A Study On Poliovirus And Reovirus Isolated From The Specimens Of SARS Patients

Severe acute respiratory syndrome (SARS) is an emerging infectious disease, on April 16, 2003, WHO announced that a new coronavirus mutant, SARS Coronavirus, is the pathogen of SARS. However, the virologist in Institute of Microbiology and Epidemiology, Academy of Military Medical Sciences had isolated the reovirus from the first SARS patients and her mother in Beijing. When we investigated the sequencing of the reovirus further, much to our surprise, we detected the poliovirus RNA in the specimens. To study the pathogens of SARS, the cell culture reverse transcription-polymerase chain reaction (RT-PCR), serum neutralization test, and serology test were used to determine the clinical specimens during the onset of SARS and recovery of SARS 2 years later.During the onset of SARS, the HEp-2 cell lines were used to isolate the agent from 4 nasopharyngeal swabs. After 3 days of incubation, a cytopathic effect(CPE) were seen on HEp-2 -cell cultures inoculated with nasopharyngeal swabs, and the viral RNA in the tissue-culture supernatant was analyzed with a random reverse-transcriptase (RT)-PCR assay. The 4 supernatants were tested for poliovirus and reovirus with 4 positive results for poliovirus and 3 positive for reovirus. The results of serum neutralization test showed that the neutralization of virus by antibodies to poliovirus types 1 could prevent CPE in tissue culture, but neutralization of virus by reovirus antibodies still leads to CPE. These results showed that polioviruses type 1 existed in the 4 nasopharyngeal swabs, and the reovirus maybe a new type of reovirus.The viral RNA in the 4 supernatants of cell cultures were amplified by RT-PCR using specific primers, in order to detect the viral genotypes, the PCR products of all the samples were cloned into pGEM- T-easy vector individually and white clone of each PCR product were chosen to sequence. The sequencing results showed that 4 were positive for poliovirus type 1 and 3 were positive for reovirus.In order to identify the status of these virus in the patients diagnosed with SARS,a total of 44 clinical specimens from 25 patients with SARS were tested for poliovirus and reovirus, the poliovirus was 60 percent (15/25 ) and the reovirus was 18.2 percent(8/25) among these patients, whereas the poliovirus was 4 percent(l/25) and reovirus was not detected at all the controls. All sequences were 99 percent identical to the Human poliovirus 1 strain Sabin 1, but back mutations have occurred at 2 primary attenuating mutation sites. Sequencing of these RNA samples showed high homologies with the reference strain of Human poliovirus 1 strain Sabin 1, but back mutations have occurred at the the primary attenuating mutation sites, nt480 and nt 2795. The same results were got from the postmortem kidney tissue and small intestine tissue from 1 patient diagnosed with SARS. The difference of positive rate for poliovirus was statistically significant at the 0.01 significance level between the SARS patients and the controls.In the follow-up study of SARS patients recoveried 2 years later, RT-PCR was used for testing the clinical specimens from 8 patients with none positive results of SARS-CoV and reovirus, 4 positive for poliovirus type 1 in the stools from 4 persons. The positive rating for the SARS-CoV antibody in the serums were 37.5 percent, whereas the SARS-CoV antibody was not detected at all the healthy controls;the antibody to poliovirus was 50 percent in the patients, but was 92 percent in the healthy controls. The difference of the positive rate for IgG antibodies to poliovirus, was statistically significant at the 0.01 significance level between the SARS patients followed up and the healthy controls.The high positive rating of poliovirus in SARS patients gave us a clue that poliovirus may be associated with SARS> but it still needs the further study. After recovering from SARS 2 years later, the positive rating of poliovirus in the stools of SARS patients was still very high, and more importantly, back mutations still exsisted at the attenuating mutation sites which play an important role in the poliomyelitis, this may be a potential hazard to threaten the aim of the final push to rid the world of polio. It suggests that we should pay attention to the present immunization strategy of the Oral Polio Vaccine(OPV).