Megakaryocytic infection and thrombocytopenia in African swine fever

Pigs infected with an African swine fever field isolate of modified virulence became acutely thrombocytopenic four to five days after the onset of fever and viremia. By eight days after inoculation, all pigs were thrombocytopenic. Immunofluorescence microscopy demonstrated that 2 to 10% of the megakaryocytes were infected. By 13 days after inoculation, platelet counts returned to within normal limits, and there was megakaryocytic hyperplasia despite a continued viremia. Secondary complications delayed the return of normal circulating platelet levels in some pigs. The clinical findings of African swine fever are discussed in light of the gross and histologic lesions.     

Review of African swine fever outbreaks history in South Africa: From 1926 to 2018

The article reviews the outbreaks and distribution of African swine fever (ASF) in South Africa since the first probable outbreak that occurred in the Koedoesrand Ward in 1926. Retrospective data on the ASF outbreaks in South Africa were obtained from the World Organisation for Animal Health (OIE) disease database and the South African veterinary services annual reports in addition to published articles and online sources. South Africa has experienced many outbreaks that can be divided into 2 time periods: the period before the development of the OIE diseases database (1993) and the period after. More than 141 outbreaks of ASF were reported during the first period. Since the development of OIE disease database, 72 outbreaks directly involving 2968 cases, 2187 dead and 2358 killed pigs mainly in smallholder pig farms were reported. The median number of cases for a given ASF outbreak is 17, but in 50% of outbreaks no pigs were killed for prevention. The most important ASF outbreak was reported in April 2014 in the Greater Zeerust district (North West province) involving 326 cases and 1462 killed pigs. However, the outbreak with highest mortality involving 250 pigs was reported in 2016 (Free State province). According to phylogenetic analysis, nine p72 genotypes (I, III, IV, VII, VIII, XIX, XX, XXI and XXII) have been identified in South Africa. Season-wise, more outbreaks were recorded during summer. It was also observed that the OIE disease database could contain errors that would have been introduced through compiled forms at country level. Spatiotemporal studies on ASF outbreaks in South Africa are therefore required in order to assess statistically and quantitatively the clustering of outbreaks over space and time.     

African swine fever among slaughter pigs in Mubende district, Uganda

Owing to frequent reports of suspected outbreaks and the presence of reservoir hosts and vectors (warthogs, bushpigs and O. moubata ticks), African swine fever (ASF) is believed to be an endemic disease in Uganda. There have, however, been very few studies carried out to confirm its existence in Uganda. This study was carried out to describe the prevalence of ASF based on pathologic lesions and analysis of serum samples from slaughtered pigs during a suspected outbreak in the Mubende district of Uganda. The study was based on visits to 22 slaughterhouses where individual pigs were randomly selected for a detailed ante-mortem and post-mortem inspections. Sera were also collected for laboratory analysis. A total of 997 pigs (53.7% male and 46.3% female) were examined for lesions suggestive of ASF and sero-positivity of sera for ASF antibodies. The sera were tested using enzyme-linked immunosorbent assay (ELISA) and positive samples were further confirmed with an immunoblot assay. The results showed that 3.8% (38/997) of the pigs examined had clinical signs and post-mortem lesions suggestive of ASF. Two of 997 (0.2%) sera analysed were positive for ASF antibodies. Of the sub-counties investigated, Bagezza (12%) and Kiyuni (11%) had the highest prevalence of lesions suggestive of ASF based on ante- and post-mortem examination results, while Mubende town council (1.7%) had the lowest. This study found a low number of pigs (3.8%) with lesions suggestive of ASF at slaughter and an even lower number of pigs (0.2%) that were seropositive at slaughter, however a significantly higher number of pigs were slaughtered during the outbreak as a strategy for farmers to avoid losses associated with mortality.     

