Several versions of the rapidly evolving H7N9 bird flu virus are circulating within China, epidemiologists said Tuesday.

The novel influenza A virus, a combination of three similar viruses found in chickens, ducks, and wild birds, emerged in China in February and has sickened more than 100 people in China and Taiwan, killing at least 20. Among three early cases reported in Hangzhou, Zhejiang Province in China, two of the patients had contact with environmental sources — namely, live poultry markets.

Testing of chicken cages and feces from the market visited by one of the two patients were positive for the virus, indicating a direct connection between the poultry source and human infection, researchers reported Tuesday in the journal Science China: Life Sciences. Funded by China and Hangzhou Province, the researchers analyzed the DNA sequences from the viruses found in that province in addition to H7N9 viral sequences available in databases. The sequencing showed divergence between samples from one of the earlier patients and others from the province, suggesting that "several H7N9 viruses are circulating in Hangzhou," the authors wrote.

However, "it is uncertain whether the diversity of H7N9 in Hangzhou is the result of host adaptation, or predates the transmission to humans from an avian source."

Researchers said the origin and development of the novel flu virus remains unknown, though a study involving animal models yielded some insight into the disease's pathogenicity.

"A glutamine to isoleucine substitution was observed at position 226 of the hemagglutinin amino acid sequence in the newly sequenced virus," the authors wrote. "Isoleucine has similar characteristics to leucine, which was previously shown to be a pivotal amino acid in the binding of avian- or human-type receptor, and might be essential for pathogenicity in cases of airborne viral transmission. This substitution was observed for the first time at this site in H7N9, which may indicate a novel host adaptation feature of the H7 virus."

The study suggests the disease continues to mutate rapidly, and that researchers should further explore the significance of the receptor binding properties of Q226I protein sequence in the virus — as well as the significance of the substitutions, in both live organisms and laboratory sequencing.

World Health Organization Warns Of Bird Flu Epidemic, Tuesday

On Tuesday, Sri Lanka suspended meat imports from China and redoubled surveillance of wild birds migrating from that country, after the World Health Organization (WHO) warned of an epidemic.

Thousands of wid birds migrate to Sri Lank from China annually, according to Dr. W.K. de Silva, animal production and health department director with the Sri Lanka government. "We have doubled the number of samples that we collect from wild birds, particularly those that migrate to certain wetlands in Sri Lanka," he told media.

"We will intensify the checks until the WHO warning is lifted," he said.

Source: Li J, Yu X F, Pu X Y, et al. Environmental connections of novel avian-origin H7N9 influenza virus infection and virus adaptation to the human. Sci China Life Sci, 2013, 56(6), 485-492. doi: 10.1007/s11427-013-4491-3.