Genome characterization of Rift Valley fever virus isolated from cattle, goats and sheep during interepidemic periods in Kenya.

Rift Valley fever virus (RVFV) is a mosquito-borne RNA virus of the Phlebovirus genus in the phenuviridae family. Its genome is trisegmented with small (S), medium (M) and large (L) fragments. In nature, the virus exists as a single serotype that is responsible for outbreaks of Rift Valley fever (RVF), a zoonotic disease that often occurs in Africa and the Middle East. RVFV genomes are thought to undergo both recombination and reassortment and investigations of these events is important for monitoring the emergence of virulent strains and understanding the evolutionary characteristics of this virus. The aim of this study was to characterize the genomes of RVFV isolates from cattle, sheep, and goats collected during an interepidemic period in Kenya between June 2016 and November 2021. A total of 691 serum samples from cattle (n = 144), goats (n = 185) and sheep (n = 362) were analysed at the Central Veterinary Laboratories. The competitive IgM-capture ELISA, was used to screen the samples; 205 samples (29.67%) tested positive for RVFV. Of the 205 positive samples, 42 (20.5%) were from cattle, 57 (27.8%) from goats, and 106 (51.7%) from sheep. All the IgM-positive samples were further analyzed by qPCR, and 24 (11.71%) tested positive with Ct values ranging from 14.788 to 38.286. Two samples, 201808HABDVS from sheep and 201810CML3DVS from cattle, had Ct values of less than 20.0 and yielded whole genome sequences with 96.8 and 96.4 coverage, respectively. There was no statistically significant evidence of recombination in any of the three segments and also phylogenetic analysis showed no evidence of reassortment in the two isolated RVFV segments when compared with other isolates of different lineages from previous outbreaks whose genomes are deposited in the GenBank. No evidence of reassortment leaves room for other factors to be the most probable contributors of change in virulence, pathogenicity and emergence of highly virulent strains of the RVFV.

[First detection of Rift Valley Fever Virus among Culex pipiens in Tahoua, Niger]. / Détection du virus de la fièvre de la vallée du Rift chez Culex pipiens à Tahoua au Niger.

Background: The Rift Valley Fever (RVF) is an arbovirus disease responsible of regular epizootics and epidemics in sub-Saharan Africa and Arabian Peninsula. In 2016, Niger experienced its first outbreak of RVF in Tahoua region, which resulted in high consequences in animal and human health. The aim of this study was to investigate on the RVFV circulation among potential vectors of the disease. Methods: This was a cross-sectional survey carried out in Tahoua and Agadez regions in August 2021. Adult mosquitoes were collected by using the morning spray in human dwellings and the CDC light trap methods. After morphological identification, viral RNA was extracted. The RNA was extracted by using QIAamp Viral RNA Mini Kit (Qiagen). The RVFV detection was performed by using the qRT-PCR method. Results: A total of 2487 insects (1978 mosquitoes, 509 sandflies and 251 biting midges) were identified and divided into three families (Culicidae, Psychodidae and Ceratopogonidae). The Culicidae family composed of the Culex genus being the most abundant with a predominance of Cx.pipiens (31.88%; n = 793) followed by Mansonia sp (21.51%; n = 535), Anophelesgambiae s.l. (8.44%; n = 210), An. pharoensis (0.72%; n = 18), An. rufipes (0.48%; n = 12), Cx. quinquefasciatus (6.39%; n = 159), the Psychodidae with sandflies (20.46%; n = 509), and the Ceratopogonidae with Culicoides genus (10.09%; n = 251). The qRT-PCR carried out on a sample of mosquitoes (N = 96) highlighted that one individual of Cx.pipiens was found positive to RVFV. This specimen was from Tassara locality (Tahoua) and collected by CDC Light Trap method. Conclusion: This study reveals for the first time the circulation of RVFV among Cx.pipiens in Niger and highlights the possible vectorial role of this vector in the disease transmission. Further investigations should be carried out to identify the biological and ecological determinants that support the maintenance of the virus in this area in order to guide control interventions.

Characterization of mosquito host-biting networks of potential Rift Valley fever virus vectors in north-eastern KwaZulu-Natal province, South Africa.

