Rift Valley Fever Virus—How and Where Virus Is Maintained During Inter-epidemic Periods

Widening geographic range of Rift Valley fever disease clusters associated with climate change in East Africa

BACKGROUND

Recent epidemiology of Rift Valley fever (RVF) disease in Africa suggests growing frequency and expanding geographic range of small disease clusters in regions that previously had not reported the disease. We investigated factors associated with the phenomenon by characterising recent RVF disease events in East Africa.

METHODS

Data on 100 disease events (2008-2022) from Kenya, Uganda and Tanzania were obtained from public databases and institutions, and modelled against possible geoecological risk factors of occurrence including altitude, soil type, rainfall/precipitation, temperature, normalised difference vegetation index (NDVI), livestock production system, land-use change and long-term climatic variations. Decadal climatic variations between 1980 and 2022 were evaluated for association with the changing disease pattern.

RESULTS

Of 100 events, 91% were small RVF clusters with a median of one human (IQR, 1-3) and three livestock cases (IQR, 2-7). These clusters exhibited minimal human mortality (IQR, 0-1), and occurred primarily in highlands (67%), with 35% reported in areas that had never reported RVF disease. Multivariate regression analysis of geoecological variables showed a positive correlation between occurrence and increasing temperature and rainfall. A 1°C increase in temperature and a 1-unit increase in NDVI, one months prior were associated with increased RVF incidence rate ratios of 1.20 (95% CI 1.1, 1.2) and 1.93 (95% CI 1.01, 3.71), respectively. Long-term climatic trends showed a significant decadal increase in annual mean temperature (0.12-0.3°C/decade, p<0.05), associated with decreasing rainfall in arid and semi-arid lowlands but increasing rainfall trends in highlands (p<0.05). These hotter and wetter highlands showed increasing frequency of RVF clusters, accounting for 76% and 43% in Uganda and Kenya, respectively.

CONCLUSION

These findings demonstrate the changing epidemiology of RVF disease. The widening geographic range of disease is associated with climatic variations, with the likely impact of wider dispersal of virus to new areas of endemicity and future epidemics.

Widening geographic range of Rift Valley fever disease clusters associated with climate change in East Africa

Background

Recent epidemiology of Rift Valley fever (RVF) disease in Africa suggests growing frequency and expanding geographic range of small disease clusters in regions that previously had not reported the disease. We investigated factors associated with the phenomenon by characterizing recent RVF disease events in East Africa.

Methods

Data on 100 disease events (2008 - 2022) from Kenya, Uganda, and Tanzania were obtained from public databases and institutions, and modeled against possible geo-ecological risk factors of occurrence including altitude, soil type, rainfall/precipitation, temperature, normalized difference vegetation index (NDVI), livestock production system, land-use change, and long-term climatic variations. Decadal climatic variations between 1980-2022 were evaluated for association with the changing disease pattern.

Results

Of 100 events, 91% were small RVF clusters with a median of one human (IQR, 1-3) and 3 livestock cases (IQR, 2-7). These clusters exhibited minimal human mortality (IQR 0-1), and occurred primarily in highlands (67%), with 35% reported in areas that had never reported RVF disease. Multivariate regression analysis of geo-ecological variables showed a positive correlation between occurrence and increasing temperature and rainfall. A 1oC increase in temperature and 1-unit increase in NDVI, 1-3 months prior were associated with increased RVF incidence rate ratios (IRR) of 1.20 (95% CI 1.1,1.2) and 9.88 (95% CI 0.85, 119.52), respectively. Long-term climatic trends showed significant decadal increase in annual mean temperature (0.12 to 0.3oC/decade, P<0.05), associated with decreasing rainfall in arid and semi-arid lowlands but increasing rainfall trends in highlands (P<0.05). These hotter and wetter highlands showed increasing frequency of RVF clusters, accounting for 76% and 43% in Uganda and Kenya, respectively.

