Rift Valley fever in Namibia, 2010

Re-Emergence of Rift Valley Fever Virus Lineage H in Senegal in 2022: In Vitro Characterization and Impact on Its Global Emergence in West Africa

Rift Valley fever (RVF) is a re-emerging vector-borne zoonosis with a high public health and veterinary impact. In West Africa, many lineages were previously detected, but since 2020, lineage H from South Africa has been the main cause of the outbreaks. In this study, clinical samples collected through national surveillance were screened for RVF virus (RVFV) acute infection by RT-PCR and IgM ELISA tests. Sequencing, genome mapping and in vitro phenotypic characterization in mammal cells were performed on RT-PCR positive samples in comparison with other epidemic lineages (G and C). Four RVFV human cases were detected in Senegal and the sequence analyses revealed that the strains belonged to lineage H. The in vitro kinetics and genome mapping showed different replication efficiency profiles for the tested RVFV lineages and non-conservative mutations, which were more common to lineage G or specific to lineage H. Our findings showed the re-emergence of lineage H in Senegal in 2022, its high viral replication efficiency in vitro and support the findings that genetic diversity affects viral replication. This study gives new insights into the biological properties of lineage H and calls for deeper studies to better assess its potential to cause a future threat in Senegal.

Contemporary epidemiological data of Rift Valley fever virus in humans, mosquitoes and other animal species in Africa: A systematic review and meta-analysis

Rift Valley fever (RVF) is a severe zoonotic mosquito-borne disease that represents an important threat to human and animal health, with major public health and socioeconomic impacts. This disease is endemic throughout many African countries and the Arabian Peninsula. This systematic review with meta-analysis was conducted to determine the RVF prevalence in humans, mosquitoes and other animal species in Africa. The review also provides contemporary data on RVF case fatality rate (CFR) in humans. In this systematic review with meta-analysis, a comprehensive literature search was conducted on the PubMed, Embase, Web of Science and Global Index Medicus databases from January 2000 to June 2022 to identify relevant studies. Pooled CFR and prevalence estimates were calculated using the random-effects model. Subgroup analysis and sensitivity analysis were performed, and the I2 -statistic was used to investigate a potential source of heterogeneity. A total of 205 articles were included in the final analysis. The overall RVF CFR in humans was found to be 27.5% [95% CI = 8.0-52.5]. The overall pooled prevalence was 7.8% [95% CI = 6.2-9.6] in humans and 9.3% [95% CI = 8.1-10.6] in animals, respectively. The RVF prevalence in individual mosquitoes ranged from 0.0% to 25%. Subgroup analysis showed substantial heterogeneity with respect to geographical regions and human categories. The study shows that there is a correspondingly similar prevalence of RVF in human and animals; however, human CFR is much higher than the observed prevalence. The lack of a surveillance programme and the fact that this virus has subclinical circulation in animals and humans could explain these observations. The implementation of a One Health approach for RVF surveillance and control would be of great interest for human and animal health.

Immunogenicity and safety studies of an inactivated vaccine against Rift Valley fever

Rift Valley fever (RVF) is an emerging transboundary, mosquito-borne, zoonotic viral disease caused by a single serotype of a virus belonging to the Phenuiviridae family (genus Phlebovirus). It is considered an important threat to both agriculture and public health in endemic areas, because the virus, transmitted by different mosquito genera, leads to abortions in susceptible animal hosts especially sheep, goat, cattle, and buffaloes, resulting in severe economic losses. Humans can also acquire the infection, and the major sources are represented by the direct contact with infected animal blood, aerosol, consumption of unpasteurized contaminated milk and the bite of infected mosquitoes. Actually, the EU territory does not seem to be exposed to an imminent risk of RVFV introduction, however, the recent outbreaks in a French overseas department and some cases detected in Turkey, Tunisia and Libya, raised the attention of the EU for a possible risk of introduction of infected vectors. Thus, there is an urgent need to develop new therapeutic and/or preventive drugs, such as vaccines. In our work, we studied the immunogenicity of an inactivated and adjuvanted vaccine produced using a Namibian field strain of RVF virus (RVFV). The vaccine object of this study was formulated with Montanide Pet Gel A, a polymer-based adjuvant that has been previously reported for its promising safety profile and for the capacity to elicit a strong immune response. The produced inactivated vaccine was tested on six sheep and the level of IgM and IgG after the immunization of animals was evaluated by a commercial competitive ELISA, in order to assess the immunogenicity profile of our vaccine and to evaluate its potential use, as an alternative to the attenuated vaccines commercially available, in case of Rift Valley fever epidemic disease on EU territory. Following the administration of the second dose, 35 days after the first one, all animals seroconverted.

