08 October 2009
West Nile virus transmission with human cases in Italy, August - September 2009
In 2009, to date 16 human cases of West Nile neuroinvasive disease (WNND) have been reported in Italy, in three regions: Veneto, Emilia-Romagna and Lombardia. The number of cases is higher compared with last year when nine cases were identified (eight cases of WNND and one case of West Nile fever) and the geographical distribution indicates spread from east to west.
West Nile virus (WNV) infection is transmitted in natural cycles between birds and mosquitoes, particularly Culex spp. mosquitoes. Humans and horses are susceptible, dead-end hosts. Firstly identified in tropical Africa, WNV infection has been evidenced in northern Africa, Israel, India and Australia  and progressively spread in the Americas since 1999. WNV has been the cause of outbreaks and sporadic cases in central, eastern and Mediterranean Europe for more than 45 years.
In Italy, the first cases of equine WNV infection were detected in 1998, but no human cases were reported at that time . The first human cases of WNV infection in Italy, including neuroinvasive forms, were identified in 2008 . A total of nine human cases were reported by two regions: five confirmed cases of West Nile neuroinvasive disease (WNND) (four identified retrospectively) and one case of West Nile fever were recorded in Veneto, all in the province of Rovigo , and three confirmed WNND cases were detected in Emilia-Romagna [5,6].
Veneto and Emilia-Romagna implemented an active surveillance of farm workers that yielded a seroprevalence of 1.5% and 3.1% respectively [3-6]. In the Emilia-Romagna region, a seroprevalence study of blood donors was also performed, showing a seroprevalence of 0.7-0.8% . Apart from human cases, equine WNV infections have also been detected in the same regions . No human cases were described in other Italian regions during the summer of 2008.
Human cases of WNND reoccurred in the summer 2009. Hereby we briefly describe these cases and discuss possible implications for public health.
WNND surveillance in Italy
Following the identification of the first human cases of WNV infection in Italy in 2008, specific WNND surveillance systems were set up in the affected regions of Emilia-Romagna and Veneto. The case definitions used are presented in Table 1 [3,5]. Both systems collect data on human cases of WNND every year between 15 June and 31 October. In both regions animal and vector surveillance for WNV is also in place.
Table 1. Case definition of West Nile neuroinvasive disease (WNND), surveillance programme in Veneto and Emilia-Romagna regions, Italy, 2008-2009
In Lombardia region, a surveillance system for neuroinvasive diseases has been in place since 2008. Cases from all age-groups are tested for a large panel of viruses and bacteria, including WNV. No cases of neuroinvasive disease due to WNV were detected in Lombardia in 2008.
In addition to surveillance of human cases, a national veterinary plan for WNV surveillance has been implemented since 2008 .
A total of 16 confirmed cases of WNND were reported to the regional surveillance systems in three Italian regions between August and September 2009. Detailed information is presented in Table 2.
Table 2. Confirmed cases of West Nile neuroinvasive disease (WNND) in Italy, August - September 2009 (n=16)
The distribution of human cases of WNND by month of symptom onset and geographical location in the years 2008 and 2009 is shown in Figure 1 and Figure 2 (A and B).
Figure 1. Human cases of West Nile neuroinvasive disease (WNND) in Veneto and Emilia-Romagna regions, Italy, 2008-2009 (n=24)
Figure 2. Geographical distribution of human cases of West Nile neuroinvasive disease (WNND), Italy, 2008 (A) and 2009 (B) (n=24)
A detailed description of the epidemiological situation in the affected regions is reported below.
Since the end of August 2009, six human cases of WNND were reported to the regional surveillance system (Table 2). Five cases were observed in the area of Rovigo town and one case in the area between the provinces Rovigo and Venezia. The cases (four males and two females) were between 62 to 82 years old. Virus-specific IgM and IgG were detected in cerebrospinal fluid (CSF) and serum specimens by immunoglobulin M antibody (IgM) capture enzyme-linked immunosorbent assay (MAC-ELISA). The cerebrospinal fluid and serum specimens were obtained from the patients upon their first presentation to the clinic. Diagnosis was confirmed by the plaque-reduction neutralisation test (PRNT). All patients were hospitalised and they are still in critical condition. One patient from the province of Rovigo died.
