Recent Circulation of West Nile Virus and Potentially Other Closely Related Flaviviruses in Southern France

Abstract

In recent years, the number of West Nile virus (WNV) cases reported in horses and humans has increased dramatically throughout the Mediterranean basin. Furthermore, the emergence of Usutu virus (USUV) in Austria in 2001, and its subsequent expansion to Hungary, Spain, Italy, Switzerland, the United Kingdom, and Germany, has given added cause for concern regarding the impact of the spread of flaviviruses on human and animal health in western Europe. Despite frequent detection of WNV and USUV cases in neighboring countries, no case of WNV has been detected in France since 2006 and USUV has never been reported. However, recent investigations focused on detecting the circulation of flaviviruses in France are lacking. We investigated the circulation of WNV and USUV viruses in wild birds in southern France on the basis of a serological survey conducted on a sentinel species, the magpie (Pica pica), in the Camargue area from November, 2009, to December, 2010. We detected WNV-neutralizing antibodies at a high titer (160) in a second-year bird showing recent exposure to WNV, although no WNV case has been detected in humans or in horses since 2004 in the Camargue. In addition, we observed low titers (10 or 20) of USUV-specific antibodies in six magpies, two of which were also seropositive for WNV. Such low titers do not give grounds for concluding that these birds had been exposed to USUV; cross-reactions at low titers may occur between antigenically closely related flaviviruses. But these results urge for further investigations into the circulation of flaviviruses in southern France. They also emphasize the necessity of undertaking epidemiological studies on a long-term basis, rather than over short periods following public health crises, to gain insight into viral dynamics within natural reservoirs.

Population structure of the soft tick Ornithodoros maritimus and its associated infectious agents within a colony of its seabird host Larus michahellis

“…and a type of West Nile Virus (a Flavivirus) were also detected in ticks, but could not be confirmed. Both agents are known to be transmitted by different species of soft ticks (Lawrie et al., 2004, Cutler, 2010) and WNV has been previously reported in the Camargue region (Balança et al., 2009, Vittecoq et al., 2013, Pradier et al., 2014). However, a previous study of Yellow-legged gulls on Carteau did not find evidence for the presence of Flavivirus antibodies in eggs, suggesting that WNV and other related viruses may not have circulated in gulls at that time (Arnal et al., 2014).…”

Flaviviruses in Europe: Complex Circulation Patterns and Their Consequences for the Diagnosis and Control of West Nile Disease

“…In contrast to WNV, it rarely causes severe neurological symptoms in humans, but virulent strains have caused considerable bird mortality, especially in blackbirds ( Turdus merula ) in central Europe, starting in Austria in 2001 [67,68]. USUV is known to circulate in Hungary, Switzerland, Italy, Spain, the Czech Republic and Germany [69,70,71,72,73,74,75], and USUV neutralizing antibodies were recently found in animals in France and Croatia [76,77]. …”

Importance of Wetlands Management for West Nile Virus Circulation Risk, Camargue, Southern France

“…However, serological studies conducted from 2005–2007 in wild birds in Camargue showed that two juveniles sampled in 2006 were seropositive and that another seroconverted in 2007, thus revealing circulation of the virus in Camargue during this period [8]. In another investigation, conducted in this area during 2009, a high titer of WNV-neutralizing antibodies was found in a second year magpie ( Pica pica ), indicating its recent exposure to the virus [9]. Thus, despite evidence of the regular circulation of WNV in wild birds in Camargue, no clinical case has been reported in this area since 2004.…”