Observations on rift valley fever virus and vaccines in Egypt

Ability of a dynamical climate sensitive disease model to reproduce historical Rift Valley Fever outbreaks over Africa

Rift Valley Fever (RVF) is a zoonosis transmitted by Aedes and Culex mosquitoes, and is considered a priority pathogen by the WHO. RVF epidemics mostly occur in Africa and can decimate livestock herds, causing significant economic losses and posing health risks for humans. RVF transmission is associated with the occurrence of El Niño events that cause floods in eastern Africa and favour the emergence of mosquitoes in wetlands. Different risk models have been developed to forecast RVF transmission risk but very few studies have validated models at pan-African scale. This study aims to validate the skill of the Liverpool Rift Valley Fever model (LRVF) in reproducing RVF epidemics over Africa and to explore the relationship between simulated climatic suitability for RVF transmission and large-scale climate modes of variability such as the El Niño Southern Oscillation (ENSO) and the Dipole Mode Index (DMI). Our results show that the LRVF model correctly simulates RVF transmission hotspots and reproduces large epidemics that affected African countries. LRVF was able to correctly reproduce major RVF epidemics in Somalia, Kenya, Zambia and to a lesser extent for Mauritania and Senegal. The positive phases of ENSO and DMI are associated with an increased risk of RVF over the Horn of Africa, with important time lags. Following research activities should focus on the development of predictive modelling systems at different time scales.

Advancements in Rift Valley fever vaccines: a historical overview and prospects for next generation candidates

Rift Valley fever (RVF) is a zoonotic viral disease transmitted by mosquitoes and causes abortion storms, fetal malformations, and newborn animal deaths in livestock ruminants. In humans, RVF can manifest as hemorrhagic fever, encephalitis, or retinitis. Outbreaks of RVF have been occurring in Africa since the early 20th century and continue to pose a threat to both humans and animals in various regions such as Africa, Madagascar, the Comoros, Saudi Arabia, and Yemen. The development of RVF vaccines is crucial in preventing mortality and morbidity and reducing the spread of the virus. While several veterinary vaccines have been licensed in endemic countries, there are currently no licensed RVF vaccines for human use. This review provides an overview of the existing RVF vaccines, as well as potential candidates for future studies on RVF vaccine development, including next-generation vaccines that show promise in combating the disease in both humans and animals.

Seroprevalence of Rift Valley Fever virus in one-humped camels (Camelus dromedaries) in Egypt

Rift Valley fever (RVF) is a mosquito-borne viral disease that affects a variety of domestic animals, including cattle, sheep, goats, and camels, and has zoonotic potential. Although the rift valley fever virus (RVFV) is usually asymptomatic in camels, it can induce abortion in some pregnant animals. In the current study, a serosurvey was carried out to investigate the prevalence of RVFV antibodies and related risk factors in camels from four Egyptian governorates. A total of 400 serum samples were examined for anti-RVFV antibodies using a competitive enzyme-linked immunosorbent assay (c-ELISA). The results revealed that the overall prevalence of RVF among examined camels was 21.5% and the disease was more prevalent in Kafr ElSheikh governorate in Nile Delta of Egypt. In addition, the age group of camels with more than 5 years (OR=4.49, 95%CI: 1.39-14.49), the female sex (OR=3.38, 95%CI: 1.51-7.58), the emaciated animals (OR=1.52, 95%CI: 0.86-2.66), the summer season's infection (OR=5.98, 95%CI: 1.79-19.93), the presence of mosquitoes (OR= 2.88, 95%CI: 1.39-5.95), and the absence of mosquitoes control (OR=3.97, 95%CI: 2.09-7.57) were identified as risk factors for RVFV infection. The results of this study support knowledge on the risk factors for RVFV infection and demonstrate that camels raising in Egypt have RVFV antibodies. Quarantine measures or vaccination program should be implemented to reduce the likelihood of RVFV introduction, dissemination among susceptible animals, and ultimately transmission to humans.

Replication Kinetics of a Candidate Live-Attenuated Vaccine for Cache Valley Virus in Aedes albopictus

Background: The emergence or re-emergence of several orthobunyaviruses (order: Bunyavirales; family: Peribunyaviridae), including Cache Valley virus (CVV) and Oropouche virus, warrants the development and evaluation of candidate live-attenuated vaccines (LAVs). Ideally, these vaccines would elicit long-lasting immunity with one single immunization. Materials and Methods: Since the deletion of two virulence factors, NSs and NSm, has been shown to attenuate the virulence phenotype of orthobunyaviruses, phleboviruses, and nairoviruses, genetic manipulation of the viral genome is considered an effective strategy for the rational design of candidate LAVs for bunyaviruses across multiple families. In addition, the deletion of Rift Valley fever virus NSs and NSm genes has been shown to reduce transmission by mosquitoes. Results: In this study, the ability of a CVV mutant lacking the NSs and NSm genes (2delCVV) to replicate in intrathoracically injected Aedes albopictus was compared with the parental wild-type CVV (wtCVV) 6V633 strain. In contrast to the robust replication of wtCVV in injected mosquitoes, the multiplication kinetics of the 2delCVV mutant was reduced by more than a 100-fold. Conclusion: These results suggest that the deletion of NSm and NSs genes is a feasible approach to rationally design candidate orthobunyavirus LAVs that are highly attenuated in mosquitoes and, therefore, pose little risk of reversion to virulence and transmission.

A survey of bluetongue infection in one-humped camels (Camelus Dromedarius); seroprevalence and risk factors analysis

Bluetongue (BT) is an insect-borne, non-contagious viral disease which affects domestic ruminants including camels and is transmitted by Culicoides spp. Clinical symptoms of BT are typically seen in sheep, although subclinical BT infections are mostly seen in cattle, goats, and camelids. The goal of the present study was to evaluate the sero-prevalence of Bluetongue virus (BTV) in camels from some governorates in Egypt's southern and northern regions, as well as the infection's potential risk factors. During 2020-2021, a cross sectional study was conducted to screen presence of anti-BTV antibodies in 400 serum samples, which were collected randomly from camels, examined using competitive enzyme-linked immunosorbent assay (cELISA). The sera of 102 out of 400 camels tested positive for BTV, representing a frequency of 25.5%. Moreover, the odds of sero-positivity were higher among camels living in Aswan (OR = 5.33, 95%CI: 2.35-12.11), especially in females (OR = 2.63, 95%CI = 1.44-4.09) during summer season (OR = 2.40, 95%CI = 1.20-4.81). Furthermore, the probability of getting BTV infection increased when camels were exposed to the insect vectors (OR = 1.63, 95%CI = 0.87-3.09). The high prevalence of BTV in camels in several Egyptian regions highlights the need for more epidemiological investigations of BTV infection in other ruminant species in order to better control BT disease in these regions.