非洲猪瘟对我国养猪业的影响与防控建议

非洲猪瘟是由非洲猪瘟病毒引起的一种高度接触传染性、广泛出血性猪病毒病,死亡率可高达100%,无商品化疫苗可用于其预防。自8月初我国爆发首例非洲猪瘟疫情以来,截至11月5日,短短三个月时间里,已有14个省累计爆发58起疫情,扑杀生猪近50万头,直接经济损失数十亿元,给我国养猪业造成了巨大冲击。面对前所未有的非洲猪瘟疫情,我国政府的应对是果断有力的,但也面临种种挑战。本文对我国非洲猪瘟疫情形势及其对相关行业的影响进行了分析,总结了非洲猪瘟防控的重点和难点,并针对目前的形势,提出了遏制非洲猪瘟疫情进一步蔓延的建议和对策。     

Investigation of African swine fever in slaughtered pigs,Plateau state,Nigeria, 2004-2006

The occurrence of African swine fever (ASF) DNA in slaughtered pigs in the major pig producing areas of Plateau state over a 2-year period was investigated. Three hundred fifty-nine pig tissue samples from five local government councils (LGCs) were analyzed by clinical signs (C/S), postmortem (PM) lesions and polymerase chain reaction (PCR). The results of diagnosis made by C/S and PM were compared to results obtained by PCR. Out of the 359 abattoir samples, 13 (3.62%) were positive by examination of C/S and PM lesions while 346 (96.38%) were negative. Jos-north LGC had the highest occurrence of PCR positive samples (31 samples); Panyam in Mangu LGC had no positive result. PCR analysis identified 53 positive samples (14.76%); more than 40 were identified on the field. Of the samples, 306 were PCR negative, thus giving a true ASF status of pigs in Plateau state. Analysis of the results, variables involved in the ASF spread and predictable effects of such findings in the pig industry in Plateau state and Nigeria as a whole is discussed.     

Molecular characterization of African swine fever virus isolates originating from outbreaks in the Russian Federation between 2007 and 2011

African swine fever is one of the most important viral diseases of pigs and which caused significant economic damage on the pig production worldwide. Nowadays, it is still present on the African continent, in Transcaucasus countries (TCC), on Island of Sardinia and in Russia. Outbreaks of the disease have been reported in Russia for the last four years, affected especially the Southern Federal District of the country. Since 2010, a new outbreak area has been observed in the Northwestern Federal District. In order to study the evolution of African swine fever virus (ASFV) isolates, strains were collected in the Russian Federation from 2007 to 2011 and investigated by means of partial sequencing and fragment length polymorphism. In detail, 7 variable regions, namely B646L, E183L, I196L, B602L, I73R/I329R, I78R/I215L and KP86R were investigated. Phylogenetic analyses revealed 100% nucleotide identity of B646L and E183L gene sequences of all examined isolates. All isolates formed one genetic cluster within genotype II. Moreover, no amplified fragment length polymorphism (AFLP) was observed for B602L, I196L, I73R/I329R, and I78R/I215L genes. The flanking primers used to amplify the KP86R gene failed to amplify a product in all the isolates. The obtained data strongly suggests that only one ASFV virus variant caused the outbreaks from 2007 to 2011 in the territory of the Russian Federation.     

Sanitary measures in piggeries,awareness, and risk factors of African swine fever in Benue State,Nigeria

The present study describes assessment of sanitary measures in piggeries of Benue State, Nigeria, to identify the risk factors of African swine fever. Questionnaires were distributed to 74 respondents consisting of piggery owners and attendants in different piggeries across 12 local government areas (LGAs) to collect data for this study. Sanitary measures in piggeries were observed to be generally very poor, though respondents admitted being aware of ASF. Piggeries located within 1-km radius of a slaughter slab (OR?=?9.2, 95% CI 3.0–28.8; p?<?0.0001) and piggeries near refuse dump sites (OR?=?3.0, 95% CI 1.0–9.5; p?<?0.05) showed higher chances of African swine fever virus (ASFV) infection, while piggeries where farm workers wear their work clothes outside of the piggery premises (OR?=?0.2, 95% CI 0.1–0.7; p?<?0.01) indicate less chances of infection but had a significantly associated p value thus were identified as potential risk factors. The study concluded that pigs in Benue State are still at risk of an ASF outbreak. Proper sanitary and hygienic practices are advocated and emphasized in piggeries, while routine surveillance for African swine fever virus antibodies in pigs in Benue State is strongly recommended to provide a reliable reference database to plan for the prevention of any devastating ASF outbreak.

