Ecological surveillance for West Nile virus in Catalonia: early alert in public health

Epidemics caused by West Nile virus have caused serious diseases in Europe in the last years. No acute infection was detected in domestic animal populations in Catalonia during the ecological surveillance for the virus in 2007-2011. Virus was not detected in mosquitoes either. However, local virus or other closely related flaviviruses transmission was occurring among bird populations.

West Nile virus (WNV) is a widespread zoonotic pathogen that maintains its enzootic cycle principally between birds and mosquitoes. Since 2008, some epidemics in Southern and Eastern Europe have caused serious neurological disease in humans and equines including some fatal cases .

During the 2007-2011 period, researchers of CReSA analysed samples from 298 equines, 100 sentinel chickens, 1086 wild birds and 39 599 mosquitoes. During these 5 years, no acute WNV infection was detected in domestic animal populations in Catalonia. WNV was not detected in mosquitoes either. Nevertheless, several seroconversions in resident and migrant wild birds indicate that local WNV or other closely related flaviviruses transmission was occurring among bird populations. These data indicate that bird and mosquito surveillance can detect otherwise silent transmission of flaviviruses and give some insights regarding possible avian hosts and vectors in a European setting.

This work has been published in:  Alba A, Allepuz A, Napp S, Soler M, Selga I, Aranda C, Casal J, Pages N, Hayes EB, Busquets N. Ecological Surveillance for West Nile in Catalonia (Spain), Learning from a Five-Year Period of Follow-up. Zoonoses Public Health. 2013 Apr 17. doi: 10.1111/zph.12048.


The West Nile virus surveillance

WNV is a widespread zoonotic pathogen that maintains its enzootic cycle principally between birds and ornithophilic mosquitoes. Several mammals (mainly horses and humans), as well as amphibians and reptiles, can also be infected, but are considered dead end hosts, since the viraemia is generally too low to infect mosquitoes. WNV is a member of the Japanese encephalitis virus (JEV) antigenic complex of the genus Flavivirus.

In the last 30 years, several sporadic outbreaks of WN in horses and humans have been reported in regions of Europe and the Mediterranean Basin . In Europe, in the absence of large-scale bird mortality, neurological signs in horses have been often the sole indication of local presence of the virus. Since 2008, some epidemics in Southern and Eastern Europe have caused serious neurological disease in humans and equines including some fatal cases . In 2010 the WNV activity has also been confirmed in humans and horses in the south of Spain. WNV seroconversions had not only been previously detected both in birds and horses in that area , but also in birds of nearby areas.

To enhance early detection of WNV transmission, an integrated ecological surveillance system was implemented in Catalonia (north-eastern Spain) from 2007 to 2011. This system incorporated passive and active equine surveillance, periodical testing of chicken sentinels in wetland areas, serosurveillance wild birds and testing of adult mosquitoes.

More information:

Dr Anna Alba Casals
Researcher of CReSA
Email: ana.alba@cresa.uab.cat
Phone no.: +34 935814557

Dr Núria Busquets Martí
Researcher of CReSA
Email: nuria.busquets@cresa.uab.cat
Phone no.: +34 935814342

Download the full paper (PubMed): http://www.ncbi.nlm.nih.gov/pubmed/23590452

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