Research on West Nile Virus in St. S. Nicolau Institute of Virology

In 1996 the "St.S. Nicolau" Institute of Virology, working together with a US team from the National Center for Infectious Diseases, Division of Vector Borne Infectious Diseases, CDC, Fort Collins, CO and US Army Medical Institute of Infectious Diseases, Ft. Detrick, Frederick, MD, identified West Nile virus as the etiological agent of a large outbreak of meningoencepalitis in Romania (500 clinical cases and a case-fatality rate approaching 5%). It was the first time when this virus, endemic in the Middle East, and usually associated with a mild febrile infection, appeared in Europe as an emerging pathogen. The uniform seroprevalence rates in all age groups recorded in a postepidemic serosurveyÂ suggested that the virus was newly introduced in an immunologically naÃ¯ve population.

This may explain the unprecedented number of neurological cases and deaths especially among elderly. Data from the 1996 WNV outbreak in Bucharest indicate that more than 50% of the WN elderly patients admitted to tertiary-care had neurological disease. Seventy-eight per cent had encephalitis and, of those, 82% developed neuromuscular dysfunction within several days. In all cases, advanced age and a compromised immune system were associated with a severe disease outcome.

Virus isolation was performed by inoculation in rabbit kidney and Vero cell cultures as well as by intracerebral inoculation of 8 to 16 new borne mice. Isolates were identified by plaques reduction neutralization assays. IgM antibody-capture enzyme immunoassay and IgG indirect ELISA tests were developed in IVN for WNV antibody testing. During the 1996 epidemic in Romania, an unexpected early onset of the intrathecal specific humoral immune response, before serum immunoglobulin synthesis, was recorded in patients for whom paired CSF and serum samples collected in the same day were investigated. Good correlation was established between optical density and antibody titers for both IgM and IgG immunoassays. No crossreactivity of anti-WN antibody with other flaviviruses antigenic groups was found in early seroconversion samples.

IVN implemented new and sensible diagnostic techniques for arboviruses detection in all species participating in the epidemic cycle: mosquito vectors, birds, horses, humans.Â The availability of virus isolates and genomic sequences from birds and human brain tissue permitted the discovery of links between this WNV in North America and the Romanian isolate (Lanciotti RS, Roehrig JT, Deubel V et al., Origin of the West Nile virus responsible for an outbreak of encephalitis in the northeastern United States. Science 1999; 286: 2333-7).

Since then basic and clinical research studies were conducted to better understand the factors influencing the pattern of emergence and distribution of West Nile virus as well as the effect of genetic variation on the virusâ€™ spread and virulence and to prevent and control spread of the disease by enhancing passive human and veterinary surveillance. During 1997-2000, 39 scattered human cases of clinical West Nile virus infection (mean, 10 per year), including 5 (13%) fatal cases were diagnosed serologically in Romania, but epidemic disease did not recur. Â Future projects are aimed at establishing a sentinel system in an endemic area (the Danube Delta) in order to improve the national and regional capacity of prevention of future emerging arboviral outbreaks.