Epidemiology of Mosquito-Borne Viruses in Egypt: A Systematic Review

There are at least five common mosquito-borne viruses (MBVs) recorded in Egypt, including dengue virus (DENV), Rift Valley fever virus (RVFV), West Nile virus (WNV), Chikungunya virus, and Sindbis virus. Unexpected outbreaks caused by MBVs reflect the deficiencies of the MBV surveillance system in Egypt. This systematic review characterized the epidemiology of MBV prevalence in Egypt. Human, animal, and vector prevalence studies on MBVs in Egypt were retrieved from Web of Science, PubMed, and Bing Scholar, and 33 eligible studies were included for further analyses. The monophyletic characterization of the RVFV and WNV strains found in Egypt, which spans about half a century, suggests that both RVFV and WNV are widely transmitted in this nation. Moreover, the seropositive rates of DENV and WNV in hosts were on the rise in recent years, and spillover events of DENV and WNV to other countries from Egypt have been recorded. The common drawback for surveillance of MBVs in Egypt is the lack of seroprevalence studies on MBVs, especially in this century. It is necessary to evaluate endemic transmission risk, establish an early warning system for MBVs, and develop a sound joint system for medical care and public health for managing MBVs in Egypt.

Genetic Characterization of Rift Valley Fever Virus in Insectivorous Bats, Egypt

Background: The endemic character of Rift Valley fever (RVF) disease points toward an interepidemic reservoir. Although not yet identified, bats and rodents may be implicated in RVF virus (RVFV) epidemiology. In this study, we investigated the putative role of Egyptian frugivorous and insectivorous bats in RVFV epidemiology in Egypt. Methods: From 2019 to 2021, 200 bats of two different species from six Egyptian governorates were tested for phleboviruses using real-time RT-PCR (rRT-PCR) and sequence analysis. Results: Screening through rRT-PCR showed evidence of the RVFV genome only in insectivorous bats. Partial sequence and phylogenetic analysis based on S and M genome segments showed that these viruses are genetically similar to those circulating (clade A) in livestock and humans during previously reported RVFV outbreaks in 1977/78 and 2003 in Egypt. Conclusions: Our molecular data suggest that the bat Pipistrellus deserti could play a role in RVFV ecology in Egypt.

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.

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.

Insights into the Pathogenesis of Viral Haemorrhagic Fever Based on Virus Tropism and Tissue Lesions of Natural Rift Valley Fever

Rift Valley fever phlebovirus (RVFV) infects humans and a wide range of ungulates and historically has caused devastating epidemics in Africa and the Arabian Peninsula. Lesions of naturally infected cases of Rift Valley fever (RVF) have only been described in detail in sheep with a few reports concerning cattle and humans. The most frequently observed lesion in both ruminants and humans is randomly distributed necrosis, particularly in the liver. Lesions supportive of vascular endothelial injury are also present and include mild hydropericardium, hydrothorax and ascites; marked pulmonary congestion and oedema; lymph node congestion and oedema; and haemorrhages in many tissues. Although a complete understanding of RVF pathogenesis is still lacking, antigen-presenting cells in the skin are likely the early targets of the virus. Following suppression of type I IFN production and necrosis of dermal cells, RVFV spreads systemically, resulting in infection and necrosis of other cells in a variety of organs. Failure of both the innate and adaptive immune responses to control infection is exacerbated by apoptosis of lymphocytes. An excessive pro-inflammatory cytokine and chemokine response leads to microcirculatory dysfunction. Additionally, impairment of the coagulation system results in widespread haemorrhages. Fatal outcomes result from multiorgan failure, oedema in many organs (including the lungs and brain), hypotension, and circulatory shock. Here, we summarize current understanding of RVF cellular tropism as informed by lesions caused by natural infections. We specifically examine how extant knowledge informs current understanding regarding pathogenesis of the haemorrhagic fever form of RVF, identifying opportunities for future research.

Rift Valley Fever: a Threat to Pregnant Women Hiding in Plain Sight?

The potential for emerging mosquito-borne viruses to cause fetal infection in pregnant women was overlooked until the Zika fever outbreak several years ago. Rift Valley fever virus (RVFV) is an emerging arbovirus with a long history of fetal infection and death in pregnant livestock. The effect of RVFV infection on pregnant women is not well understood. This Gem examines the effects that this important emerging pathogen has during pregnancy, its potential impact on pregnant women, and the current research efforts designed to understand and mitigate adverse effects of RVFV infection during pregnancy.

Exploring Prokaryotic and Eukaryotic Microbiomes Helps in Detecting Tick-Borne Infectious Agents in the Blood of Camels

Dromedary camels (Camelus dromedarius) are widely distributed in Africa, the Middle East and northern India. In this study, we aimed to detect tick-borne pathogens through investigating prokaryotic and eukaryotic microorganisms in camel blood based on a metagenomic approach and then to characterize potentially pathogenic organisms using traditional molecular techniques. We showed that the bacteria circulating in the blood of camels is dominated by Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria. At the genus level, Sediminibacterium, Hydrotalea, Bradyrhizobium and Anaplasma were the most abundant taxa. Eukaryotic profile was dominated by Fungi, Charophyta and Apicomplexa. At the genus level, Theileria was detected in 10 out of 18 samples, while Sarcocystis, Hoplorhynchus and Stylocephalus were detected in one sample each. Our metagenomic approach was successful in the detection of several pathogens or potential pathogens including Anaplasma sp., Theileria ovis, Th. separata, Th. annulate, Th. mutans-like and uncharacterized Theileria sp. For further characterization, we provided the partial sequences of citrate synthase (gltA) and heat-shock protein (groEL) genes of Candidatus Anaplasma camelii. We also detected Trypanosoma evansi type A using polymerase chain reaction (PCR) targeting the internal transcribed spacer 1 (ITS1) region. This combined metagenomic and traditional approach will contribute to a better understanding of the epidemiology of pathogens including tick-borne bacteria and protozoa in animals.

A serological and hematological study on Rift valley fever and associated risk factors in aborted sheep at Kurdistan province in west of Iran

Rift Valley fever (RVF) is a disease caused by RVF virus (RVFV) which can cause infections in a range of wild and domestic ruminants as well as in humans and characterized by an increased incidence of abortion in ruminants. This study aims to survey the seroprevalence and risk factors of this zoonose among aborted sheep in Kurdistan province, the west of Iran. 182 blood samples were collected from aborted sheep during the past one month under age groups <1, ≥1-3, >3-5 year in four seasons in two groups of border and non-border cities of Kurdistan province. The presence of RVFV-specific Antibodies was investigated by using competitive ELISA. Indirect immunofluorescence assay (IIFA) was used to confirm positive samples, after separation of serum, as well as blood samples were analyzed for description of hematological parameters. Of a total sheep sampled 1.65 % (n = 3) were positive for RVFV antibodies in both test. The results of IIFA were correlated with the ELISA results. All of the positive samples showed leucopenia and had significant relation with seroprevalence of RVF (P < 0.05). The seroprevalence of RVF in the border cities were significantly higher than other group (P < 0.05) Age of sheep and season had no significant effect on prevalence of RVF (P > 0.05). Results obtained in this study indicated the presence of low-level RVFV circulation among the sheep of Kurdistan Province in Iran, so it is necessary to carry out further studies in other areas of Iran. Doing an epidemiologically study aimed at isolating RVFV in the ruminants of Kurdistan province is recommended. The risk factor of bordering with Iran's western neighbor (Iraq) requires seriously control of the exchange of animals and the relevant products between the two countries.

