This project mainly studies viral agent, its diagnosis and transmission vector of encephalitis and unknown fever. It belongs to medical microbiology and it is very important for clinics, public health and prevention.

A new type of coltiviruses has been successfully isolated from sera of patients with unknown fever and from cerebral spinal fluid (CSF) of patients with encephalitis. It was first reported in China in 1990. The viruses were named Banna virus because they were isolated from patients in Xishuang Banna area in Yunnan province. Then the same viruses of Banna virus were isolated again from patients with fever of unknown origin in Mong Ding in Yunnan province.

      Over the past ten years, more than one hundred Banna viruses have also been isolated from mosquitoes collected from Hainan, Yunnan, gunsu, Beijing, Shenyang in East-north of China. It was found that there was high isolation rate from mosquitoes and it was widely distributed in China. So mosquito was the main transmission vector. The same viruses were also isolated from pigs and calfs.

All new isolates mentioned above were identified by their biological properties, serological methods, Polyacrylamide Gel Electrophoresis (PAGE) as well as electron microscope examination.  It was found that the genome of the new isolates, which composed of 12 segments of double stranded (ds) RNA by PAGE, is called coltiviruses, genus coltiviruses, a family of Reoviridae. However, it was significantly different in biological properties, RNA profile, genotype and transmission vector etc between Chinese isolates and that of Colorado tick fever virus (CTFV), which is the type species of this genus.

      In order to demonstrate infection of coltiviruses in human, serological test of sera from patients was carried out. There were four fold and more rise of coltiviruses antibodies in paired serum collected from patients of suspected Japanese encephalitis, viral encephalitis and unknown fever using antigen prepared by new isolate with high and stable titer.

Most of the isolates in China belong to B2 subgroup by sequence analysis. Comparison of   nucleic acid sequence of BJ95-75 and Yn-6 with other coltiviruses strain such as Banna strain, high homology of segments 12th and 9th of isolates (Beijing95-75, YN-6) from mosquitoes and the same areas of earlier isolate Banna virus form patients was found.      

Two training courses have been held in 1996 and 1997 to introduce coltiviruses isolated from China, to study diseases caused by coltiviruses, and to identify coltiviruses by PAGE, serological diagnosis and RT-PCR etc. The detection of coltiviruses infection in patients with encephalitis was carried out by some hospitals and anti-epidemic stations.