BACKGROUND: Rift Valley fever virus (RVFV) is a zoonotic mosquito-borne virus with serious implications for livestock health, human health, and the economy in Africa, and is suspected to be endemic in north-eastern KwaZulu-Natal (KZN), South Africa. The vectors of RVFV in this area are poorly known, although several species, such as Aedes (Neomelaniconion) mcintoshi, Aedes (Neomelaniconion) circumluteolus, Aedes (Aedimorphus) durbanensis, and Culex (Lasioconops) poicilipes may be involved. The aim of the study was to determine the vertebrate blood meal sources of potential RVFV mosquito vectors in north-eastern KZN and to characterize the host-biting network. METHODS: Blood-fed mosquitoes were collected monthly from November 2019 to February 2023 using a backpack aspirator, CO2-baited Centers for Disease Control and Prevention (CDC) miniature light traps and tent traps, in the vicinity of water bodies and livestock farming households. The mosquitoes were morphologically identified. DNA was extracted from individual mosquitoes and used as templates to amplify the vertebrate cytochrome c oxidase I (COI) and cytochrome b (cytb) genes using conventional polymerase chain reaction (PCR). Amplicons were sequenced and queried in GenBank and the Barcode of Life Data systems to identify the vertebrate blood meal sources and confirm mosquito identifications. All mosquitoes were screened for RVFV using real time reverse transcription (RT)-PCR. RESULTS: We identified the mammalian (88.8%) and avian (11.3%) blood meal sources from 409 blood-fed mosquitoes. Aedes circumluteolus (n = 128) made up the largest proportion of collected mosquitoes. Cattle (n = 195) and nyala (n = 61) were the most frequent domestic and wild hosts, respectively. Bipartite network analysis showed that the rural network consisted of more host-biting interactions than the reserve network. All mosquitoes tested negative for RVFV. CONCLUSIONS: Several mosquito species, including Ae. circumluteolus, and vertebrate host species, including cattle and nyala, could play a central role in RVFV transmission. Future research in this region should focus on these species to better understand RVFV amplification.

Isolation of Rift Valley Fever Virus from Field Specimens Using Cell Culture Approaches.

Several techniques have been developed to diagnose Rift Valley fever infection. Viral isolation is one of the most difficult techniques to apply but offers great opportunities for further research. It is useful, for example, for the development of an accurate diagnostic test suitable for screening for Rift Valley fever virus infection, specific treatments by testing known antiviral molecules that act on the replication cycle to assess their therapeutic or even prophylactic potential, therapeutic applications, and vaccine candidates. Understanding how the virus replicates and interacts with the host cell and organism and identifying biomarkers of infection or new targets for the development of treatments are made possible through field virus isolates. Biosafety level 3 conditions are a pre-requisite for viral isolation by a trained staff member. Here, we describe the procedure to isolate Rift Valley fever virus from field samples by cell culture.

Detection and Diagnosis of Rift Valley Fever Virus.

Rift Valley fever virus (RVFV) is a globally important mosquito-borne virus that can also be directly transmitted via aerosolization of body fluids from infected animals. RVFV outbreaks cause mass mortality of young livestock and abortions in animals. In most severe human cases, the disease can progress to hemorrhagic fever and encephalitis, leading to death. RVF has a significant economic impact due to the loss of livestock that is a great challenge for people who depend on animals for income and food. Several vaccines are available for animal use, but none are yet licensed for use in human populations. This situation emphasizes the need to have robust and efficient diagnostic methods that can be used for early case confirmation, assessment of seroprevalence, and virus surveillance as well as vaccine efficacy evaluation. Despite the existence of different diagnostic methods for RVFV, we still have untimely reporting or underreporting of cases, probably due to lack of appropriate surveillance systems or diagnostic tools in some endemic countries. Here, we describe different methods available for detection and diagnosis of RVFV.

Aedes aegypti Vector Competence Assay for Rift Valley Fever Virus Using Artificial Blood Meal.

Vector competence assays allow to measure, in the laboratory, the ability of a mosquito to get infected and then retransmit an arbovirus while mimicking natural vector infection route. Aedes aegypti is a major vector of arboviruses worldwide and thus a reference species used in vector competence assays. Rift Valley fever virus (RVFV) is a major public health threat, mostly in Africa, that infects humans and animals through the bite of mosquito vectors. Here, we describe vector competence assay of Aedes aegypti mosquitoes for RVFV, from mosquito exposure to the virus through an infectious artificial blood meal to the measurement of virus prevalence in the mosquito's body, head, and saliva.

