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

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.

Antiviral and protective effect of small interfering RNAs against rift valley fever virus in vitro

BACKGROUND

Rift Valley Fever Virus (RVFV) is an arbovirus, a zoonotic disease that resurfaces as a potential hazard beyond geographic boundaries. Fever that can proceed to encephalitis, retinitis, hemorrhagic fever, and death is the main manifestation observed in human infections. RVFV has no authorized medication. The RNA interference (RNAi) gene silencing pathway is extremely well conserved. By targeting specific genes, small interfering RNA (siRNA) can be used to suppress viral replication. The aim of this study was to design specific siRNAs against RVFV and evaluate their prophylactic and antiviral effects on the Vero cells.

METHODS AND RESULTS

Various siRNAs were designed using different bioinformatics tools. Three unique candidates were tested against an Egyptian sheep cell culture-adapted strain BSL-2 that suppressed RVFV N mRNA expression. SiRNAs were transfected a day before RVFV infection (pre-transfection), and 1 h after the viral infection (post-transfection), and were evaluated to detect the silencing activity and gene expression decrease using real-time PCR and a TCID50 endpoint test. The degree of N protein expression was determined by western blot 48 h after viral infection. D2 which targets the (488-506 nucleotides), the middle region of RVFV N mRNA was the most effective siRNA at 30 nM concentration, it almost eliminates N mRNA expression when utilized as antiviral or preventive therapy. siRNAs had a stronger antiviral silencing impact when they were post-transfected into Vero cells.

CONCLUSION

Pre and post-transfection of siRNAs significantly reduced RVFV titer in cell lines, offering novel and potentially effective anti-RVFV epidemics and epizootics therapy.

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.

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.

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.

Amphiphilic Poly(N-Vinylpyrrolidone) Nanoparticles Loaded with DNA Plasmids Encoding Gn and Gc Glycoproteins of the Rift Valley Fever Virus: Preparation and In Vivo Evaluation

The aim of the study was to develop amphiphilic poly(N-vinylpyrrolidone) (PVP) nanoparticles (NPs) loaded with DNA plasmids encoding Gn and Gc glycoproteins of the Rift Valley fever virus (RVFV) and to study the humoral response in vivo. DNA plasmids were protected from extracellular nucleases by loading in NPs from PVP derivatives modified with amino acids β-alanine (Ala7-PVPOD4000) or glycine (Gly7.5-PVP-OD4000) fabricated by the original self-assembly technique. The obtained NPs were administered in mice and the enhancement of humoral response compared to this one in case of immunization with native DNA plasmids was demonstrated. The NPs loaded with DNA plasmids are promising for the fabrication of various DNA particulate vaccines.

First serological evidence of the Rift Valley fever Phlebovirus in Tunisian camels

Rift Valley fever (RVF) is a mosquito-borne zoonosis that severely impacts livelihoods, national and international economies, and human health. Few studies have investigated the prevalence of this infection in Tunisian livestock. The present report aimed to update the epidemiological status and identify the risk factors associated with this RVF virus infection in the one-humped dromedary camel from arid areas. A total of 470 sera of apparently healthy camels (Camelus dromedarius) were collected from six governorates from southern and central Tunisia. Samples were tested by a competitive Enzyme Linked Immunosorbent Assay (ELISA). An overall, 162 camels (34%, 95%CI: 0.1-0.4) were seropositive to RVF virus antigen. Logistic regression model revealed three potential risk factors associated with the infection. A meaningful high seropositivity was observed among aged camels (>10 years-old) (40%) (P=0.001; OR=3.367). Besides, camels raised in small flocks particularly intended for meat production showed a high level of seropositivity (37%) (P=0.013; OR=13.173). Animals having close contact with other ruminants showed high seroprevalence (37%) (P=0.022; OR=10.919). This report indicated that Tunisian one-humped dromedaries were exposed to this virus and may contribute to its dissemination among farmers and other livestock. Furthers studies are urgently required to isolate and characterize this virus, evaluate the potential risk of human infection particularly in farmers, veterinarians and slaughterhouse workers and finally to program a serious strategy for RVF control.

