Uganda has shut its border with the Democratic Republic of Congo in one of East Africa’s most aggressive disease-control measures in years, as fears grow that a fast-moving Ebola outbreak could spiral into a wider regional crisis.

The four-week closure takes effect immediately and applies to nearly all cross-border movement except humanitarian missions, security operations, cargo transport, and Ebola response teams.

The move comes as Congo battles a worsening outbreak of the rare Bundibugyo strain of Ebola, which has recorded nearly 1,000 suspected infections and more than 220 suspected deaths, according to health authorities and the World Health Organization.

Unlike previous Ebola outbreaks that were partly contained with vaccines and experimental treatments, the Bundibugyo strain currently has no approved vaccine or specific treatment, raising fears among regional governments and international health agencies.

For Uganda, the threat is not theoretical.