This report describes the epidemiology of WNV in an heavily populated area where this infection appeared recently in horses and humans. In particular, the implementation of a strategy for assuring the safety of blood donation is described.
An epidemiological surveillance system directed at the rapid detection of WNV has been established since the last decade in Italy, due to the high diffusion of mosquitoes vectors. This system is based on the monitoring of sentinel animals located in different areas of the country. The data obtained from this activity indicated a possible circulation of WNV in the flat area of the lower Po river valley during the summer of 2008. In September 2008 the first cases of WNV related diseases in horses from this area were confirmed by laboratory investigations at the National Veterinary Reference Centre for exotic disease. Based on these data a surveillance for the human meningo-encephalitis was established. On September 20th 2008, the Laboratory of the Regional Reference Centre for Microbiological Emergency (CRREM), in Bologna, reported the first case of neuro-invasive WNV disease in a female patient living in a small village located in the middle of the area where the horses infection have been reported. This patient suffered from sudden onset of meningo-encephalitis and a specific IgM and IgG response to WNV was identified. Up to mid November 2008, two additional cases of WNV neuro-invasive disease have been identified by CRREM. All these cases have been further confirmed by the National Reference Laboratory for Arboviruses in Rome. As of November 14th 2008, the total number of horses that showed the presence of a specific antibody response to WNV was 354, with 21 animals also positive for viral RNA by RT-PCR. These epidemiological data prompted for the immediate necessity of a system to assess the safety of blood donations harvested in the area of WNV diffusion, that accounts for a total at risk population of about 1.8 millions subjects. Based on guidelines from the National Blood Centre, a nucleic acid amplification test (NAAT) based and CE marked method, (PROCLEIX West Nile Virus, Chiron) was chosen a screening technique by the CRREM in Bologna. Due to the high number of samples, including plasma specimens from donors patients for solid organs and tissues (> 200) that need to be tested per day, this methods has been performed by using the PROCLEIX TIGRIS automated system.
Since the beginning of the automated screening testing (October 10th, 2008) more than 6000 plasma samples from blood and organs/tissues donors have been evaluated, with a mean daily number of samples tested of 204. Up to November 15th no positive samples among the blood or organ donors were detected. The use of the automated \u201cwalk-away\u201d instrumentation allowed the release of results within 6 hours from the arrival of the samples and required only one unit of personnel to perform the test. In addition, the results have been reported in a time schedule that fit the requirements for solid organ donation in six cases.
The screening activity for the safety assessment of blood and organ donations is presently scheduled until November 30th, due to the seasonal decline of the vectors activity. A plan of activities for the next season is currently under development. The screening season will be from May 1st to November 30th and the activation would be dependent on the results of a seroprevalence studies that has been undertaken by CRREM on a 11.000 blood donors population from the WNV affected area. The identification of the exact sero-prevalence ratio and the geographical distribution of the seropositive population would be extremely useful in order to define the WNV NAAT screening activity for the next vector season