Conclusion

These findings demonstrate the changing epidemiology of RVF disease. The widening geographic range of disease is associated with climatic variations, with the likely impact of wider dispersal of virus to new areas of endemicity and future epidemics.

Key questions

What is already known on this topic?: Rift Valley fever is recognized for its association with heavy rainfall, flooding, and El Niño rains in the East African region. A growing body of recent studies has highlighted a shifting landscape of the disease, marked by an expanding geographic range and an increasing number of small RVF clusters.What this study adds: This study challenges previous beliefs about RVF, revealing that it predominantly occurs in small clusters rather than large outbreaks, and its association with El Niño is not as pronounced as previously thought. Over 65% of these clusters are concentrated in the highlands of Kenya and Uganda, with 35% occurring in previously unaffected regions, accompanied by an increase in temperature and total rainfall between 1980 and 2022, along with a rise in the annual number of rainy days. Notably, the observed rainfall increases are particularly significant during the short-rains season (October-December), aligning with a secondary peak in RVF incidence. In contrast, the lowlands of East Africa, where typical RVF epidemics occur, display smaller and more varied trends in annual rainfall.How this study might affect research, practice, or policy: The worldwide consequence of the expanding RVF cluster is the broader dispersion of the virus, leading to the establishment of new regions with virus endemicity. This escalation heightens the risk of more extensive extreme-weather-associated RVF epidemics in the future. Global public health institutions must persist in developing preparedness and response strategies for such scenarios. This involves the creation and approval of human RVF vaccines and therapeutics, coupled with a rapid distribution plan through regional banks.

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.

Ecological and subject-level drivers of interepidemic Rift Valley fever virus exposure in humans and livestock in Northern Kenya

Nearly a century after the first reports of Rift Valley fever (RVF) were documented in Kenya, questions on the transmission dynamics of the disease remain. Specifically, data on viral maintenance in the quiescent years between epidemics is limited. We implemented a cross-sectional study in northern Kenya to determine the seroprevalence, risk factors, and ecological predictors of RVF in humans and livestock during an interepidemic period. Six hundred seventy-six human and 1,864 livestock samples were screened for anti-RVF Immunoglobulin G (IgG). Out of the 1,864 livestock samples tested for IgG, a subset of 1,103 samples was randomly selected for additional testing to detect the presence of anti-RVFV Immunoglobulin M (IgM). The anti-RVF virus (RVFV) IgG seropositivity in livestock and humans was 21.7% and 28.4%, respectively. RVFV IgM was detected in 0.4% of the livestock samples. Participation in the slaughter of livestock and age were positively associated with RVFV exposure in humans, while age was a significant factor in livestock. We detected significant interaction between rainfall and elevation's influence on livestock seropositivity, while in humans, elevation was negatively associated with RVF virus exposure. The linear increase of human and livestock exposure with age suggests an endemic transmission cycle, further corroborated by the detection of IgM antibodies in livestock.

Multivalent viral particles elicit safe and efficient immunoprotection against Nipah Hendra and Ebola viruses

Experimental vaccines for the deadly zoonotic Nipah (NiV), Hendra (HeV), and Ebola (EBOV) viruses have focused on targeting individual viruses, although their geographical and bat reservoir host overlaps warrant creation of multivalent vaccines. Here we explored whether replication-incompetent pseudotyped vesicular stomatitis virus (VSV) virions or NiV-based virus-like particles (VLPs) were suitable multivalent vaccine platforms by co-incorporating multiple surface glycoproteins from NiV, HeV, and EBOV onto these virions. We then enhanced the vaccines' thermotolerance using carbohydrates to enhance applicability in global regions that lack cold-chain infrastructure. Excitingly, in a Syrian hamster model of disease, the VSV multivalent vaccine elicited safe, strong, and protective neutralizing antibody responses against challenge with NiV, HeV, or EBOV. Our study provides proof-of-principle evidence that replication-incompetent multivalent viral particle vaccines are sufficient to provide protection against multiple zoonotic deadly viruses with high pandemic potential.

