得重组杆状病毒。Western blot和夹心法ELISA分析表明ASFV p72基因在昆虫细胞sf9中获得了正确表达,重组p72蛋白可以被特异性抗ASFV血清、p72单克隆抗体识别,表明该蛋白特异性强、活性稳定,具有良好的抗原性。为进一步研究p72蛋白的结构、功能和免疫学特性奠定基础。     

Inhibitory effect of African swine fever virus on lectin-dependent swine lymphocyte proliferation

The incubation of swine peripheral blood mononuclear cells (PBMC) with African swine fever (ASF) virus preparations strongly inhibited the proliferative response of lymphocytes to PHA and other lectins. The inhibition, which persisted after inactivation of the virus by UV radiation, was dependent upon the dose and the time that virus preparations were present in cultures. When virus preparations were fractionated by ultracentrifugation, the inhibitory activity resulted to be soluble, whereas no activity was found in the sedimented viral fraction. However, the preincubation during 4 days of this sedimented fraction with swine PBMC, before the addition of the mitogen, restored the inhibitory activity. The results obtained suggest that the inhibition is mediated by one or more soluble factors released by swine PBMC after coincubation with ASF virus in a time dependent process. These factors show a molecular weight between 40 and 80 kDa by gel filtration chromatography. The inhibitory activity described in the present paper is an indication of inhibition of lymphocyte function produced by ASF virus which can help to understand how this virus escapes from the host immune system.     

Negative staining of a non-haemadsorbing strain of African swine fever virus.

Since the application of negative staining, preceded by fixation, prevents the disruption and distortion of the capsid of the African swine fever virus, improved contrast and evaluation of the appearance and size of virus particles in the electron microscope is possible and, in addition, the icosahedral shape of the virus is demonstrable. The mature virus particle contains at least 2 capsid layers and an outer envelope.     

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).     

Prevalence of African swine fever virus and classical swine fever virus antibodies in pigs in Benue State,Nigeria

Tropical Animal Health and Production - This study investigated the prevalence of African swine fever virus (ASFV) and classical swine fever virus (CSFV) antibodies in pigs in Benue State, Nigeria....     

非洲猪瘟病毒微芯片荧光PCR快速检测技术的建立及初步应用

非洲猪瘟缺乏安全有效的疫苗,其防控有赖于及时、准确的诊断和消毒灭源.本研究在对非洲猪瘟病毒(Afri-can swine fever virus,ASFV)B646L基因序列进行分析的基础上设计引物、探针,建立了基于微芯片的ASFV免提取荧光PCR检测技术.特异性试验结果显示,微芯片PCR可用于我国不同地区ASFV毒株...     

非洲猪瘟病毒传播方式及控制措施

非洲猪瘟(African swine fever,ASF)是由非洲猪瘟病毒(African swine fever virus,ASFV)引起的一种急性、热性、高度传染性疫病,感染猪以发热和全身性出血为主要特征,病程短、病死率高。非洲猪瘟主要流行于非洲国家,随后相继传入西欧、南美洲、东欧,以及亚洲国家,对全球养猪业、食品安全和猪及其产品国际贸易产生了严重危害和深远影响。现结合参考文献和我国非洲猪瘟发生、控制情况,分析了非洲猪瘟病毒传播动力学、传播方式,提出防控非洲猪瘟的主要措施。