Research Progress on Epidemiology of African Swine Fever

African swine fever (ASF) is mainly occurred in Africa.It invades into Europe and America by chance,then invades in to Eastern Europe and the Caucasus area.And it has not been controlled until now.African swine fever virus (ASFV) can spread by soft tick vectors and affect wild and domestic pigs.The ability of the virus to survive within a particular ecosystem is defined by the ecology of its wild host populations and the characteristics of livestock production systems.African swine fever is viral disease of domestic and wild pigs which leads high mortality and causes great economic losses due to absence of available vaccine and treatment.Apart from prevention and culling,there are no other control measures.Prevention and control of the infection require good understanding of its epidemiology,so that targeted measures can be carried out.     

非洲猪瘟流行病学研究进展

非洲猪瘟(African swine fever,ASF)主要在非洲大陆流行,它通过偶然机会侵入到欧洲和美洲,之后进一步侵袭到了东欧和高加索地区,且到目前也未完全控制。非洲猪瘟病毒(African swine fever virus,ASFV)可通过软蜱传播,感染野猪和家猪,其在特定生态系统中的生存能力由它所在的野生宿主种群和畜牧生产系统来界定。ASF是可导致家猪和野猪死亡率极高的病毒性疾病,且因缺少有效的疫苗和治疗方法而造成巨大的经济损失。除了预防和扑杀,暂无其他更好的应对方法,所以需要很好地了解ASF流行病学,预防和控制其传播,以便实施更多有针对性的措施。     

Experimental transmission of African swine fever virus by Ornithodoros savignyi (Audouin)

The 'sand tampan', Ornithodoros savignyi, is susceptible to oral infection with African swine fever (ASF) virus in the laboratory. Infected ticks can transmit the virus transstadially and are able to maintain it for at least 106 days. Transmission of ASF virus by infected ticks to healthy pigs was achieved on five separate occasions between 50 and 106 days after infection. Pigs infected in this way developed typical acute African swine fever. The distribution of O savignyi in Africa suggests that this tick could be a natural field vector of ASF.     

Pathogenicity of endophytic entomopathogenic fungi to Ornithodoros erraticus and Ornithodoros moubata (Acari: Argasidae)

The argasid ticks O. erraticus and O. moubata are of great medical and veterinary importance because they are vectors of the African swine fever virus and several species of human relapsing fever borreliae. Biocontrol of these ticks using entomopathogenic fungi has not been previously reported. We examined the pathogenicity to different developmental stages of these two argasids of six strains of the fungal species Beauveria bassiana (strains Bb1764 and Bb2157), Lecanicillium lecanii (strains Ll586, Ll618 and Ll3047) and Tolypocladium cylindrosporum (strain Tc3398). Three strains, Bb1764, Bb2157, and Tc3398, caused in Spanish O. erraticus mean mortality rates between 34.4% and 62% in 14-28 days post-inoculation. Additionally, Bb2157 also induced in African O. moubata mean mortality rates of 31.9%. The remaining strains caused lower mortality rates and were not considered effective. This is the first study in which some strains of entomopathogenic fungi are found to be effective against argasid ticks of the genus Ornithodoros, and its results might justify further efforts towards the application of entomopathogenic fungal strains as anti-argasid biocontrol agents.     

Antigens from the midgut membranes of Ornithodoros erraticus induce lethal anti-tick immune responses in pigs and mice

Ornithodoros erraticus is an argasid tick that can transmit severe diseases such as human relapsing fever and African swine fever. In southern Europe O. erraticus lives in close association with swine on free-range pig farms. Application of acaricides for the eradication of O. erraticus from pig farms is inefficient. This is the reason why we tried to develop an anti-O. erraticus vaccine as alternative method of control. Accordingly, we were prompted to investigate the protective possibilities of a midgut membrane extract from the parasite (GME) that has not been studied hitherto. Administration of the GME with Freund's adjuvants (FAs) to pigs and mice induced a protective response able to kill 80% of the immature forms of the parasite in the first 72 h post-feeding and to reduce the fecundity of females by more than 50%. The action of the vaccine is the result of damage to the midgut wall of the argasid, and, in mice, it has been shown that this damage is mediated by activation of the complement system. In pigs, the administration of GME with alum, instead of with FAs, reduced the degree of protection. The protective antigens of the GME were expressed by all the developmental stages examined and are probably proteins from the luminal membrane of midgut epithelial cells. These antigens were seen to be more abundant in recently fed parasites than in fasting specimens, suggesting that their expression is induced after blood ingestion.     

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。     

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.     