Rift Valley fever in northern Senegal: A modelling approach to analyse the processes underlying virus circulation recurrence

Rift Valley fever (RVF) is endemic in northern Senegal, a Sahelian area characterized by a temporary pond network that drive both RVF mosquito population dynamics and nomadic herd movements. To investigate the mechanisms that explain RVF recurrent circulation, we modelled a realistic epidemiological system at the pond level integrating vector population dynamics, resident and nomadic ruminant herd population dynamics, and nomadic herd movements recorded in Younoufere area. To calibrate the model, serological surveys were performed in 2015–2016 on both resident and nomadic domestic herds in the same area. Mosquito population dynamics were obtained from a published model trained in the same region. Model comparison techniques were used to compare five different scenarios of virus introduction by nomadic herds associated or not with vertical transmission in Aedes vexans. Our serological results confirmed a long lasting RVF endemicity in resident herds (IgG seroprevalence rate of 15.3%, n = 222), and provided the first estimation of RVF IgG seroprevalence in nomadic herds in West Africa (12.4%, n = 660). Multivariate analysis of serological data suggested an amplification of the transmission cycle during the rainy season with a peak of circulation at the end of that season. The best scenario of virus introduction combined yearly introductions of RVFV from 2008 to 2015 (the study period) by nomadic herds, with a proportion of viraemic individuals predicted to be larger in animals arriving during the 2^nd half of the rainy season (3.4%). This result is coherent with the IgM prevalence rate (4%) found in nomadic herds sampled during the 2^nd half of the rainy season. Although the existence of a vertical transmission mechanism in Aedes cannot be ruled out, our model demonstrates that nomadic movements are sufficient to account for this endemic circulation in northern Senegal.

Rift Valley fever (RVF) is one of the most important vector borne disease in Africa, seriously affecting the health of domestic ruminants and humans and leading to severe economic consequences. This disease is endemic in northern Senegal, a Sahelian area characterized by a temporary pond network that drive both RVF mosquito population dynamics and nomadic herd movements. Two non-exclusive mechanisms may support this endemicity: recurrent introductions of the virus by nomadic animals, and vertical transmission of the virus (i.e. from infected female mosquito to eggs) in local Aedes populations. The authors followed resident and nomadic domestic herds for 1 year. They used the data thus obtained to model a realistic epidemiological system at the pond level integrating vector population dynamics, resident and nomadic ruminant herd population dynamics. They found that the best scenario explaining RVF remanence combined yearly introductions of RVFV by nomadic herds, with a viraemic proportion predicted to be larger in animals arriving during the 2^nd half of the rainy season, which is consistent with an amplification of virus circulation in the area during the rainy season. Although the existence of a vertical transmission mechanism in Aedes cannot be ruled out, their results demonstrates that nomadic movements are sufficient to account for this endemic circulation in northern Senegal.

Seroprevalence of some viral and bacterial zoonoses in domestic ruminants in Medina

OBJECTIVE

The study aimed to explore the seroprevalence of some bacterial (Brucella spp., Chlamydia abortus) and viral [Rift Valley fever virus (RVFV), foot and mouth disease virus (FMDV)] zoonoses in domestic ruminants in Medina.

MATERIALS AND METHODS

A total of 1,000 blood samples from 665 sheep, 228 goats, and 107 camels were collected from the central slaughterhouse, private farms, and veterinary clinics affiliated to the Ministry of Agriculture. The samples were screened using the Enzyme-Linked Immunosorbent Assay (ELISA). The results were statistically analyzed using Statistical Package for the Social Sciences version 20.

RESULTS

Brucella was found in 7.7%, 8.8%, and 6.5% of sheep, goats, and camel's sera, respectively. In humans, Brucella abortus and Brucella melitensis had higher frequencies in males (61.3%, 59.8%) than in females (38.7%, 40.2%). Chlamydia abortus was reported only in sheep at a rate of 0.75%. RVFV was prevalent in sheep (10.7%) and goats (17.9%). FMDV was reported in 27.8% of sheep and 7.9% of goats. There was a highly statistical significance between Brucella, RVFV, and FMDV seropositivity and locally bred animals (p < 0.01). Multiple seropositivities have been reported among sheep and goats. Brucella was commonly observed in mixed infection with other bacterial and viral agents under study.

CONCLUSION

The surveyed viral and bacterial agents were prevalent in ruminants in the Medina region. Since Medina is an important destination for pilgrims from all over the world, therefore, an integrated approach involving strict control measures and routine vaccination programs should be adopted to reduce the possibility of global epidemics.