Zoonotic Pathogens of Dromedary Camels in Kenya: A Systematised Review

Kenya is home to Africa’s third largest population of dromedary camels, and production at commercial and local levels are increasingly important. In pastoral and nomadic communities in the arid and semi-arid lands (ASALs), camels play a vital role in food security, while commercial milk production and formalized export markets are rapidly emerging as camel populations expand into non-traditional areas. Until recently, little focus was placed on camels as hosts of zoonotic disease, but the emergence of Middle Eastern respiratory coronavirus (MERS-CoV) in 2012, and the discovery of exposure to the virus in Kenyan camels, highlighted the need for further understanding of this area. This systematised review utilised a robust search strategy to assess the occurrence of camel-associated zoonoses in Kenya and to evaluate the quality of the published literature. Seventy-four studies were identified, covering sixteen pathogens, with an increasing number of good quality studies in recent years. Despite this, the area remains under-researched and there is a lack of robust, high-quality research. Trypanosome spp., Echinococcus granulosus and Brucella spp. appeared most frequently in the literature. Pathogens with the highest reported prevalence were MERS-CoV (0–100%), Echinococcus granulosa (7–60%) and Rift Valley fever virus (7–57%). Exposure to Brucella spp., Coxiella burnetii and Crimean-Congo haemorrhagic fever virus showed higher levels in camel or camel-associated vectors than other livestock species, although brucellosis was the only disease for which there was robust evidence linking camel and human exposure. Zoonotic agents with less severe human health outcomes, such as Dermatophilosus congolensis and contagious ecthyma, were also represented in the literature. This review provides an important summary of the scope and quality of current knowledge. It demonstrates that further research, and improved adherence to robust study design and reporting are essential if the zoonotic risk from camels in Kenya, and elsewhere, is to be better understood.

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.

Rift Valley Fever - epidemiological update and risk of introduction into Europe

Rift Valley fever (RVF) is a vector-borne disease transmitted by a broad spectrum of mosquito species, especially Aedes and Culex genus, to animals (domestic and wild ruminants and camels) and humans. Rift Valley fever is endemic in sub-Saharan Africa and in the Arabian Peninsula, with periodic epidemics characterised by 5-15 years of inter-epizootic periods. In the last two decades, RVF was notified in new African regions (e.g. Sahel), RVF epidemics occurred more frequently and low-level enzootic virus circulation has been demonstrated in livestock in various areas. Recent outbreaks in a French overseas department and some seropositive cases detected in Turkey, Tunisia and Libya raised the attention of the EU for a possible incursion into neighbouring countries. The movement of live animals is the most important pathway for RVF spread from the African endemic areas to North Africa and the Middle East. The movement of infected animals and infected vectors when shipped by flights, containers or road transport is considered as other plausible pathways of introduction into Europe. The overall risk of introduction of RVF into EU through the movement of infected animals is very low in all the EU regions and in all MSs (less than one epidemic every 500 years), given the strict EU animal import policy. The same level of risk of introduction in all the EU regions was estimated also considering the movement of infected vectors, with the highest level for Belgium, Greece, Malta, the Netherlands (one epidemic every 228-700 years), mainly linked to the number of connections by air and sea transports with African RVF infected countries. Although the EU territory does not seem to be directly exposed to an imminent risk of RVFV introduction, the risk of further spread into countries neighbouring the EU and the risks of possible introduction of infected vectors, suggest that EU authorities need to strengthen their surveillance and response capacities, as well as the collaboration with North African and Middle Eastern countries.

Mechanisms of inter-epidemic maintenance of Rift Valley fever phlebovirus

Rift Valley fever phlebovirus (RVFV) is an arthropod-borne virus that has caused substantial epidemics throughout Africa and in the Arabian Peninsula. The virus can cause severe disease in livestock and humans and therefore the control and prevention of viral outbreaks is of utmost importance. The epidemiology of RVFV has some particular characteristics. Unexpected and significant epidemics have been observed in spatially and temporally divergent patterns across the African continent. Sudden epidemics in previously unaffected areas are followed by periods of long-term apparent absence of virus and sudden, unpredictable reoccurrence in disparate regions. Therefore, the elucidation of underlying mechanisms of viral maintenance is one of the largest gaps in the knowledge of RVFV ecology. It remains unknown whether the virus needs to be reintroduced before RVF outbreaks can occur, or if unperceived viral circulation in local vertebrates or mosquitoes is sufficient for maintenance of the virus. To gain insight into these knowledge gaps, we here review existing data that describe potential mechanisms of RVFV maintenance, as well as molecular and serological studies in endemic and non-endemic areas that provide evidence of an inter- or pre-epidemic virus presence. Basic and country-specific mechanisms of RVFV introduction into non-endemic countries are summarized and an overview of studies using mathematical modeling of RVFV persistence is given.

Rift Valley fever: biology and epidemiology

Rift Valley fever (RVF) is a mosquito-borne viral zoonosis that was first discovered in Kenya in 1930 and is now endemic throughout multiple African countries and the Arabian Peninsula. RVF virus primarily infects domestic livestock (sheep, goats, cattle) causing high rates of neonatal mortality and abortion, with human infection resulting in a wide variety of clinical outcomes, ranging from self-limiting febrile illness to life-threatening haemorrhagic diatheses, and miscarriage in pregnant women. Since its discovery, RVF has caused many outbreaks in Africa and the Arabian Peninsula with major impacts on human and animal health. However, options for the control of RVF outbreaks are limited by the lack of licensed human vaccines or therapeutics. For this reason, RVF is prioritized by the World Health Organization for urgent research and development of countermeasures for the prevention and control of future outbreaks. In this review, we highlight the current understanding of RVF, including its epidemiology, pathogenesis, clinical manifestations and status of vaccine development.

A Review of Zoonotic Pathogens of Dromedary Camels

Dromedary, or one-humped, camels Camelus dromedarius are an almost exclusively domesticated species that are common in arid areas as both beasts of burden and production animals for meat and milk. Currently, there are approximately 30 million dromedary camels, with highest numbers in Africa and the Middle East. The hardiness of camels in arid regions has made humans more dependent on them, especially as a stable protein source. Camels also carry and may transmit disease-causing agents to humans and other animals. The ability for camels to act as a point source or vector for disease is a concern due to increasing human demands for meat, lack of biosafety and biosecurity protocols in many regions, and a growth in the interface with wildlife as camel herds become sympatric with non-domestic species. We conducted a literature review of camel-borne zoonotic diseases and found that the majority of publications (65%) focused on Middle East respiratory syndrome (MERS), brucellosis, Echinococcus granulosus, and Rift Valley fever. The high fatality from MERS outbreaks during 2012-2016 elicited an immediate response from the research community as demonstrated by a surge of MERS-related publications. However, we contend that other camel-borne diseases such as Yersinia pestis, Coxiella burnetii, and Crimean-Congo hemorrhagic fever are just as important to include in surveillance efforts. Camel populations, particularly in sub-Saharan Africa, are increasing exponentially in response to prolonged droughts, and thus, the risk of zoonoses increases as well. In this review, we provide an overview of the major zoonotic diseases present in dromedary camels, their risk to humans, and recommendations to minimize spillover events.

