The Ongoing Epidemic of West Nile Virus in Greece: The Contribution of Biological Vectors and Reservoirs and the Importance of Climate and Socioeconomic Factors Revisited

Abstract

Emerging infectious diseases have inflicted a significant health and socioeconomic burden upon the global population and governments worldwide. West Nile virus, a zoonotic, mosquito-borne flavivirus, was originally isolated in 1937 from a febrile patient in the West Nile Province of Uganda. It remained confined mainly to Africa, the Middle East, and parts of Europe and Australia until 1999, circulating in an enzootic mosquito-bird transmission cycle. Since the beginning of the 21st century, a new, neurotropic, more virulent strain was isolated from human outbreaks initially occurring in North America and later expanding to South and South-eastern Europe. Since 2010, when the first epidemic was recorded in Greece, annual incidence has fluctuated significantly. A variety of environmental, biological and socioeconomic factors have been globally addressed as potential regulators of the anticipated intensity of the annual incidence rate; circulation within the zoonotic reservoirs, recruitment and adaptation of new potent arthropod vectors, average winter and summer temperatures, precipitation during the early summer months, and socioeconomic factors, such as the emergence and progression of urbanization and the development of densely populated areas in association with insufficient health policy measures. This paper presents a review of the biological and socioenvironmental factors influencing the dynamics of the epidemics of West Nile virus (WNV) cases in Greece, one of the highest-ranked European countries in terms of annual incidence. To date, WNV remains an unpredictable opponent as is also the case with other emerging infectious diseases, forcing the National Health systems to develop response strategies, control the number of infections, and shorten the duration of the epidemics, thus minimizing the impact on human and material resources.

Keywords: Greece; WNV; emerging infectious disease; endemic.

Scheme 1

The WNV Transmission Cycle: The virus circulates between vectors (mainly Culex spp. mosquitoes and the reservoir hosts; it accidentaly infects dead-end hosts (humans, equids).

Figure 1

Mean monthly climatic anomalies and hydrological variables of Greece for the years 2018–2023 and their comparison with the intensity of annual local WNV epidemics (a) for January, (b) April, and (c) July. Data were extracted from the Copernicus Climate Change Service/ECMWF. Circles correlate the big epidemics of 2010 and 2018 with the climatic variables.

Figure 2

Map of Greece with total numbers of human WNV cases throughout the 13.5-year period 2010–2023, by prefecture. White colour represents prefectures where no human cases were observed.