Unexpected Rift Valley Fever Outbreak, Northern Mauritania

During September–October 2010, an unprecedented outbreak of Rift Valley fever was reported in the northern Sahelian region of Mauritania after exceptionally heavy rainfall. Camels probably played a central role in the local amplification of the virus. We describe the main clinical signs (hemorrhagic fever, icterus, and nervous symptoms) observed during the outbreak

Charakterisierung des immunmodulatorischen Effektes von Wild-Typ Rift-Tal-Fieber-Virus-Stämmen

Rift Valley fever Phlebovirus (RVFV) ist ein Mitglied der Familie Bunyaviridae. Es wird durch Stechmücken übertragen und ist in der Lage zahlreiche Wirtspezies zu infizieren. Beim Menschen kann die Infektion zu Hepatitis, hämorrhagischem Fieber und Enzephalitis mit tödlichem Ausgang führen. Bei Rindern verläuft die Infektion von Jungtieren in der Regel tödlich, weiterhin kommt es zu Fehlgeburten oder Missbildungen bei den Föten nach Infektion schwangerer Tiere. Die Erkrankung ist in Ägypten und vielen afrikanischen Ländern südlich der Sahara endemisch, und führt dort immer wieder zu epizootischen Ausbrüchen mit begleitenden Epidemien. Die unterschiedliche Virulenz verschiedener RVFV Isolate könnte auf die Effektivität zurückzuführen sein, mit der das Virus die angeborene und/oder die adaptive Immunität unterläuft, was auch den starke Variabilität des klinischen Bildes der Erkrankung bei den suszeptiblen Wirtsspezies erklären könnte. Interferon-β (IFN-β) ist eine zentrale Komponente des angeborenen Immunantwort. Daher wurde die IFN-β-antagonistische Funktion des NSs-Proteins von RVFV Isolaten unterschiedlicher Herkunft (Säugetiere, Menschen und Insekten) nach Klonierung und Sequenzierung des jeweiligen Nichtstruktur S-Segment (NSs) Gens untersucht. Die immunmodulatorische Funktion von NSs wurde dahingehend charakterisiert, inwieweit die jeweiligen NSs Proteine in einem Reporter Assay System in der Lage waren, die Aktivierung des humanen IFN-β Promotors zu unterdrücken. Weiterhin wurde mittels Immunfluoreszenz die Expression von NSs in Vero E6 Zellen untersucht. Zwei RVFV NSs-Proteine (aus den Isolaten R7 und R18) hatten die Fähigkeit verloren, die Aktivierung des IFN-β Promotors zu unterdrücken, alle anderen 24 NSs Protein waren effiziente Inhibitoren der IFN-β Promotor¬aktivität. Weiterhin waren R7-NSs und R18-NSs im Gegensatz zu Wildtyp RVFV-NSs nicht in der Lage nukleäre Filamente zu bilden, obwohl dieses Expressionsmuster eigentlich typisch für RVFV-NSs ist. Die Sequenzierung von R18-NSs ergab, dass im Vergleich zu Wildtyp RVFV-NSs eine große Deletion im NSs-Leseraster auftritt, die identisch zu der bei dem apathogenen Stamm RVFV Clone 13 beschriebenen Mutation ist und zu einem funktionslosen NSs-Protein führt. Anhand von Sequenzvergleichen ergab sich, dass es sich bei dem Stamm R18 tatsächlich um ein Clone 13 Isolat handelt. Im Gegensatz zu R18-NSs enthält R7-NSs lediglich eine Punktmutation im NSs-Gen, die auf Aminosäureebene zu einem Austausch von Leucin durch Prolin an Position 115 führt. Interessanterweise hat diese Punktmutation einen ähnlichen Effekt wie die große Deletion im Leseraster des Clone 13-NSs. R10-NSs war die einzige Variante, die effizient die Aktivierung des IFN-β Promotors unterdrückte aber keine nukleären Filamente bildete. Dies konnte auf einen Austausch von Leucin durch Prolin an Aminosäureposition 107 zurückgeführt werden. Diese Ergebnisse erlauben den Schluss, dass eine ku rze Domäne die die Aminosäuren 107 bis 115 umfasst essentiell für die Funktionen von NSs ist. Dendritische Zellen (DCs) sind professionelle Antigen-präsentierende Zellen und stellen eine Verbindung zwischen angeborener und adaptiver Immunität dar. Daher wurde der Effekt von RVFV-Infektionen auf die DC-Funktion untersucht. Experimente mit primären humanen myeloiden und plasmacytoiden DCs (mDCs/pDCs) ergaben, dass der Wildtyp-Stamm RVFV ZH548 nur in mDCs replizieren kann, dass es aber sowohl in pDCs als auch mDCs nur zu einer unvollständigen Aktivierung nach RVFV-Infektion kommt. Die Produktion von proinflammatorischem Interleukin 6 sowie die fehlende Produktion von Typ I Interferonen in pDCs und mDCs nach Infektion mit RVFV könnten für die schweren Krankheitsverläufe mitverantwortlich sein. Interessanterweise induzierte auch der Stamm RVFV Cone 13, der in Nichtimmunzellen ein effizienter Typ I IFN-Induktor ist, kein IFN in DCs. Die Kombination von unvollständiger DC-Aktvierung bei gleichzeitig fehlender IFN-Produktion nach Infektion mit Wildtyp RVFV und Clone 13 lässt darauf schließen, dass RVFV die ersten Schritte der adaptiven Immunantwort unabhängig vom Vorhandensein eines funktionellen NSs-Proteins unterläuft und möglicherweise infizierte mDCs zur Ausbreitung im infizierten Wirt nutzt

