EMERGING VIRAL PATHOGENS IN LONG-TERM EXPATRIATES .2. DENGUE VIRUS

Dengue virus infections have been well known for many years; still den gue virus is regarded as an 'emerging' pathogen, as the disease profil e is changing. Its geographical range and overall incidence, and the i ncidence of the associated complications, dengue haemorrhagic fever (D HF) and dengue shock syndrome (DSS), are on the increase. Modern-day t ravel and increasing urbanization seem to be the main contributing fac tors. In order to estimate the risk of infection during long-term stay s in dengue-endemic countries, we tested sera obtained from 323 develo pment aid workers and their family members who had spent on average 9. 8 years in dengue-endemic regions for the presence of dengue virus ant ibodies. Dengue virus antibody screening was done by a commercially av ailable immunofluorescence test (IF). Reactive samples were re-tested by an in-house IF and also tested for cross-reactivity to yellow fever virus using yellow fever IF and neutralization test (NT). Evaluation of the results revealed that the screening test has a specificity of a t least 63.2% In 12 of Ig initially positive cases crossreacting antib odies against yellow fever virus could be ruled out. Three cases remai ned indeterminable, whereas four of the reactive and Io (out of 12) of the borderline reactive cases showed crossreactivity with yellow feve r virus, probably due to previous vaccination. We found seroprevalence rates of 4.3% with no significant differences related to gender or ar ea of upbringing. Seroprevalence rates were evaluated according to reg ion of suspected or confirmed infection. In two cases the dengue infec tion had taken a classical clinical course; in another three cases an extraordinary febrile illness was reported in the history. None of the other seropositive individuals had a history of an illness possibly a ttributable to dengue virus infection. Our results show that there def initely is a risk for long-term expatriates to acquire (mostly non-or oligo-symptomatic) dengue infection, which might be important especial ly in the light of the supposed aetiology of DHF or DSS as a secondary infection with another dengue virus serotype.