Detection of Rift Valley Fever Virus Lineage H from South Africa through Syndromic Sentinel Surveillance Network in Senegal

Background

Rift Valley fever virus (RVFV) is an arbovirus that causes epizootics and epidemics among livestock population and humans. Our surveillance system has revealed multiple emergences and re-emergences of RVFV in West Africa over the last decade.

Methods

The Sentinel Syndromic Surveillance Network in Senegal (4S) has been implemented since 2011. Samples from human suspected arbovirus infection in 4S sentinel sites were sent to Institut Pasteur de Dakar (IPD), where arbovirus diagnosis by enzyme-linked immunosorbent assay (ELISA), real-time reverse transcription polymerase chain reaction (RT-PCR), and virus isolation was performed. Overall, IPD has received a total of 1149 samples from arboviral suspected patients through the 4S network from January to December 2020. These samples were screened for 7 arboviruses including RVFV. Whole-genome sequencing of positive RVFV samples by RT-PCR was performed using the Illumina Miseq platform followed by genome assembly. Phylogenetic analyses were performed using MEGA X.

Results

Out of the 1149 arbovirus suspected cases, 4 RVFV-positive samples were detected with RT-PCR while 5 RVFV-positive samples were detected by ELISA. Complete genome sequences were obtained for 3 strains among the 4 positive samples by RT-PCR. Phylogenetic analyses indicated an emergence of a virus first described in South Africa during a major outbreak.

Conclusions

This strong surveillance system allowed the detection of an RVFV outbreak in Senegal in 2020. The obtained genomes clustered with strains from South Africa belonging to lineage H. This calls for implementation of a strong surveillance system for wild animals, humans, and livestock simultaneously in all African countries.

Rift valley fever in Africa with the emerging interest in Libya

Rift valley fever (RVF) is an acute vector-borne viral zoonotic disease of domestic and wild ruminants. The RVF virus (RVFV) belonging to the Phlebovirus genus of the Bunyaviridae family causes this disease. Studies have shown that mosquitoes are the vectors that transmit RVFV. Specifically, Aedes and Culex mosquito species are among the many vectors of this virus, which affects not only sheep, goats, buffalo, cattle, and camels but also human beings. Since the 30s of the last century, RVF struck Africa, and to a lesser extent, Asian continents, with subsequent episodes of epizootic, epidemic, and sporadic outbreaks. These outbreaks, therefore, resulted in the cumulative loss of thousands of human lives, thereby disrupting the livestock market or only those with seropositive cases. After that outbreak episode, RVF was not reported in Libya until January 13, 2020, where it was reported for the 1st time in a flock of sheep and goats in the southern region of the country. Although insufficient evidence to support RVF clinical cases among the confirmed seropositive animals exists, neither human cases nor death were reported in Libya. Yet, the overtime expansion of RVF kinetics in the Libyan neighborhoods, in addition to the instability and security vacuum experienced in the country, lack of outbreak preparedness, and the availability of suitable climatic and disease vector factors, makes this country a possible future scene candidate for RVF expansion. Urgently, strengthening veterinary services (VS) and laboratory diagnostic capacities, including improvement of monitoring and surveillance activity programs, should be implemented in areas at risk (where imported animals crossing borders from Libyan neighborhoods and competent vectors are found) at national, sub-national, and regional levels. The Libyan government should also implement a tripartite framework (one health approach) among the veterinary public health, public health authority, and environmental sanitation sectors to implement RVF surveillance protocols, along with an active partnership with competent international bodies (OIE, FAO, and WHO). Therefore, this review comprises the most updated data regarding the epidemiological situation of RVF infections and its socioeconomic impacts on African and Asian continents, and also emphasize the emerging interest of RVF in Libya.