Microencapsulated plasmids expressing Gn and Gc glycoproteins of Rift Valley Fever virus enhance humoral immune response in mice

OBJECTIVES

The aim of the current study was to develop biodegradable alginate (ALG)/poly-L-lysine (PLL) microcapsules (MC) with entrapped plasmids expressing Gn and Gc glycoproteins of Rift Valley Fever virus (RVFV) and to evaluate the humoral immune response in mice.

RESULTS

Expressing phRVF/Gn and phRVF/Gc plasmids which encode full-sized Gn and Gc glycoproteins and contain signal fusion protein F sequences of human parainfluenza (HPIV-1) were constructed. To protect the plasmids from cleavage by extracellular nucleases, they were entrapped into multilayer ALG/PLL microcapsules by layer-by-layer technique. To study the efficacy of humoral immune response, both native and microencapsulated plasmids were injected intramuscular into BALB/c mice. The humoral response in the mice immunized with free plasmids was characterized by virus-neutralizing antibody induction (with titres 1:4 to 1:8), while the injection of microencapsulated plasmids allowed to increase the titre level (from 1:16 to 1:32).

CONCLUSION

The plasmids microencapsulated in biodegradable MC could be promising for development of DNA vaccines against RVFV.

Seroprevalence of Rift valley fever in South African domestic and wild suids (1999-2016)

Rift valley fever (RVF) is a vector-borne viral disease of domestic ruminants, camels and man, characterized by widespread abortions and neonatal deaths in animals, and flu-like symptoms, which can progress to hepatitis and encephalitis in humans. The disease is endemic in Africa, Saudi Arabia and Yemen, and outbreaks occur after periods of high rainfall, or in environments supporting the proliferation of RVF virus (RVFV)-infected mosquito vectors. The domestic and wild animal maintenance hosts of RVFV, which may serve as sources of virus during inter-epidemic periods (IEPs) and contribute to occurrence of sporadic outbreaks, remain unknown, although reports indicate that the African buffalo (Syncerus caffer) may play a role. Due to the close proximity of the habitats of domestic pigs and warthogs to those of known domestic and wild ruminant RVFV maintenance hosts respectively, our study investigated their possible role in the epidemiology of RVF in South Africa by evaluating RVFV exposure and seroconversion in suids. A total of 107 warthog and 3,984 domestic pig sera from 2 and all 9 provinces of South Africa, respectively, were screened for presence of RVFV neutralizing antibodies using the virus neutralization test (VNT). Sero-positivity rates of 1.87% (95% CI: 0.01%-6.9%) and 0.68% (95% CI: 0.49%-1.04%) were observed for warthogs and domestic pigs, respectively, but true prevalence rates, taking test sensitivity and specificity into account, were lower for both groups. There was a strong association between the results of the two groups (χ²  = 0.75, p = .38), and differences in prevalence between the epidemic and IEPs were non-significant for all suid samples tested (p > .05). This study, which provides the first evidence of probable exposure and infection of South African domestic pigs and warthogs to RVFV, indicates that further investigations are warranted, to fully clarify the role of suids in the epidemiology of RVF.

Rift Valley fever virus in small ruminants in the Democratic Republic of the Congo

Rift Valley fever (RVF) is a zoonotic viral disease caused by the RVF phlebovirus (RVFV) that infects a variety of animal species including sheep and goats. Sera (n = 893) collected between 2013 and 2015 from randomly selected indigenous sheep and goats in seven provinces of the Democratic Republic of the Congo (DRC) were tested for the presence of specific immunoglobulin G (IgG) and M (IgM) against RVFV, using two commercially available enzyme-linked immunosorbent assays. The reverse transcription polymerase chain reaction (RT-PCR) was also used to detect RVFV nucleic acid. There was significant variation in true seroprevalence of RVFV for both sheep and goats between the seven provinces investigated. Values ranged from 0.0 (95% confidence interval [CI] 0.0-6.55) to 23.81 (95% CI 12.03-41.76) for goat and 0.0 (95% CI 0.0-7.56) to 37.11 (95% CI 15.48-65.94) for sheep, respectively. One serum (1.85%) out of 54 that tested positive for IgG was found to be IgM-positive. This same sample was also positive by RT-PCR indicating an active or recent infection. These findings report the presence of RVFV in small ruminants in the DRC for the first time and indicate variations in exposure to the virus in different parts of the country.

