A higher risk: A Kenyan study has found that HIV-positive men with low CD4 counts are at a higher risk of reinfection with bilharzia. Taken with other evidence, including resistance to reinfection that appears with age and after treatment that kills the flukes that cause bilharzia, researchers argue that a preventive vaccine may be possible. A study from Zimbabwe has failed to confirm previous reports that people with HIV were less likely to shed bilharzia in their urine than people without HIV. Both studies reflect a growing recognition of the importance of interactions between widespread, mostly tropical, diseases and HIV.