Guidelines for In Vitro Production and Quantification of Rift Valley Fever Virus.

Rift Valley fever virus (RVFV) is an arthropod-borne virus (arbovirus) responsible for a severe zoonotic disease affecting a wide range of domestic and wild ruminants as well as humans. RVFV is endemic in many African countries and has also caused outbreaks in Madagascar and Arabian Peninsula. With regard to its wide geographical distribution, its potential to emerge in a new area, and its capability to trigger major health and economic crisis, it is essential to study and better understand several aspects of its life cycle and, in particular, its interactions with mammalian hosts and arthropod vectors. To do so, it is key for researchers to be able to amplify in vitro viral strains isolated from the field and determine accurately the viral titers of RVFV stocks. In this chapter, we present protocols that can be easily implemented to produce and titrate RVFV stocks in your laboratory.

Making Rift Valley Fever Viral Particles Fluorescent.

Rift Valley fever virus (RVFV) is a mosquito-borne pathogen that represents a significant threat to both human and veterinary public health. Since its discovery in the Great Rift Valley of Kenya in the 1930s, the virus has spread across Africa and beyond, now posing a risk of introduction into Southern Europe and Asia. Despite recent progresses, early RVFV-host cell interactions remain largely uncharacterized. In this method chapter, we delineate the procedure for labeling RVFV particles with fluorescent organic dyes. This approach makes it feasible to visualize single viral particles in both fixed and living cells and study RVFV entry into host cells. We provide additional examples with two viruses closely related to RVFV, namely, Toscana virus and Uukuniemi virus. Furthermore, we illustrate how to utilize fluorescent viral particles to examine and quantify each step of the cell entry program of RVFV, which includes state-of-the-art fluorescence-based detection techniques such as fluorescence microscopy, flow cytometry, and fluorimetry.

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.

Genomic Epidemiology of Rift Valley Fever Virus Involved in the 2018 and 2022 Outbreaks in Livestock in Rwanda.

Rift Valley fever (RVF), a mosquito-borne transboundary zoonosis, was first confirmed in Rwanda's livestock in 2012 and since then sporadic cases have been reported almost every year. In 2018, the country experienced its first large outbreak, which was followed by a second one in 2022. To determine the circulating virus lineages and their ancestral origin, two genome sequences from the 2018 outbreak, and thirty-six, forty-one, and thirty-eight sequences of small (S), medium (M), and large (L) genome segments, respectively, from the 2022 outbreak were generated. All of the samples from the 2022 outbreak were collected from slaughterhouses. Both maximum likelihood and Bayesian-based phylogenetic analyses were performed. The findings showed that RVF viruses belonging to a single lineage, C, were circulating during the two outbreaks, and shared a recent common ancestor with RVF viruses isolated in Uganda between 2016 and 2019, and were also linked to the 2006/2007 largest East Africa RVF outbreak reported in Kenya, Tanzania, and Somalia. Alongside the wild-type viruses, genetic evidence of the RVFV Clone 13 vaccine strain was found in slaughterhouse animals, demonstrating a possible occupational risk of exposure with unknown outcome for people working in meat-related industry. These results provide additional evidence of the ongoing wide spread of RVFV lineage C in Africa and emphasize the need for an effective national and international One Health-based collaborative approach in responding to RVF emergencies.

Rift Valley Fever.

Rift Valley fever (RVF) is a zoonotic viral disease that affects domestic and wild ruminants such as cattle, sheep, goats, camels, and buffaloes. Rift valley fever virus (RVFV), the causative agent of RVF, can also infect humans. RVFV is an arthropod-borne virus (arbovirus) that is primarily spread through the bites of infected mosquitoes or exposure to infected blood. RVFV was first isolated and characterized in the Rift Valley of Kenya in 1931 and is endemic throughout sub-Saharan Africa, including Comoros and Madagascar, the Arabian Peninsula (Saudi Arabia and Yemen), and Mayotte.

