Serological survey of Rift Valley fever in sheep on the Ivory Coast]

A serological survey of Rift Valley fever was carried out in sheep in C?te-d'Ivoire. Thousand and fifty one seras collected between 1988 and 1990 in the South of the country were tested for IgG and IgM by ELISA with two objectives: determining the incidence of the Rift Valley fever and analysing the role of this virus in reproductive failure and abortion. The incidence rate was 6.85%. No difference was found between the three different geographic areas nor between the three years of the survey. Antibody prevalence increased significantly with age. The Rift Valley fever must be considered as enzootic in C?te-d'Ivoire. A significant relationship was found between positivity and abortion in ewes. Thus, the economic impact of Rift Valley fever has to be studied. The presence of antibodies in young animals aged from 6 months to 1 year, showed a recent activity of the virus; a permanent epidemio-surveillance of the Rift Valley fever in C?te-d'Ivoire is needed, because of the potential risk for human population in contact with the animals.     

裂谷热的研究新进展

在非洲,裂谷热引起了严重的公共卫生安全和经济危害的问题,并且该病对世界其他国家和地区构成严重的威胁。该病已作为全球优先防范的跨境动物疫病之一,本文从裂谷热的流行病学特点、传播的风险因素、发病机理、诊断技术和疫苗研究等5个方面概述了其最新研究进展,旨在为研究更加有效的方法来防控裂谷热病毒的传播。     

Rift Valley fever virus(Bunyaviridae: Phlebovirus): an update on pathogenesis, molecular epidemiology, vectors, diagnostics and prevention

Rift Valley fever(RVF) virus is an arbovirus in the Bunyaviridae family that, from phylogenetic analysis, appears to have first emerged in the mid-19th century and was only identified at the beginning of the 1930's in the Rift Valley region of Kenya. Despite being an arbovirus with a relatively simple but temporally and geographically stable genome, this zoonotic virus has already demonstrated a real capacity for emerging in new territories, as exemplified by the outbreaks in Egypt (1977), Western Africa (1988) and the Arabian Peninsula (2000), or for re-emerging after long periods of silence as observed very recently in Kenya and South Africa. The presence of competent vectors in countries previously free of RVF, the high viral titres in viraemic animals and the global changes in climate, travel and trade all contribute to make this virus a threat that must not be neglected as the consequences of RVF are dramatic, both for human and animal health. In this review, we present the latest advances in RVF virus research. In spite of this renewed interest, aspects of the epidemiology of RVF virus are still not fully understood and safe, effective vaccines are still not freely available for protecting humans and livestock against the dramatic consequences of this virus.     

Complement fixing antibodies against arboviruses in horses at Lagos, Nigeria

Sixty-two sera horse collected from two stables at Lagos, Nigeria, were tested for complement fixing antibody to 8 arbovirus antigens; Chikungunya, Igbo-Ora, Yellow fever, Wesselsbron, West Nile, Potiskum, Uganda S and Rift Valley fever. Ten per cent of the horse sera examined contained CF antibody to one or more of the test antigens and indicated considerable arbovirus activity in the two stables. Reactions with flavivirus antigens were most common and the highest antibody titres were obtained with Wesselsbron and Yellow fever viruses. Eleven per cent of the sera tested reacted with alphavirus antigens while 10 per cent were positive for Rift Valley fever virus CF antibodies.     

Seroprevalence of Rift Valley fever virus in cattle in the Democratic Republic of the Congo

Tropical Animal Health and Production - This study aimed at assessing the serological and virological status of Rift Valley fever virus (RVFV) in cattle from four climatically diverse zones of the...     

Competitive ELISA for the detection of antibodies to Rift Valley fever virus in goats and cattle

Rift Valley fever virus (RVFV) is one of the important emerging viral diseases of serious impact in public health and animal hygiene both in human and animal industries. In this study, we developed a monoclonal antibody-based competitive ELISA for the detection of antibodies to RVFV in goats and cattle. The recombinant N protein of RVFV was expressed in E. coli with a six-histidine tag, and the purified N protein was used for detecting antigen with a competitive monoclonal antibody against RVFV antibodies. The competitive ELISA (C-ELISA) could detect antibodies at 9-11 days after inoculation in goats and cattle with a sensitivity of 94.7% (virus neutralization titer >32) and specificity of 99.7%, respectively. In addition, the C-ELISA did not show any cross-reactivity with positive sera against arboviruses such as Akabane, Aino, Chuzan, Ibaraki and bovine ephemeral fever virus, which are prevalent viral agents in ruminant animals throughout Southeast Asia. The results of the present study indicate that the C-ELISA is a simple, rapid and convenient serodiagnostic method for RVFV in goats and cattle.     

