Prevalence of antibodies to West Nile fever, sandfly fever Sicilian, and sandfly fever Naples viruses in healthy adults in Israel

Background: The arbovirus infections West Nile fever (WNF) and sandfly fever (SFF) are both endemic in the Middle East. Despite the fact that the mosquito and sandfly vectors of these viruses are still found in Israel, SFF has not been reported since 1948, whereas outbreaks of WNF occur periodically. It is suspected that some of the cases of nonspecific febrile illnesses in Israel may in fact be either WNF or SFF. Aim: To determine the extent of past arbovirus infections in subgroups of Israeli soldiers. Methods: Sera from random samples of three groups of healthy soldiers aged 18-20 (n=273), 21-30 (n=497), and 40-55 years (n=285) were examined for IgG and IgM antibodies to West Nile virus (WNV), sandfly fever Sicilian virus (SFSV), and sandfly fever Naples virus (SFNV), using an ELISA method. Results: The prevalence of antibodies increased with age for all three viruses examined, and ranged from 7.0%, 0, and 2.8%, for WNV, SFSV, and SFNV, respectively, in soldiers aged 18-20 years, to 41.9%, 23.7%, and 30.8%, in those aged 40-55 years. The percentage of seropositives for IgG who were also IgM positive were 1.0%, 5.9%, and 3.4%, for WNV, SFSV, and SFNV, respectively. 17.5% of the seropositives for WNV were also positive for SFSV, as compared with 5.7% among the WNV-seronegatives. Among the seropositives for WNV, 23.99% were positive for SFNV, compared with 9.1% of WNV seronegatives. 48.2% of seropositives for SFSV were positive for SFNV, as compared with 8.4% for SFSV-seronegatives. In the age group 40-55 years, there were significantly higher prevalence rates in those born in Israel compared with those born abroad. Conclusions: There is still significant exposure to WNV, SFSV, and SFNV in Israel. Arboviruses are probably responsible for many cases of non-specific febrile illness in this region.