First Report of the Emergence of Peste des Petits Ruminants Lineage IV Virus in Senegal

Peste des petits ruminants (PPR) is a highly contagious viral disease and one of the deadliest affecting wild goats, sheep, and small ruminants; however, goats are generally more sensitive. The causative agent is the Peste des Petits Ruminants virus (PPRV), which is a single-stranded RNA virus of negative polarity belonging to the Paramyxoviridae family. In February 2020, an active outbreak of PPR was reported in a herd of a transhumant farmer in the village of Gainth Pathé (department of Kounguel, Kaffrine region, Senegal). Of the ten swabs collected from the goats, eight returned a positive result through a quantitative real-time PCR. The sample that yielded the strongest signal from the quantitative real-time PCR was further analyzed with a conventional PCR amplification and direct amplicon sequencing. A phylogenetic analysis showed that the sequence of the PPR virus obtained belonged to lineage IV. These results confirm those found in the countries bordering Senegal and reinforce the hypothesis of the importance of animal mobility between these neighboring countries in the control of PPRV. In perspective, following the discovery of this lineage IV in Senegal, a study on its dispersion is underway throughout the national territory. The results that will emerge from this study, associated with detailed data on animal movements and epidemiological data, will provide appropriate and effective information to improve PPR surveillance and control strategies with a view to its eradication

Application of exponential random graph models to determine nomadic herders' movements in Senegal

International audienceUnderstanding human and animal mobility patterns is a key to predict local and global disease spread. We analysed the nomad herds' movement network in a pilot area of northern Senegal and used exponential random graph models (ERGM) to investigate the reasons behind these movements. We interviewed 132 nomadic herders to collect information about nomad herd structures, movements, and reasons for taking specific routes or gathering in certain areas. We constructed a spatially explicit network with villages as the nodes and nomad herds' movements as the connecting edges. The final ERGM showed that node and edge attributes such as presence of cattle in the herd (odds ratio = 12, CI: 5.3, 27.3), morbidity (odds ratio = 3.6, CI: 2.3, 5.7), and lack of water (odds ratio = 2, CI: 1.3, 3.1) were important predictors of nomad herds' movements. This study not only provides valuable information for monitoring important livestock diseases such as Rift Valley Fever in Senegal, but also helps implement outreach, education, and intervention programs for other emerging and endemic diseases affecting nomadic herds

It’s risky to wander in September: Modelling the epidemic potential of Rift Valley fever in a Sahelian setting

