Age Distribution Among Patients at High Risk for Human T-Cell Lymphotrophic Virus Type I Infection

Abstract

Human T-celllymphotropic virus type I (HTL V-I) is a human retrovirus associated with adult T cell leukemia and tropical spastic paraparesis. We recently reported a high incidence of HTLV-I infection in Israeli Jews originating from the city of Mashhad in Iran [1, 2]. There is a characteristic age-dependent increase in the seroprevalence of HTLV-I infection in areas of endemicity. This increase typically occurs in adulthood and is higher in females than in males throughout their lifetimes [3, 4]. It is not fully understood whether age, immunity, and the CNS are distinctive factors or cofactors associated with morbid­ ity in elderly populations. We designed the present study to investigate whether there is an age-dependent increase in the incidence of HTLV-I infection in a population at high risk; the results of our investigation were designed to be used as a model for CNS infectivity in the elderly. The Jews of Mashhad were persecuted because of their religious beliefs since 1747, but they secretly continued to practice the Jewish religion and to intermarry, resulting in families that are closely related genetically. We included 321 Iranian Jews of Mash­ hadi origin (either the subject or at least one of his or her parents was born in Mashhad) in our study. All subjects underwent physi­ cal and neurological examination, and samples of peripheral blood were obtained from each subject after informed consent was ob­ tained. Sera were tested for antibodies to HTLV-I with use of the gelatin-particle agglutination test, and genomic DNA was ampli­ fied as previously reported [2]. Statistical analysis was performed with analysis of variance (ANOVA). Of the 321 subjects included in the study, 203 were female and 118 were male (mean age z SD, 45.7::':: 22.3 years). Fifty­ eight (18%) of the 321 subjects (38 females and 20 males; mean age z SD, 50::':: 17.3 years) were positive for HTLV-I antibody by serological testing and by peR analysis. Of the 58 HTLV-I infected subjects, 36 were asymptomatic carriers, whereas 22 (14 females and 8 men; 38%) had signs of spastic paraparesis. None of the 263 subjects who were not infected had abnormali­ ties of the pyramidal tract compatible with spastic paraparesis.