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Usutu virus persistence and West Nile virus inactivity in the Emilia-Romagna region (Italy) in 2011.

Calzolari M, Bonilauri P, Bellini R, Albieri A, Defilippo F, Tamba M, Tassinari M, Gelati A, Cordioli P, Angelini P, Dottori M - PLoS ONE (2013)

Bottom Line: From 2008 to 2011, 946,213 mosquitoes, sampled between May and October, were tested; 86.5% were Cx. pipiens.West Nile virus was detected in 2008, 2009, and 2010, but not in 2011.Reported results are comparable with a peri-Mediterranean circulation of the West Nile virus lineage 1 related strain, which became undetectable in the environment after two to three years of obvious circulation.

View Article: PubMed Central - PubMed

Affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna B. Ubertini (IZSLER), Brescia, Italy. mattia.calzolari@izsler.it

ABSTRACT

Background: The circulation of West Nile virus and Usutu virus was detected in the Emilia-Romagna region in 2008 and 2009. To evaluate the extent of circulation of both viruses, environmental surveillance, based on bird and mosquito testing, was conducted in 2008 and gradually improved over the years.

Methods: In February-March 2009-2011, 5,993 hibernating mosquitoes were manually sampled, out of which 80.1% were Culex pipiens; none tested positive for the viruses. From 2008 to 2011, 946,213 mosquitoes, sampled between May and October, were tested; 86.5% were Cx. pipiens. West Nile virus was detected in 32 Cx. pipiens pools, and Usutu virus was detected in 229 mosquito pools (217 Cx. pipiens, 10 Aedes albopictus, one Anopheles maculipennis s.l., and one Aedes caspius). From 2009 to 2011, of 4,546 birds collected, 42 tested positive for West Nile virus and 48 for Usutu virus. West Nile virus and Usutu virus showed different patterns of activity during the 2008-2011 surveillance period. West Nile virus was detected in 2008, 2009, and 2010, but not in 2011. Usutu virus, however, was continuously active throughout 2009, 2010, and 2011.

Conclusions: The data strongly suggest that both viruses overwinter in the surveyed area rather than being continually reintroduced every season. The lack of hibernating mosquitoes testing positive for the viruses and the presence of positive birds sampled early in the season support the hypothesis that the viruses overwinter in birds rather than in mosquitoes. Herd immunity in key bird species could explain the decline of West Nile virus observed in 2011, while the persistence of Usutu virus may be explained by not yet identified reservoirs. Reported results are comparable with a peri-Mediterranean circulation of the West Nile virus lineage 1 related strain, which became undetectable in the environment after two to three years of obvious circulation.

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Percentage of positive Culex pipiens pools and actively and passively collected birds for the survey month in different years.
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pone-0063978-g003: Percentage of positive Culex pipiens pools and actively and passively collected birds for the survey month in different years.

Mentions: WNV and USUV showed different patterns of activity during the surveillance period 2008–2011 in the Emilia-Romagna region. WNV was detected in 2008, 2009, and 2010, but in 2011 no positive birds or mosquitoes were reported. However, USUV was continuously active throughout 2009, 2010, and 2011 (Figure 2, Figure 3). Despite the limited length of the 2011 USUV sequences, obtained with the two diagnostic PCRs, the high identity with previous year sequences suggests that the virus overwintered in the region [2]. Previous data also strongly sustain the hypothesis of overwintering for WNV between 2008 and 2010 [2], [3], [4]. The geographic distribution of the viruses in the territory over several years of surveillance also supports the hypothesis of overwintering of both viruses, rather than different reintroductions.


Usutu virus persistence and West Nile virus inactivity in the Emilia-Romagna region (Italy) in 2011.

Calzolari M, Bonilauri P, Bellini R, Albieri A, Defilippo F, Tamba M, Tassinari M, Gelati A, Cordioli P, Angelini P, Dottori M - PLoS ONE (2013)

Percentage of positive Culex pipiens pools and actively and passively collected birds for the survey month in different years.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3646878&req=5

pone-0063978-g003: Percentage of positive Culex pipiens pools and actively and passively collected birds for the survey month in different years.
Mentions: WNV and USUV showed different patterns of activity during the surveillance period 2008–2011 in the Emilia-Romagna region. WNV was detected in 2008, 2009, and 2010, but in 2011 no positive birds or mosquitoes were reported. However, USUV was continuously active throughout 2009, 2010, and 2011 (Figure 2, Figure 3). Despite the limited length of the 2011 USUV sequences, obtained with the two diagnostic PCRs, the high identity with previous year sequences suggests that the virus overwintered in the region [2]. Previous data also strongly sustain the hypothesis of overwintering for WNV between 2008 and 2010 [2], [3], [4]. The geographic distribution of the viruses in the territory over several years of surveillance also supports the hypothesis of overwintering of both viruses, rather than different reintroductions.

Bottom Line: From 2008 to 2011, 946,213 mosquitoes, sampled between May and October, were tested; 86.5% were Cx. pipiens.West Nile virus was detected in 2008, 2009, and 2010, but not in 2011.Reported results are comparable with a peri-Mediterranean circulation of the West Nile virus lineage 1 related strain, which became undetectable in the environment after two to three years of obvious circulation.

View Article: PubMed Central - PubMed

Affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna B. Ubertini (IZSLER), Brescia, Italy. mattia.calzolari@izsler.it

ABSTRACT

Background: The circulation of West Nile virus and Usutu virus was detected in the Emilia-Romagna region in 2008 and 2009. To evaluate the extent of circulation of both viruses, environmental surveillance, based on bird and mosquito testing, was conducted in 2008 and gradually improved over the years.

Methods: In February-March 2009-2011, 5,993 hibernating mosquitoes were manually sampled, out of which 80.1% were Culex pipiens; none tested positive for the viruses. From 2008 to 2011, 946,213 mosquitoes, sampled between May and October, were tested; 86.5% were Cx. pipiens. West Nile virus was detected in 32 Cx. pipiens pools, and Usutu virus was detected in 229 mosquito pools (217 Cx. pipiens, 10 Aedes albopictus, one Anopheles maculipennis s.l., and one Aedes caspius). From 2009 to 2011, of 4,546 birds collected, 42 tested positive for West Nile virus and 48 for Usutu virus. West Nile virus and Usutu virus showed different patterns of activity during the 2008-2011 surveillance period. West Nile virus was detected in 2008, 2009, and 2010, but not in 2011. Usutu virus, however, was continuously active throughout 2009, 2010, and 2011.

Conclusions: The data strongly suggest that both viruses overwinter in the surveyed area rather than being continually reintroduced every season. The lack of hibernating mosquitoes testing positive for the viruses and the presence of positive birds sampled early in the season support the hypothesis that the viruses overwinter in birds rather than in mosquitoes. Herd immunity in key bird species could explain the decline of West Nile virus observed in 2011, while the persistence of Usutu virus may be explained by not yet identified reservoirs. Reported results are comparable with a peri-Mediterranean circulation of the West Nile virus lineage 1 related strain, which became undetectable in the environment after two to three years of obvious circulation.

Show MeSH
Related in: MedlinePlus