A flood survivor wades through mud as he salvages belongings Saturday in Azakhel, near Nowshera, northwest Pakistan. A case of the deadly waterborne disease cholera has been confirmed in Pakistan’s flood-ravaged northwest, and aid workers expect there to be more, the U.N. said Saturday.

Sukkur, Pakistan ? The deadly, waterborne disease cholera has surfaced in flood-ravaged Pakistan, the U.N. confirmed Saturday, adding to the misery of 20 million people the government says have been made homeless by the disaster. A fresh surge of floodwater swelled the Indus River, threatening previously spared cities and towns in the south.

The crisis has battered Pakistan’s economy and undermined its political stability at a time when the United States needs its steadfast cooperation against Islamist extremism. The U.N. has appealed for an initial $460 million to provide relief to Pakistan but has said the country will need billions to rebuild once the floodwaters recede.

Because of the flooding, Pakistan canceled celebrations Saturday marking its creation and independence from Britain in 1947. President Asif Ali Zardari met with flood victims in the northwest, and U.N. Secretary-General Ban Ki-moon was expected to visit affected regions on Sunday.

The floods have killed about 1,500 people, and aid workers have warned that diseases could raise that toll.

One case of cholera was confirmed in Mingora, the main town in the northwest’s Swat Valley, U.N. spokesman Maurizio Giuliano said Saturday. But other cases were suspected, and aid workers are now responding to all those exhibiting acute watery diarrhea as if it is cholera, Giuliano said.

Cholera can lead to severe dehydration and death without prompt treatment, and containing cholera outbreaks is considered a high priority following floods.