The One Health Approach is Necessary for the Control of Rift Valley Fever Infections in Egypt: A Comprehensive Review

Rift Valley fever (RVF) is an emerging transboundary, mosquito-borne, zoonotic viral disease caused high morbidity and mortality in both human and ruminant populations. It is considered an important threat to both agriculture and public health in African and the Middle Eastern countries including Egypt. Five major RVF epidemics have been reported in Egypt (1977, 1993, 1994, 1997, and 2003). The virus is transmitted in Egypt by different mosquito’s genera such as Aedes, Culex, Anopheles, and Mansonia, leading to abortions in susceptible animal hosts especially sheep, goat, cattle, and buffaloes. Recurrent RVF outbreaks in Egypt have been attributed in part to the lack of routine surveillance for the virus. These periodic epizootics have resulted in severe economic losses. We posit that there is a critical need for new approaches to RVF control that will prevent or at least reduce future morbidity and economic stress. One Health is an integrated approach for the understanding and management of animal, human, and environmental determinants of complex problems such as RVF. Employing the One Health approach, one might engage local communities in surveillance and control of RVF efforts, rather than continuing their current status as passive victims of the periodic RVF incursions. This review focuses upon endemic and epidemic status of RVF in Egypt, the virus vectors and their ecology, transmission dynamics, risk factors, and the ecology of the RVF at the animal/human interface, prevention, and control measures, and the use of environmental and climate data in surveillance systems to predict disease outbreaks.

Rift Valley fever virus: a serological survey in Libyan ruminants

A serological survey was carried out in Libya to investigate the circulation of Rift Valley fever virus (RVFV) among domestic ruminants. A total of 857 serum samples were collected from year 2015 to 2016 in eleven provinces of Libya belonging to five branches of the country. Samples were tested for RVFV antibodies using a competitive Enzyme-Linked Immunosorbent Assay (c-ELISA). Antibodies specific for RVFV were not detected in any of the 857 samples. However, a statistical analysis was carried out to assess the maximum expected number of infected animals and the maximum expected prevalence of RVFV among Libyan ruminants' populations according to the sampled population. The overall maximum expected prevalence was estimated to be 1.8% for cattle and 0.4% for small ruminants. Results seem to exclude the circulation of RVFV, however, a surveillance plan should be implemented in areas at risk of RVFV introduction.

Rift Valley fever in animals and humans: Current perspectives

Rift Valley fever (RVF) is an ecologically complex emerging arboviral disease that causes significant illness in both livestock and people. This review article is designed to assist the reader in understanding the varied aspects of RVF disease in animals and humans. The historical facets of RVF disease, including the evolution of human outbreaks, are presented and discussed. The different clinical presentations of human RVF disease and the underlying causes are then addressed. We explore the exposure and transmission potential of RVF in animals and people. In the concluding section, we discuss the historical role of RVF as a biological weapon. We conclude with an outline of the important unanswered questions for ongoing research into this important zoonotic disease.

Rift Valley Fever in Egypt and other African countries: Historical review, recent outbreaks and possibility of disease occurrence in Egypt

This article reviews and discusses the historical and recent status of Rift Valley Fever (RVF) in Egypt and the other African countries based on the available and scattered reports. The recent outbreaks in African countries were reviewed and mapped out. Four major epidemics have been recorded in Egypt (1977, 1978, 1993 and 2003). The outbreak resulted in unpredicted human disease with severe clinical manifestations and heavy mortality as well as many abortions and deaths in sheep, goats, cattle, water buffalo and camels. Of the 18 culicine mosquito species that occur in Egypt, Culex pipiens and Cx. antennatus were implicated as vectors of RVF in Egypt based on their natural infection with RVF virus. Aedes caspius was also suspected of disseminating the virus among livestock based on host feeding and vector competence studies. The epidemiological factors related to the introduction and spread of RVF in Egypt are discussed. The study concluded that due to the availability and abundance of the potential vectors, suitability of environmental conditions, continuous importation of livestock's from Sudan, and the close association of susceptible domestic animals with humans, the RVF virus could possibly occur and circulate in Egypt.

Rift Valley fever vaccines: current and future needs

Rift Valley fever (RVF) is a zoonotic mosquito-borne bunyaviral disease associated with high abortion rates, neonatal deaths, and fetal malformations in ruminants, and mild to severe disease in humans. Outbreaks of RVF cause huge economic losses and public health impacts in endemic countries in Africa and the Arabian Peninsula. A proper vaccination strategy is important for preventing or minimizing outbreaks. Vaccination against RVF is not practiced in many countries, however, due to absence or irregular occurrences of outbreaks, despite serological evidence of RVF viral activity. Nonetheless, effective vaccination strategies, and functional national and international multi-disciplinary networks, remain crucial for ensuring availability of vaccines and supporting execution of vaccination in high risk areas for efficient response to RVF alerts and outbreaks.

Understanding the legal trade of cattle and camels and the derived risk of Rift Valley Fever introduction into and transmission within Egypt

Rift Valley Fever (RVF) is a mosquito-borne zoonosis, which may cause significant losses for the livestock sector and have serious public health implications. Egypt has been repeatedly affected by RVF epidemics, mainly associated to the importation of animals from sub-Saharan countries, where the disease is endemic. The objective of our study was the improvement of the surveillance and control strategies implemented in Egypt. In order to do that, first we evaluated the legal trade of live animals into and within Egypt. Then, we assessed the risk of Rift Valley Fever virus (RVFV) transmission within the country using a multi-criteria evaluation approach. Finally, we combined the animal trade and the risk of RVFV transmission data to identify those areas and periods in which the introduction of RVFV is more likely. Our results indicate that the main risk of RVFV introduction is posed by the continuous flow of large number of camels coming from Sudan. The risk of RVFV transmission by vectors is restricted to the areas surrounding the Nile river, and does not vary significantly throughout the year. Imported camels are taken to quarantines, where the risk of RVFV transmission by vectors is generally low. Then, they are taken to animal markets or slaughterhouses, many located in populated areas, where the risk of RVFV transmission to animals or humans is much higher. The measures currently implemented (quarantines, vaccination or testing) seem to have a limited effect in reducing the risk of RVFV introduction, and therefore other (risk-based) surveillance strategies are proposed.

Colorimetric Detection of Unamplified Rift Valley Fever Virus Genetic Material Using Unmodified Gold Nanoparticles

Rift Valley fever virus (RVFV) is considered an enzootic virus in Africa. RVFV has caused several outbreaks in Egypt, sub-Saharan Africa and the Arabian Peninsula and is responsible for high mortality in ruminants and haemorrhagic fever in severe human cases. Although there are several molecular and serological diagnostic techniques used to detect this arthropod-borne virus with high sensitivity and efficiency, there is a need for a fast and reliable field screening test for rapid outbreak recording and containment. In this study, we developed a prototype point-of-care diagnostic test specific for RVFV detection using unmodified gold nanoparticles (AuNPs) that change colour in the presence of RVFV RNA, resulting in a simple but sensitive assay. The nanogold assay provides qualitative results showing the presence of the RVFV RNA in different sample types. The assay showed high accuracy and specificity, with a detection limit of 10 RNA copies/reaction, comparable with quantitative reverse transcription polymerase chain reaction. The assay result could be determined within 30 min with no need for specific detection instruments. To our knowledge, this is the first field test prototype to directly detect the RNA of RVFV without amplification using AuNPs.