Purification and characterization of a 45-kDa concealed antigen from the midgut membranes of Ornithodoros erraticus that induces lethal anti-tick immune responses in pigs

Ornithodoros erraticus is an argasid tick that can transmit severe diseases such as human relapsing fever and African swine fever. In the search for a vaccine against this parasite, a crude extract of tick midgut membranes (GME) was obtained that in pigs and mice induced a protective response able to kill up to 80% of the nymphs in the first 72 h post-feeding and to reduce the fecundity of females by more than 50%. To identify the protective antigens, the GME was subjected to successive biochemical fractionations and the resulting simpler protein fractions were inoculated in pigs. A 45-kDa antigen, the so-called Oe45, was detected, purified and demonstrated to be responsible for the protection induced by the GME. Oe45 seems to be a membrane protein that is presumably expressed on the luminal membrane of midgut epithelial cells. Oe45 consists of at least two differently charged bands (cationic and neutral), which show antigenic cross-reactivity. The possibility that these bands might be different isoforms of the same protein is discussed. Although Oe45 is constitutively expressed at low levels throughout the trophogonic cycle, its expression is up-regulated by the ingestion of blood, as suggested by the higher levels observed between 6 and 72 h post-feeding.     

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。     

Subolesin/akirin orthologs from Ornithodoros spp. soft ticks: cloning, RNAi gene silencing and protective effect of the recombinant proteins

Subolesin/akirin is a well characterized protective antigen highly conserved across vector species and thus potentially useful for the development of a broad-spectrum vaccine for the control of arthropod infestations including hard ticks, mosquitoes, sand flies and the poultry red mite Dermanyssus gallinae. Soft ticks could be also targeted by this vaccine if proved that the soft tick subolesin orthologs are conserved and induce protective immune responses too. However, to date no soft tick subolesin orthologs have been fully characterized nor tested as recombinant antigens in vaccination trials. The objectives of the present work were to clone and characterize the subolesin orthologs from two important vector species of soft ticks as Ornithodoros erraticus and O. moubata, to evaluate the effect of subolesin gene silencing by RNAi, and to test the protective value of the recombinant antigens in vaccination trials. The obtained results demonstrate that both soft tick subolesins are highly conserved showing more than 69% and 74% identity with those of hard ticks in their nucleotide and amino acid sequences, respectively. Additionally, we demonstrate that both soft ticks possess fully operative RNAi machinery, and that subolesin gene silencing by dsRNA injection inhibits oviposition indicating the involvement of subolesin in tick reproduction. Finally, vaccination with the recombinant soft tick subolesins induced a partial protective effect resulting in the reduction of the oviposition rate. These preliminary results encourage further studies on the use of recombinant subolesins as vaccines for the control of soft tick infestations, either alone or in combination with other specific molecules.     

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。     

An electron microscopic study of Cytoecetes phagocytophila infection in Ixodes ricinus

Tick-borne fever, caused by a rickettsia-like organism, Cytoecetes phagocytophila, is transmitted by the sheep tick Ixodes ricinus. An electron microscopic technique was developed to examine I ricinus for C phagocytophila infection. Infected and uninfected ticks were obtained from a laboratory maintained tick culture. All stages of I ricinus collected from one field site were examined; 44 per cent of nymphae and 32 per cent of adults were infected with C phagocytophila, but larvae were uninfected. This supports the previously held theory of transtadial, but not transovarial transmission of tick-borne fever.     

African swine fever virus infection of the bushpig (Potamochoerus porcus) and its significance in the epidemiology of the disease

Warthog (Phacochoerus aethiopicus), giant forest hog (Hylochoerus meinertzhageni) and bushpig (Potamochoerus porcus) are known to be susceptible to infection with African swine fever (ASF) virus. Little however, is known about the ecology of the disease in the bushpig. This study has shown that the bushpig remains viraemic for between 35 and 91 days following infection during which time it is able to infect the tick vector O. moubata. These ticks were able to transmit the disease to pigs. The virus persists in the lymphatic tissues for less than 34 weeks. Bushpigs infected with LIL 20/1 virus but not VIC T90/1 virus transmitted infection to in-contact pigs. Infected domestic pigs did not transmit the infection to in-contact bushpigs. ASF virus was able to replicate in in vitro cultures of bushpig leucocytes and endothelial cells. Recovered bushpigs could be re-infected with some strains of virus but not others. While it has been demonstrated that bushpigs remain carriers of ASFV following infection a complete understanding of their significance in the epidemiology of the disease awaits further investigations of their association with O. moubata.     