Since the end of August 2009, eight human cases of WNND were reported to the regional surveillance system in the provinces of Modena (one case), Ferrara (five cases), Imola (one case) and Bologna (one case). Of these, seven are in critical condition and one died. Ages of cases ranged from 62 to 78 years (Table 2). Virus-specific IgM and IgG were detected in CSF and serum specimens by MAC-ELISA and immunofluorescence assays (IFA). Diagnoses were confirmed by PCR. To date, 57 possible cases of WNND have been referred to the Regional Reference Centre for Microbiological Emergencies (CRREM) laboratory in Bologna and excluded after negative results of laboratory test.
Since September 2009, two confirmed cases of WNND were hospitalised in Emilia-Romagna region (Modena) and they are still in critical condition. The two cases were resident in Lombardia, in the province of Mantua bordering Emilia-Romagna region (Table 2). Virus-specific IgM and IgG were detected in CSF and serum specimens by MAC-ELISA and IFA in the CRREM laboratory in Bologna. In all cases the diagnoses were confirmed by PCR.
Control measures implemented
Vector control measures consisted in regular mosquito spraying activities (adulticide and larvicide) especially at public events, in the affected regions. In addition, Emilia-Romagna region implemented public education messages on self-protection from mosquito bites on the region’s public health authority website.
Regarding blood, tissue and organ safety, between 1 August and 30 October 2009, Italy applies nucleic acid amplification technology (NAT) screening on all blood donations from residents in the provinces of Ferrara (Emilia-Romagna), Rovigo (Veneto) and Mantua (Lombardy). The objective of this screening is to quantify the viral circulation in these provinces among blood donors and to ensure the early implementation of appropriate blood safety measures. The first NAT-positive blood donation is considered as a trigger to defer further donations from the province of residence of the donor, independent of the identification of human cases of WNND. In case of positivity, blood donors who have spent at least one night in affected provinces are deferred for 28 days. This policy is implemented nationwide.
The occurrence of human cases of WNND in Italy is indicative of the ongoing WNV activity. In Italy, the provinces of Ferrara (Emilia-Romagna), Rovigo (Veneto) and Mantua (Lombardy) are considered high risk areas of transmission of WNV, and equine cases of WNV infection were also confirmed there .
Compared to the summer of 2008, a larger geographical area was affected by WNV infection in 2009. In particular, the virus expanded its activity apparently moving from east to west. These changes were immediately detected by the public health authorities, which started the NAT screening of all blood donors in the newly affected provinces, in order not to defer donations from these areas. For this reason the exchange of data between human, animal and vector sector is crucial, as experienced in the Emilia-Romagna region where weekly reports with detailed description of WNV infections in humans, animals and vectors have been made since the beginning of 2009.
The national public health authorities are now considering the implementation of a nationwide enhanced human surveillance system in Italy, in order to include all those regions where the circulation of WNV has been reported (Emilia-Romagna, Lombardia, Veneto and Toscana) together with animal and vector surveillance .
Disseminating the information regarding the presence of WNV among clinicians could help public health authorities to rapidly identify new human cases of WNND, in order to implement control measures to reduce the transmission of the virus. This should be done in an integrated approach including veterinary and entomological surveillance in order to better monitor the situation in areas with favourable ecological conditions for WNV cycle.*
The authors acknowledge the European Centre for Disease Prevention and Control (ECDC) for the conclusions formulated in the Threat Assessment on West Nile virus transmission with human cases in Italy.*
On request of the authors, the last paragraph of the article was replaced and the acknowledgement was added on 9 October 2009.
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