     

饲料营养免疫对非洲猪瘟防控的作用

非洲猪瘟疫情的暴发对我国养猪产业造成了严重影响。尽管农业部门、科研专家和养猪工作者通过提高生物安全手段防控非洲猪瘟,对恢复我国生猪养殖数量和猪肉自给能力取得了相应效果,但随之而来的是猪群应激增加、饲料营养的有效性降低和猪群抗病力降低等问题。文章结合非洲猪瘟病毒特点和防控现状等,从饲料营养免疫的视角,分析如何减少猪群应激和提升猪群免疫力,以期为非洲猪瘟的综合防控提供思路。     

Contribution of market value chain to the control of African swine fever in Zambia

Tropical Animal Health and Production - African swine fever (ASF) is a worldwide disease of pigs endemic in most sub-Saharan African countries. Zambia has been experiencing outbreaks of ASF for...     

非洲猪瘟背景下生猪产业链价格波动及传导研究——以河北省为例

非洲猪瘟疫情的暴发对我国生猪产业,尤其是生猪产业链价格产生巨大影响。为研究非洲猪瘟背景下河北省生猪产业链价格波动及传导机制,文章选取河北省2018年8月至2020年6月周度平均仔猪价格、生猪价格和猪肉价格作为生猪产业链价格代表,通过构建协整和误差修正模型、格兰杰因果检验方法分析非洲猪瘟对生猪产业链内部价格传导过程的影响。研究结果表明：非洲猪瘟背景下河北省生猪产业链价格存在长期均衡关系,但其上下游价格传导受阻,而屠宰场和销售市场的垂直整合度增强;生猪产业链中存在一定的反向误差修正机制;生猪产业链上、中游对下游价格的影响更为明显,并据此提出非洲猪瘟背景下河北省调控生猪产业链价格的政策建议。     

非洲猪瘟研究进展及防控措施

非洲猪瘟(African swine fever,ASF)是由非洲猪瘟病毒科、非洲猪瘟病毒属的唯一成员非洲猪瘟病毒(African swine fever virus,ASFV)引起的一种高致死率、高抵抗力、严格接触性的病毒性疾病,对所有年龄段的家猪和野猪均具有感染性。我国非洲猪瘟传入疫情的出现,对养猪生产构成严重威胁,必将冲击生猪产业的健康稳定发展。本文介绍ASF的病原、流行病学特点,并总结防控措施,以期为ASF的进一步防控提供参考。     

Co-circulation of two genetically distinct viruses in an outbreak of African swine fever in Mozambique: no evidence for individual co-infection

In 1998, domestic pigs originating from villages within a 40 km radius of Ulongwe in the northern Tete Province of Mozambique were held in a quarantine facility for a 3-month period prior to their importation into South Africa. Eight of a total of 25 pigs died within the first 3 weeks of quarantine of what appeared clinically and on post mortem examination to be African swine fever (ASF). Organs were collected and preserved in formol-glycerosaline and the presence of ASF virus in these specimens was confirmed by three independent polymerase chain reaction (PCR) tests. Two gene regions were characterised, namely the C-terminus end of the major immunodominant protein VP72 and the central variable region (CVR) of the 9RL open reading frame (ORF). Results confirmed the presence of two genetically distinct viruses circulating simultaneously within a single outbreak focus. However, despite the pigs being housed within the same facility, no evidence of co-infection was observed within individual animals. Comparison of the two 1998 virus variants with viruses causing historical outbreaks of the disease in Mozambique revealed that these viruses belong to two distinct genotypes which are unrelated to viruses causing outbreaks between 1960 and 1994. In addition, the CVR and p72 gene regions of one of the 1998 Mozambique virus variants (variant-40) was shown to be identical to the virus recovered from an ASF outbreak in Madagascar in the same year, whilst the other (variant-92) was identical to a 1988 pig isolate from Zambia.     

