The Council of Agriculture (COA) on Monday night made public the genome sequences of the rabies virus strains collected from Formosan ferret-badgers.
What can so far be determined from the sequences is that the virus “is closely related to a virus strain found in China’s ferret-badgers,” the council said yesterday, nevertheless adding that the virus might have been in Taiwan “for a while.”
According to the published results, the nucleotide sequence similarity between the isolate glycoprotein (G) genes of the virus strains obtained from the Formosan ferret-badgers ranges from 91.5 percent to 99.9 percent. Moreover, the percentage of genetic relatedness among the isolates determined by analysis of the nucleoprotein (N) gene sequence, on the other hand, ranges from 91.5 percent to 100 percent.
On the much speculated relationship between rabies virus strains found in Taiwan and China, Animal Health Research Institute Director-General Tsai Hsiang-jung (蔡向榮) said that the percentage similarity between the strains, determined by an analysis of G gene sequences, ranged from 87.8 percent to 89.6 percent, while the N gene sequences had a similarity of 87.7 percent to 91.3 percent.
The institute concluded that the rabies virus strain isolated from Formosan ferret-badgers is the most similar to that found in China’s ferret-badgers, rather than strains in the US and Mexico.
“China is also the only country with a rabies infection in ferret-badgers [apart from Taiwan]. With this piece of epidemiological information, accompanied by the genetic similarity, we conclude that the virus strain is related to China’s strain,” Tsai said.
However, Tsai added that the similarity between the Taiwanese and Chinese strains does not necessarily mean that the Taiwanese virus was imported from China.
Tsai said that based on the analyzed genome sequences, the nine virus strains collected can be sorted into three groups — one group from Nantou and Taichung, the second from Yunlin, Tainan and Kaohsiung and another from Taitung.
“The differences between the [three] local groups can be up to 7 percent to 8 percent [in terms of sequences of G and N genes],” Tsai said.
“This means that it is possible that the rabies virus has been in Taiwan for a while and has been evolving,” Tsai said.
In other words, it is possible that Taiwan’s rabies virus is an independent lineage, Tsai said.
As to the question how long the rabies virus has been in Taiwan, Tsai said with the data so far at hand the answer is not clear.
“The difference might also be a result of the fact that the three local groups have different virus sources or became infected at different points in time,” Tsai added.
When it was pointed out at the briefing that the nine rabies virus isolates were only partially sequenced, Tsai said there would hardly be any major difference to the final results when the complete genome sequence is done.
However, Wang Hurng-yi (王弘毅), an associate professor of clinical medicine at National Taiwan University, came to a different conclusion using the same partial data published by the council.
Wang said he conducted his own analysis with a different approach, with more species and regions included as factors.
At another press conference held by wildlife protection groups criticizing government’s prevention measures yesterday, Wang was cited as concluding that the Taiwanese strain is indeed an independent lineage, with the strains found in China’s ferret-badgers and dogs, and those found in dogs in the Philippines within its sister group.