A spokesman at Scotland's Health Protection Agency said Thursday all of the people stricken with the bacterial disease were heroin users.
Experts say contaminated heroin or another powder-like substance used to dilute the drug may have spread the disease.
Only a handful of anthrax cases have been reported in the United Kingdom in the past decade. The disease mostly affects people exposed to contaminated animal hides and other animal products.
Anthrax can be treated with antibiotics if caught early, and does not usually spread from person to person.
