On December 29, 2011, a man infected with a subclade of the H5N1 virus was confirmed in Shenzhen, China. The clinical symptoms and
immune factors of the patient were investigated and the phylogenetic and molecular characteristics of the virus were analyzed. High
fever, rapid development of serious
pneumonia and multi-organ failure were the main clinical symptoms. Arterial blood gas analysis showed that PaCO2 rose sharply and PO2 decreased. Leukocyte and platelet counts decreased rapidly. Peripheral blood lymphocyte counts indicated
lymphopenia and inverted ratios of CD4(+) to CD8(+) cells.
Cytokine analysis showed that the levels of serum
IL-6,
IL-10, and IFN-r continued to increase, whereas the levels of
IL-12 and TNFs decreased during the
clinical course. MCP-1 and IP-10 remained at a high level after
infection. Phylogenetic analysis confirmed that the virus A/Shenzhen/1/2011 belongs to the new subclade 2.3.2.1. An Arg (R) insertion at P6 and an RP8I substitution in the HA cleavage site motif were detected in the virus. Compared to the
vaccine strain, 16 specific substitutions occurred in the HA1
protein. Some of them were located on the receptor-binding site, glycosylation site and the region of the
antigenic determinant. In summary, serious complications and
immune system disorders were the main features of the
infection with H5N1. Gene variation did not weaken the highly pathogenic features of viruses and the pathogenicity and antigenicity of the new subclade virus were changed.