An outbreak of Rift Valley fever among peri-urban dairy cattle in northern Tanzania

BACKGROUND

Human and animal cases of Rift Valley fever (RVF) are typically only reported during large outbreaks. The occurrence of RVF cases that go undetected by national surveillance systems in the period between these outbreaks is considered likely. The last reported cases of RVF in Tanzania occurred during a large outbreak in 2007-2008.

METHODS

Samples collected between 2017 and 2019 from livestock suffering abortion across northern Tanzania were retrospectively tested for evidence of RVF virus infection using serology and reverse transcription quantitative polymerase chain reaction (RT-qPCR).

RESULTS

A total of 14 RVF-associated cattle abortions were identified among dairy cattle in a peri-urban area surrounding the town of Moshi. RVF cases occurred from May to August 2018 and were considered to represent an undetected, small-scale RVF outbreak. Milk samples from 3 of 14 cases (21%) were found to be RT-qPCR positive. Genotyping revealed circulation of RVF viruses from two distinct lineages.

CONCLUSIONS

RVF outbreaks can occur more often in endemic settings than would be expected on the basis of detection by national surveillance. The occurrence of RVF cases among peri-urban dairy cattle and evidence for viral shedding in milk, also highlights potentially emerging risks for RVF associated with increasing urban and peri-urban livestock populations.

Inter-epidemic Rift Valley fever virus infection incidence and risks for zoonotic spillover in northern Tanzania

Rift Valley fever virus (RVFV) is a mosquito-borne pathogen that has caused epidemics involving people and animals across Africa and the Arabian Peninsula. A number of studies have found evidence for the circulation of RVFV among livestock between these epidemics but the population-level incidence of infection during this inter-epidemic period (IEP) is rarely reported. General force of infection (FOI) models were applied to age-adjusted cross-sectional serological data to reconstruct the annual FOI and population-level incidence of RVFV infection among cattle, goats, and sheep in northern Tanzania from 2009 through 2015, a period without reported Rift Valley fever (RVF) cases in people or animals. To evaluate the potential for zoonotic RVFV spillover during this period, the relationship between village-level livestock RVFV FOI and human RVFV seropositivity was quantified using multi-level logistic regression. The predicted average annual incidence was 72 (95% Credible Interval [CrI] 63, 81) RVFV infections per 10,000 animals and 96 (95% CrI 81, 113), 79 (95% CrI 62, 98), and 39 (95% CrI 28, 52) per 10,000 cattle, sheep, and goats, respectively. There was variation in transmission intensity between study villages, with the highest estimated village-level FOI 2.49% (95% CrI 1.89, 3.23) and the lowest 0.12% (95% CrI 0.02, 0.43). The human RVFV seroprevalence was 8.2% (95% Confidence Interval 6.2, 10.9). Human seropositivity was strongly associated with the village-level FOI in livestock, with the odds of seropositivity in an individual person increasing by around 1.2 times (95% CrI 1.1, 1.3) for each additional annual RVFV seroconversion per 1,000 animals. A history of raw milk consumption was also positively associated with human seropositivity. RVFV has circulated at apparently low levels among livestock in northern Tanzania in the period since the last reported epidemic. Although our data do not allow us to confirm human RVFV infections during the IEP, a strong association between human seropositivity and the FOI in cattle, goats, and sheep supports the hypothesis that RVFV circulation among livestock during the IEP poses a risk for undetected zoonotic spillover in northern Tanzania. We provide further evidence for the likely role of raw milk consumption in RVFV transmission from animals to people.