A Comprehensive Review of Common Bacterial, Parasitic and Viral Zoonoses at the Human-Animal Interface in Egypt

Egypt has a unique geographical location connecting the three old-world continents Africa, Asia and Europe. It is the country with the highest population density in the Middle East, Northern Africa and the Mediterranean basin. This review summarizes the prevalence, reservoirs, sources of human infection and control regimes of common bacterial, parasitic and viral zoonoses in animals and humans in Egypt. There is a gap of knowledge conerning the epidemiology of zoonotic diseases at the human-animal interface in different localities in Egypt. Some zoonotic agents are “exotic” for Egypt (e.g., MERS-CoV and Crimean-Congo hemorrhagic fever virus), others are endemic (e.g., Brucellosis, Schistosomiasis and Avian influenza). Transboundary transmission of emerging pathogens from and to Egypt occurred via different routes, mainly importation/exportation of apparently healthy animals or migratory birds. Control of the infectious agents and multidrug resistant bacteria in the veterinary sector is on the frontline for infection control in humans. The implementation of control programs significantly decreased the prevalence of some zoonoses, such as schistosomiasis and fascioliasis, in some localities within the country. Sustainable awareness, education and training targeting groups at high risk (veterinarians, farmers, abattoir workers, nurses, etc.) are important to lessen the burden of zoonotic diseases among Egyptians. There is an urgent need for collaborative surveillance and intervention plans for the control of these diseases in Egypt.

Rift Valley Fever

Rift Valley fever (RVF) is a severe veterinary disease of livestock that also causes moderate to severe illness in people. The life cycle of RVF is complex and involves mosquitoes, livestock, people, and the environment. RVF virus is transmitted from either mosquitoes or farm animals to humans, but is generally not transmitted from person to person. People can develop different diseases after infection, including febrile illness, ocular disease, hemorrhagic fever, or encephalitis. There is a significant risk for emergence of RVF into new locations, which would affect human health and livestock industries.

Rift Valley fever vaccines: an overview of the safety and efficacy of the live-attenuated MP-12 vaccine candidate

INTRODUCTION

Rift Valley fever (RVF) is a mosquito-borne zoonotic viral disease endemic to Africa and the Arabian Peninsula. High rates of abortion among infected ruminants and hemorrhagic fever in infected humans are major public health concerns. Commercially available veterinary RVF vaccines are important for preventing the spread of the Rift Valley fever virus (RVFV) in endemic countries; however, RVFV outbreaks continue to occur frequently in endemic countries in the 21st century. In the U.S., the live-attenuated MP-12 vaccine has been developed for both animal and human vaccination. This vaccine strain is well attenuated, and a single dose induces neutralizing antibodies in both ruminants and humans. Areas covered: This review describes scientific evidences of MP-12 vaccine efficacy and safety, as well as MP-12 variants recently developed by reverse genetics, in comparison with other RVF vaccines. Expert commentary: The containment of active RVF outbreaks and long-term protection from RVF exposure to infected mosquitoes are important goals for RVF vaccination. MP-12 vaccine will allow immediate vaccination of susceptible animals in case of an unexpected RVF outbreak in the U.S., whereas MP-12 vaccine may be also useful for the RVF control in endemic regions.

Camel as a transboundary vector for emerging exotic Salmonella serovars

The current study was conducted to shed light on the role of imported camels as a transboundary vector for emerging exotic Salmonella serovars. Fecal samples were collected from 206 camels directly after slaughtering including 25 local camels and 181 imported ones as well as stool specimens were obtained from 50 slaughterhouse workers at the same abattoir. The obtained samples were cultured while Salmonella serovars were identified through Gram's stain films, biochemical tests and serotyping with antisera kit. Moreover, the obtained Salmonella serovars were examined by PCR for the presence of invA and stn genes. The overall prevalence of Salmonella serovars among the examined camels was 8.3%. Stn gene was detected in the vast majority of exotic strains (11/14) 78.6% including emerging serovars such as Salmonella Saintpaul, S. Chester, S. Typhimurium whereas only one isolate from local camels carried stn gene (1/3) 33.3%. On the other hand, none of the examined humans yielded positive result. Our findings highlight the potential role of imported camels as a transboundary vector for exotic emerging Salomenella serovars.

Seroprevalence of Rift Valley fever virus in livestock during inter-epidemic period in Egypt, 2014/15

Background

Rift Valley fever virus (RVFV) caused several outbreaks throughout the African continent and the Arabian Peninsula posing significant threat to human and animal health. In Egypt the first and most important Rift Valley fever epidemic occurred during 1977/78 with a multitude of infected humans and huge economic losses in livestock. After this major outbreak, RVF epidemics re-occurred in irregular intervals between 1993 and 2003. Seroprevalence of anti-RVFV antibodies in livestock during inter-epidemic periods can be used for supporting the evaluation of the present risk exposure for animal and public health. A serosurvey was conducted during 2014/2015 in non-vaccinated livestock including camels, sheep, goats and buffalos in different areas of the Nile River Delta as well as the furthermost southeast of Egypt to investigate the presence of anti-RVFV antibodies for further evaluating of the risk exposure for animal and human health. All animals integrated in this study were born after the last Egyptian RVF epidemic in 2003 and sampled buffalos and small ruminants were not imported from other endemic countries.

Results

A total of 873 serum samples from apparently healthy animals from different host species (camels: n = 221; sheep: n = 438; goats: n = 26; buffalo: n = 188) were tested serologically using RVFV competition ELISA, virus neutralization test and/or an indirect immunofluorescence assay, depending on available serum volume. Sera were assessed positive when virus neutralization test alone or least two assays produced consistent positive results. The overall seroprevalence was 2.29% (95%CI: 1.51–3.07) ranging from 0% in goats, 0.46% in sheep (95%CI: 0.41–0.5), and 3.17% in camels (95%CI: 0.86–5.48) up to 5.85% in buffalos (95%CI: 2.75–8.95).

Conclusion

Our findings assume currently low level of circulating virus in the investigated areas and suggest minor indication for a new RVF epidemic. Further the results may indicate that during long inter-epidemic periods, maintenance of the virus occur in vectors and also most probably in buffaloes within cryptic cycle where sporadic, small and local epidemics may occur. Therefore, comprehensive and well-designed surveillance activities are urgently needed to detect first evidence for transition from endemic to epidemic cycle.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-017-0993-8) contains supplementary material, which is available to authorized users.

Rift Valley fever virus infections in Egyptian cattle and their prevention

Rift Valley fever virus (RVFV) causes consistently severe outbreaks with high public health impacts and economic losses in livestock in many African countries and has also been introduced to Saudi Arabia and Yemen. Egypt with its four large outbreaks in the last 40 years represents the northernmost endemic area of RVFV. The purpose of this study was to provide an insight into the current anti-RVFV antibody status in immunized as well as non-immunized dairy cattle from the Nile Delta of Egypt. During 2013-2015, a total of 4,167 dairy cattle from four governorates including Dakahlia, Damietta, Gharbia and Port Said were investigated. All cattle were born after 2007 and therewith after the last reported Egyptian RVFV outbreak in 2003. The samples derived from vaccinated animals from 26 different dairy farms as well as non-immunized cattle from 27 different smallholding flocks. All samples were examined following a three-part analysis including a commercially available competition ELISA, an in-house immunofluorescence assay and a virus neutralization test. Additionally, a subset of samples was analysed for acute infections using IgM ELISA and real-time reverse transcriptase PCR. The results indicated that the RVFV is still circulating in Egypt as about 10% of the non-immunized animals exhibited RVFV-specific antibodies. Surprisingly, the antibody prevalence in immunized animals was not significantly higher than that in non-vaccinated animals which points out the need for further evaluation of the vaccination programme. Due to the substantial role of livestock in the amplification and transmission of RVFV, further recurrent monitoring of the antibody prevalence in susceptible species is highly warranted.