Genetic Diversity of Rift Valley Fever Strains Circulating in Namibia in 2010 and 2011

Outbreaks of Rift Valley fever (RVF) occurred in Namibia in 2010 and 2011. Complete genome characterization was obtained from virus isolates collected during disease outbreaks in southern Namibia in 2010 and from wildlife in Etosha National Park in 2011, close to the area where RVF outbreaks occurred in domestic livestock. The virus strains were sequenced using Sanger sequencing (Namibia_2010) or next generation sequencing (Namibia_2011). A sequence-independent, single-primer amplification (SISPA) protocol was used in combination with the Illumina Next 500 sequencer. Phylogenetic analysis of the sequences of the small (S), medium (M), and large (L) genome segments of RVF virus (RVFV) provided evidence that two distinct RVFV strains circulated in the country. The strain collected in Namibia in 2010 is genetically similar to RVFV strains circulating in South Africa in 2009 and 2010, confirming that the outbreaks reported in the southern part of Namibia in 2010 were caused by possible dissemination of the infection from South Africa. Isolates collected in 2011 were close to RVFV isolates from 2010 collected in humans in Sudan and which belong to the large lineage containing RVFV strains that caused an outbreak in 2006–2008 in eastern Africa. This investigation showed that the RVFV strains circulating in Namibia in 2010 and 2011 were from two different introductions and that RVFV has the ability to move across regions. This supports the need for risk-based surveillance and monitoring.

External quality assessment of Rift Valley fever diagnosis in 17 veterinary laboratories of the Mediterranean and Black Sea regions

Rift Valley fever (RVF) is an arboviral zoonosis that primarily affects ruminants but can also cause illness in humans. The increasing impact of RVF in Africa and Middle East and the risk of expansion to other areas such as Europe, where competent mosquitos are already established, require the implementation of efficient surveillance programs in animal populations. For that, it is pivotal to regularly assess the performance of existing diagnostic tests and to evaluate the capacity of veterinary labs of endemic and non-endemic countries to detect the infection in an accurate and timely manner. In this context, the animal virology network of the MediLabSecure project organized between October 2016 and March 2017 an external quality assessment (EQA) to evaluate the RVF diagnostic capacities of beneficiary veterinary labs. This EQA was conceived as the last step of a training curriculum that included 2 diagnostic workshops that were organized by INIA-CISA (Spain) in 2015 and 2016. Seventeen veterinary diagnostic labs from 17 countries in the Mediterranean and Black Sea regions participated in this EQA. The exercise consisted of two panels of samples for molecular and serological detection of the virus. The laboratories were also provided with positive controls and all the kits and reagents necessary to perform the recommended diagnostic techniques. All the labs were able to apply the different protocols and to provide the results on time. The performance was good in the molecular panel with 70.6% of participants reporting 100% correct results, and excellent in the serological panel with 100% correct results reported by 94.1% of the labs. This EQA provided a good overview of the RVFV diagnostic capacities of the involved labs and demonstrated that most of them were able to correctly identify the virus genome and antibodies in different animal samples.

Risk assessment for the Rift Valley fever occurrence in China: Special concern in south-west border areas

Rift Valley fever (RVF) is a mosquito-borne zoonotic disease. Since its first outbreak in 1930, RVF epidemics have caused huge economic losses and public health impacts in Africa. In 2000, RVF became a disease of global concern as it spread to the Arabian Peninsula. In our study, a Geographic Information System-based risk assessment for the occurrence of Rift Valley fever in China was established by means of ecological niche modelling. Based on occurrence records (RVF records from FAO EMPRES-i, vector records from literatures and GBIF) and high-resolution environmental layers, the prediction maps of RVF occurrence probability and distribution of five potential RVF vectors in China were modelled using Maxent. An internal validation was adopted for model verification, and high AUC values were obtained (0.918 for RVF and 0.837-0.992 for vectors). By overlaying the RVF prediction map with the combined RVF vector prediction map using Fuzzy overlay tool ('AND' operator) of ArcMap 10.2, we got the first risk map of possible RVF vector transmission. This map was further overlaid with the latest livestock distribution map ('AND' operator) to generate the second risk map of possible RVF threat to domestic livestock. The south-west border provinces in China, Yunnan, Guangxi and Tibet were predicted to have a high possibility of RVF occurrence. Conditions conducive to the local amplification of RVF also exist in these areas. Temperature seasonality, mean temperature of dry season and precipitation of the driest month were considered as key environmental variables for RVF, and common environmental conditions were found conductive for vectors. It is suggested to establish proper surveillance systems in south-west border areas to minimize the possibility of RVF invasion. Our findings can serve as a valuable reference for prevention measures to be implemented.