No evidence of Rift Valley fever antibodies in veterinarians and sheep in Northern Palestine

Background and Aim:

Rift Valley fever virus (RVFV) is a vector-borne virus that causes RVF in humans and ruminants. The clinical symptoms in humans and animals are non-specific and often misdiagnosed, but abortions in ruminants and high mortality in young animals are characteristic. Since the initial outbreak in the Rift Valley area in Kenya, the disease has spread to most African countries and the Middle East. The presence and epidemiological status of RVFV in humans and animals in Palestine are unknown. This study aimed to investigate the presence and risk factors for RVF seroprevalence in veterinarians, as occupational hazard professionals, and sheep, as highly susceptible animals, in Northern Palestine.

Materials and Methods:

A cross-sectional study was conducted. Data and blood samples of 280 Assaf sheep and 100 veterinarians in close occupational contact with sheep were collected between August and September 2020 using an indirect enzyme-linked immunosorbent assay.

Results:

No evidence of RVF antibodies was found in any human or animal sample.

Conclusion:

Our results suggest that RVFV has not circulated in livestock in Northern Palestine, yet. Surveillance and response capabilities and cooperation with the nearby endemic regions are recommended. The distribution of competent vectors in Palestine, associated with global climate change and the role of wild animals, might be a possible route for RVF spreading to Palestine from neighboring countries.

Risk factors for Rift Valley fever virus seropositivity in one-humped camels (Camelus dromedarius) and pastoralist knowledge and practices in Northern Nigeria

Rift Valley fever (RVF) is a complex emerging arboviral hemorrhagic disease that causes significant illness in animals and humans. Camel trade across the land borders between Nigeria and the Niger Republic occurs frequently and poses a significant risk for RVF transmission to pastoralists and traders. We carried a cross-sectional study between November 2016 and April 2017 in two northern States (Katsina and Jigawa) known for camel trade in Nigeria to investigate the seroprevalence and potential risk factors for RVFV occurrence. We collected 720 sera and administered questionnaire to pastoralists. We used the competitive enzyme-linked immunosorbent assay (c-ELISA) to determine the previous exposure to RVFV infection. We retrieved  environmental information from public data sources that might explain RVFV seropositivity at  the LGA level. To asses potential risk factors,we categorized LGAs with RVFV as "1" and those without a case" 0". We fitted a logistic model to the data  and estimated odds ratios and 95% confidence intervals. An overall 19.9% prevalence was reported among camel herd-the highest seropositivity (33.3%) was recorded in SuleTankarkar LGA. In the multivariable model, only rain-fed croplands was significantly associated with RVFV antibodies occurrence p = 0.048 (OR = 0.87, 95% CI: 0.76-0.99). Only a minority of the respondents, 19.3% (n = 17/88), knew that RVF is zoonotic. Separation of healthy animals from the infected animals was carried out by 53.4% (47/88) pastoralists while 59.1% (52/88) pastoralists still use ethnoveterinary practices to control or mitigate disease outbreaks. Our study demonstrates the presence of RVFV antibodies among camel in Nigeria and the associated risk factors. These findings highlight the need for enhancing surveillance and control efforts and the public health education of camel pastoralists. Further investigation to unravel the zoonotic transmission potential to pastoralists and other animal species is pertinent.

Survey of antibodies to Rift Valley fever virus and associated risk factors in one-humped camels (Camelus dromedarius) slaughtered in Maiduguri abattoir, Borno State, Nigeria

