LONDON, England (CNN) -- A meningitis outbreak is threatening the lives of tens of thousands of people in Darfur, according to an aid agency expelled from the country last week.



A Doctors without Borders medic helps a sick child in a Darfur refugee camp.



Humanitarian organization Doctors Without Borders, also known as Médecins Sans Frontières (MSF), says it was preparing to vaccinate around 100,000 people in southern and western Darfur against meningitis, when it was told to leave the country.



"We were in the process of organizing a vaccination campaign. At the moment  there's no one there that can take over those activities, which is really worrying," Gemma Davies of MSF told CNN.



The country's Ministry of Health officially declared a meningitis outbreak on March 2 at the Kalma Camp, which shelters more than 90,000 refugees in southern Darfur.



"Living in such close proximity, the potential for this outbreak to spread quickly is quite high, Davies, MSF project coordinator for South Darfur, told CNN.



"With no health care providers to give vaccinations, and with no one to manage the meningitis cases when they come, it's really concerning," she added.



The vaccination campaign was due to begin on March 7, but it is now unclear if or when it will resume, as reports of government harassment of aid workers continue.



Davies told CNN she experienced no harassment, and said government officials had  been in contact with only the head of MSF's regional operations.



"We haven't actually been given any reason on why we were expelled," she said. "We have absolutely no idea when we'll be able to return."



Doctors Without Borders was among 13 aid agencies, including Mercy Corps and the International Rescue Committee, that were ordered by the government to shut down their operations in Sudan last week.



So far the agency has confirmed 32 meningitis cases and four deaths, and has seen dozens of other suspected cases.



Thousands of unvaccinated refugees and villagers are now exposed to the airborne disease in densely populated camps and villages throughout Sudan.



"One of our priorities is to get another organization to take over our programs there," Davies added.



The medical relief agency says it doubts though that other any other organizations have the capacity to deal with a meningitis epidemic.



Davies also said she is worried about the cut-off of MSF's feeding and maternal delivery services: "We had over 100 patients on our feeding program that now won't be receiving any follow up."



The decision by the Sudanese government to throw out the aid groups came a day after the International Criminal Court at The Hague issued an arrest warrant for Sudanese President Omar Hassan al-Bashir for war crimes and crimes against humanity in Darfur.



However, not all international aid organizations are affected. Others including World Vision international continues its work, which reaches approximately 500,000 internally displaced people in South Sudan.



The U.N. has received reports that international staff members of five non-governmental organizations had been detained for up to four hours.



Speaking on the phone from Nairobi, an aid worker, who asked not to be identified for fear of further harassment, told CNN that his colleagues who remained in Khartoum were being intimidated and threatened by government agents.



In some cases Sudanese government representatives "had started gathering banking details and confiscating computers, communications equipment and vehicles from the NGOs", a U.N spokesman said at a news conference last week.



Last week, the U.N. warned that the loss of  NGOs in Sudan would cause 1.1 million people to go without food aid and health care, and more than 1 million to have no access to water.



Oxfam, whose work focuses on providing safe drinking water, was one of the aid groups who were told their registration to operate in Sudan was no longer valid. Ninety percent of their staff are Sudanese nationals, who mostly remain in country, unable to continue their relief work under threat of arrest.



"These agencies are vital implementation partners for the United Nations and account for at least half of the humanitarian capacity in
Who is the head of the Sudanese government? What disease threatened many residents of Darfur? Amount that is at risk of starvation after the aid agencies were expelled? Aid workers were detained by what government? Who has been detained by the Sudanese government? What caused a risk of starvation for over a million people? What number of people are at risk of starvation? What illness threatens hundreds of thousands of people in Darfur? What number of people are threatened by meningitis?
President Omar Hassan al-Bashir meningitis 1.1 million Sudanese international staff members of five non-governmental organizations A meningitis outbreak 1.1 million meningitis tens of thousands
question: Who is the head of the Sudanese government?, answer: President Omar Hassan al-Bashir | question: What disease threatened many residents of Darfur?, answer: meningitis | question: Amount that is at risk of starvation after the aid agencies were expelled?, answer: 1.1 million | question: Aid workers were detained by what government?, answer: Sudanese | question: Who has been detained by the Sudanese government?, answer: international staff members of five non-governmental organizations | question: What caused a risk of starvation for over a million people?, answer: A meningitis outbreak | question: What number of people are at risk of starvation?, answer: 1.1 million | question: What illness threatens hundreds of thousands of people in Darfur?, answer: meningitis | question: What number of people are threatened by meningitis?, answer: tens of thousands