Livestock Challenge Models of Rift Valley Fever for Agricultural Vaccine Testing

Since the discovery of Rift Valley Fever virus (RVFV) in Kenya in 1930, the virus has become widespread throughout most of Africa and is characterized by sporadic outbreaks. A mosquito-borne pathogen, RVFV is poised to move beyond the African continent and the Middle East and emerge in Europe and Asia. There is a risk that RVFV could also appear in the Americas, similar to the West Nile virus. In light of this potential threat, multiple studies have been undertaken to establish international surveillance programs and diagnostic tools, develop models of transmission dynamics and risk factors for infection, and to develop a variety of vaccines as countermeasures. Furthermore, considerable efforts to establish reliable challenge models of Rift Valley fever virus have been made and platforms for testing potential vaccines and therapeutics in target species have been established. This review emphasizes the progress and insights from a North American perspective to establish challenge models in target livestock such as cattle, sheep, and goats in comparisons to other researchers' reports. A brief summary of the potential role of wildlife, such as buffalo and white-tailed deer as reservoir species will also be discussed.

Systematic Review of Important Viral Diseases in Africa in Light of the 'One Health' Concept

Emerging and re-emerging viral diseases are of great public health concern. The recent emergence of Severe Acute Respiratory Syndrome (SARS) related coronavirus (SARS-CoV-2) in December 2019 in China, which causes COVID-19 disease in humans, and its current spread to several countries, leading to the first pandemic in history to be caused by a coronavirus, highlights the significance of zoonotic viral diseases. Rift Valley fever, rabies, West Nile, chikungunya, dengue, yellow fever, Crimean-Congo hemorrhagic fever, Ebola, and influenza viruses among many other viruses have been reported from different African countries. The paucity of information, lack of knowledge, limited resources, and climate change, coupled with cultural traditions make the African continent a hotspot for vector-borne and zoonotic viral diseases, which may spread globally. Currently, there is no information available on the status of virus diseases in Africa. This systematic review highlights the available information about viral diseases, including zoonotic and vector-borne diseases, reported in Africa. The findings will help us understand the trend of emerging and re-emerging virus diseases within the African continent. The findings recommend active surveillance of viral diseases and strict implementation of One Health measures in Africa to improve human public health and reduce the possibility of potential pandemics due to zoonotic viruses.

The challenging management of Rift Valley Fever in humans: literature review of the clinical disease and algorithm proposal

Rift Valley Fever (RVF) is an emerging zoonotic arbovirus with a complex cycle of transmission that makes difficult the prediction of its expansion. Recent outbreaks outside Africa have led to rediscover the human disease but it remains poorly known. The wide spectrum of acute and delayed manifestations with potential unfavorable outcome much complicate the management of suspected cases and prediction of morbidity and mortality during an outbreak. We reviewed literature data on bio-clinical characteristics and treatments of RVF human illness. We identified gaps in the field and provided a practical algorithm to assist clinicians in the cases assessment, determination of setting of care and prolonged follow-up.