Seroprevalence of Rift Valley fever in cattle of smallholder farmers in Kwilu Province in the Democratic Republic of Congo

Rift Valley fever (RVF) is a zoonotic mosquito-borne disease caused by RVF virus (RVFV) that causes abortions and high mortalities in livestock and is also associated with acute and fatal disease in humans. In the Democratic Republic of Congo (DRC), information on the epidemiology of RVF is limited, particularly among cattle reared by smallholder farmers. This cross-sectional study was conducted to investigate the seroprevalence of RVF in cattle raised by smallholder farmers in Kwilu Province of DRC, which has not yet reported an RVF epidemic. A total of 677 cattle sera were collected from four territories and tested for anti-RVFV antibodies using immunofluorescent assay and enzyme-linked immunosorbent assay. The overall seroprevalence of anti-RVFV IgG was 6.5% (44/677) (95% CI 4.81-8.7). There was a statistically significant difference in the seroprevalence among the territories (χ² = 28.79, p < 0.001). Territory seroprevalences were as follows: Idiofa 14.08% (95% CI 9.78-19.76), Bulungu 4.14% (95% CI 1.83-8.68), Gungu 3.21% (95% CI 1.41-6.78), and Masi-Manimba 1.19% (95% CI 0.06-7.37). Seroprevalence differed significantly among age categories (p = 0.0017) and ecosystem (p < 0.001). The seroprevalence of animals aged between 1 and 2 years was 20.0% (95% CI 8.4-39.13) and was higher than group aged <1 year, between 2 and 3 years, and > 3 years. Forest area (18.92% (95% CI 12.35-27.7)) had higher seropositivity than savannah area (4.06% (95% CI 2.65-6.12)). Sex difference was not significant (χ² = 0.14, p = 0.704). These findings indicate that cattle in Kwilu Province had been exposed to RVFV, which represents a significant risk for both livestock and human health.

Towards harmonisation of entomological surveillance in the Mediterranean area

BACKGROUND

The Mediterranean Basin is historically a hotspot for trade, transport, and migration. As a result, countries surrounding the Mediterranean Sea share common public health threats. Among them are vector-borne diseases, and in particular, mosquito-borne viral diseases are prime candidates as (re)emerging diseases and are likely to spread across the area. Improving preparedness and response capacities to these threats at the regional level is therefore a major issue. The implementation of entomological surveillance is, in particular, of utmost importance. Guidance in designing entomological surveillance systems is critical, and these systems may pursue different specific objectives depending on the disease. The purpose of the proposed review is to draw up guidelines for designing effective and sustainable entomological surveillance systems in order to improve preparedness and response. However, we make it clear that there is no universal surveillance system, so the thinking behind harmonisation is to define evidence-based standards in order to promote best practises, identify the most appropriate surveillance activities, and optimise the use of resources. Such guidance is aimed at policymakers and diverse stakeholders and is intended to be used as a framework for the implementation of entomological surveillance programmes. It will also be useful to collaborate and share information with health professionals involved in other areas of disease surveillance. Medical entomologists and vector control professionals will be able to refer to this report to advocate for tailored entomological surveillance strategies. The main threats targeted in this review are the vectors of dengue virus, chikungunya virus, Zika virus, West Nile virus, and Rift Valley fever virus. The vectors of all these arboviruses are mosquitoes.

METHODS

Current knowledge on vector surveillance in the Mediterranean area is reviewed. The analysis was carried out by a collaboration of the medical entomology experts in the region, all of whom belong to the MediLabSecure network, which is currently funded by the European Union and represents an international effort encompassing 19 countries in the Mediterranean and Black Sea region.

FINDINGS

Robust surveillance systems are required to address the globalisation of emerging arboviruses. The prevention and management of mosquito-borne viral diseases must be addressed in the prism of a One Health strategy that includes entomological surveillance as an integral part of the policy. Entomological surveillance systems should be designed according to the entomological and epidemiological context and must have well-defined objectives in order to effect a tailored and graduated response. We therefore rely on different scenarios according to different entomological and epidemiological contexts and set out detailed objectives of surveillance. The development of multidisciplinary networks involving both academics and public authorities will provide resources to address these health challenges by promoting good practises in surveillance (identification of surveillance aims, design of surveillance systems, data collection, dissemination of surveillance results, evaluation of surveillance activities) and through the sharing of effective knowledge and information. These networks will also contribute to capacity building and stronger collaborations between sectors at both the local and regional levels. Finally, concrete guidance is offered on the vector of the main arbovirus based on the current situation in the area.