Mosquito survey in Mauritania: Detection of Rift Valley fever virus and dengue virus and the determination of feeding patterns.

In Mauritania, several mosquito-borne viruses have been reported that can cause devastating diseases in animals and humans. However, monitoring data on their occurrence and local distribution are limited. Rift Valley fever virus (RVFV) is an arthropod-borne virus that causes major outbreaks throughout the African continent and the Arabian Peninsula. The first Rift Valley fever (RVF) epidemic in Mauritania occurred in 1987 and since then the country has been affected by recurrent outbreaks of the disease. To gain information on the occurrence of RVFV as well as other mosquito-borne viruses and their vectors in Mauritania, we collected and examined 4,950 mosquitoes, belonging to four genera and 14 species. The mosquitoes were captured during 2018 in the capital Nouakchott and in southern parts of Mauritania. Evidence of RVFV was found in a mosquito pool of female Anopheles pharoensis mosquitoes collected in December on a farm near the Senegal River. At that time, 37.5% of 16 tested Montbéliarde cattle on the farm showed RVFV-specific IgM antibodies. Additionally, we detected IgM antibodies in 10.7% of 28 indigenous cattle that had been sampled on the same farm one month earlier. To obtain information on potential RVFV reservoir hosts, blood meals of captured engorged mosquitoes were analyzed. The mosquitoes mainly fed on humans (urban areas) and cattle (rural areas), but also on small ruminants, donkeys, cats, dogs and straw-colored fruit bats. Results of this study demonstrate the circulation of RVFV in Mauritania and thus the need for further research to investigate the distribution of the virus and its vectors. Furthermore, factors that may contribute to its maintenance should be analyzed more closely. In addition, two mosquito pools containing Aedes aegypti and Culex quinquefasciatus mosquitoes showed evidence of dengue virus (DENV) 2 circulation in the city of Rosso. Further studies are therefore needed to also examine DENV circulation in Mauritania.

Identification of drivers of Rift Valley fever after the 2013-14 outbreak in Senegal using serological data in small ruminants.

Rift Valley fever (RVF) is a mosquito-borne disease mostly affecting wild and domestic ruminants. It is widespread in Africa, with spillovers in the Arab Peninsula and the southwestern Indian Ocean. Although RVF has been circulating in West Africa for more than 30 years, its epidemiology is still not clearly understood. In 2013, an RVF outbreak hit Senegal in new areas that weren't ever affected before. To assess the extent of the spread of RVF virus, a national serological survey was implemented in young small ruminants (6-18 months old), between November 2014 and January 2015 (after the rainy season) in 139 villages. Additionally, the drivers of this spread were identified. For this purpose, we used a beta-binomial ([Formula: see text]) logistic regression model. An Integrated Nested Laplace Approximation (INLA) approach was used to fit the spatial model. Lower cumulative rainfall, and higher accessibility were both associated with a higher RVFV seroprevalence. The spatial patterns of fitted RVFV seroprevalence pointed densely populated areas of western Senegal as being at higher risk of RVFV infection in small ruminants than rural or southeastern areas. Thus, because slaughtering infected animals and processing their fresh meat is an important RVFV transmission route for humans, more human populations might have been exposed to RVFV during the 2013-2014 outbreak than in previous outbreaks in Senegal.

Experimental Infection of Domestic Piglets (Sus scrofa) with Rift Valley Fever Virus.

Rift Valley fever phlebovirus (RVFV) is a mosquito-transmitted phlebovirus (Family: Phenuiviridae, Order: Bunyavirales) causing severe neonatal mortality and abortion primarily in domestic ruminants. The susceptibility of young domestic swine to RVFV and this species' role in geographic expansion and establishment of viral endemicity is unclear. Six commercially bred Landrace-cross piglets were inoculated subcutaneously with 105 plaque-forming units of RVFV ZH501 strain and two piglets received a sham inoculum. All animals were monitored for clinical signs, viremia, viral shedding, and antibody response for 14 days. Piglets did not develop evidence of clinical disease, become febrile, or experience decreased weight gain during the study period. A brief lymphopenia followed by progressive lymphocytosis was observed following inoculation in all piglets. Four piglets developed a brief viremia for 2 days post-inoculation and three of these had detectable virus in oronasal secretions three days post-inoculation. Primary inoculated piglets seroconverted and those that developed detectable viremias had the highest titers assessed by serum neutralization (1:64-1:256). Two viremic piglets had a lymphoplasmacytic encephalitis with glial nodules; RVFV was not detected by immunohistochemistry in these sections. While young piglets do not appear to readily develop clinical disease following RVFV infection, results suggest swine could be subclinically infected with RVFV.

