Tweet
West Nile Virus Circulation In The EpiSouth Countries and Neighbouring Areas?Seasons 2010 and 2011 - Update 1st June 2012 (EpiSouth, abstract)
[Source: EpiSouth, website: (LINK). Abstract, edited.]
West Nile Virus Circulation In The EpiSouth Countries and Neighbouring Areas?Seasons 2010 and 2011 - Update 1st June 2012
Authors: C.Giese, F. A?t El Belghiti, P. Barboza and all National EpiSouth Focal Points.
This document was elaborated with the information provided by National EpiSouth Focal Point and the contribution of work packages on Laboratory network and Coordination.
KEY POINTS
BACKGROUND
West Nile Virus (WNV) is a flavivirus belonging to the Japanese encephalitis antigenic complex. It has been discovered in 1937 in Uganda, and its circulation has been documented in Africa, the Americas, Asia, Europe and the Middle East.
WN is a mosquito-borne infection affecting mainly wild birds and transmitted by different mosquitoes? species mainly Culex spp and Aedes spp. Human and mammals, especially horses, are occasional hosts and play limited roles in the natural cycle. Several WNV subtypes have been described. Previous European and Mediterranean basin outbreaks were due to lineage 1 strains whereas lineage 2 strains circulating mainly in Sub-Saharan Africa and Madagascar were considered non-pathogenic in human and horses.
Recent publications from South Africa and Russia suggest that lineage 2 strains could be more pathogenic for human and horses than initially considered.
Humans are mainly infected through the bite of an infected mosquito but transmission through blood transfusion or organ transplants also occurs.
The incubation period is usually 3 to 14 days. Around 80% of human infections are asymptomatic. The 20% symptomatic cases present a usually self-limited fever syndrome and less than 1% of WNV infections develops a severe form potentially lethal (i.e. meningitis, encephalitis or paralysis).
Treatment is mainly symptomatic and no vaccine is available for humans (only for horses). Among severe cases, case fatality rate (CFR) ranges from 3 to 15 % and is higher in elderly. In 2010, unprecedented WN viral circulation occurred in the Mediterranean region and WNV infections were reported in 9 EpiSouth countries (cf. note on WNV in EpiSouth countries, in 2010). Since the first documented outbreak in 1951 in Israel, outbreaks or sporadic WNV circulation has been documented in countries of the Balkans, Middle-East, North-Africa and Southern Europe.
Large outbreaks affecting several hundred cases were described in Romania in 1996-1997, in Tunisia in 1997, in Southern Russia in 1999 (mainly in Volgograd, Astrakhan and Krasnodar regions) and in Israel in 2000. Up to 2010, these events remained restricted to limited geographical settings.
DATA COLLECTION
Data regarding numbers of human and animal cases diagnosed in 2010 and 2011, and the nature of WNV surveillance and laboratory capacities were collected from the 27 EpiSouth countries. On 27th January 2012, questionnaires were sent to EpiSouth focal points. Data were also consolidated with data provided by the WP4 on Laboratory networks.
Official reports issued by OIE and MoH/MoA were also considered for cases counts. All 27 EpiSouth countries provided information regarding their current epidemiological situation and/or their WNV Surveillance system in 2010 and/or 2011. This analysis aims at comparing 2010 and 2011 WNV seasons in terms of epidemiological situation (number of cases and geographic distribution) and surveillance systems.
In this note, the number of reported cases corresponds to the suspect and confirmed cases, based on the national definitions (of suspect and confirmed cases). In the course of a known and ongoing epidemic not all cases have to be fully biologically confirmed especially those occurring in well identified endemic zones. Therefore in endemic countries biological confirmation procedures may change over time (e.g. only through serology and not through PCR or sero-neutralisation). Therefore, within all cases, the proportion of biologically confirmed and suspect cases is subject to changes. For instance in Greece in 2010, 262 human biologically confirmed cases and 2 suspect cases were reported versus 53 human confirmed cases and 48 suspect cases reported in 2011.
In this respect, both confirmed and suspect human cases were considered for the analysis when at least part of the cases was biologically confirmed. Conversely, for countries where only clinically suspect cases were detected, these suspect cases were not considered for the case count and the viral circulation among humans.