RVFV Infection in Goats by Different Routes of Inoculation

Rift Valley fever virus (RVFV) is a zoonotic arbovirus of the Phenuiviridae family. Infection causes abortions in pregnant animals, high mortality in neonate animals, and mild to severe symptoms in both people and animals. There is currently an ongoing effort to produce safe and efficacious veterinary vaccines against RVFV in livestock to protect against both primary infection in animals and zoonotic infections in people. To test the efficacy of these vaccines, it is essential to have a reliable challenge model in relevant target species, including ruminants. We evaluated two goat breeds (Nubian and LaMancha), three routes of inoculation (intranasal, mosquito-primed subcutaneous, and subcutaneous) using an infectious dose of 10⁷ pfu/mL, a virus strain from the 2006–2007 Kenyan/Sudan outbreak and compared the effect of using virus stocks produced in either mammalian or mosquito cells. Our results demonstrated that the highest and longest viremia titers were achieved in Nubian goats. The Nubian breed was also efficient at producing clinical signs, consistent viremia (peak viremia: 1.2 × 10³–1.0 × 10⁵ pfu/mL serum), nasal and oral shedding of viral RNA (1.5 × 10¹–8 × 10⁶ genome copies/swab), a systemic infection of tissues, and robust antibody responses regardless of the inoculation route. The Nubian goat breed and a needle-free intranasal inoculation technique could both be utilized in future vaccine and challenge studies. These studies are important for preventing the spread and outbreak of zoonotic viruses like RVFV and are supported by the Canadian-led BSL4ZNet network.

High seroprevalence of Rift Valley fever phlebovirus in domestic ruminants and African Buffaloes in Mozambique shows need for intensified surveillance

Introduction: Rift Valley fever (RVF) is an arthropod-borne disease that affects both animals and humans. RVF phlebovirus (RVFPV) is widespread in Africa and Arabian Peninsula. In Mozambique, outbreaks were reported in South; seroprevalence studies performed in livestock and water buffaloes were limited to central and south regions. We evaluated the seroprevalence of RVFPV among domestic ruminants and African buffaloes from 7 of 10 provinces of Mozambique, to understand the distribution of RVFPV and provide data for further RVF control programs.

Materials and methods: A total of 1581 blood samples were collected in cattle, 1117 in goats, 85 in sheep and 69 in African buffaloes, between 2013 and 2014, and the obtained sera were analyzed by ELISA.

Results and discussion: The overall seroprevalence of RVFPV domestic ruminants and African buffaloes was 25.6%. The highest was observed in cattle (37.3%) and African buffaloes (30.4%), which were higher than in previous studies within Mozambique. In south and central regions, the overall seroprevalences were higher (14.9%–62.4%) than in the north.

Conclusion: This study showed the presence of anti-RVFPV antibodies in animals from all sampled provinces, suggesting that RVFPV is actively circulating among domestic ruminants and African buffaloes in Mozambique, therefore surveillance should be intensified.

Overlapping CD8+ and CD4+ T-cell epitopes identification for the progression of epitope-based peptide vaccine from nucleocapsid and glycoprotein of emerging Rift Valley fever virus using immunoinformatics approach

Rift Valley fever virus (RVFV) is an emergent arthropod-borne zoonotic infectious viral pathogen which causes fatal diseases in the humans and ruminants. Currently, no effective and licensed vaccine is available for the prevention of RVFV infection in endemic as well as in non-endemic regions. So, an immunoinformatics-driven genome-wide screening approach was performed for the identification of overlapping CD8+ and CD4+ T-cell epitopes and also linear B-cell epitopes from the conserved sequences of the nucleocapsid (N) and glycoprotein (G) of RVFV. We identified overlapping 99.39% conserved 1 CD8+ T-cell epitope (MMHPSFAGM) from N protein and 100% conserved 7 epitopes (AVFALAPVV, LAVFALAPV, FALAPVVFA, VFALAPVVF, IAMTVLPAL, FFDWFSGLM, and FLLIYLGRT) from G protein and also identified IL-4 and IFN-γ induced (99.39% conserved) 1 N protein CD4+ T-cell epitope (HMMHPSFAGMVDPSL) and 100% conserved 5 G protein CD4+ T-cell epitopes (LPALAVFALAPVVFA, PALAVFALAPVVFAE, GIAMTVLPALAVFAL, GSWNFFDWFSGLMSW, and FFLLIYLGRTGLSKM). The overlapping CD8+ and CD4+ T-cell epitopes were bound with most conserved HLA-C*12:03 and HLA-DRB1*01:01, respectively with the high binding affinity (kcal/mol). The combined population coverage analysis revealed that the allele frequencies of these epitopes are high in endemic and non-endemic regions. Besides, we found 100% conserved and non-allergenic 2 decamer B-cell epitopes, GVCEVGVQAL and RVFNCIDWVH of G protein had the sequence similarity with the nonamer CD8+ T-cell epitopes, VCEVGVQAL and RVFNCIDWV, respectively. Consequently, these epitopes may be used for the development of epitope-based peptide vaccine against emerging RVFV. However, in vivo and in vitro experiments are required for their efficient use as a vaccine.

