The US Centers for Disease Control has begun distributing an experimental diagnostic test for the deadly SARS virus to laboratories.
Diagnosing the virus which causes SARS remains a major problem in controlling the spread of the potentially fatal disease. The World Health Organization cautions that the tests available so far are unreliable; full information on the reliability of the new US test is still unknown.
鈥淭he development of commercial diagnostic tests for SARS has progressed more slowly than initially hope,鈥� it said in a statement on Monday. 鈥淧art of the problem arises from certain unusual features of SARS that make this disease an especially difficult scientific challenge.鈥�
Advertisement
The US test, being offered to 100 specialised laboratories, uses a technology called polymerase chain reaction (PCR) to detect the RNA of the deadly SARS coronavirus in samples of body fluids like respiratory secretions or urine. But because scientists do not know exactly how well the test will perform, patients are to be asked for their written consent before it is given.
鈥淭his experimental test marks a significant step forward in our ability to confront and ultimately overcome this new disease, and its development embodies the commitment of our department to protecting the public health,鈥� said Tommy Thompson, US Health and Human Services Secretary.
The deadly virus which jumped from exotic mammals to humans in China鈥檚 Guangdong province in November 2002, has claimed over 770 lives and caused over 8000 infections worldwide according to the latest figures.
Unusual behaviour
快猫短视频s across the globe are racing to find a reliable and fast diagnostic test for the super-pneumonia. Potential tests are either based on using PCR to detect the genetic material of the virus, or detecting antibodies 鈥� the body鈥檚 immune reaction to invaders 鈥� against SARS.
However, SARS is unlike most viruses in that it does not cause the body to shed vast quantities of SARS coronavirus during the first few days of the disease, says the WHO.
鈥淰irus shedding peaks in respiratory specimens and in stools around 10 days after onset of the clinical illness. In effect, this unusual behaviour creates the need for tests having a particularly high sensitivity,鈥� it said the statement. The WHO adds: 鈥淪uch tests do not yet exist.鈥�
And because the body鈥檚 immune system takes five or six days to respond to an attack by the SARS coronavirus, antibody tests cannot be used till about day 10 of the illness. In some cases, antibody tests are ineffective up to day 21.
Chinese researchers are working on an antibody test which they claim can detect SARS in some patients as early as the first week.
The test is able to detect antibodies in 10 to 11 percent of SARS patients during their first week of fever, 50 percent of patients in their second week of and nearly 100 percent of patients after the second week, said Bi Shengli, deputy director of the Chinese Center for Disease Control and Prevention鈥檚 Institute for Viral Disease Control and Prevention, according to AFP News.
A reliable test for SARS is crucial, as patients are most likely to infect others during the initial phase of the disease.
Meanwhile, the number of new SARS cases in the China 鈥� the worst-hit country 鈥� has remained in single figures for eight consecutive days. But a spokesman for the WHO expressed concern over how these figures were being collected.