饲料安全和品质在非洲猪瘟防控中的作用及对策

自2018年8月非洲猪瘟在我国发生以来,生猪产业遭受了前所未有的打击,目前非洲猪瘟仍然没有有效疫苗,生猪复产任务任重道远。在非洲猪瘟防控常态化新形势下,饲料的安全和品质是非洲猪瘟防控中的重要一环。文章综述了饲料安全和品质在非洲猪瘟防控中的作用以及应对策略,为当前非洲猪瘟疫情下饲料安全和生猪健康养殖提供参考。     

Evaluation of an enzyme-linked immunosorbent assay to detect specific antibodies in pigs infested with the tick Ornithodoros erraticus (Argasidae)

Ornithodoros erraticus is known to transmit the virus that causes the highly contagious disease, African Swine Fever, in Spain. As part of the disease eradication campaign, an ELISA test to detect specific antibodies against the tick was developed. The ELISA, using salivary gland preparations as an antigen, showed high sensitivity and was able to detect as few as 10 adult ticks. The specific antibodies were detected in the sera 6 weeks after the primary infestation and strongly increased after the challenge. The utility of this test under field conditions was also tested.     

养殖场非洲猪瘟防控措施及实践

2018年8月3日,农业农村部发布辽宁沈阳发生全国首例非洲猪瘟。至今,全国32个省、自治区、直辖市、特别行政区公布共发生149起非洲猪瘟疫情,超过116万头猪只被扑杀。面对前所未有的非洲猪瘟,目前尚无有效的药物和疫苗预防,养猪行业面临种种危机。文章对非洲猪瘟及其危害做了简要介绍,并提出了防控非洲猪瘟的措施和建议。     

猪场重要虫媒及其传播病原研究进展

近年来,非洲猪瘟、牛结节性皮肤病等外来可由虫媒传播的疫病肆虐中国,而一些已在国外流行的虫媒传播病原如非洲马瘟等传入中国的风险也越来越高,严重危害中国畜牧养殖业的发展和公共卫生安全。特别是2018年8月以来非洲猪瘟在中国的流行给养猪业带来重要警示信息,即防止猪场媒介生物进入并阻断其携带病原的传播将成为猪场生物安全的重点。蚊、蝇、蠓及蜱等是猪场和发病猪群传播疫病的重要虫媒因素,虫媒种类及从虫媒中分离到的病毒、细菌、寄生虫等病原种类繁杂,虫媒生物特性的差异对病原的传播方式和传播能力也不尽相同。鉴于此,作者详细归纳了猪场存在的主要虫媒种类及其传播的重要猪病病原,包括猪乙型脑炎病毒、猪繁殖与呼吸综合征病毒、非洲猪瘟病毒、盖塔病毒、猪肠道冠状病毒、大肠杆菌、猪链球菌等,并探讨其危害性和传播风险,以降低猪场虫媒传播疾病所带来的经济损失。     

Updated distribution and host records for the argasid tick Ornithodoros (Pavlovskyella) zumpti: A potential vector of African swine fever virus in South Africa

African swine fever virus (ASFV) causes a lethal and contagious disease of domestic pigs. In South Africa, the virus historically circulated in warthogs and ornithodorid ticks that were only found in warthog burrows in the north of the country. Regulations implemented in 1935 to prevent transfer of infected animals or products to the south initially proved effective but from 2016 there have been outbreaks of disease in the south that cannot be traced to transfer of infection from the north. From 1963 there were widespread translocations of warthogs to the south, initially from a source considered to be free of ornithodorid ticks. We undertook to determine whether sylvatic circulation of ASFV occurs in the south, including identification of potential new vectors, through testing extralimital warthogs for antibody and ticks for virus. Results of testing warthogs for antibody and other species of ticks for virus will be presented separately. Here we report finding Ornithodoros (Pavlovskyella) zumpti ticks in warthog burrows for the first time. This occurred in the Eastern Cape Province (ECP) in 2019. Since African swine fever was recognised in the ECP for the first time in 2020 and outbreaks of the disease in domestic pigs continue to occur there, priority should be given to determining the distribution range and vector potential of O. (P.) zumpti for ASFV.     

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。     

非洲猪瘟血清学诊断技术研究进展

非洲猪瘟是一种病毒性、出血性、接触传播性疾病,具有极高的致死率。我国作为养猪大国,非洲猪瘟给我国造成巨大的经济损失。由于我国目前尚未有可用的商品化疫苗,只有尽早地发现非洲猪瘟并严格实施流行病学调查、消杀灭源才能有效防控非洲猪瘟。随着非洲猪瘟流行特征的变化,非典型临床病例、慢性感染猪逐渐增多,病毒血症不明显并且排毒不规律,仅靠病原学存在漏检可能,而血清学检测可作为病原学检测的补充,对于非洲猪瘟临床诊断具有重要意义。本文从流行病学、病毒结构、诊断标识以及现阶段常用的非洲猪瘟血清学检测方法进行综述,供非洲猪瘟血清学诊断研究以及疫情防控工作者参考。