The threat of disease is rising in Pakistan as the country continues to recover from the most destructive flooding in its history.

More than 20 million people are homeless and 1,500 have died from the floods brought on by this year's monsoon season.

The World Health Organization is now concerned of a possible cholera outbreak, following reports that someone had fallen victim to the disease in the northwest Swat Valley.

WHO officials want Pakistan to investigate the case since cholera can spread rapidly after flooding and other disasters. The United Nations said Monday that 3.5 million Pakistani children are at risk of deadly, water-born diseases.

"What concerns us the most is water and health. There is a shortage of clean water," he added.

Getting aid to victims is still a problem in the region. The scale of the disaster has overwhelmed authorities, making relief distribution a slow and inadequate process.

Most of the food, water, and supplies being delivered to Pakistan is from other countries and international aid groups -- rather than the Pakistani government.

Monday, hundreds of people blocked a major highway with stones and garbage near the hard-hit Sukkur area in Sindh, complaining of the slow dispersal of aid. They claimed government officials only handed out food when media were present.

"They are throwing packets of food to us like we are dogs," one protestor said. "They are making people fight for these packets."

The U.N. also warned that unless farmers manage to plant their winter crop of wheat in mid-September as normal, there could continue to be food shortages in the region. Much of Pakistan's prime land for planting has been wiped out.