A review of zoonotic disease surveillance supported by the Armed Forces Health Surveillance Center

The Armed Forces Health Surveillance Center (AFHSC), Division of Global Emerging Infections Surveillance and Response System conducts disease surveillance through a global network of US Department of Defense research laboratories and partnerships with foreign ministries of agriculture, health and livestock development in over 90 countries worldwide. In 2010, AFHSC supported zoonosis survey efforts were organized into four main categories: (i) development of field assays for animal disease surveillance during deployments and in resource limited environments, (ii) determining zoonotic disease prevalence in high-contact species which may serve as important reservoirs of diseases and sources of transmission, (iii) surveillance in high-risk human populations which are more likely to become exposed and subsequently infected with zoonotic pathogens and (iv) surveillance at the human-animal interface examining zoonotic disease prevalence and transmission within and between human and animal populations. These efforts have aided in the detection, identification and quantification of the burden of zoonotic diseases such as anthrax, brucellosis, Crimean Congo haemorrhagic fever, dengue fever, Hantaan virus, influenza, Lassa fever, leptospirosis, melioidosis, Q fever, Rift Valley fever, sandfly fever Sicilian virus, sandfly fever Naples virus, tuberculosis and West Nile virus, which are of military and public health importance. Future zoonotic surveillance efforts will seek to develop local capacity for zoonotic surveillance focusing on high risk populations at the human-animal interface.     

Experimental Rift Valley fever in West African Dwarf sheep.

West African Dwarf sheep were challenged with a low mouse brain-passaged Rift Valley fever virus (Ib-AR 55172) isolated from Nigeria. Viraemia, mild febrile reaction and neutralising antibodies were demonstrated in inoculated animals.     

Recombinant DNA technology for the preparation of subunit vaccines

Recombinant DNA technology appears to be on the verge of producing safe and effective protein vaccines for animal and human diseases. The procedure is applicable to most viruses because their isolated surface proteins generally possess immunogenic activity. Strategies used for the preparation and cloning of the appropriate genes depend on the characteristics of the viral genomes: whether DNA or RNA; their size, strandedness, and segmentation; and whether messenger RNA are monocistronic or polycistronic. Cloned surface proteins of foot-and-mouth disease and hepatitis B viruses are being tested for possible use as practical vaccines. Two doses of the cloned foot-and-mouth disease viral protein have elicited large amounts of neutralizing antibody and have protected cattle and swine against challenge exposure with the virus. Surface proteins have also been cloned for the viruses of fowl plague, influenza, vesicular stomatitis, rabies, and herpes simplex. Cloning is in progress for surface proteins of viruses causing canine parvovirus gastroenteritis, human papillomas, infectious bovine rhinotracheitis, Rift Valley fever, and paramyxovirus diseases. In addition, advances in recombinant DNA and other facilitating technologies have rekindled interest in the chemical synthesis of polypeptide vaccines for viral diseases. The bioengineering of bacterial vaccines is also under way. Proteinaceous pili of enterotoxigenic Escherichia coli are being produced in E coli K-12 strains for use as vaccines against neonatal diarrheal diseases of livestock.     

The transmission potential of Rift Valley fever virus among livestock in the Netherlands: a modelling study

Abstracts

Rift Valley fever virus (RVFV) is a zoonotic vector-borne infection and causes a potentially severe disease. Many mammals are susceptible to infection including important livestock species. Although currently confined to Africa and the near-East, this disease causes concern in countries in temperate climates where both hosts and potential vectors are present, such as the Netherlands. Currently, an assessment of the probability of an outbreak occurring in this country is missing. To evaluate the transmission potential of RVFV, a mathematical model was developed and used to determine the initial growth and the Floquet ratio, which are indicators of the probability of an outbreak and of persistence in a periodic changing environment caused by seasonality. We show that several areas of the Netherlands have a high transmission potential and risk of persistence of the infection. Counter-intuitively, these are the sparsely populated livestock areas, due to the high vector-host ratios in these areas. Culex pipiens s.l. is found to be the main driver of the spread and persistence, because it is by far the most abundant mosquito. Our investigation underscores the importance to determine the vector competence of this mosquito species for RVFV and its host preference.     

