| Summary: | Pogosta disease is a mosquito-borne viral disease in Finland, which is clinically manifested by rash and arthritis; larger outbreaks occur in 7-year intervals. The causative agent of the disease has been suspected of being closely related to Sindbis virus (SINV). We isolated SINV from five patients with acute Pogosta disease during an outbreak in fall 2002 in Finland. One virus strain was recovered from a whole blood sample and four other strains from skin lesions. The etiology of Pogosta disease was confirmed by these first Finnish SINV strains, which also represent the first human SINV isolates from Europe. Phylogenetic analysis indicates that the Finnish SINV strains are closely related to the viral agents that were previously isolated from mosquitoes and that are related clinically similar diseases in nearby geographic areas. Sindbis virus (SINV), a member of the Western equine encephalomyelitis virus complex of the genus Alphavirus in the family Togaviridae, was first isolated in 1952 in the Nile River delta in Egypt from a pool of Culex pipiens and Cx. univittatus mosquitoes (1). SINV is an enveloped virus with a genome of single-stranded, positive-polarity 11.7-kb RNA (2). The genomic 49S RNA also serves as mRNA in the infected cell. Translation of the genomic RNA produces the four nonstructural proteins nsP1–4. The 26S subgenomic mRNA is translated to produce the polyprotein from which E1, E2, and C structural proteins are processed. The seroprevalence of SINV antibodies among the Finnish population is approximately 2 % (3); however, the prevalence varies considerably between different parts of the country. The typical clinical picture of Pogosta disease includes arthritis, maculopapular rash, and sometimes low fever, fatigue, and muscle pain (4; Kurkela et al., unpub. data). Clinically similar or identical diseases are Ockelbo disease (known as August–September disease) in Sweden and Karelian fever in Russian Karelia (5–7). Ockelbo disease was first found in Sweden in 1967 (8). A larger
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