Current Status of Rift Valley Fever Vaccine Development

Rift Valley Fever (RVF) is a mosquito-borne zoonotic disease that presents a substantial threat to human and public health. It is caused by Rift Valley fever phlebovirus (RVFV), which belongs to the genus Phlebovirus and the family Phenuiviridae within the order Bunyavirales. The wide distribution of competent vectors in non-endemic areas coupled with global climate change poses a significant threat of the transboundary spread of RVFV. In the last decade, an improved understanding of the molecular biology of RVFV has facilitated significant progress in the development of novel vaccines, including DIVA (differentiating infected from vaccinated animals) vaccines. Despite these advances, there is no fully licensed vaccine for veterinary or human use available in non-endemic countries, whereas in endemic countries, there is no clear policy or practice of routine/strategic livestock vaccinations as a preventive or mitigating strategy against potential RVF disease outbreaks. The purpose of this review was to provide an update on the status of RVF vaccine development and provide perspectives on the best strategies for disease control. Herein, we argue that the routine or strategic vaccination of livestock could be the best control approach for preventing the outbreak and spread of future disease.

Rift Valley fever trasmission dynamics described by compartmental models

Rift Valley fever (RVF) is one of the most important zoonotic Transboundary Animal Diseases able to cross international borders and cause devastating effect on animal health and food security. Climate changes and the presence of competent vectors in the most of the current RVF-free temperate countries strongly support the inclusion of RVF virus (RVFV) among the most significant emerging viral threats for public and animal health. The transmission of RVFV is driven by complex eco-climatic factors making the epidemiology of RVF infection difficult to study and to understand. Mathematical, statistical and spatial models are often used to explain the mechanisms underlying these biological processes, providing new and effective tools to plan measures for public health protection. In this paper we performed a systematic literature review on RVF published papers with the aim of identifying and describing the most recent papers developing compartmental models for the study of RVFV transmission dynamics.

Rift Valley Fever Virus among Wild Ruminants, Etosha National Park, Namibia, 2011

After a May 2011 outbreak of Rift Valley fever among livestock northeast of Etosha National Park, Namibia, wild ruminants in the park were tested for the virus. Antibodies were detected in springbok, wildebeest, and black-faced impala, and viral RNA was detected in springbok. Seroprevalence was high, and immune response was long lasting.

Serological Evidence of Rift Valley Fever Virus Circulation in Domestic Cattle and African Buffalo in Northern Botswana (2010-2011)

Rift Valley fever (RVF) is endemic in many countries in Sub-Saharan Africa and is responsible for severe outbreaks in livestock characterized by a sudden onset of abortions and high neonatal mortality. During the last decade, several outbreaks have occurred in Southern Africa, with a very limited number of cases reported in Botswana. To date, published information on the occurrence of RVF in wild and domestic animals from Botswana is very scarce and outdated, despite being critical to national and regional disease control. To address this gap, 863 cattle and 150 buffalo sampled at the interface between livestock areas and the Chobe National Park (CNP) and the Okavango Delta (OD) were screened for the presence of RVF virus (RVFV) neutralizing antibodies. Antibodies were detected in 5.7% (n = 863), 95% confidence intervals (CI) (4.3–7.5%) of cattle and 12.7% (n = 150), 95% CI (7.8–19.5%) of buffalo samples. The overall prevalence was significantly higher (p = 0.0016) for buffalo [12.7%] than for cattle [5.7%]. Equally, when comparing RVF seroprevalence in both wildlife areas for all pooled bovid species, it was significantly higher in CNP than in OD (9.5 vs. 4%, respectively; p = 0.0004). Our data provide the first evidence of wide circulation of RVFV in both buffalo and cattle populations in Northern Botswana and highlight the need for further epidemiological and ecological investigations on RVF at the wildlife–livestock–human interface in this region.

