The Scientist web site has a good article on the hunt for the cause of SARS. The web site requires registration to access its articles but the registration is free and the site has generally good quality articles. Donald Lowe, head of the Department of Microbiology at Mount Sinai Hospital in Toronto thinks the hunt for the cause will succeed rather more quickly than similar hunts in the past.
But it took six months to identify the Legionella pneumophila bacterium as the cause of Legionnaire's disease, the pneumonia that attacked an old soldiers' convention in Philadelphia in 1976. Could it take just as long to identify the cause of SARS?
Unlikely, Lowe thinks. "Since Legionella, the molecular world has changed dramatically — if we have any evidence of an infectious particle, we can amplify the DNA or RNA, sequence it, and therefore be able more rapidly and accurately to define an agent. Unless we are dealing with a virus which is difficult to grow."
The New Scientist reports that a Canadian lab has ruled out 250 types of pathogens by testing samples from Canadian SARS victims.
Teams in Hong Kong and Germany said they had found evidence of a virus known as a paramyxovirus in at least some of the patients with the illness, called severe acute respiratory syndrome.
They stressed that more tests are needed before the virus is pinned down as the culprit, but said it is the best clue yet about the cause of the syndrome, which may have killed as many as 14 people and sickened hundreds more.
One of the Hong Kong scientists involved in the search for the pathogen is confident that his group has isolated the virus and that it looks like a paramyxovirus.
"We've identified the virus," said Dr. John Tam, a microbiologist at the Chinese University of Hong Kong, at a news conference late Tuesday. "We used an electronic microscope and found the virus in patient samples."
John Oxford, professor of Virology at Queen Mary's School of Medicine, said a similar virus had been discovered in Holland last year.
"It is rather slow-moving, rather restricted to families and hospitals, not a rip-roaring affair, but still very nasty.
Viruses in the Paramyxoviridae family include many common, well-known agents associated with respiratory infections, such as respiratory syncytial virus, and childhood illnesses, including the viruses that cause mumps and measles. Some of these viruses are widespread, particularly during the winter season. Screening of specimens could therefore be expected to detect particles of these common viruses. At this point, it cannot be ruled out entirely that tests for the SARS agent are detecting such “background” viruses rather than the true causative agent.
The Paramyxoviridae family also includes two recently recognized pathogens, Hendra virus and Nipah virus. These related viruses are unusual in the family in that they can infect and cause potentially fatal disease in a number of animal hosts, including humans. Most other viruses in the family tend to infect a single animal species only.
Nipah virus first began to cause deaths in humans in Peninsular Malaysia in 1998 in persons in close contact with pigs. The outbreak caused 265 cases of human encephalitis, including 105 deaths. Two separate outbreaks of Hendra virus, associated with severe respiratory disease in horses, caused two human deaths in Australia in 1994 and 1995. No human-to-human transmission was documented in either outbreak. No treatment was available for cases caused by either of these two viruses. Human-to-human transmission did not occur.
Even if the virus seen by the Hong Kong and German scientists via electron microscope is the infectious agent causing this disease and is from the paramyxoviridae family of viruses it is probably a previously unknown pathogen and not one of the known existing members of the paramyxoviridae family.
Still, Dr. Klaus Stöhr, a virologist and epidemiologist who is leading the health organization's scientific team investigating the illness, said that none of those viruses had caused a disease like the one under investigation, which doctors are calling severe acute respiratory syndrome, or SARS. Instead, the findings suggest that the virus might be a hitherto unknown member of the paramyxoviridae family.
If the SARS illness is positively identified as being caused by the paramyxovirus which the Hong Kong and German researchers have isolated then the only existing antiviral drug that might work against it is Ribavirin. Anti-viral drug development historically has been much more difficult than anti-microbial drug development. To date vaccines have been far more effective than anti-virals and this is likely to continue to be the case (though HIV is an exception to this pattern since HIV vaccine development has proven so hard to do). Other viruses of the paramyxoviridae family include measles and mumps and of course vaccines do exist for them. It therefore seems reasonable to expect that if the SARS illness is being caused by paramyxovirus the development of a vaccine should be possible.
Drug development time and vaccine development time are both usually measured in years. An exception to this is influenza. For influenza every year vaccines for new strains are usually developed within months of when the new strains are first detected. However, if this SARS pathogen is a paramyxovirus it is probably a species unknown to scientists and perhaps even from a genus heretofore unknown. Therefore developing a vaccine for it will require a lot more work to first understand it to a level of detail that would make vaccine development possible.
In the short to medium term the best line of defense against the SARS pathogen is likely to remain the rapid isolation of its victims. But the work to isolate and identify the virus is important because it will lead to tests for its presence. The ability to test and detect it will lead to a much more rapid ability to identify and isolate those who are infected by the virus. That, in turn, will help to prevent its spread. Therefore the race going on to identify and characterize the SARS pathogen could lead to a fairly rapid benefit for the public health.
Update: The SARS illness spread from China. It started there in November 2002. The Chinese government was very irresponsible for not telling the rest of the world about the illness until after it had spread to outside of China.
Although the outbreak in Guangdong province started in November, health officials said almost nothing publicly for months afterward. Chinese officials gave their first report of the outbreak in Guangdong province to the World Health Organization on Sunday, saying that the outbreak was abating on its own. The report raised hopes at the World Health Organization that it would burn itself out elsewhere as well.
Because millions of poor Chinese people live in close proximity with chickens and pigs new strains of influenza sometimes jump across from other species into humans. These strains have a much greater potential to be very virulent in humans than the strains that emerge from within the human population. Therefore China is the most probable origin of an influenza whose lethality could rival the so-called Spanish flu of the 1918 pandemic. For China to be slow about notifying the rest of the world about a newly emerging illness is therefore an extremely dangerous practice. Governments and public health officials around the world should be sharply critical of China's lapse in its responsibility in this matter.
Update III: The extent of the Chinese government's irresponsibility in failing to inform the rest of the world of the emergence of the SARS disease before it escaped from Guangdong province China is brought into sharp relief by the revelation of how SARS disease crossed over into Hong Kong. The carrier is now believed to have been a Guangdong doctor aged 64 who stayed in a Hong Kong hotel and infected 6 other people staying on the same floor of the hotel.
Director Margaret Chan said the source of the outbreak appeared to be a Guangzhou doctor who stayed at the Metropole Hotel in Waterloo Road last month and infected six others.
Had the Hong Kong medical establishment been properly informed of the threat it is very likely that hospitals would have been operating with a far higher degree of caution when examining new admittees and those who became ill with this disease would have been diagnosed and isolated much more rapidly. The Chinese government deserves a serious loud dose of criticism for its handling of this matter.
Update IV: SARS is now suspected of being caused by a coronavirus. Blood serum from recovered victims has had gamma globulin extracted from it and injected into the bodies of those with very severe SARS and the gamma globulin treatments have been very effective in treating severe cases of SARS.
"Facts have proven that in at least 20 of our patients who went through very smooth recovery, their serum has been used to treat very severe sufferers and that has been very successful," said Leung Ping-chung, a professor and surgeon at the Prince of Wales Hospital in Hong Kong, considered ground zero of the outbreak.
Also see my more recent post Fears Grow That SARS May Spread Into Pandemic.
|Share |||Randall Parker, 2003 March 19 10:26 PM Dangers Natural Bio|