JUBA, Sudan: An outbreak of a parasitic tropical disease has killed more than 300 people in southern Sudan – and the worst of the health crisis is yet to come, officials say. The World Health Organization says the outbreak of kala azar, which began in September 2009 and has intensified in recent months, is the biggest health problem facing Southern Sudan. More than 7,000 cases – many of them in the region's most remote and insecure areas – have been reported this year by WHO and southern Sudanese health authorities. The outbreak of cases is the region's worst since 1991. More than 300 people have died since September 2009, WHO says, but officials fear the disease could spread for several more months. “We don't know when it will end,” said Dr. Abdinasir Abubakar, a WHO medical officer in southern Sudan, said in an interview this week. Health officials, he said, are “struggling to respond to the outbreak because it is beyond what we had planned.” Transmitted through sand flies, the parasite that causes the contagious disease mainly affects children whose immune systems are compromised by malnutrition. In the recent outbreak, 90 percent of patients were children under the age of 17. Symptoms include fever or acute malnutrition, and patients are often described as “wasting away.” Nine out of 10 patients with kala azar will die if they do not receive treatment, according to Doctors Without Borders. Patients can die within weeks if not treated. The peak of the outbreak is predicted to come between December and January, coinciding with Southern Sudan's plans for a Jan. 9 independence referendum. That referendum is widely predicted to result in the creation of the world's newest country. Kala Azar – a Hindi word meaning “Black Death” – erupted during Sudan's two-decade civil war that ended in 2005, killing hundreds of thousands of people in Southern Sudan. Also called visceral leishmaniasis, the disease causes high fever, swelling of the spleen and massive weight loss. Survivors can be badly scarred. About 500,000 new cases appear every year in the world, according to the World Health Organization. Most occur in Sudan, Bangladesh, India, Nepal and Brazil. Doctors Without Borders has opened three emergency treatment sites in Southern Sudan to respond to the outbreak. The group says it has seen a sharp uptick in kala azar cases since August, which is normally the disease's low season. Southern Sudan has seen more timely rains and better harvests because of the those rains, but food stocks have been low.“People are still suffering from malnutrition because of the situation of the past two years,” Abubakar said, referring to periods of drought. The outbreak is the most severe in several extremely remote and insecure parts of Jonglei and Upper Nile states.