Posted on 05/27/2003 9:44:06 AM PDT by Dog Gone
Blood tests of people who worked with exotic animals in markets in southern China show that a significant proportion apparently had been infected with the SARS virus, suggesting that some people may become infected without becoming ill, according to World Health Organization officials.
The findings are from two separate studies of workers in markets in Guangdong Province, and they strengthen the SARS link between animals and humans, the officials said in interviews Monday.
At the same time, scientists at Hong Kong University announced that they were developing what could become the first experimental vaccine for severe acute respiratory syndrome. They said they hoped to start testing the vaccine on animals in early June.
The scientists provided few details about the vaccine except to say that human trials of any SARS vaccine would not be started until after findings of animal experiments were known, and perhaps not even then. They said preliminary results of the animal experiments would not be known for at least six months.
Last week, scientists in Hong Kong and at the Center for Disease Control in Shenzhen, in Guangdong just across the Hong Kong border, reported finding the SARS virus in three species of animals - Himalayan, or masked, palm civets; raccoon dogs; and badgers - bought at a food market in Shenzhen. That discovery suggested, but did not prove, that the SARS virus infects animals in the wild, making it virtually impossible to eradicate the disease.
One of the two new studies involved workers at the same market in Shenzhen. Dr. Klaus Stoehr, the scientific director of WHO's investigation of SARS in Geneva, said that a team of virologists headed by Dr. Malik Peiris of Hong Kong University tested blood taken from 10 market workers and found antibodies to the SARS virus in five. Antibodies are specific proteins that the immune system forms when it mounts an attack against a microbe. But antibody tests obtained in such screening samples cannot determine when an individual was infected. The workers with positive tests were said to be healthy and did not recall having had a SARS-like illness recently, Stoehr said. Scientists at the Center for Disease Control in Guangdong performed a similar screening study among 508 people working in a larger group of wholesale markets of exotic animals, Stoehr said. Of those, 66, or 13 percent, had antibodies to the SARS virus. No information was available on the medical histories of the infected workers, he said.
Although the findings are not definitive, they strengthen the suggestion that animals play a role in transmitting SARS, Stoehr said. The findings, he said, "suggest that the spectrum of disease is wider than what we saw" when SARS was first detected in March as a severe form of atypical pneumonia in patients in Hanoi and Hong Kong.
There are many possible reasons why the percentage of infected workers varied in the two studies and why those infected apparently did not become ill. For example, the sensitivity of the tests used by the two laboratories may have varied. Also, the amount of virus to which the workers were exposed may have been small, thus reducing the chances of more serious illness.
Dr. David Heymann, executive director of communicable diseases for WHO, said that scientists needed to conduct similar antibody screening studies to determine the frequency of SARS infection among people who do not work in the markets but live in the same area.
Lennon Tsang, a spokesman for Hong Kong University, said that the SARS vaccine would be derived from an "inactivated' strain of the coronavirus that WHO says is the cause of SARS. The vaccine uses a "noninfectious" form of the virus, he said, declining to discuss whether the vaccine would use dead virus or an attenuated, or weakened, strain. Although scientists often use the word "inactivated" loosely in describing vaccines, they generally use it for vaccines derived from killed virus. One example is the injected Salk polio vaccine.
Scientists use the word "attenuated" to describe vaccines derived from live virus that has been weakened by growing it for long periods in test tubes. An example is the oral Sabin polio vaccine.
The university issued a terse statement disclosing its plans for the trials after a local newspaper reported that animal tests would begin soon.
A scientist who is knowledgeable about the research said a strain of the SARS virus had been inactivated with the aim of inserting it in the nostrils of mice to see how the immune system of mice responded to it.
From the commentary:
[The presence of an] additional 29-nucleotide sequence coupled with minor variations in the 4 strains would suggest that all 4 had the additional 29-nucleotide sequence. If these reports are correct, infection of civet cats with feed contaminated with the SARS coronavirus in feces seems unlikely. The above [circumstances are most compatible] with the existence of a natural civet cat coronavirus with a 29-nucleotide sequence [that has been lost as it jumped from civet cat to human].
The Chinese/Hong Kong researchers have not said whether the animal handlers they tested had the extra 29-nucleotide version of SARS. This version of SARS may not be able to survive in humans. But if it does it may explain both the presence of SARS antibodies in the animal handlers, and the lack of symptoms.
The study I saw on this was of "suspected" SARS cases compared with "probable" SARS cases. They did not test a supposedly "clean" control group.
The "suspected" cases were people who were known to have potential exposure, and were symptomatic at a relatively mild level. The test used showed 20% of these people had the SARS virus. To further muddy the waters, no other researchers have duplicated the results and the study is causing a lot of academic wrangling.
The U.S. CDC has done a "clean" control group test, and found no SARS virus in this group.
Dr. Jenner developed vaccination after he observed how cowmaids did not get smallpox.
Are all these animals closely related?
I observe that pigs, the commonest farm animal in China, are also omnivores.
Thanks. I wonder if they have checked other animals and if not why not. ...and if they have not checked other animals, why did they select these to check? (Just tossing out questions.)
Thanks. I didn't catch that. I'm wondering if we should ban the importation of these animals as Japan is doing?
Good idea. Maybe we should check our zoo workers who are around those animals here.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.