Sero-prevalences of selected cattle diseases in the Kafue flats of Zambia

Sera from five traditionally managed herds grazing in the Kafue flats were tested for antibodies to bovine viral diarrhoea-mucosal disease (BVD-MD), parainfluenza 3 (PI3), infectious bovine rhinotracheitis-infectious pustular vulvovaginitis (IBR-IPV), bovine adenovirus 3 (BAV3) and Bluetongue (BT). The sero-prevalences of the first four diseases were respectively 76.2, 94.4, 42.1 and 87.4%. Five samples (2.3%) gave doubtful reactions for BT. Prevalences of 28.5% for brucellosis, 14% for Rift Valley fever (RFV), 0.9% for Q fever and 11.2% for chlamydiosis were also recorded. Significantly higher values for BVD-MD (p<0.005), IBR-IPV (p<0.01) and brucellosis (p<0.05) were found in animals over 1 year of age. No differences were recorded between herds or between male and female animals.The high concentration of wild and domestic ruminants grazing together in the flood plains during the dry season may be a major determinant of the high values observed. Traditional farmers, slaughterhouse workers and other people involved in livestock production are particularly at risk of contracting brucellosis and RVF because of the high prevalences in cattle and local habits favourable to their transmission.     

Comparison of the pathogenicity for pregnant sheep of Rift Valley fever virus and a live attenuated vaccine

A live attenuated mutant of Rift Valley fever virus, MV P12, was previously shown to be non-pathogenic in young lambs, but capable of producing protective immunity. The studies reported here show that the abortion in sheep caused by an infection with virulent virus is the result of necrosis of the maternal villi and cotyledons arising from an acute inflammation of the maternal caruncles. Pregnant ewes infected with the attenuated mutant virus MV P12 showed none of these lesions in the placenta and gave birth to healthy lambs. Colostrum from ewes infected with MV P12 virus was able to induce protective immunity in the offspring. These data along with previously published results suggest that the mutant virus MV P12 is an excellent candidate for use as a live attenuated veterinary vaccine.     

Rift Valley fever in Madagascar in 1991. Sero-epidemiological studies in cattle]

Rift Valley fever (RVF) virus was detected for the first time in Madagascar in 1979, but without any impact on human and animal populations. However, in 1990 and 1991, several outbreaks with massive cattle abortions were described. Since that period, seroepidemiological surveys have been conducted on the East coast and in the highlands (outbreak areas), in the high cattle density regions, and in the national slaughter house in Antananarivo. A high RVF IgM antibody prevalence was detected in the outbreak areas during the epizootics. This IgM prevalence thereafter decreased and was followed by an IgG high prevalence in all tested regions. Hypotheses on the occurrence of the virus in Madagascar, outbreak origins and virus circulation on the island are discussed.     

An epizootic of Rift Valley fever in Egypt in 1977

A disease causing increased mortality and abortion in domestic animals during a 1977 epizootic in Egypt was identified as Rift Valley fever (RVF) virus. The epizootic included extensive human involvement reflected clinically as either an acute febrile, ocular, encephalitic, or fatal haemorrhagic form of RVF disease. The virus was again isolated from humans and animals during a second RVF epizootic in the summer of 1978.     

First serological investigation of peste-des-petits-ruminants and Rift Valley fever in Tunisia

This study, carried out between September 2006 and January 2007, is the first cross-sectional serological investigation of peste-des-petits-ruminants (PPR) and Rift Valley fever (RVF) in Tunisia. The objective was to assess the potential need to develop a dual, recombinant PPR–RVF vaccine and how such a vaccine might be utilised in Tunisia. An overall PPR seroprevalence of 7.45% was determined, a finding supported by the high specificity (99.4%) and sensitivity (94.5%) of the ELISA used. On assessment of the diversity and density of mosquitoes in the sampling area, four species of RVF-vectors of the genus Aedes and Culex were identified. However, no serological evidence of RVF was found despite the use of a highly sensitive ELISA (99–100%). Larger scale investigations are underway to confirm these findings and the continuation of the emergency vaccination program against these two diseases remains valid.     

Risk assessment of the introduction of Rift Valley fever from the Horn of Africa to Yemen via legal trade of small ruminants

Rift Valley fever (RVF) is a mosquito-borne viral zoonosis of increasing global importance. Occurring since 1930 across Africa, it was detected for the first time in Saudi Arabia and Yemen in September 2000, leading to human deaths and major losses in livestock populations. Assuming the virus has not survived in Yemen or has been circulating at a low level, authors qualitatively assessed the likelihood of “re-introduction” of RVF into Yemen through the legal importation of small ruminants from the Horn of Africa. The overall probability of introduction was assessed very low to medium, increasing during festival periods and higher when considering a direct transmission exposure as compared to a vectorial transmission exposure. The uncertainty was considered to be medium underlining important gaps in information that need to be fulfilled in the region. Options to reduce the risk are proposed and discussed, including possible improvements of the current Yemeni quarantine system.     

