After a 2-year hiatus, West Nile virus has re-emerged in Greece, spreading to new territories, according to researchers from the University of Athens Medical School.
Since the country’s first documented outbreak in 2010, West Nile virus (WNV) cases were identified in several regions, mostly in municipalities of southern and northern Attica, according to Athanassios Tsakris, MD, PhD, head of the Microbiology Department at the University of Athens Medical School, and colleagues. WNV transmission persisted in Greece until 2014. However, no new cases were reported in 2015 or 2016.
Despite the absence of infections in people, serological testing revealed that the virus was still circulating in birds, Tsakris said in a press release. The decline in human infections may have been the result of mosquito management strategies and other preventive measures that were implemented to reduce exposure.
“Additionally, the development of immune response against WNV may have reduced human cases by depleting the susceptible human population,” Tsakris said in the release. “It is also possible that WNV caused infections that were asymptomatic, as occurs in approximately 80% of cases, or that remained undetected, including neuroinvasive cases. Of course, climatic conditions cannot be excluded since virus replication rate within mosquitoes, as well as vector competence and population dynamic, are mainly weather dependent.”
Forty-five cases of West Nile virus infection were reported in Greece between July and September 2017. Most were found in areas with no documented history of transmission.
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After 2 years with no new WNV infections, the Hellenic CDC was notified of 45 laboratory-confirmed cases between July and September 2017, according to the researchers. More than half (57.8%) of these patients were diagnosed with West Nile neuroinvasive disease. The remaining cases were characterized as West Nile fever. Five deaths occurred among adults aged older than 70 years with underlying conditions.
All new infections originated from southern Greece, the researchers reported. Forty cases were detected in previously unaffected regions, including Argolis (n = 37) and Corinth prefecture (n = 3). Another case was identified in Crete, while the remaining four occurred in the previously affected prefectures of northwestern Peloponnese (Achaia and Ilia).
According to Tsakris, the re-emergence of WNV and its expansion into new areas suggest that Greece’s ecological and climatic conditions are suitable for WNV circulation. Therefore, he said, future transmission may occur.
“The risk of WNV transmission is complex and multifactorial; it concerns the virus, the vectors, the animal reservoirs, the environmental conditions and human behavior,” Tsakris said in the release. “Preventing or reducing WNV transmission depends on [successfully] controlling [the] vector’s abundance or interruption of human-vector contact. Also, targeted WNV surveillance within mosquito populations may contribute to the well-timed detection of the virus prior to its emergence in equine species or human populations.” – by Stephanie Viguers
Tsakris A, et al. Abstract P0550. Presented at: European Congress of Clinical Microbiology and Infectious Diseases; April 21-24, 2017; Madrid.
Disclosure: Tsakris reports no relevant financial disclosures.