Spatial prediction of Crimean Congo hemorrhagic fever virus seroprevalence among livestock in Uganda

Longitudinal seroprevalence of Crimean-Congo hemorrhagic fever virus in Southern Uganda

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne disease endemic to many regions of Africa, the Middle East, Southeast Asia and the Balkans. Caused by the CCHF virus (CCHFV), CCHF has been a recognized cause of illness in Uganda since the 1950s and recently, more intensive surveillance suggests CCHFV is widely endemic within the country. Most surveillance has been focused on the Ugandan cattle corridor due to the risk of CCHFV exposure associated with livestock practices. Here we evaluated the seroprevalence of CCHFV in several Southern Ugandan communities outside the cattle corridor combined with longitudinal sample sets to measure the immune response to CCHFV for up to a decade. Interestingly, across three community types, agrarian, trading and fishing, we detected CCHFV seroprevalence in all three but found the highest seroprevalence in fishing communities. We also measured consistent CCHFV-specific antibody responses for up to a decade. Our findings support the conclusion that CCHFV is widely endemic in Uganda and highlight that additional communities may be at risk for CCHFV exposure.

Geospatial and modelling analyses reveal diverse tick and tick-associated microbes in the East African Community

BACKGROUND

The continuous geographic expansion of ticks and the emergence of tick-borne diseases have raised tremendous global public health concerns, particularly in the East African Community (EAC). This study aimed to investigate the distribution of ticks and tick-associated microbes and to predict the potential extension of dominant tick species in the EAC.

METHODS

Data were collected from literature reviews and related websites and analyzed using ArcGIS to generate maps showing the geographical distribution of ticks and associated microbes. Meta-analyses were conducted to estimate the positive rates of microbes. Ecological niche modelling was used to project the potential expansion of predominant tick species.

RESULTS

A total of 138 tick species were recorded in the seven EAC countries, including five genera of the Argasidae family, eight of the Ixodidae family, and monospecific Nuttalliellidae. Overall, 64 tick-associated microbes, including 22 viruses, 26 bacteria, and 16 protists, were identified, of which 43 (11 viruses, 21 bacteria, and 11 protists) were pathogenic to humans or animals. Among them, 5 (2 viruses and 3 bacteria) have been reported in humans, while 10 pathogens (1 virus, 4 bacteria, and 5 protists) have been reported in animals. The predictive model identified suitable habitats for four dominant tick species, with certain species flourishing under ideal conditions, such as elevation, temperature, and vegetation. Our study revealed that ticks might affect broader areas where they have never been previously reported.

CONCLUSIONS

Ticks are widely prevalent in the EAC, and some ticks harbor a variety of microbial agents that can have significant pathogenetic implications for human and animal health. Therefore, EAC authorities and medical personnel should acknowledge the potential threat posed by ticks and tick-associated pathogens to the well-being of people and animals. Surveillance and etiological diagnosis should be enhanced to control ticks and prevent tick-borne infections.

Improving risk analysis of the environmental drivers of the spillover, emergence/re-emergence and spread of Crimean-Congo haemorrhagic fever virus, Marburg virus and Middle East respiratory syndrome coronavirus in the East Africa Region

INTRODUCTION

Emerging and/or re-emerging infectious diseases (EIDs) in the East Africa region are associated with climate change-induced environmental drivers. There is a need for a comprehensive understanding of these environmental drivers and to adopt an integrated risk analysis (IRA) framework for addressing a combination of the biological, environmental and socioeconomic factors that increase population vulnerabilities to EID risks to inform biological risk mitigation and cross-sectoral decision-making. The aim of this integrative review was to identify knowledge gaps and contribute to a holistic understanding about the environmental drivers of Crimean-Congo haemorrhagic fever virus (CCHFV), Marburg virus (MARV) and Middle East respiratory syndrome coronavirus (MERS-CoV) infections in the East Africa Region to improve IRA processes at the environment-animal-human exposure interface.

METHODS

An integrative review search was carried out to identify relevant studies and reports from 2000 to 2024. Searches were conducted in bibliographic databases and global institutional websites. Inclusion criteria were studies and reports (in English) addressing environmental drivers of CCHFV, MARV and MERS-CoV infections across countries in the East Africa region, existing risk frameworks/methodological tools and/or One Health policy recommendations for risk analysis of environmentally driven biological threats.