New data regarding distribution of cattle ticks in the south-western Indian Ocean islands

Recent studies have produced new insight into the origin and distribution of some cattle ticks in the south-western Indian Ocean islands. Rhipicephalus appendiculatus, introduced from Tanzania in 2002, is now well established on Grande Comore but has not yet reached the other islands of the archipelago (Mohéli, Anjouan and Mayotte). Only one of the two clades identified in Africa has settled so far. Amblyomma variegatum, which was not supposed to be able to persist in the Antananarivo region (1300 m) nor in other Malagasy regions of high altitude without regular introductions of ticks by infested cattle, is now endemic as a general rule up to 1600 m although other regions of lower altitude (1400 m) are still free of the tick. This species remains confined in a small area of the west coast on La Reunion Island. On the contrary, Hyalomma dromedarii could not settle on Madagascar where it was introduced in 2008 and Rhipicephalus evertsi evertsi is not yet present in Grande Comore despite regular introductions by infested cattle from Tanzania. A phylogeographic approach has been carried out at an intra-specific level for A. variegatum. This study has led to the identification of two main lineages, one covering all species distribution and one restricted to East Africa and the Indian Ocean area. These two lineages are in sympatry in Madagascar where a high genetic diversity has been described, whereas a lower genetic diversity is observed on other islands. These results seem to agree with the historical data concerning the introduction of the tick in the Indian Ocean area.     

裂谷热病毒Gn蛋白主要抗原区的串联表达和多克隆抗体制备

裂谷热(Rift Valley fever,RVF)是由裂谷热病毒(Rift Valley fever virus,RVFV)引起的一种烈性人兽共患传染病。RVFV囊膜蛋白Gn可诱导产生中和抗体,是RVFV检测方法和疫苗研究的重要抗原靶标。本研究通过分析蛋白抗原位点信息,构建包含Gn蛋白两个主要抗原区域的重组表达载体,随后将质粒转化至BL21感受态细胞,以IPTG诱导重组蛋白表达并优化蛋白表达条件,通过Western Blot鉴定重组蛋白;将重组蛋白免疫BALB/c小鼠,制备多克隆抗体,并以ELISA、Western Blot、IFA检测多克隆抗体的反应性。结果显示:诱导表达的Gn重组蛋白分子质量约为45 kDa;蛋白表达条件优化为IPTG终浓度0.25 mmol/L,诱导时间5 h;Western Blot鉴定发现蛋白成功表达。通过ELISA测定小鼠三免后血清抗体,结果发现抗体效价大于1:51200;Western Blot检测显示,制备的多抗血清能与重组蛋白发生反应;进一步的IFA检测结果表明,制备的多克隆抗体可与真核质粒转染细胞中表达的Gn蛋白反应。本研究获得的Gn重组蛋白及制备的多克隆抗体为后续RVFV检测方法的建立奠定了基础。     

Zoonotic aspects of arenavirus infections

To date, the International Committee for Taxonomy of Viruses recognizes that the family Arenaviridae contains a unique genus Arenavirus that includes 22 viral species. There are nine additional arenaviruses that either have been discovered recently, or which taxonomic status remains pending. Arenaviruses have been classified according to their antigenic properties into two groups, the Lassa-Lymphocytic choriomeningitis (LCM) serocomplex and the Tacaribe serocomplex which has been further divided into four evolutionary lineages. Each arenavirus is more or less tightly associated with a mammal host. The distribution of the host dictates the distribution of the virus. Humans may become infected by arenaviruses through direct contact with infected rodents, including bites, or through inhalation of infectious rodent excreta and secreta. Lassa, Junin, Machupo, Guanarito, and Sabia viruses are known to cause a severe hemorrhagic fever, in western Africa, Argentina, Bolivia, Venezuela, and Brazil, respectively. Infection by LCM virus can result in acute central nervous system disease, congenital malformations, and infection in organ transplantation recipients. Detection of arenaviruses in their animal host can be achieved by virus isolation, and has recently taken advantage of PCR-based techniques. The approach based on consensus degenerate primers has shown efficient for both detection of known arenaviruses, and discovery of new arenaviruses.