SURVEILLANCE SYSTEMS
25 countries provided information on their West Nile surveillance system.
As of 24th April 2012, the situation in 2011 was as followed:
LABORATORY CAPACITIES
Laboratory capacities (cf. Table 1, Map 2).
EPIDEMIOLOGICAL SITUATION Overview .
Of the 27 EpiSouth countries:
In humans:
According to data reported by EpiSouth countries:
In 2010, 485 human WN infections were reported in 9 countries: Albania, Greece, Israel, Italy, Palestine, Romania, Spain, Tunisia & Turkey. For Albania, Greece and Turkey, these clinical WN human cases were the first ever reported in the countries.
In 2011, 232 human WN infections were reported in 8 countries: Albania, Greece, Israel, Italy, Former Yugoslav Republic of Macedonia (FYR-Macedonia), Romania, Tunisia & Turkey. For FYR-Macedonia these cases were the first reported in the country. Note for Albania, the child affected in 2010 was retrospectively notified in 2011. There were approximately 50% less WN human infections in 2011 compared to 2010. 2 countries affected in 2010 (Spain and Palestine) did not report any WNV infections in human in 2011.
In equine:
In 2010, 8 countries reported equine WN cases: Bulgaria, Greece, Israel, Italy, Morocco, Romania, Spain and Turkey.
In 2011, only 4 countries reported equine WN cases: Greece, Israel, Italy and Spain. Half of the countries reporting equine cases in 2010 were reporting cases in 2011. In 2010, Morocco and Bulgaria reported equine cases only (no human cases), same for Spain in 2011.
Lineage
Understanding the genetic relations between the viruses circulating across the area would be essential to better understand the dynamic of the viral circulation in the Mediterranean area. Unfortunately, lineage and molecular analysis are delicate techniques requiring genetic sequencing that are not widely available. Therefore genetic information allowing describing viral circulation in 2010-2011 is very scarce.
Based on data available in countries strains both lineage 1 and lineage 2 have been identified :
_________
-------
West Nile Virus Circulation In The EpiSouth Countries and Neighbouring Areas?Seasons 2010 and 2011 - Update 1st June 2012
Authors: C.Giese, F. A?t El Belghiti, P. Barboza and all National EpiSouth Focal Points.
This document was elaborated with the information provided by National EpiSouth Focal Point and the contribution of work packages on Laboratory network and Coordination.
KEY POINTS
- Following the unprecedented West Nile Virus (WNV) outbreak in 2010 in the Mediterranean region, the close monitoring of the 2011 season was crucial to better appraise WNV circulation in the area.
- Although number of reported cases was lower, the 2011 season confirmed the unusual WNV dynamic in the Mediterranean basin observed in 2010.
- In 2010, 485 human cases were reported in 9 EpiSouth countries, 54% of these cases occurred in Greece.
- In 2011, 232 human cases were reported in 8 countries, with 43% of them in Greece.
- A limited geographical extension was reported within previously affected countries and to a new country but on a larger scale the affected regions remain comparable to the ones observed in 2010.
- During both seasons, viral circulation was more intense in the Eastern part of the Mediterranean.
- Lineage 2 was isolated in at least 3 countries of the eastern Mediterranean and one country in the West, while lineage 1 was detected in the West only.
- During both years, outbreaks were identified on all major birds? migratory routes crossing the Mediterranean region.
- Sustained transmission cannot be excluded in the coming year.
- Genetic information is too scarce to allow detailed description of the dynamic.
- Emphasis should be put on gathering biological data.
BACKGROUND
West Nile Virus (WNV) is a flavivirus belonging to the Japanese encephalitis antigenic complex. It has been discovered in 1937 in Uganda, and its circulation has been documented in Africa, the Americas, Asia, Europe and the Middle East.
WN is a mosquito-borne infection affecting mainly wild birds and transmitted by different mosquitoes? species mainly Culex spp and Aedes spp. Human and mammals, especially horses, are occasional hosts and play limited roles in the natural cycle. Several WNV subtypes have been described. Previous European and Mediterranean basin outbreaks were due to lineage 1 strains whereas lineage 2 strains circulating mainly in Sub-Saharan Africa and Madagascar were considered non-pathogenic in human and horses.