First External Quality Assessment of Molecular and Serological Detection of Rift Valley Fever in the Western Mediterranean Region

Rift Valley fever (RVF) is a mosquito-borne viral zoonosis which affects humans and a wide range of domestic and wild ruminants. The large spread of RVF in Africa and its potential to emerge beyond its geographic range requires the development of surveillance strategies to promptly detect the disease outbreaks in order to implement efficient control measures, which could prevent the widespread of the virus to humans. The Animal Health Mediterranean Network (REMESA) linking some Northern African countries as Algeria, Egypt, Libya, Mauritania, Morocco, Tunisia with Southern European ones as France, Italy, Portugal and Spain aims at improving the animal health in the Western Mediterranean Region since 2009. In this context, a first assessment of the diagnostic capacities of the laboratories involved in the RVF surveillance was performed. The first proficiency testing (external quality assessment--EQA) for the detection of the viral genome and antibodies of RVF virus (RVFV) was carried out from October 2013 to February 2014. Ten laboratories participated from 6 different countries (4 from North Africa and 2 from Europe). Six laboratories participated in the ring trial for both viral RNA and antibodies detection methods, while four laboratories participated exclusively in the antibodies detection ring trial. For the EQA targeting the viral RNA detection methods 5 out of 6 laboratories reported 100% of correct results. One laboratory misidentified 2 positive samples as negative and 3 positive samples as doubtful indicating a need for corrective actions. For the EQA targeting IgG and IgM antibodies methods 9 out of the 10 laboratories reported 100% of correct results, whilst one laboratory reported all correct results except one false-positive. These two ring trials provide evidence that most of the participating laboratories are capable to detect RVF antibodies and viral RNA thus recognizing RVF infection in affected ruminants with the diagnostic methods currently available.

A Spatial Analysis of Rift Valley Fever Virus Seropositivity in Domestic Ruminants in Tanzania

Rift Valley fever (RVF) is an acute arthropod-borne viral zoonotic disease primarily occurring in Africa. Since RVF-like disease was reported in Tanzania in 1930, outbreaks of the disease have been reported mainly from the eastern ecosystem of the Great Rift Valley. This cross-sectional study was carried out to describe the variation in RVF virus (RVFV) seropositivity in domestic ruminants between selected villages in the eastern and western Rift Valley ecosystems in Tanzania, and identify potential risk factors. Three study villages were purposively selected from each of the two Rift Valley ecosystems. Serum samples from randomly selected domestic ruminants (n = 1,435) were tested for the presence of specific immunoglobulin G (IgG) and M (IgM), using RVF enzyme-linked immunosorbent assay methods. Mixed effects logistic regression modelling was used to investigate the association between potential risk factors and RVFV seropositivity. The overall RVFV seroprevalence (n = 1,435) in domestic ruminants was 25.8% and species specific seroprevalence was 29.7%, 27.7% and 22.0% in sheep (n = 148), cattle (n = 756) and goats (n = 531), respectively. The odds of seropositivity were significantly higher in animals sampled from the villages in the eastern than those in the western Rift Valley ecosystem (OR = 1.88, CI: 1.41, 2.51; p<0.001), in animals sampled from villages with soils of good than those with soils of poor water holding capacity (OR = 1.97; 95% CI: 1.58, 3.02; p< 0.001), and in animals which had been introduced than in animals born within the herd (OR = 5.08, CI: 2.74, 9.44; p< 0.001). Compared with animals aged 1-2 years, those aged 3 and 4-5 years had 3.40 (CI: 2.49, 4.64; p< 0.001) and 3.31 (CI: 2.27, 4.82, p< 0.001) times the odds of seropositivity. The findings confirm exposure to RVFV in all the study villages, but with a higher prevalence in the study villages from the eastern Rift Valley ecosystem.