Experimental Pathological Study of Acute African Swine Fever

To study the clinicopathology and histopathology of African swine fever (ASF), and to explore the internal relationship between pathological changes and disease occurrence and development and its pathological mechanism, 13 Landrace pigs with bodyweight about 20 kg were intramuscular injected with African swine fever virus (ASFV), strain Pig/HLJ/18 at a dose of 10²HAD₅₀·mL^-1. During the experiment, all the dead pigs were systematically dissected and sampled, paraffin sections were produced, and haematoxylin-eosin staining was performed. Clinicopathological evaluation standards for acute ASF were established, then pathological lesions (classification variables) were expressed by counting frequency and percentage, and the lesion degree (continuous variables) was graded and scored according to different pathological changes of various tissues and organs. The results showed that all infected pigs were in line with the clinical characteristics of ASF, including acute, febrile and highly infectious, with a 100% incidence rate and 100% mortality. The dead pigs showed typical characteristics of septicemia, cadavers prone to corruption, blood clotting adverse or hemolysis, rigor mortis incomplete. The main pathological lesions were hemorrhagic necrotizing lymphadenitis, acute inflammatory splenomegaly (septic spleen), cerebral edema, pulmonary edema and lung consolidation et al. The spleen and lymphonodus are the target organs attacked by ASFV, with the most significant lesions, the earliest occurrence time, the longest duration and the highest frequency. The most prominent pathological changes are blood circulation disorders, including multiple pathological manifestations such as edema, hyperemia, congestion, hemorrhage, infarction, disseminated intravascular coagulation (DIC), and the most important characteristics are hemorrhagic lesions. The inflammatory reaction of lymphocytic exudation caused by ASFV runs through the whole process, especially in the middle and later stages of the course. The results suggest that the main pathological process of acute African swine fever is a typical immune/inflammatory cascade reaction and severe systemic blood circulation disorder, which resulted in the high incidence rate and high mortality rate of acute ASF.     

急性非洲猪瘟的实验病理学研究

旨在通过对非洲猪瘟临床病理学和组织病理学的研究,探讨病理学变化与疾病发生发展的内在关系及其病理机制。选用体重20 kg左右的长白猪13头,肌内注射非洲猪瘟病毒毒株Pig/HLJ/18,剂量10²HAD₅₀·mL^-1。试验期间的死亡猪,全部进行系统剖检和取材,制备石蜡切片,苏木素伊红染色。建立病理学评价标准,病变（无序分类变量）用频率和百分比表示,病变程度（有序分类变量）按各组织器官的不同病变进行分级和评分。结果表明,发病猪符合非洲猪瘟急性、热性、高传染性等临床特征,发病率100%,病死率100%。病死猪表现败血症典型特征,尸体易腐败,血凝不良或溶血,尸僵不全。主要病理损伤为出血性坏死性淋巴结炎、急性炎性脾肿（败血脾）、脑水肿、肺水肿和肺实变等。脾和淋巴结是非洲猪瘟病毒攻击的靶器官,病变最为显著,出现时间最早,持续时间最长,发生频率最高。病理变化以血液循环障碍尤为突出,包括水肿、充血、淤血、出血、梗死和弥散性血管内凝血等多种病理表现,出血性病变为其最主要的特征。非洲猪瘟病毒引发的以淋巴细胞渗出为主的炎症反应贯穿始终,在病程的中后期表现更为明显。结果提示,急性非洲猪瘟的主要病理过程为典型的免疫/炎症级联反应和严重的全身血液循环障碍,共同导致急性非洲猪瘟的高发病率和高死亡率。     

饲料添加剂在非洲猪瘟防控中的作用

非洲猪瘟是一种烈性传染病,其暴发给全球养猪业带来了巨大的损失。至今尚未研发成功相应的疫苗。文章主要探讨了新型添加剂中草药饲料添加剂、微生态制剂对于猪只非特殊免疫力的调节以及对防控非洲猪瘟所起的作用。     

Detection and genetic characterization of porcine circovirus type 2 (PCV2) in pigs from Croatia

Porcine circovirus type 2 (PCV2) from the Circoviridae family has recently been associated with two serious diseases of swine, post-weaning multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS). During 2002, several outbreaks of clinical disease in pigs with weights ranging from 10 to 70 kg occurred on four farms in different locations in Croatia. The signs were consistent with PMWS and PDNS. Apart from progressive weight loss, pneumonia and/or diarrhoea, multifocal erythematous skin lesions and dermal necrosis were also observed. The PCR results obtained from PCV2 specific oligonucleotide primers confirmed a PCV2 infection. In addition, archive samples that were classical swine fever virus positive and derived from domestic pigs during an outbreak in 1997 were included in this study and one out of the three isolates was found to be positive for PCV2. For a better epizootiological understanding, genetic typing of representative isolates was carried out and compared with available isolates reported in the GenBank databases.     