Phylogeography of Rift Valley Fever Virus in Africa and the Arabian Peninsula

Rift Valley Fever is an acute zoonotic viral disease caused by Rift Valley Fever virus (RVFV) that affects ruminants and humans in Sub-Saharan Africa and the Arabian Peninsula. We used phylogenetic analyses to understand the demographic history of RVFV populations, using sequence data from the three minigenomic segments of the virus. We used phylogeographic approaches to infer RVFV historical movement patterns across its geographic range, and to reconstruct transitions among host species. Results revealed broad circulation of the virus in East Africa, with many lineages originating in Kenya. Arrival of RVFV in Madagascar resulted from three major waves of virus introduction: the first from Zimbabwe, and the second and third from Kenya. The two major outbreaks in Egypt since 1977 possibly resulted from a long-distance introduction from Zimbabwe during the 1970s, and a single introduction took RVFV from Kenya to Saudi Arabia. Movement of the virus between Kenya and Sudan, and CAR and Zimbabwe, was in both directions. Viral populations in West Africa appear to have resulted from a single introduction from Central African Republic. The overall picture of RVFV history is thus one of considerable mobility, and dynamic evolution and biogeography, emphasizing its invasive potential, potentially more broadly than its current distributional limits.

Rift Valley Fever is an acute zoonotic viral disease caused by Rift Valley Fever virus (RVFV) that affects ruminants and humans in Sub-Saharan Africa and the Arabian Peninsula. We used phylogenetic approaches that take sampling date into account to understand the demographic history of RVFV populations, using sequence data from the three minigenomic segments of the virus. We found evidence of broad circulation of the virus in East Africa, with many lineages originating in Kenya, with single and multiple introductions of RVFV among countries. The overall picture of RVFV history is thus one of considerable mobility, and dynamic evolution and biogeography, emphasizing its invasive potential, potentially more broadly than its current distributional limits.

Public Health Benefits from Livestock Rift Valley Fever Control: A Simulation of Two Epidemics in Kenya

In controlling Rift Valley fever, public health sector optimises health benefits by considering cost-effective control options. We modelled cost-effectiveness of livestock RVF control from a public health perspective in Kenya. Analysis was limited to pastoral and agro-pastoral system high-risk areas, for a 10-year period incorporating two epidemics: 2006/2007 and a hypothetical one in 2014/2015. Four integrated strategies (baseline and alternatives), combined from three vaccination and two surveillance options, were compared. Baseline strategy included annual vaccination of 1.2-11% animals plus passive surveillance and monitoring of nine sentinel herds. Compared to the baseline, two alternatives assumed improved vaccination coverage. A herd dynamic RVF animal simulation model produced number of animals infected under each strategy. A second mathematical model implemented in R estimated number people who would be infected by the infected animals. The 2006/2007 RVF epidemic resulted in 3974 undiscounted, unweighted disability adjusted life years (DALYs). Improving vaccination coverage to 41-51% (2012) and 27-33% (2014) 3 years before the hypothetical 2014/2015 outbreak can avert close to 1200 DALYs. Improved vaccinations showed cost-effectiveness (CE) values of US$ 43-53 per DALY averted. The baseline practice is not cost-effective to the public health sector.

Safety and Efficacy Profile of Commercial Veterinary Vaccines against Rift Valley Fever: A Review Study

Rift Valley Fever (RVF) is an infectious illness with serious clinical manifestations and health consequences in humans as well as a wide range of domestic ruminants. This review provides significant information about the prevention options of RVF along with the safety-efficacy profile of commercial vaccines and some of RVF vaccination strategies. Information presented in this paper was obtained through a systematic investigation of published data about RVF vaccines. Like other viral diseases, the prevention of RVF relies heavily on immunization of susceptible herds with safe and cost-effective vaccine that is able to confer long-term protective immunity. Several strains of RVF vaccines have been developed and are available in commercial production including Formalin-Inactivated vaccine, live attenuated Smithburn vaccine, and the most recent Clone13. Although Formalin-Inactivated vaccine and live attenuated Smithburn vaccine are immunogenic and widely used in prevention programs, they proved to be accompanied by significant concerns. Despite Clone13 vaccine being suggested as safe in pregnant ewes and as highly immunogenic along with its potential for differentiating infected from vaccinated animals (DIVA), a recent study raised concerns about the safety of the vaccine during the first trimester of gestation. Accordingly, RVF vaccines that are currently available in the market to a significant extent do not fulfill the requirements of safety, potency, and DIVA. These adverse effects stressed the need for developing new vaccines with an excellent safety profile to bridge the gap in safety and immunity. Bringing RVF vaccine candidates to local markets besides the absence of validated serological test for DIVA remain the major challenges of RVF control.

Rift Valley fever virus: Unanswered questions

This mosquito-borne pathogen of humans and animals respects no international or geographic boundaries. It is currently found in parts of Africa and the Arabian Peninsula where periodic outbreaks of severe and fatal disease occur, and threatens to spread into other geographic regions. In recent years, modern molecular techniques have led to many breakthroughs deepening our understanding of the mechanisms of RVFV virulence, phylogenetics, and the creation of several next-generation vaccine candidates. Despite tremendous progress in these areas, other challenges remain in RVF disease pathogenesis, the virus life-cycle, and outbreak response preparedness that deserve our attention. Here we discuss and highlight ten key knowledge gaps and challenges in RVFV research. Answers to these key questions may lead to the development of new effective therapeutics and enhanced control strategies for this serious human and veterinary health threat.

Transmission Dynamics of Rift Valley Fever Virus: Effects of Live and Killed Vaccines on Epizootic Outbreaks and Enzootic Maintenance

Rift Valley fever virus (RVFV) is an arthropod-borne viral pathogen that causes significant morbidity and mortality in small ruminants throughout Africa and the Middle East. Due to the sporadic and explosive nature of RVF outbreaks, vaccination has proved challenging to reduce RVFV infection in the ruminant population. Currently, there are two available types of vaccines, live and killed, in endemic areas. In this study, two mathematical models have been developed to explore the impact of live and killed vaccines on the transmission dynamics of RVFV. We demonstrate in general that vaccination helps reduce the severity of RVF outbreaks and that less delay in implementation and more vaccination attempts and effective vaccines can reduce the outbreak magnitude and the endemic number of RVFV. However, an introduction of a number of ruminants vaccinated by live vaccines in RVFV-free areas may cause an outbreak and RVFV may become endemic if there is sustained use of live vaccines. Other factors that are the important determinants of RVF outbreaks include: unsustained vaccination programs, recruitment of susceptible ruminants, and the seasonal abundance of mosquitoes.