Recent publications from South Africa and Russia suggest that lineage 2 strains could be more pathogenic for human and horses than initially considered.
Humans are mainly infected through the bite of an infected mosquito but transmission through blood transfusion or organ transplants also occurs.
The incubation period is usually 3 to 14 days. Around 80% of human infections are asymptomatic. The 20% symptomatic cases present a usually self-limited fever syndrome and less than 1% of WNV infections develops a severe form potentially lethal (i.e. meningitis, encephalitis or paralysis).
Treatment is mainly symptomatic and no vaccine is available for humans (only for horses). Among severe cases, case fatality rate (CFR) ranges from 3 to 15 % and is higher in elderly. In 2010, unprecedented WN viral circulation occurred in the Mediterranean region and WNV infections were reported in 9 EpiSouth countries (cf. note on WNV in EpiSouth countries, in 2010). Since the first documented outbreak in 1951 in Israel, outbreaks or sporadic WNV circulation has been documented in countries of the Balkans, Middle-East, North-Africa and Southern Europe.
Large outbreaks affecting several hundred cases were described in Romania in 1996-1997, in Tunisia in 1997, in Southern Russia in 1999 (mainly in Volgograd, Astrakhan and Krasnodar regions) and in Israel in 2000. Up to 2010, these events remained restricted to limited geographical settings.
DATA COLLECTION
Data regarding numbers of human and animal cases diagnosed in 2010 and 2011, and the nature of WNV surveillance and laboratory capacities were collected from the 27 EpiSouth countries. On 27th January 2012, questionnaires were sent to EpiSouth focal points. Data were also consolidated with data provided by the WP4 on Laboratory networks.
Official reports issued by OIE and MoH/MoA were also considered for cases counts. All 27 EpiSouth countries provided information regarding their current epidemiological situation and/or their WNV Surveillance system in 2010 and/or 2011. This analysis aims at comparing 2010 and 2011 WNV seasons in terms of epidemiological situation (number of cases and geographic distribution) and surveillance systems.
In this note, the number of reported cases corresponds to the suspect and confirmed cases, based on the national definitions (of suspect and confirmed cases). In the course of a known and ongoing epidemic not all cases have to be fully biologically confirmed especially those occurring in well identified endemic zones. Therefore in endemic countries biological confirmation procedures may change over time (e.g. only through serology and not through PCR or sero-neutralisation). Therefore, within all cases, the proportion of biologically confirmed and suspect cases is subject to changes. For instance in Greece in 2010, 262 human biologically confirmed cases and 2 suspect cases were reported versus 53 human confirmed cases and 48 suspect cases reported in 2011.
In this respect, both confirmed and suspect human cases were considered for the analysis when at least part of the cases was biologically confirmed. Conversely, for countries where only clinically suspect cases were detected, these suspect cases were not considered for the case count and the viral circulation among humans.
SURVEILLANCE SYSTEMS
25 countries provided information on their West Nile surveillance system.
As of 24th April 2012, the situation in 2011 was as followed:
- 18 countries have a human surveillance system: 12 countries have a permanent surveillance system (in process of implementation for Bulgaria in 2011), 3 have a seasonal surveillance system and 3 have a combination of both.
- 14 countries have an equine surveillance system: 9 countries maintain permanent equine surveillance system (new for Croatia and Serbia in 2011), 3 have seasonal surveillance (new for the FYR-Macedonia in 2011), and 2 have a combination of both.
- Among the 10 countries having bird surveillance, 4 maintain a permanent surveillance and 4 have a seasonal surveillance, while 2 countries have a combination of permanent and seasonal surveillance (Bulgaria and Serbia).
- 7 countries have neither human nor equine surveillance. To date, these countries never reported West Nile cases (cf. Table 1, Map 1).
LABORATORY CAPACITIES
Laboratory capacities (cf. Table 1, Map 2).
- Among the 25 countries for which information is available, 22 have a national reference laboratory among which 19 have the capacity to diagnostic WNV cases.
