Towards a better understanding of Rift Valley fever epidemiology in the south-west of the Indian Ocean

Rift Valley fever virus (Phlebovirus, Bunyaviridae) is an arbovirus causing intermittent epizootics and sporadic epidemics primarily in East Africa. Infection causes severe and often fatal illness in young sheep, goats and cattle. Domestic animals and humans can be contaminated by close contact with infectious tissues or through mosquito infectious bites. Rift Valley fever virus was historically restricted to sub-Saharan countries. The probability of Rift Valley fever emerging in virgin areas is likely to be increasing. Its geographical range has extended over the past years. As a recent example, autochthonous cases of Rift Valley fever were recorded in 2007–2008 in Mayotte in the Indian Ocean. It has been proposed that a single infected animal that enters a naive country is sufficient to initiate a major outbreak before Rift Valley fever virus would ever be detected. Unless vaccines are available and widely used to limit its expansion, Rift Valley fever will continue to be a critical issue for human and animal health in the region of the Indian Ocean.     

A Systematic Scoping Study of the Socio‐Economic Impact of Rift Valley Fever: Research Gaps and Needs

Rift Valley fever (RVF) is a severe mosquito‐borne disease affecting humans and domestic ruminants. RVF virus has been reported in most African countries, as well as in the Arabic Peninsula. This paper reviews the different types of socio‐economic impact induced by RVF disease and the attempts to evaluate them. Of the 52 papers selected for this review, 13 types of socio‐economic impact were identified according to the sector impacted, the level and temporal scale of the impact. RVF has a dramatic impact on producers and livestock industries, affecting public and animal health, food security and the livelihood of the pastoralist communities. RVF also has an impact on international trade and other agro‐industries. The risk of introducing RVF into disease‐free countries via the importation of an infected animal or mosquito is real, and the consequent restriction of access to export markets may induce dramatic economic consequences for national and local economies. Despite the important threat of RVF, few studies have been conducted to assess the socio‐economic impact of the disease. The 17 studies identified for quantitative analysis in this review relied only on partial cost analysis, with limited reference to mid‐ and long‐term impact, public health or risk mitigation measures. However, the estimated impacts were high (ranging from $5 to $470 million USD losses). To reduce the impact of RVF, early detection and rapid response should be implemented. Comprehensive disease impact studies are required to provide decision‐makers with science‐based information on the best intervention measure to implement ensuring efficient resource allocation. Through the analysis of RVF socio‐economic impact, this scoping study proposes insights into the mechanisms underpinning its often‐underestimated importance. This study highlights the need for comparative socio‐economic studies to help decision‐makers with their choices related to RVF disease management.     

A Rift Valley fever atlas for Africa

Rift Valley fever (RVF) epidemics have serious consequences for human and animal health and the livestock trade. Recent epidemics have occurred in previously unaffected regions, increasing concerns that the geographical range of RVF will continue to expand. We conducted an extensive, systematic review of the literature to obtain serological data for RVF in Africa, collected between 1970 and 2000 from human, livestock and wild ungulate populations. Aims were to calculate sub-national estimates of RVF infection prevalence and to define areas where no information was available. We presented the data (aggregated at the first administrative level of countries) using a geographical information system. Data from 71 publications were used to build a spatially explicit Bayesian logistic-regression model, with spatial and non-spatial random effects, allowing us to identify clusters of high and low RVF seroprevalence, and fixed effects that described the disparate nature of the survey subjects and methods. Significant high-prevalence clusters encompassed areas that had experienced epidemics during the late 20th century and significant low-prevalence clusters were located in contiguous areas of Western and Central Africa.     

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.     

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.     

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.     

Ability of a mutagenized virus variant to protect young lambs from Rift Valley fever

A live attenuated vaccine virus variant of Rift Valley fever (RVF) virus was developed by passaging a human isolate in tissue culture under the influence of the mutagen 5-fluorouracil. This virus variant (MV P12) has been assessed in this study as to its suitability as a vaccine, by testing its pathogenicity in young lambs and measuring its ability to induce a protective immune response. Even high doses of the vaccine virus failed to induce any of the clinical or histopathologic changes associated with classical RVF virus infection. Although the vaccine induced mild pyrexia when given in high doses, viremia was not induced. Neutralizing antibody and a protective immune response was elicited with even low doses of vaccine virus. These data, along with data of other workers on the lack of abortigenicity of this virus variant, indicate that the MV P12 variant of RVF virus is an excellent candidate for a safe and effective vaccine against RVF.     