Lay perceptions of risk factors for Rift Valley fever in a pastoral community in northeastern Kenya

BACKGROUND

Human behavioral factors have been found to be central in the transmission of Rift Valley fever. Consumption of contaminated meat and milk in particular have been identified as one of the key risk factors for the transmission of Rift Valley fever in humans. In pastoral communities, livestock is the main source of livelihood from which many benefits such as food as well as economic and cultural services are derived. Zoonotic diseases therefore have a great impact on pastoral communities livelihoods. However, lay perceptions regarding the transmission of these diseases including Rift Valley fever hampers their effective control. This study investigated the lay perceptions of risks for Rift Valley fever transmission in a pastoral community in northeastern Kenya.

METHODS

A qualitative study was carried out in Ijara district, Kenya which was one of the hotspots of Rift Valley during the 2006/2007 outbreak. Data were collected using focus group discussions and narratives guided by checklists. Eight focus group discussions consisting of 83 participants and six narratives were conducted. Data was transcribed, coded and analysed according to Emergent themes.

RESULTS

The participants reported that they had experienced Rift Valley fever in their livestock especially sheep and in humans both in 1997/1998 and 2006/2007. However, they believed that infections in humans occurred as a result of mosquito bites and had little to do with their consumption of meat, milk and blood from infected livestock. The participants in this study indicated that they had heard of the risks of acquiring the disease through consumption of livestock products but their experiences did not tally with the information they had received hence to them, Rift Valley fever was not transmissible through their dietary practices.

CONCLUSIONS

Though the communities in this region were aware of Rift Valley fever, they did not have elaborate information regarding the disease transmission dynamics to humans. To avoid misconception about transmission of the disease, intervention strategies, require to be accompanied by comprehensive explanations of the dynamics of its transmission. It is necessary to develop appropriate interventions that take into consideration, lay perceptions of risk factors for the disease and communities' livelihood strategies.

A model for the coupling of the Greater Bairam and local environmental factors in promoting Rift-Valley Fever epizootics in Egypt

OBJECTIVES

Rift-Valley Fever (RVF) is a zoonotic mosquito-borne disease in Africa and the Arabian Peninsula. Drivers for this disease vary by region and are not well understood for North African countries such as Egypt. A deeper understanding of RVF risk factors would inform disease management policies.

STUDY DESIGN

The present study employs mathematical and computational modeling techniques to ascertain the extent to which the severity of RVF epizootics in Egypt differs depending on the interaction between imported ruminant and environmentally-constrained mosquito populations.

METHODS

An ordinary differential system of equations, a numerical model, and an individual-based model (IBM) were constructed to represent RVF disease dynamics between localized mosquitoes and ruminants being imported into Egypt for the Greater Bairam. Four cases, corresponding to the Greater Bairam's occurrence during distinct quarters of the solar year, were set up in both models to assess whether the different season-associated mosquito populations present during the Greater Bairam resulted in RVF epizootics of variable magnitudes.

RESULTS

The numerical model and the IBM produced nearly identical results: ruminant and mosquito population plots for both models were similar in shape and magnitude for all four cases. In both models, all four cases differed in the severity of their corresponding simulated RVF epizootics. The four cases, ranked by the severity of the simulated RVF epizootics in descending order, correspond with the occurrence of the Greater Bairam on the following months: July, October, April, and January. The numerical model was assessed for sensitivity with respect to parameter values and exhibited a high degree of robustness.

CONCLUSIONS

Limiting the importation of infected ruminants beginning one month prior to the Greater Bairam festival (on years in which the festival falls between the months of July and October: 2014-2022) might be a feasible way of mitigating future RVF epizootics in Egypt.

Serum levels of inflammatory cytokines in Rift Valley fever patients are indicative of severe disease

BACKGROUND

Rift Valley fever (RVF) is a mosquito-borne viral zoonosis affecting domestic and wild ruminants, camels and humans. Outbreaks of RVF are characterized by a sudden onset of abortions and high mortality amongst domestic ruminants. Humans develop disease ranging from a mild flu-like illness to more severe complications including hemorrhagic syndrome, ocular and neurological lesions and death. During the RVF outbreak in South Africa in 2010/11, a total of 278 human cases were laboratory confirmed, including 25 deaths. The role of the host inflammatory response to RVF pathogenesis is not completely understood.

METHODS

Virus load in serum from human fatal and non-fatal cases was determined by standard tissue culture infective dose 50 (TCID50) titration on Vero cells. Patient serum concentration of chemokines and cytokines involved in inflammatory responses (IL-8, RANTES, CXCL9, MCP-1, IP-10, IL-1β, IL-6, IL-10, TNF and IL-12p70) was determined using cytometric bead assays and flow cytometry.

RESULTS

Fatal cases had a 1-log10 higher TCID50/ml serum concentration of RVF virus (RVFV) than survivors (p < 0.05). There were no significant sequence differences between isolates recovered from fatal and non-fatal cases. Chemokines and pro- and anti-inflammatory cytokines were detected at significantly increased (IL-8, CXCL9, MCP-1, IP-10, IL-10) or decreased (RANTES) levels when comparing fatal cases to infected survivors and uninfected controls, or when comparing combined infected patients to uninfected controls.

CONCLUSIONS

The results suggest that regulation of the host inflammatory responses plays an important role in the outcome of RVFV infection in humans. Dysregulation of the inflammatory response contributes to a fatal outcome. The cytokines and chemokines identified in this study that correlate with fatal outcomes warrant further investigation as markers for disease severity.

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.

Evaluation of the Efficacy, Potential for Vector Transmission, and Duration of Immunity of MP-12, an Attenuated Rift Valley Fever Virus Vaccine Candidate, in Sheep

Rift Valley fever virus (RVFV) causes serious disease in ruminants and humans in Africa. In North America, there are susceptible ruminant hosts and competent mosquito vectors, yet there are no fully licensed animal vaccines for this arthropod-borne virus, should it be introduced. Studies in sheep and cattle have found the attenuated strain of RVFV, MP-12, to be both safe and efficacious based on early testing, and a 2-year conditional license for use in U.S. livestock has been issued. The purpose of this study was to further determine the vaccine's potential to infect mosquitoes, the duration of humoral immunity to 24 months postvaccination, and the ability to prevent disease and viremia from a virulent challenge. Vaccination experiments conducted in sheep found no evidence of a potential for vector transmission to 4 North American mosquito species. Neutralizing antibodies were elicited, with titers of >1:40 still present at 24 months postvaccination. Vaccinates were protected from clinical signs and detectable viremia after challenge with virulent virus, while control sheep had fever and high-titered viremia extending for 5 days. Antibodies to three viral proteins (nucleocapsid N, the N-terminal half of glycoprotein GN, and the nonstructural protein from the short segment NSs) were also detected to 24 months using competitive enzyme-linked immunosorbent assays. This study demonstrates that the MP-12 vaccine given as a single dose in sheep generates protective immunity to a virulent challenge with antibody duration of at least 2 years, with no evidence of a risk for vector transmission.