Rift Valley fever (RVF) is an emerging mosquito-borne zoonosis that threatens public health and animal agriculture in the endemic areas causing devastating epizootics characterized by abortion storms and high mortalities, especially in newborn animals. A cross-sectional study was conducted to determine the seroprevalence and investigate risk factors associated with exposure to the virus in camels slaughtered in Maiduguri abattoir, Borno State of Nigeria. Camels presented for slaughtered were sampled and data on age, sex, source or origin, utility, presence of post-mortem lesions, body weights and body condition score were collected. Blood samples were collected and sera were harvested and stored at - 20 °C until tested. The sera were tested using a commercial ELISA kit based on the manufacturer's instructions. The overall seroprevalence in the study was 20.7% (95% CI, 13.6-30.0). The analysis showed no significant differences between the presence of antibodies and variables that included the sex of camels (χ² = 0.015, df = 1, p = 0.904) and the presence of post-mortem lesion on the carcass (χ² = 0.009, df = 1, p = 0.925). There were significant differences between presence of antibodies and three variables that included the age (χ² = 4.89, df = 1, p = 0.027), the source (χ² = 7.077, df = 2, p = 0.029) and the main utility (χ² = 8.057, df = 3, p = 0.045) of the camels. It was concluded that camels presented for slaughter at the Maiduguri abattoir have evidence of exposure to the RVF virus and maybe means of transmission of the virus. Regular monitoring and control of transboundary animal movements were recommended in the study area.

Zoonoses and global epidemics

PURPOSE OF REVIEW

The purpose of the review is to summarize recent advances in understanding the origins, drivers and clinical context of zoonotic disease epidemics and pandemics. In addition, we aimed to highlight the role of clinicians in identifying sentinel cases of zoonotic disease outbreaks.

RECENT FINDINGS

The majority of emerging infectious disease events over recent decades, including the COVID-19 pandemic, have been caused by zoonotic viruses and bacteria. In particular, coronaviruses, haemorrhagic fever viruses, arboviruses and influenza A viruses have caused significant epidemics globally. There have been recent advances in understanding the origins and drivers of zoonotic epidemics, yet there are gaps in diagnostic capacity and clinical training about zoonoses.

SUMMARY

Identifying the origins of zoonotic pathogens, understanding factors influencing disease transmission and improving the diagnostic capacity of clinicians will be crucial to early detection and prevention of further epidemics of zoonoses.

Metal Nanoparticles: a Promising Treatment for Viral and Arboviral Infections

Globally, viral diseases continue to pose a significant threat to public health. Recent outbreaks, such as influenza, coronavirus, Ebola, and dengue, have emphasized the urgent need for new antiviral therapeutics. Considerable efforts have focused on developing metal nanoparticles for the treatment of several pathogenic viruses. As a result of these efforts, metal nanoparticles are demonstrating promising antiviral activity against pathogenic surrogates and clinical isolates. This review summarizes the application of metal nanoparticles for the treatment of viral infections. It provides information on synthesis methods, size-related properties, nano-bio-interaction, and immunological effects of metal nanoparticles. This article also addresses critical criteria and considerations for developing clinically translatable nanosized metal particles to treat viral diseases.

The role of wildlife in the epidemiology and control of Foot-and-mouth-disease And Similar Transboundary (FAST) animal diseases: A review

Transboundary Animal Diseases (TADs) are notifiable diseases which are highly transmissible and have the potential for rapid spread regardless of national borders. Many TADs are shared between domestic animals and wildlife, with the potential to affect both livestock sector and wildlife conservation and eventually, public health in the case of zoonosis. The European Commission for the Control of Foot-and-Mouth Disease (EuFMD), a commission of the Food and Agriculture Organization of the United Nations (FAO), has grouped six TADs as 'Foot-and-mouth disease (FMD) And Similar Transboundary animal diseases' (FAST diseases). FAST diseases are ruminant infections caused by viruses, for which vaccination is a control option. The EuFMD hold-FAST strategy aims primarily at addressing the threat represented by FAST diseases for Europe. Prevention and control of FAST diseases might benefit from assessing the role of wildlife. We reviewed the role of wildlife as indicators, victims, bridge hosts or maintenance hosts for the six TADs included in the EuFMD hold-FAST strategy: FMD, peste des petits ruminants, lumpy skin disease, sheep and goatpox, Rift Valley fever and bovine ephemeral fever. We observed that wildlife can act as indicator species. In addition, they are occasionally victims of disease outbreaks, and they are often relevant for disease management as either bridge or maintenance hosts. Wildlife deserves to become a key component of future integrated surveillance and disease control strategies in an ever-changing world. It is advisable to increase our knowledge on wildlife roles in relevant TADs to improve our preparedness in case of an outbreak in previously disease-free regions, where wildlife may be significant for disease surveillance and control.