Virus-like particle-based countermeasures against Rift Valley fever virus

Rift Valley fever virus (RVFV) is an arbovirus that causes significant morbidity and mortality in both humans and livestock. With increased world travel and the threat of bioterrorism, there is a real risk of RVFV spreading to na?ve geographical areas (Trans. R. Soc. Trop. Med. Hyg., 73, 1979, 618; MMWR Morb. Mortal. Wkly Rep., 49, 2000, 905). The introduction of RVFV would cause critical public health, agricultural and economic damage. Despite the clear need for an efficacious vaccine, there are no United States (US) Food and Drug Administration or US Department of Agriculture approved vaccines against RVFV. To address this need, a virus-like particle (VLP)-based vaccine candidate was developed. First, a non-replicating chimeric RVF VLP vaccine candidate was generated that protected mice and rats against a lethal RVFV challenge. This was followed by the development and optimization of conditions for production of RVF VLPs in insect and mammalian cells. Immunological studies demonstrated that VLP-based vaccine candidates elicit both humoral and cellular immune responses. Subsequent challenge studies using a lethal wild-type RVFV strain under high-containment conditions showed that RVF VLP vaccine candidates can completely protect mice and rats.     

Towards real-time prediction of Rift Valley fever epidemics in Africa

Outbreaks of Rift Valley fever (RVF) virus in Africa are characterized by distinct spatial and temporal patterns that are directly related to specific environmental parameters associated with mosquito vectors that function in the maintenance (endemic) and transmission (epizootic) cycles of the virus. National Oceanic and Atmospheric Administration (NOAA) satellites with limited resolution (1 km) can indirectly measure rainfall inexpensively over subcontinental or continental areas at a high temporal frequency, and identify regions with a high potential for viral activity. Within regions of likely viral activity, mosquito vector-breeding habitats (dambos) are identified and mapped with archived, high-quality, cloud-free, higher resolution data from LANDSAT (thematic mapper resolution 30 m) and SPOT (multispectral resolution 20 m) satellites. Active sensors, like airborne synthetic aperture radar systems (range resolution 1.6 m), are capable of detecting flooded habitats, even through cloud cover. By identifying flooded habitats within regions with a high likelihood of RVF activity, the potential source foci of an outbreak may be detected close to real-time and control efforts implemented prior to the start of a RVF epidemic/epizootic.     

Screening for Rift Valley fever infection in northern Somalia: a GIS based survey method to overcome the lack of sampling frame

Following repeated import bans imposed by Saudi Arabia on livestock originated from Somalia due to suspicion of Rift Valley fever (RVF) presence and the severe socio-economic consequences of this, it was imperative for the Somaliland government to carry out surveillance activities in order to determine the status of transboundary diseases in its territory. A GIS computer software (Arcview) was used to overcome the lack of lists of sampling sites due to the high mobility of pastoral nomadic herds in the study area. This method proved very convenient and flexible for the random selection of sampling sites and thus the compliance with the requirements by the World Organisation for Animal Health (OIE) for statistically valid methods if the surveillance outcome is to meet international recognition and acceptance. Screening in Somaliland in 2001 and in Puntland in 2003 which targeted mainly sheep and goats aged 1-2 years (97% of surveyed animals) revealed no signs compatible with the disease but an overall sero-prevalence of 2+/-0.02% (90/4570) and 5+/-0.3% (206/4050), respectively. The spatial distribution showed clusters of high sero-prevalence located mostly in the Nugal Valley. This trend was confirmed by the follow-up survey implemented in Somaliland in 2004 with a herd prevalence of 80+/-6% and a within-herd prevalence up to 50% located again in the Nugal Valley. This result suggests the maintenance and increase of RVF virus activity in the valley. In addition conditions favourable to the breeding and survival of the vector population and the high density of livestock make the Nugal Valley an area of high risk for a RVF outbreak where sentinel herds will be placed.     

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。     

Re-infection of wildlife populations with rinderpest virus on the periphery of the Somali ecosystem in East Africa

We report surveillance for rinderpest virus in wildlife populations in three major ecosystems of East Africa: Great Rift Valley, Somali and Tsavo from 1994 to 2003. Three hundred and eighty wild animals were sampled for detection of rinderpest virus, antigen or genome and 1133 sampled for antibody in sera from Kenya, Uganda, Ethiopia and Tanzania from 20 species. This was done modifying for wildlife the internationally recommended standards for rinderpest investigation and diagnosis in livestock. The animals were selected according to susceptibility and preference given to gregarious species, and populations were selected according to abundance, availability and association with livestock. Rinderpest virus, antigen and/or genome were detected in Kenya; within Tsavo, Nairobi and Meru National Parks. Serological results from 864 animals (of which 65% were buffalo) from the region were selected as unequivocal; showing the temporal and spatial aspects of past epidemics. Recent infection has been only in or peripheral to the Somali ecosystem (in Kenya). Our evidence supports the hypothesis that wildlife is not important in the long-term maintenance of rinderpest and that wildlife are infected sporadically most likely from a cattle source, although this needs to be proven in the Somali ecosystem. Wildlife will continue to be a key to monitoring the remaining virus circulation in Africa.     