Mosquitoes and the Environment in Nile Delta Villages with Previous Rift Valley Fever Activity

Egypt is affected by serious human and animal mosquito-borne diseases such as Rift Valley fever (RVF). We investigated how potential RVF virus mosquito vector populations are affected by environmental conditions in the Nile Delta region of Egypt by collecting mosquitoes and environmental data from 3 key governorates before and after 2012 seasonal flooding. We found that environmental effects varied among species, life stages, pre- and postflood groupings, and geographic populations of the same species, and that mosquito community composition could change after flooding. Our study provides preliminary data for modeling mosquitoes and mosquito-borne diseases in the Nile Delta region.

Identifying Areas Suitable for the Occurrence of Rift Valley Fever in North Africa: Implications for Surveillance

Rift Valley fever (RVF) is a vector-borne zoonotic disease that has caused widespread outbreaks throughout Africa and the Arabian Peninsula, with serious consequences for livestock-based economies and public health. Although there have never been any reports of RVF in Morocco, Algeria, Tunisia and Libya, it is a priority disease in the Maghreb, due to the threat of introduction of the virus through transboundary livestock movements or infected mosquito vectors. However, the implementation of surveillance activities and early warning contingency plans requires better knowledge of the epidemiological situation. We conducted a multicriteria decision analysis, integrating host distribution with a combination of important ecological factors that drive mosquito abundance, to identify hotspots and suitable time periods for RVF enzootic circulation (i.e. stable transmission at a low to moderate level for an extended period of time) and an RVF epizootic event (i.e. a sudden occurrence of a large number of infected animals over a large geographic area) in the Maghreb. We also modelled vector species distribution using available information on vector presence and habitat preference. We found that the northern regions of the Maghreb were moderately suitable for RVF enzootics, but highly suitable for RVF epizootics. The vector species distribution model identified these regions as the most favourable mosquito habitats. Due to the low density of animal hosts and arid conditions, the desert region showed low RVF suitability, except in oases. However, the presence of competent vectors in putative unsuitable areas underlines the need for further assessments of mosquito habitat preference. This study produced monthly RVF suitability maps useful for animal health managers and veterinary services involved in designing risk-based surveillance programmes. The suitability maps can be further enhanced using existing country-specific sources of information and by incorporating knowledge - as it becomes available - on the epidemiology of the disease and distribution of vectors in the Maghreb.

Arboviruses pathogenic for domestic and wild animals

The objective of this chapter is to provide an updated and concise systematic review on taxonomy, history, arthropod vectors, vertebrate hosts, animal disease, and geographic distribution of all arboviruses known to date to cause disease in homeotherm (endotherm) vertebrates, except those affecting exclusively man. Fifty arboviruses pathogenic for animals have been documented worldwide, belonging to seven families: Togaviridae (mosquito-borne Eastern, Western, and Venezuelan equine encephalilitis viruses; Sindbis, Middelburg, Getah, and Semliki Forest viruses), Flaviviridae (mosquito-borne yellow fever, Japanese encephalitis, Murray Valley encephalitis, West Nile, Usutu, Israel turkey meningoencephalitis, Tembusu and Wesselsbron viruses; tick-borne encephalitis, louping ill, Omsk hemorrhagic fever, Kyasanur Forest disease, and Tyuleniy viruses), Bunyaviridae (tick-borne Nairobi sheep disease, Soldado, and Bhanja viruses; mosquito-borne Rift Valley fever, La Crosse, Snowshoe hare, and Cache Valley viruses; biting midges-borne Main Drain, Akabane, Aino, Shuni, and Schmallenberg viruses), Reoviridae (biting midges-borne African horse sickness, Kasba, bluetongue, epizootic hemorrhagic disease of deer, Ibaraki, equine encephalosis, Peruvian horse sickness, and Yunnan viruses), Rhabdoviridae (sandfly/mosquito-borne bovine ephemeral fever, vesicular stomatitis-Indiana, vesicular stomatitis-New Jersey, vesicular stomatitis-Alagoas, and Coccal viruses), Orthomyxoviridae (tick-borne Thogoto virus), and Asfarviridae (tick-borne African swine fever virus). They are transmitted to animals by five groups of hematophagous arthropods of the subphyllum Chelicerata (order Acarina, families Ixodidae and Argasidae-ticks) or members of the class Insecta: mosquitoes (family Culicidae); biting midges (family Ceratopogonidae); sandflies (subfamily Phlebotominae); and cimicid bugs (family Cimicidae). Arboviral diseases in endotherm animals may therefore be classified as: tick-borne (louping ill and tick-borne encephalitis, Omsk hemorrhagic fever, Kyasanur Forest disease, Tyuleniy fever, Nairobi sheep disease, Soldado fever, Bhanja fever, Thogoto fever, African swine fever), mosquito-borne (Eastern, Western, and Venezuelan equine encephalomyelitides, Highlands J disease, Getah disease, Semliki Forest disease, yellow fever, Japanese encephalitis, Murray Valley encephalitis, West Nile encephalitis, Usutu disease, Israel turkey meningoencephalitis, Tembusu disease/duck egg-drop syndrome, Wesselsbron disease, La Crosse encephalitis, Snowshoe hare encephalitis, Cache Valley disease, Main Drain disease, Rift Valley fever, Peruvian horse sickness, Yunnan disease), sandfly-borne (vesicular stomatitis-Indiana, New Jersey, and Alagoas, Cocal disease), midge-borne (Akabane disease, Aino disease, Schmallenberg disease, Shuni disease, African horse sickness, Kasba disease, bluetongue, epizootic hemorrhagic disease of deer, Ibaraki disease, equine encephalosis, bovine ephemeral fever, Kotonkan disease), and cimicid-borne (Buggy Creek disease). Animals infected with these arboviruses regularly develop a febrile disease accompanied by various nonspecific symptoms; however, additional severe syndromes may occur: neurological diseases (meningitis, encephalitis, encephalomyelitis); hemorrhagic symptoms; abortions and congenital disorders; or vesicular stomatitis. Certain arboviral diseases cause significant economic losses in domestic animals-for example, Eastern, Western and Venezuelan equine encephalitides, West Nile encephalitis, Nairobi sheep disease, Rift Valley fever, Akabane fever, Schmallenberg disease (emerged recently in Europe), African horse sickness, bluetongue, vesicular stomatitis, and African swine fever; all of these (except for Akabane and Schmallenberg diseases) are notifiable to the World Organisation for Animal Health (OIE, 2012).

Molecular and serological studies on the Rift Valley fever outbreak in Mauritania in 2010

Rift Valley fever virus (RVFV) is a vector-borne RNA virus affecting humans, livestock and wildlife. In October/November 2010, after a period of unusually heavy rainfall, a Rift Valley fever outbreak occurred in northern Mauritania causing clinical cases in cattle, sheep, goats and camels, 21 of which were of lethal outcome. The aim of this study was to obtain further information on the continuation of RVF virus activity and spread in animal species in Mauritania after this outbreak. We therefore tested sera from small ruminants, cattle and camels for the presence of viral RNA and antibodies against RVFV. These sera were collected in different parts of the country from December 2010 to February 2011 and tested with three different ELISAs and an indirect immunofluorescence assay. The results show a high seroprevalence of RVFV IgM and IgG antibodies of about 57% in all animals investigated. Moreover, in four camel sera, viral RNA was detected emphasizing the important role camels played during the latest RVF outbreak in Mauritania. The study demonstrates the continuous spread of RVFV in Mauritania after initial emergence and highlights the potential role of small ruminants and camels in virus dissemination.