Susceptibility and barriers to infection of Colorado mosquitoes with Rift Valley fever virus.

Rift Valley fever virus (RVFV) causes morbidity and mortality in humans and domestic ungulates in sub-Saharan Africa, Egypt, and the Arabian Peninsula. Mosquito vectors transmit RVFV between vertebrates by bite, and also vertically to produce infectious progeny. Arrival of RVFV into the United States by infected mosquitoes or humans could result in significant impacts on food security, human health, and wildlife health. Elucidation of the vectors involved in the post-introduction RVFV ecology is paramount to rapid implementation of vector control. We performed vector competence experiments in which field-collected mosquitoes were orally exposed to an epidemic strain of RVFV via infectious blood meals. We targeted floodwater Aedes species known to feed on cattle, and/or deer species (Aedes melanimon Dyar, Aedes increpitus Dyar, Aedes vexans [Meigen]). Two permanent-water-breeding species were targeted as well: Culiseta inornata (Williston) of unknown competence considering United States populations, and Culex tarsalis Coquillett as a control species for which transmission efficiency is known. We tested the potential for midgut infection, midgut escape (dissemination), ovarian infection (vertical transmission), and transmission by bite (infectious saliva). Tissues were assayed by plaque assay and RT-qPCR, to quantify infectious virus and confirm virus identity. Tissue infection data were analyzed using a within-host model under a Bayesian framework to determine the probabilities of infection outcomes (midgut-limited infection, disseminated infection, etc.) while estimating barriers to infection between tissues. Permanent-water-breeding mosquitoes (Cx. tarsalis and Cs. inornata) exhibited more efficient horizontal transmission, as well as potential for vertical transmission, which is contrary to the current assumptions of RVFV ecology. Barrier estimates trended higher for Aedes spp., suggesting systemic factors in the differences between these species and Cx. tarsalis and Cs. inornata. These data indicate higher potential for vertical transmission than previously appreciated, and support the consensus of RVFV transmission including a broad range of potential vectors.

Sporadic Rift Valley Fever Outbreaks in Humans and Animals in Uganda, October 2017-January 2018.

Introduction: Rift Valley fever (RVF) is a mosquito-borne viral zoonosis. The Uganda Ministry of Health received alerts of suspected viral haemorrhagic fever in humans from Kiruhura, Buikwe, Kiboga, and Mityana districts. Laboratory results from Uganda Virus Research Institute indicated that human cases were positive for Rift Valley fever virus (RVFV) by polymerase chain reaction. We investigated to determine the scope of outbreaks, identify exposure factors, and recommend evidence-based control and prevention measures. Methods: A suspected case was defined as a person with acute fever onset, negative malaria test result, and at least two of the following symptoms: headache, muscle or joint pain, bleeding, and any gastroenteritis symptom (nausea, vomiting, abdominal pain, diarrhoea) in a resident of Kiruhura, Buikwe, Mityana, and Kiboga districts from 1st October 2017 to 30th January 2018. A confirmed case was defined as a suspected case with laboratory confirmation by either detection of RVF nucleic acid by reverse-transcriptase polymerase chain reaction (RT-PCR) or demonstration of serum IgM or IgG antibodies by ELISA. Community case finding was conducted in all affected districts. In-depth interviews were conducted with human cases that were infected with RVF who included herdsmen and slaughterers/meat handlers to identify exposure factors for RVF infection. A total of 24 human and 362 animal blood samples were tested. Animal blood samples were purposively collected from farms that had reported stormy abortions in livestock and unexplained death of animals after a short illness (107 cattle, 83 goats, and 43 sheep). Convenient sampling for the wildlife (10 zebras, 1 topi, and 1 impala) was conducted to investigate infection in animals from Kiruhura, Buikwe, Mityana, and Kiboga districts. Human blood was tested for anti-RVFV IgM and IgG and animal blood for anti-RVFV IgG. Environmental assessments were conducted during the outbreaks in all the affected districts. Results: Sporadic RVF outbreaks occurred from mid-October 2017 to mid-January 2018 affecting humans, domestic animals, and wildlife. Human cases were reported from Kiruhura, Buikwe, Kiboga, and Mityana districts. Of the 24 human blood samples tested, anti-RVFV IgG was detected in 7 (29%) human samples; 1 human sample had detectable IgM only, and 6 had both IgM and IgG. Three of the seven confirmed human cases died among humans. Results from testing animal blood samples obtained from Kiruhura district indicated that 44% (64/146) cattle, 46% (35/76) goats, and 45% (9/20) sheep tested positive for RVF. Among wildlife, (1/10) zebras, (1/1) topi, and (1/1) impala tested positive for RVFV by serological tests. One blood sample from sheep in Kiboga district tested RVFV positive. All the human cases were exposed through contact or consumption of meat from infected animals. Conclusion: RVF outbreaks occurred in humans and animals in Kiruhura, Buikwe, Mityana, and Kiboga districts. Human cases were potentially infected through contact with infected animals and their products.