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.     

Cloning and expression of Rift Valley fever virus nucleocapsid (N) protein and evaluation of a N-protein based indirect ELISA for the detection of specific IgG and IgM antibodies in domestic ruminants

Serodiagnosis of Rift Valley fever (RVF) currently relies on the use of live or inactivated whole virus as antigens. The recombinant nucleocapsid (N) protein of RVF virus was tested for diagnostic applicability in an indirect enzyme-linked immunosorbent assay (I-ELISA), using sera from experimentally infected sheep (n=128), vaccinated sheep (n=240), and field-collected sera from sheep (n=251), goats (n=362) and cattle (n=100). The N-protein based I-ELISA performed at least as good as VN and HI tests. In goat the diagnostic sensitivity (D-Sn) and specificity (D-Sp) of the I-ELISA was 100% when using the anti-species IgG conjugate. Using protein G as a detection system, the D-Sn and D-Sp in goats were 99.4% and 99.5%, in sheep field sera both 100%, in cattle 100% and 98.3%, respectively. The I-ELISA based on recombinant N-protein has the potential to complement the traditional assays for serodiagnosis of RVF. Advantages of the N-protein are its safety, stability and cost-effectiveness in use and production.     

Vaccination with Rift Valley fever virus live attenuated vaccine strain Smithburn caused meningoencephalitis in alpacas

Rift Valley fever (RVF) is a zoonotic, viral, mosquito-borne disease that causes considerable morbidity and mortality in humans and livestock in Africa and the Arabian Peninsula. In June 2018, 4 alpaca inoculated subcutaneously with live attenuated RVF virus (RVFV) Smithburn strain exhibited pyrexia, aberrant vocalization, anorexia, neurologic signs, and respiratory distress. One animal died the evening of inoculation, and 2 at ~20 d post-inoculation. Concern regarding potential vaccine strain reversion to wild-type RVFV or vaccine-induced disease prompted autopsy of the latter two. Macroscopically, both alpacas had severe pulmonary edema and congestion, myocardial hemorrhages, and cyanotic mucous membranes. Histologically, they had cerebral nonsuppurative encephalomyelitis with perivascular cuffing, multifocal neuronal necrosis, gliosis, and meningitis. Lesions were more severe in the 4-mo-old cria. RVFV antigen and RNA were present in neuronal cytoplasm, by immunohistochemistry and in situ hybridization (ISH) respectively, and cerebrum was also RVFV positive by RT-rtPCR. The virus clustered in lineage K (100% sequence identity), with close association to Smithburn sequences published previously (identity: 99.1–100%). There was neither evidence of an aberrant immune-mediated reaction nor reassortment with wild-type virus. The evidence points to a pure infection with Smithburn vaccine strain as the cause of the animals’ disease.     

Rift valley fever.

Rift Valley fever virus is an arthropod-borne Phlebovirus endemic in sub-Saharan Africa. Outbreaks also have occurred in Egypt, Madagascar, and most recently in the Arabian peninsula. Large epizootics occur at irregular intervals in seasons of above-average rainfall with persistent flooding and the appearance of large numbers of floodwater-breeding Aedine mosquitoes. The virus is transmitted transovarially and can remain dormant in mosquito eggs during dry interepizootic periods. Low-level virus circulation occurs in high-rainfall forested areas, although individual cases of the disease rarely are recognized. RVF is characterized by abortion in pregnant animals and a high mortality in newborn lambs, kids, and calves. Susceptibility to disease is related to age and breed, with severe disease occurring in the young of exotic sheep and cattle breeds. RVF is a zoonosis, and human beings experience an influenza-like illness and, more rarely, complications such as encephalitis or retinitis. The virus causes a severe hepatitis, particularly in aborted fetuses and newborn lambs. The disease must be differentiated from other conditions that cause death with hepatitis and jaundice. Both an inactivated and a live attenuated vaccine are available. New-generation vaccines are being tested, because the existing mousebrain-attenuated strain induces fetal teratology or abortion in a percentage of pregnant animals. Diagnosis is based on histopathology or the demonstration of viral antigen or antibody.     

裂谷热研究进展

裂谷热是一种烈性毒性人畜共患病,被OIE列为必须报告的疫病.幼年动物感染后,病死率高达100%.人感染此病后,病死率约为1%.2010年3月,南非再度发生疫情,导致186人感染,18人死亡;并调查出154例动物感染,146例死亡,感染动物病死率高达95%.该病的流行不但对人类健康和养殖业构成威胁,其病毒还可能被用于生物...     

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,...     

The first serological evidence for Rift Valley fever infection in the camel,goitered gazelle and Anatolian water buffaloes in Turkey

Tropical Animal Health and Production - Rift valley fever (RVF), a vector-borne zoonotic disease, is caused by a phlebovirus (family Bunyaviridae). The virus was initially characterized...