- 3 have no specific reference laboratory It is worth mentioning that changes in surveillance systems resulting from the strengthening of surveillance following the unprecedented 2010 outbreak, have to be taken into account when analysing the differences between the two 2010 and 2011 seasons.
EPIDEMIOLOGICAL SITUATION Overview .
Of the 27 EpiSouth countries:
- In 2010, 11 countries reported WNV circulation in human and/or equine (cf. map 3).
- In 2011, 9 EpiSouth countries have reported WNV circulation in human and/or equine (cf. map 4).
In humans:
According to data reported by EpiSouth countries:
In 2010, 485 human WN infections were reported in 9 countries: Albania, Greece, Israel, Italy, Palestine, Romania, Spain, Tunisia & Turkey. For Albania, Greece and Turkey, these clinical WN human cases were the first ever reported in the countries.
In 2011, 232 human WN infections were reported in 8 countries: Albania, Greece, Israel, Italy, Former Yugoslav Republic of Macedonia (FYR-Macedonia), Romania, Tunisia & Turkey. For FYR-Macedonia these cases were the first reported in the country. Note for Albania, the child affected in 2010 was retrospectively notified in 2011. There were approximately 50% less WN human infections in 2011 compared to 2010. 2 countries affected in 2010 (Spain and Palestine) did not report any WNV infections in human in 2011.
In equine:
In 2010, 8 countries reported equine WN cases: Bulgaria, Greece, Israel, Italy, Morocco, Romania, Spain and Turkey.
In 2011, only 4 countries reported equine WN cases: Greece, Israel, Italy and Spain. Half of the countries reporting equine cases in 2010 were reporting cases in 2011. In 2010, Morocco and Bulgaria reported equine cases only (no human cases), same for Spain in 2011.
Lineage
Understanding the genetic relations between the viruses circulating across the area would be essential to better understand the dynamic of the viral circulation in the Mediterranean area. Unfortunately, lineage and molecular analysis are delicate techniques requiring genetic sequencing that are not widely available. Therefore genetic information allowing describing viral circulation in 2010-2011 is very scarce.
Based on data available in countries strains both lineage 1 and lineage 2 have been identified :
- Lineage 2 strain was isolated in:
- Italy, from mosquitoes1 and humans in 2011(2)
- Greece, from a human3 & mosquitoes(4,5,6) in 2010
- Romania, from human both in 2010 & 2011
- Albania, in human in 2011.
- Strains for which information was available were either related to the 2007 Volgograd strain or the Hungarian strain isolated from birds in 2004(7).
- Lineage 1 strain was isolated in:
- Italy, from humans in 2010 and 2011
- Spain, from 2 human cases in 2010.
_________
- Savini G, Capelli G, Monaco F, Polci A, Russo F, et al. Evidence of West Nile virus lineage 2 circulation in Northern Italy. Vet Microbiol. 2012.
- C Rizzo, P Salcuni, L Nicoletti, M G Ciufolini et al. Epidemiological surveillance of West Nile neuroinvasive diseases in Italy, 2008 to 2011, Eurosurveillance, Volume 17, Issue 20, 17 May 2012.
- Papa A, Politis C, Tsoukala A, Eglezou A, Bakaloudi V, Hatzitaki M, et al. West Nile virus lineage 2 from blood donor, Greece [letter]. Emerg Infect Dis]. 2012 Apr 24.
- Papa A, Xanthopoulou K, Gewehr S, Mourelatos S. Detection of West Nile virus lineage 2 in mosquitoes during a human outbreak in Greece. Clin Microbiol Infect. 2011;17(8):1176-80.
- Papa A, Bakonyi T, Xanthopoulou K, Vasquez A, Tenorio A, Nowotny N. Genetic characterization of a lineage 2 West Nile virus, Greece, 2010. Emerg Infect Dis 2011;17:920-2.
- Danis K, Papa A, Papanikolaou E et al. Ongoing outbreak of West Nile virus infection in humans, Greece, July to August 2011. Eurosurveillance 2011;16(34).
- Papa A, Politis C, Tsoukala A, Eglezou A, Bakaloudi V, Hatzitaki M, et al. West Nile virus lineage 2 from blood donor, Greece [letter]. Emerg Infect Dis]. 2012 Apr 24.
-------