RESULTS

Of the total number of studies retrieved from database searches (n=18 075) and website searches (n=44), 242 studies and reports combined were included in the review with the majority covering the environmental drivers (n=137), the risk frameworks/methodological tools (n=73) and the policy recommendations (n=32). We identified 10 categories of environmental drivers, four thematic groups of risk frameworks and three categories of policy recommendations. Overall, many of the included records on the risk frameworks/methodological tools expounded on the adoption of ecological niche modelling (ENM) for environmental monitoring of potential transmission pathways of EIDs and other biological threats.

CONCLUSION

This integrative review recommends the adoption of specialised risk mapping approaches such as ENM for environmental monitoring of EIDs under IRA processes. Findings from the review were used for the conceptualisation of an IRA framework for addressing environmentally driven EIDs.

Spatial analysis and risk mapping of Crimean-Congo hemorrhagic fever (CCHF) in Sub-saharan Africa

Crimean Congo hemorrhagic fever (CCHF) is a re-emerging tick-borne zoonosis that is caused by CCHF virus (CCHFV). The geographical distribution of the disease and factors that influence its occurrence are poorly known. We analysed historical records on its outbreaks in various countries across the sub-Saharan Africa (SSA) to identify hotspots and determine socioecological and demographicfactors associated with these outbreaks. We used data from historical outbreaks that were reported between 1981 and 2022 in various countries in SSA. To develop a common framework for merging the outbreak data and potential explanatory variables, we generated a common shapefile that combined Level 2 administrative units in all the countries. Several climatic, environmental, socioecological data were obtained from on-line GIS databases and extracted using the shapefile. The data were analysed using an approximate Bayesian hierarchical model using the R-INLA package. The outcome was a Boolean variable which indicated whether an administrative unit in the shapefile was affected in a given year or not. A neighborhood structure was also generated and used to account for spatial autocorrelation in the analysis. The final model that was obtained from the analysis was used to build a CCHF risk map. A total of 54 CCHF outbreaks were compiled across 414 districts in nine SSA countries. Factors that were positively associated with CCHF outbreaks included human population density, land area under grassland, bare soil cover and shrub cover. Conversely, high precipitation during wet months, elevated mean temperature and slope had negative effects. The risk map generated shows that CCHF occurrence risk is higher in arid and semi-arid land (ASAL) of West Africa, the Sahelian region, Central Africa, and the Eastern and Southern Africa region. The analysis identified ecological and demographic factors that are associated with CCHF outbreaks in SSA. This finding suggests the need to improve surveillance for the disease especially in the grasslands where the human population is increasing.

Epidemiology and Ecology of Usutu Virus Infection and Its Global Risk Distribution

Usutu virus (USUV) is an emerging mosquito-transmitted flavivirus with increasing incidence of human infection and geographic expansion, thus posing a potential threat to public health. In this study, we established a comprehensive spatiotemporal database encompassing USUV infections in vectors, animals, and humans worldwide by an extensive literature search. Based on this database, we characterized the geographic distribution and epidemiological features of USUV infections. By employing boosted regression tree (BRT) models, we projected the distributions of three main vectors (Culex pipiens, Aedes albopictus, and Culiseta longiareolata) and three main hosts (Turdus merula, Passer domesticus, and Ardea cinerea) to obtain the mosquito index and bird index. These indices were further incorporated as predictors into the USUV infection models. Through an ensemble learning model, we achieved a decent model performance, with an area under the curve (AUC) of 0.992. The mosquito index contributed significantly, with relative contributions estimated at 25.51%. Our estimations revealed a potential exposure area for USUV spanning 1.80 million km2 globally with approximately 1.04 billion people at risk. This can guide future surveillance efforts for USUV infections, especially for countries located within high-risk areas and those that have not yet conducted surveillance activities.

Evaluation of effectiveness and safety of Subolesin anti-tick vaccine in Ugandan multi-site field trial

Vaccines are the most effective and sustainable intervention to control ticks and tick-borne diseases (TBD). Using a personalized vaccine design based on regional tick genotypes, a Rhipicephalus appendiculatus Subolesin protective antigen was used in a field trial evaluating tick vaccine efficacy, effectiveness, and safety in cattle infested with multiple tick species in different Ugandan agro-ecological zones. Vaccination with SUB was safe with a protective capacity against anemia and infection, and reduced the number of infested cattle, tick fitness (feeding and reproduction) with vaccine effectiveness against multiple tick species between 93.2% at 167-196 days post-vaccination (dpv) and 61.4% at 251-327 dpv. Total integrated vaccine efficacy/effectiveness was estimated as 98.8%. The Subolesin-based vaccine is protective against multiple cattle tick infestations under field conditions in Uganda. These results support registration and commercialization of the vaccine to reduce tick populations and associated risks for human and animal TBD and chemical acaracides in Uganda.