Geneva, July 15 (RHC)-- The World Health Organization has warned that the cholera outbreak in Yemen could spread during the annual Hajj pilgrimage in Saudi Arabia in September.

The WHO pointed out that the pilgrimage draws two to four million Muslims each year -- of whom about 1.5 to two million are foreigners -- raising the risk from illnesses such as dengue, yellow fever, Zika virus and meningococcal disease as well as cholera. The WHO cholera expert, Dominique Legros, said reinforced surveillance and rapid tests to detect cases early helped Saudi Arabia avoid a cholera outbreak for many years.

"Don’t forget that today we are speaking of Yemen but they are receiving pilgrims from a lot of endemic countries, and they managed not to have an outbreak, essentially by making sure that living conditions, access to water in particular, hygienic conditions, are in place," he said at a regular UN briefing. "They are well-prepared in my view."

Cholera, which causes severe diarrhea and dehydration, is transmitted through contaminated drinking water and could prove fatal in up to 15 percent of untreated cases.

The incubation period of the disease is a matter of hours and once symptoms begin, cholera can kill within hours if the patient does not receive treatment. The WHO expert, however, said 80 percent of patients show no symptoms, making airport screening “useless.” "That’s why we advise countries against airport screening for patients. The Saudis don’t do that. It's useless, technically speaking," Legros said.

The United Nations has blamed Yemen’s cholera crisis on the perpetrators of the ongoing war against the impoverished country and their foreign supporters. Stephen O'Brien, the UN under-secretary-general for humanitarian affairs, told the UN Security Council that the “man-made” outbreak of the deadly disease was “a direct result” of the Saudi-led aggression and “serious violations of international law."

The UN official warned that the suspected cholera cases across Yemen had surpassed 320,000 while at least 1,740 had lost their lives after being infected. The Saudi-led war has destroyed most of Yemen’s infrastructure and put nearly half of the country’s population on the verge of famine.

Local Yemeni sources have put the death toll from the Saudi war at over 12,000, including many women and children.