Rift Valley fever and Brucella spp. in ruminants, Somalia.

BACKGROUND: Fourteen-years after the last Rift Valley fever (RVF) virus (RVFV) outbreak, Somalia still suffers from preventable transboundary diseases. The tradition of unheated milk consumption and handling of aborted materials poses a public health risk for zoonotic diseases. Limited data are available on RVF and Brucella spp. in Somali people and their animals. Hence, this study has evaluated the occurrence of RVFV and Brucella spp. antibodies in cattle, goats and sheep sera from Afgoye and Jowhar districts of Somalia. METHODS: Serum samples from 609 ruminants (201 cattle, 203 goats and 205 sheep), were serologically screened for RVF by a commercial cELISA, and Brucella species by modified Rose Bengal Plate Test (mRBPT) and a commercial iELISA. RESULTS: Two out of 609 (0.3 %; 95 %CI: 0.04-1.2 %) ruminants were RVF seropositive, both were female cattle from both districts. Anti-Brucella spp. antibodies were detected in 64/609 (10.5 %; 95 %CI: 8.2-13.2 %) ruminants by mRBPT, which were 39/201 (19.4 %) cattle, 16/203 (7.9 %) goats and 9/205 (4.4 %) sheep. Cattle were 5.2 and 2.8 times more likely to be Brucella-seropositive than sheep (p = 0.000003) and goats (p = 0.001), respectively. When mRBPT-positive samples were tested by iELISA, 29/64 (45.3 %; 95 %CI: 32.8-58.3 %) ruminant sera were positive for Brucella spp. Only 23/39 (58.9 %) cattle sera and 6/16 (37.5 %) goat sera were positive to Brucella spp. by iELISA. CONCLUSIONS: The present study showed the serological evidence of RVF and brucellosis in ruminants from Afgoye and Jowhar districts of Somalia. Considering the negligence of the zoonotic diseases at the human-animal interface in Somali communities, a One Health approach is needed to protect public health.

Large-Scale International Validation of an Indirect ELISA Based on Recombinant Nucleocapsid Protein of Rift Valley Fever Virus for the Detection of IgG Antibody in Domestic Ruminants.

Diagnostic performance of an indirect enzyme-linked immunosorbent assay (I-ELISA) based on a recombinant nucleocapsid protein (rNP) of the Rift Valley fever virus (RVFV) was validated for the detection of the IgG antibody in sheep (n = 3367), goat (n = 2632), and cattle (n = 3819) sera. Validation data sets were dichotomized according to the results of a virus neutralization test in sera obtained from RVF-endemic (Burkina Faso, Democratic Republic of Congo, Mozambique, Senegal, Uganda, and Yemen) and RVF-free countries (France, Poland, and the USA). Cut-off values were defined using the two-graph receiver operating characteristic analysis. Estimates of the diagnostic specificity of the RVFV rNP I-ELISA in animals from RVF-endemic countries ranged from 98.6% (cattle) to 99.5% (sheep) while in those originating from RVF-free countries, they ranged from 97.7% (sheep) to 98.1% (goats). Estimates of the diagnostic sensitivity in ruminants from RVF-endemic countries ranged from 90.7% (cattle) to 100% (goats). The results of this large-scale international validation study demonstrate the high diagnostic accuracy of the RVFV rNP I-ELISA. Standard incubation and inactivation procedures evaluated did not have an adverse effect on the detectable levels of the anti-RVFV IgG in ruminant sera and thus, together with recombinant antigen-based I-ELISA, provide a simple, safe, and robust diagnostic platform that can be automated and carried out outside expensive bio-containment facilities. These advantages are particularly important for less-resourced countries where there is a need to accelerate and improve RVF surveillance and research on epidemiology as well as to advance disease control measures.