Evaluation of a Virus Neutralisation Test for Detection of Rift Valley Fever Antibodies in Suid Sera

Rift Valley fever (RVF) is a vector-borne viral disease of ruminants mainly, and man, characterized by abortions and neonatal deaths in animals and flu-like to more severe symptoms that can result in death in humans. The disease is endemic in Africa, Saudi Arabia and Yemen, and outbreaks occur following proliferation of RVF virus (RVFV) infected mosquito vectors. Vertebrate animal maintenance hosts of RVFV, which serve as a source of virus during inter-epidemic periods remain unknown, with wild and domestic suids being largely overlooked. To address this, we evaluated the virus neutralization test (VNT) for RVF antibody detection in suid sera, as a first step in assessing the role of suids in the epidemiology of RVF in Africa. Testing of experimental and field sera from domestic pigs and warthogs with a commercial RVF competitive antibody ELISA, served as a reference standard against which the VNT results were compared. Results indicate that VNT can detect anti-RVFV antibodies within three days post-infection, has an analytical specificity of 100% and diagnostic sensitivity and specificity of 80% and 97%, respectively. Although labour-intensive and time-consuming, the VNT proved suitable for screening suid sera and plasma for presence of RVFV antibodies in viraemic and recovered animals.

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.

Molecular aspects of Rift Valley fever virus and the emergence of reassortants

Rift Valley fever phlebovirus (RVFV) is a mosquito-transmitted pathogen endemic to sub-Saharan Africa and the Arabian Peninsula. RVFV is a threat to both animal and human health and has costly economic consequences mainly related to livestock production and trade. Competent hosts and vectors for RVFV are widespread, existing outside of endemic countries including the USA. Thus, the possibility of RVFV spreading to the USA or other countries worldwide is of significant concern. RVFV (genus Phlebovirus) is comprised of an enveloped virion containing a three-segmented, negative-stranded RNA genome that is able to undergo genetic reassortment. Reassortment has the potential to produce viruses that are more pathogenic, easily transmissible, and that have wider vector or host range. This is especially concerning because of the wide use of live attenuated vaccine strains throughout endemic countries. This review focuses on the molecular aspects of RVFV, genetic diversity of RVFV strains, and RVFV reassortment.

First occurrence of Rift Valley fever outbreak in Niger, 2016

Rift Valley fever (RVF) is a mosquito‐borne viral zoonosis causing abortions and high mortality among animals, whereas in humans, the disease is usually mild or asymptomatic. In September 2016, the Republic of Niger declared the first RVF outbreak in the northern region of Tahoua near the Malian border. This study describes the outbreak and reports the results of serological and molecular investigations of the human and animal samples collected. Serum samples from both human and animal suspected cases have been confirmed at the Centre de Recherche Médicale et Sanitaire (CERMES) and the Laboratoire Centrale d'Elevage (LABOCEL) public health and animal reference laboratories, respectively. Techniques for biological confirmation were real time reverse transcription polymerase chain reaction (RT‐PCR) and enzyme linked immunosorbent assay (ELISA). Phylogenetic trees were established after genetic sequencing of the small and medium segments of the RVF virus (RVFV) genome. Out of the 399 human samples collected, 17 (4.3%) were confirmed positive for RVFV. Overall, 33 (8.3%) deaths occurred out of which five (29%) were among the 17 confirmed cases. Regarding animals, 45 samples were tested, three of which were RT‐PCR positive and 24 were IgG positive. The phylogenetic analyses showed that the Niger strains clustered with Senegal 2013 and Mauritania 2015 RVFV strains. This first outbreak of RVF was very challenging for public and animal health laboratories in Niger. Besides resulting in human deaths, important loss of cattle has been reported. Therefore, vigilance has to be strengthened emphasising vector control strategies and active surveillance among animals.

Epidemiological surveillance of bovine viral diarrhea and rift valley fever infections in camel

Aim:

This study was designed to investigate the current epidemiological situation of bovine viral diarrhea virus (BVDV) and rift valley fever virus (RVFV) infection of camels originating from Sudan “smuggler” and Egypt as part of our future plan for a national surveillance program in Egyptian provinces, which will aid in establishment of control strategy for animal diseases.

Materials and Methods:

This investigation was accomplished using serological diagnostic and molecular biology techniques. A total number of 200 blood samples were collected from camel (120 originated from Sudan “smuggler” and 80 from local breed) and were subjected for testing both BVDV and RVFV occurrence with different age and sex.