2019年猪病流行情况与2020年流行趋势及防控对策

文章结合实验室的监测数据,概述了2019年我国非洲猪瘟、猪繁殖与呼吸综合征、猪瘟、猪伪狂犬病、猪流行性腹泻等重要猪病的流行状况,着重总结了非洲猪瘟疫情发生情况。分析了2020年非洲猪瘟等疫病的流行趋势,同时提出了坚持生物安全、严格处置非洲猪瘟疫情等防控策略。     

An epizootic of African swine fever in Belgium and its eradication

In March 1985 an outbreak of African swine fever was diagnosed in Belgium, in the province of West Flanders. The source of the infection was probably pork imported from Spain which was fed to only one boar. A total of 12 farms were infected in the epizootic out of 185 farms which were in contact. Severe control measures were imposed and the pigs on 60 farms were slaughtered (34,041 animals). In September 1985, it was concluded that African swine fever had been eradicated. This conclusion was based mainly on a serological survey of 3008 farms (116,308 blood samples) which remained negative.     

非洲猪瘟紧急预防控制技术需求

非洲猪瘟是原发于非洲肯尼亚的猪的一种重要病毒性传染病,2018年8月3日首次发生于我国沈阳。该病来势凶猛,截至10月16日,已在我国9个省份引发39次疫情。我国非常重视非洲猪瘟防控工作,具备了较好的科技储备,但疫情形势发展超乎预期,出现许多始料未及的情况,仍需要重新梳理防控技术需求,针对性地开展防控技术研究。就此,简要介绍了非洲猪瘟的特性,归纳了我国目前非洲猪瘟防控技术需求,建议深入开展快速特异诊断技术、流行病学、病原学等急需技术研究,开展野猪和软蜱传播媒介与非洲猪瘟流行关系和非洲猪瘟免疫与疫苗等基础研究。     

Mechanism of thrombocytopenia in African swine fever

Pigs were inoculated with an African swine fever (ASF) isolate of moderate virulence, and the changes in the number of circulating blood platelets during infection were correlated with the appearance of antiviral antibody and fluctuations in total plasma hemolytic complement concentrations. Thrombocytopenia was detected by postinoculation days (PID) 7 and 8, and antiviral antibody was detected by PID 7, using an indirect immunofluorescence technique. The total hemolytic complement concentration was moderately and transiently decreased from PID 5 to 9, but was consistently low from PID 18 to 26. Pigs inoculated with an ASF virus isolate of greater virulence had a decrease in platelet counts on PID 6 and 7, and the total plasma hemolytic complement levels decreased in all pigs by PID 6 to 7. Antibody to ASF virus was not detected in pigs inoculated with the more virulent isolate. Pigs sensitized to ASF viral antigen with an inactivated-virus vaccine or by previous infection with ASF were challenge exposed. Sensitized pigs became clinically ill and thrombocytopenic by 24 to 72 hours earlier than did inoculated, nonsensitized pigs. Vaccinated pigs inoculated with homologous virus had lower blood virus concentrations than did nonvaccinated pigs. African swine fever virus-sensitized pigs inoculated with heterologous virus had a higher fatality rate than did nonsensitized pigs, and the pigs died peracutely, with only a few gross lesions in evidence. In vitro experiments demonstrated that ASF virus antigen induced platelet aggregation in platelet-rich plasma from recovered, nonviremic pigs. Viral antigen, antibody, or complement was not demonstrable on the surface of platelets from pigs inoculated with ASF virus isolate, by direct immunofluorescence testing.