"We've had 60 cases since June," said Dr. Taj Mohammed, medical officer at Quetta's Fatima Jinnah Chest Hospital.
"Eight people have died so far. It's unheard of - very unusual. I haven't seen anything like this, and there's a real risk of an epidemic among Afghan refugees."
The symptoms of the disease are compatible with Crimean-Congo Haemorrhagic Fever.
However, the World Health Organization (WHO) said it had yet to confirm any cases of the fever.
"A WHO mission went to Quetta, but WHO wishes to appeal to the public not to draw any immediate conclusions until the investigation is concluded," United Nations spokesman Eric Falt told reporters in Islamabad.
Between May and August, 40 suspected cases and 11 deaths were reported. "It is not ebola, it is an ebola-like virus," he said.
"There have been a number of cases reported by the national authorities and substantiated by WHO in Quetta...and Karachi," Falt said. "It is not new by any stretch of the imagination."
The virus might be endemic to parts of Afghanistan, but the number of patients in Quetta - they are all male, all poor and come from all over Pakistan's Baluchistan province - is unprecedented, doctors said.
About 12 of the patients were Afghan.
All the patients were held in wards isolated from the rest of the 250-bed hospital by a barbed wire fence.
The disease was carried by livestock ticks, and humans were vulnerable when they lived in close proximity with herds of sheep or goats. The virus was spread through urine, stools, blood or spit.
"The symptoms are nose-bleeds, bleeding from the rectum, even through the skin," Dr Mohammed said.
Medical technologist Dr Javed Akbar said the fact that the victims were poor and uneducated meant they had little or no appreciation of hygiene.
"They don't grasp the importance of keeping clean, of distancing themselves from their livestock," he said.
Tuberculosis, meningitis and pneumonia are also lurking aound the refugee camps on the border and in times of war the diseases tend to spread, reports CBS News' Allen Pizzey.
With U.N. agencies planning for the possible arrival of another million Afghan refugees in Pakistan because of drought and the current crisis, the doctors said they feared the Congo-Crimea virus could spread rapidly among the newcomers.
"The possibility of an epidemic has to be taken very seriously," Dr Mohammed said.
However, Halt said the only danger of a serious outbreak was if animals were also on the move with Afghan refugees.
"In the absence of animals there is no risk," he said.
The Baluchistan authorities had begun spraying animals this year to try to control the ticks.
The first known case was among Soviet troops in the Crimea in 1944 and theamong villagers living near Kisangani in the Congo in 1956.
In the isolation ward, one elderly man lay quietly on his side, dried blood caking his shirt. Blood serum was drip-fed into one arm.
"The bleeding has stopped. They're all improved, but not yet cured," said 27-year-old nurse Parween.
Only one attendant was permitted at any one time in the wards where the Crimean-Congo Haemorrhagic patients were treated to try to reduce the risk to staff.
Some years ago, two medical workers died in Pakistan after operating on a patient infected by the virus.
Parween wore overshoes, surgical gloves, a gown and a face mask.
Wasn't she afraid?
"No, not at all. It's my duty," she said.
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