Results:

Sixty-six of the 200 camels (33%) were positive for BVDV antibodies, and 44 (22%) for BVDV antigen (Ag), and 27 of the 200 camels (13.5%) were positive for RVFV immunoglobulin G (IgG) antibodies. On the other hand, the seroprevalence of BVDV for antibodies (47.5%), Ag (31.6%), and RVFV IgG antibodies (16.6%) was higher in camel originated from Sudan “smuggler” than of local breed which was 11.2% for BVDV antibodies and 7.5% for BVDV Ag, while it was 8.7% for RVFV IgG antibodies. The incidence of BVDV antibodies, Ag, and RVFV IgG antibodies was the highest in male, up to 9 years of age. The frequency of positive cases was significantly different according to the origin of samples and sex and age of camel for BVDV and RVFV. In addition, seven serologically positive samples for BVDV and five serologically positive samples for RVFV were submitted as a buffy coat for molecular detection by one-step – reverse transcription polymerase chain reaction (RT-PCR). The results demonstrated that three samples were positive for BVDV of camel originated from Sudan (smuggler), while no RVFV Ag was detected in all five samples. Sequencing and phylogenetic analysis of the amplicons obtained from positive RT-PCR samples (three samples) indicated 100% nucleotide homology with Sudan strain 2015 except only one (missense point mutation) by substitution of A to T at position 345 that changed the coded amino acids from T (Threonine) to S (Serine) at residue 115.

Conclusion:

Camels act as risk animals for the introduction of many infectious diseases from Sudan to Egypt, especially transboundary animal diseases, so strict quarantine measures should be taken during importation of live animals from Sudan to prevent the spread of such diseases.

Preliminary evaluation of diagnostic accuracy and precision of a competitive ELISA for detection of antibodies to Rift Valley fever virus in cattle and sheep sera

Rift Valley fever virus (RVFV), a mosquito-borne, zoonotic pathogen, is endemic to sub-Saharan Africa and has spread beyond the continent to the Arabian Peninsula. The high likelihood of RVFV's spread to other non-endemic countries spurs the need for development and implementation of rapid diagnostic tests and surveillance programs. In this preliminary evaluation, we assessed the diagnostic accuracy and precision of a recombinant RVFV nucleoprotein based competitive ELISA (cELISA) assay to detect RVFV antibodies compared to a plaque reduction neutralization test (PRNT₈₀), using sera of cattle and sheep that were experimentally infected with either the MP-12 RVFV vaccine or a wild-type RVFV strain, as well as using known RVFV negative sera. With the manufacturer recommended 60% inhibition for the cELISA and a 1:40 titer for the PRNT₈₀, the sensitivity and specificity of the cELISA assay was determined to be 95.1% (95% CI = 83.5-99.4%) and 91.8% (95% CI = 85.0-96.2%), respectively. Antibodies to RVFV were first detected at 5 days post inoculation (dpi) in both species' sera. The prototype cELISA is an easy to implement, sensitive, specific, and safe test for the detection of antibodies to RVFV that can be used in surveillance programs.

Environmental limits of Rift Valley fever revealed using ecoepidemiological mechanistic models

Vector-borne diseases (VBDs) of humans and domestic animals are a significant component of the global burden of disease and a key driver of poverty. The transmission cycles of VBDs are often strongly mediated by the ecological requirements of the vectors, resulting in complex transmission dynamics, including intermittent epidemics and an unclear link between environmental conditions and disease persistence. An important broader concern is the extent to which theoretical models are reliable at forecasting VBDs; infection dynamics can be complex, and the resulting systems are highly unstable. Here, we examine these problems in detail using a case study of Rift Valley fever (RVF), a high-burden disease endemic to Africa. We develop an ecoepidemiological, compartmental, mathematical model coupled to the dynamics of ambient temperature and water availability and apply it to a realistic setting using empirical environmental data from Kenya. Importantly, we identify the range of seasonally varying ambient temperatures and water-body availability that leads to either the extinction of mosquito populations and/or RVF (nonpersistent regimens) or the establishment of long-term mosquito populations and consequently, the endemicity of the RVF infection (persistent regimens). Instabilities arise when the range of the environmental variables overlaps with the threshold of persistence. The model captures the intermittent nature of RVF occurrence, which is explained as low-level circulation under the threshold of detection, with intermittent emergence sometimes after long periods. Using the approach developed here opens up the ability to improve predictions of the emergence and behaviors of epidemics of many other important VBDs.

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.

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.