Rift Valley fever virus detection in susceptible hosts with special emphasis in insects.

Rift Valley fever phlebovirus (RVFV, Phenuiviridae) is an emerging arbovirus that can cause potentially fatal disease in many host species including ruminants and humans. Thus, tools to detect this pathogen within tissue samples from routine diagnostic investigations or for research purposes are of major interest. This study compares the immunohistological usefulness of several mono- and polyclonal antibodies against RVFV epitopes in tissue samples derived from natural hosts of epidemiologic importance (sheep), potentially virus transmitting insect species (Culex quinquefasciatus, Aedes aegypti) as well as scientific infection models (mouse, Drosophila melanogaster, C6/36 cell pellet). While the nucleoprotein was the epitope most prominently detected in mammal and mosquito tissue samples, fruit fly tissues showed expression of glycoproteins only. Antibodies against non-structural proteins exhibited single cell reactions in salivary glands of mosquitoes and the C6/36 cell pellet. However, as single antibodies exhibited a cross reactivity of varying degree in non-infected specimens, a careful interpretation of positive reactions and consideration of adequate controls remains of critical importance. The results suggest that primary antibodies directed against viral nucleoproteins and glycoproteins can facilitate RVFV detection in mammals and insects, respectively, and therefore will allow RVFV detection for diagnostic and research purposes.

Serological evidence of Rift Valley fever virus infection among domestic ruminant herds in Uganda.

BACKGROUND: Prior to the first recorded outbreak of Rift Valley fever (RVF) in Uganda, in March 2016, earlier studies done until the 1970's indicated the presence of the RVF virus (RVFV) in the country, without any recorded outbreaks in either man or animals. While severe outbreaks of RVF occurred in the neighboring countries, none were reported in Uganda despite forecasts that placed some parts of Uganda at similar risk. The Ministry of Agriculture, Animal Industry and Fisheries (MAAIF) undertook studies to determine the RVF sero-prevalence in risk prone areas. Three datasets from cattle sheep and goats were obtained; one from retrospective samples collected in 2010-2011 from the northern region; the second from the western region in 2013 while the third was from a cross-sectional survey done in 2016 in the south-western region. Laboratory analysis involved the use of the Enzyme Linked Immunosorbent Assays (ELISA). Data were subjected to descriptive statistical analyses, including non-parametric chi-square tests for comparisons between districts and species in the regions. RESULTS: During the Yellow Fever outbreak investigation of 2010-2011 in the northern region, a total sero-prevalence of 6.7% was obtained for anti RVFV reacting antibodies (IgG and IgM) among the domestic ruminant population. The 2013 sero-survey in the western region showed a prevalence of 18.6% in cattle and 2.3% in small ruminants. The 2016 sero-survey in the districts of Kabale, Kanungu, Kasese, Kisoro and Rubirizi, in the south-western region, had the respective district RVF sero-prevalence of 16.0, 2.1, 0.8, 15.1and 2.7% among the domestic ruminants combined for this region; bovines exhibited the highest cumulative sero-prevalence of 15.2%, compared to 5.3 and 4.0% respectively for sheep and goats per species for the region. CONCLUSIONS: The absence of apparent outbreaks in Uganda, despite neighboring enzootic areas, having minimal restrictions to the exchange of livestock and their products across borders, suggest an unexpected RVF activity in the study areas that needs to be unraveled. Therefore, more in-depth studies are planned to mitigate the risk of an overt RVF outbreak in humans and animals as has occurred in neighboring countries.