Preliminary Evaluation of a Recombinant Rift Valley Fever Virus Glycoprotein Subunit Vaccine Providing Full Protection against Heterologous Virulent Challenge in Cattle

Rift Valley fever virus (RVFV) is a mosquito-borne zoonotic pathogen that causes periodic outbreaks of abortion in ruminant species and hemorrhagic disease in humans in sub-Saharan Africa. These outbreaks have a significant impact on veterinary and public health. Its introduction to the Arabian Peninsula in 2003 raised concerns of further spread of this transboundary pathogen to non-endemic areas. These concerns are supported by the presence of competent vectors in many non-endemic countries. There is no licensed RVF vaccine available for humans and only a conditionally licensed veterinary vaccine available in the United States. Currently employed modified live attenuated virus vaccines in endemic countries lack the ability for differentiating infected from vaccinated animals (DIVA). Previously, the efficacy of a recombinant subunit vaccine based on the RVFV Gn and Gc glycoproteins, derived from the 1977 human RVFV isolate ZH548, was demonstrated in sheep. In the current study, cattle were vaccinated subcutaneously with the Gn only, or Gn and Gc combined, with either one or two doses of the vaccine and then subjected to heterologous virus challenge with the virulent Kenya-128B-15 RVFV strain, isolated from Aedes mosquitoes in 2006. The elicited immune responses by some vaccine formulations (one or two vaccinations) conferred complete protection from RVF within 35 days after the first vaccination. Vaccines given 35 days prior to RVFV challenge prevented viremia, fever and RVFV-associated histopathological lesions. This study indicates that a recombinant RVFV glycoprotein-based subunit vaccine platform is able to prevent and control RVFV infections in target animals.

Modeling the Potential Future Distribution of Anthrax Outbreaks under Multiple Climate Change Scenarios for Kenya

The climate is changing, and such changes are projected to cause global increase in the prevalence and geographic ranges of infectious diseases such as anthrax. There is limited knowledge in the tropics with regards to expected impacts of climate change on anthrax outbreaks. We determined the future distribution of anthrax in Kenya with representative concentration pathways (RCP) 4.5 and 8.5 for year 2055. Ecological niche modelling (ENM) of boosted regression trees (BRT) was applied in predicting the potential geographic distribution of anthrax for current and future climatic conditions. The models were fitted with presence-only anthrax occurrences (n = 178) from historical archives (2011-2017), sporadic outbreak surveys (2017-2018), and active surveillance (2019-2020). The selected environmental variables in order of importance included rainfall of wettest month, mean precipitation (February, October, December, July), annual temperature range, temperature seasonality, length of longest dry season, potential evapotranspiration and slope. We found a general anthrax risk areal expansion i.e., current, 36,131 km2, RCP 4.5, 40,012 km2, and RCP 8.5, 39,835 km2. The distribution exhibited a northward shift from current to future. This prediction of the potential anthrax distribution under changing climates can inform anticipatory measures to mitigate future anthrax risk.

Farm-Level Risk Factors of Increased Abortion and Mortality in Domestic Ruminants during the 2010 Rift Valley Fever Outbreak in Central South Africa

(1) Background: Rift Valley fever (RVF) outbreaks in domestic ruminants have severe socio-economic impacts. Climate-based continental predictions providing early warnings to regions at risk for RVF outbreaks are not of a high enough resolution for ruminant owners to assess their individual risk. (2) Methods: We analyzed risk factors for RVF occurrence and severity at the farm level using the number of domestic ruminant deaths and abortions reported by farmers in central South Africa during the 2010 RVF outbreaks using a Bayesian multinomial hurdle framework. (3) Results: We found strong support that the proportion of days with precipitation, the number of water sources, and the proportion of goats in the herd were positively associated with increased severity of RVF (the numbers of deaths and abortions). We did not find an association between any risk factors and whether RVF was reported on farms. (4) Conclusions: At the farm level we identified risk factors of RVF severity; however, there was little support for risk factors of RVF occurrence. The identification of farm-level risk factors for Rift Valley fever virus (RVFV) occurrence would support and potentially improve current prediction methods and would provide animal owners with critical information needed in order to assess their herd's risk of RVFV infection.

