Global Spread of Hemorrhagic Fever Viruses: Predicting Pandemics

Abstract

As successive epidemics have swept the world, the scientific community has quickly learned from them about the emergence and transmission of communicable diseases. Epidemics usually occur when health systems are unprepared. During an unexpected epidemic, health authorities engage in damage control, fear drives action, and the desire to understand the threat is greatest. As humanity recovers, policy-makers seek scientific expertise to improve their "preparedness" to face future events.Global spread of disease is exemplified by the spread of yellow fever from Africa to the Americas, by the spread of dengue fever through transcontinental migration of mosquitos, by the relentless influenza virus pandemics, and, most recently, by the unexpected emergence of Ebola virus, spread by motorbike and long haul carriers. Other pathogens that are remarkable for their epidemic expansions include the arenavirus hemorrhagic fevers and hantavirus diseases carried by rodents over great geographic distances and the arthropod-borne viruses (West Nile, chikungunya and Zika) enabled by ecology and vector adaptations. Did we learn from the past epidemics? Are we prepared for the worst?The ultimate goal is to develop a resilient global health infrastructure. Besides acquiring treatments, vaccines, and other preventive medicine, bio-surveillance is critical to preventing disease emergence and to counteracting its spread. So far, only the western hemisphere has a large and established monitoring system; however, diseases continue to emerge sporadically, in particular in Southeast Asia and South America, illuminating the imperfections of our surveillance. Epidemics destabilize fragile governments, ravage the most vulnerable populations, and threaten the global community.Pandemic risk calculations employ new technologies like computerized maintenance of geographical and historical datasets, Geographic Information Systems (GIS), Next Generation sequencing, and Metagenomics to trace the molecular changes in pathogens during their emergence, and mathematical models to assess risk. Predictions help to pinpoint the hot spots of emergence, the populations at risk, and the pathogens under genetic evolution. Preparedness anticipates the risks, the needs of the population, the capacities of infrastructure, the sources of emergency funding, and finally, the international partnerships needed to manage a disaster before it occurs. At present, the world is in an intermediate phase of trying to reduce health disparities despite exponential population growth, political conflicts, migration, global trade, urbanization, and major environmental changes due to global warming. For the sake of humanity, we must focus on developing the necessary capacities for health surveillance, epidemic preparedness, and pandemic response.

Keywords: Global biosecurity; Pandemic; Predicting epidemic risk (i.e., pathogenic threat and vulnerability); Viral hemorrhagic fever.

Fig. 1

Mapping environmental factors that have a major impact on insect vector population (i.e., mosquitoes and ticks). This map of Laos constitutes the basis of a risk map showing part of the hazards contributing to virus vector density that could be matched with human density and pathogen prevalence leading to a risk map (spatial risk) and eventually extended through seasonality (temporal risk). Mean temperature and mean rainfalls are interpolated as climatic conditions, as environmental factors influencing the presence of mosquitoes

Fig. 2

From the point of emergence of H5N1 to the pathways of spread: The exemplary case of the highly pathogenic avian influenza virus H5N1 in Thailand. From the emergence of one imported case (red-filled circle), the pathway direction (arrowed green lines) of H5N1 infection in farms (yellow points) is reconstituted, using dates of infection and distance between farms. Results show local spread with time-to-time medium distance jumps