International audienceEstimating the epidemic potential of vector-borne diseases, along with the relative contribution of underlying mechanisms, is crucial for animal and human health worldwide. In West African Sahel, several outbreaks of Rift Valley fever (RVF) have occurred over the last decades, but uncertainty remains about the conditions necessary to trigger these outbreaks. We use the basic reproduction number (R0) as a measure of RVF epidemic potential in northern Senegal, and map its value in two distinct ecosystems, namely the Ferlo and the Senegal River delta and valley. We consider three consecutive rainy seasons (July-November 2014, 2015 and 2016) and account for several vector and animal species. We parametrize our model with estimates of Aedes vexans arabiensis, Culex poicilipes, Culex tritaeniorhynchus, cattle, sheep and goat abundances. The impact of RVF virus introduction is assessed every week over northern Senegal. We highlight September as the period of highest epidemic potential in northern Senegal, resulting from distinct dynamics in the two study areas. Spatially, in the seasonal environment of the Ferlo, we observe that high-risk locations vary between years. We show that decreased vector densities do not greatly reduce R0 and that cattle immunity has a greater impact on reducing transmission than small ruminant immunity. The host preferences of vectors and the temperature-dependent time interval between their blood meals are crucial parameters needing further biological investigations

Rapid detection of important human pathogenic Phleboviruses

Background: Rapid diagnostics are not available for several human pathogens in the genus Phlebovirus of the Bunyaviridae. Objectives: To develop RT-PCR assays for Sandfly Fever Sicilian virus (SFSV), Sandfly Fever Naples virus (SFNV), Toscana virus (TOSV) and Rift Valley Fever virus (RVFV). Study design: RNA standards were generated and used to test the performance of the assays. Results: A detection limit of 10-100 RNA molecules was determined for the SFSV, TOSV and RVFV assays. The sensitivity of the SFNV assay was not determined. The TOSV and the RVFV assays detected recent isolates from Spain and Africa, respectively. Conclusion: The assays should help to improve surveillance of pathogenic Phleboviruses

Rift Valley Fever: One Health at Play?

Rift Valley fever (RVF) is a mosquito-borne viral infection mostly encountered in Africa. In its acute form, it severely affects domestic and wild ruminants, dromedaries, and humans. It is considered as an emerging disease, with increased frequency in several regions, and a spread potential to many areas under the influence of two main drivers: Environmental (including climatic) changes and animal mobility (livestock trade, transhumance). In this chapter, we discuss the peculiarities of RVF epidemiology in Sahelian Africa and we show how the joint influence of these two drivers may trigger RVF epidemics. The public health impact of RVF can be severe, with tens of thousands of human cases and hundreds of fatalities recorded during large epidemics. Beyond its direct, negative effects on public and animal health, RVF has large economic consequences related to bans on livestock importation from infected countries. Solutions are available to improve surveillance and control of RVF in Sahelian Africa according to well-defined, risk-based strategies. The implementation of coordinated actions between Public Health and Animal Health authorities would represent an important advance in the One Health joint approach of RVF for better prevention, early detection, and reaction

Persistence of the historical lineage I of West Africa against the ongoing spread of the Asian lineage of peste des petits ruminants virus

International audiencePeste des petits ruminants (PPR) is a highly contagious disease of small ruminants. The causal agent, PPR virus (PPRV), is classified into four genetically distinct lineages. Lineage IV, originally from Asia, has shown a unique capacity to spread across Asia, the Middle East and Africa. Recent studies have reported its presence in two West African countries: Nigeria and Niger. Animals are frequently exchanged between Mali and Niger, which could allow the virus to enter and progress in Mali and to other West African countries. Here, PPRV samples were collected from sick goats between 2014 and 2017 in both Mali and in Senegal, on the border with Mali. Partial PPRV nucleoprotein gene was sequenced to identify the genetic lineage of the strains. Our results showed that lineage IV was present in south-eastern Mali in 2017. This is currently the furthest West the lineage has been detected in West Africa. Surprisingly, we identified the persistence at least until 2014 of the supposedly extinct lineage I in two regions of Mali, Segou and Sikasso. Most PPRV sequences obtained in this study belonged to lineage II, which is dominant in West Africa. Phylogenetic analyses showed a close relationship between sequences obtained at the border between Senegal and Mali, supporting the hypothesis of an important movement of the virus between the two countries. Understanding the movement of animals between these countries, where the livestock trade is not fully controlled, is very important in the design of efficient control strategies to combat this devastating disease

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

International audienceRift 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 ( B B ) 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