Crimean-Congo hemorrhagic fever virus in tortoises and Hyalomma aegyptium ticks in East Thrace, Turkey: potential of a cryptic transmission cycle

Background

Recent reports have demonstrated the presence of Crimean-Congo hemorrhagic fever virus (CCHFV) genomic material in Hyalomma aegyptium ticks feeding primarily on tortoises belonging to the genus Testudo. This raises the question if these ticks and their hosts play a role in the natural transmission dynamics of CCHFV. However, the studies are limited, and assessing the relevance of H. aegyptium in perpetuating the virus in nature, and a potential spillover to humans remains unknown. This study aimed to detect CCHFV in H. aegyptium ticks and their tortoise hosts in the East Thrace region of Turkey, where H. aegyptium is the most common human-biting tick and where a high density of tortoises of the genus Testudo can be found.

Methods

During the study period, 21 blood samples from different tortoises (2 T. hermanni and 19 T. graeca), 106 tick pools (containing 448 males, 152 females, 93 nymphs and 60 larvae) collected from 65 tortoises (5 T. hermanni and 60 T. graeca), 38 adult unfed questing ticks (25 males and 13 females, screened individually) and 14 pools (containing 8 nymphs and 266 larvae) of immature unfed questing ticks collected from the ground were screened for CCHFV genome by nested PCR and partial genomes sequenced.

Results

As a result of the screening of these 179 samples, 17 (9.5%) were detected as positive as follows: 2 of 21 blood samples (9.52%), 13 (containing 18 nymphs in 3 pools, and 52 males and 8 females in 10 pools) of 106 tick pools from tortoises (12.26%), and 2 of 38 adult questing ticks (5.26%). No positive result was determined in 14 pools of immature questing ticks.

Conclusions

Previous studies have shown that reptiles can participate in the transmission of arthropod-borne viruses, but they may contribute to different aspects of the disease ecology and evolution of tick-borne viral pathogens. Our results indicate the presence of CCHFV in questing and feeding H. aegyptium ticks as well as tortoise hosts. This may indicate that CCHFV circulates in a cryptic transmission cycle in addition to the primary transmission cycle that could play a role in the natural dynamic of the virus and the transmission to humans.

Candidate vaccines for human Rift Valley fever

Introduction: Rift Valley fever (RVF) outbreaks can cause devastating economic loss and public health concerns. RVF virus (RVFV: genus Phlebovirus family Phenuiviridae) is transmitted by mosquitoes, causes abortion in sheep, cattle, and goats, and severe diseases in humans including hemorrhagic fever, encephalitis, or retinitis. RVFV has spread from sub-Saharan Africa into Madagascar, Egypt, Saudi Arabia, and Yemen.Area covered: There are a few licensed veterinary RVF vaccines in endemic countries, whereas no licensed RVF vaccines are available for human use. There are two Investigational New Drug (IND) RVF candidate vaccines used in clinical trials. This review will discuss the development of two IND vaccines for RVF over the past 20-40 years, and further innovation for future RVF vaccines applicable for the use in endemic areas.Expert opinion: Vaccination for human RVF can protect at-risk personnel against severe RVF illness. Formalin-inactivated RVF candidate vaccine requires three doses to induce protective immunity, whereas the live-attenuated MP-12 candidate vaccine retains strong immunogenicity. Further innovation in safety, immunogenicity, and thermostability will facilitate future RVF vaccines for humans.