Avian influenza virus, Streptococcus suis serotype 2, severe acute respiratory syndrome-coronavirus and beyond: molecular epidemiology, ecology and the situation in China

Abstract

The outbreak and spread of severe acute respiratory syndrome-associated coronavirus and the subsequent identification of its animal origin study have heightened the world's awareness of animal-borne or zoonotic pathogens. In addition to SARS, the highly pathogenic avian influenza virus (AIV), H5N1, and the lower pathogenicity H9N2 AIV have expanded their host ranges to infect human beings and other mammalian species as well as birds. Even the 'well-known' reservoir animals for influenza virus, migratory birds, became victims of the highly pathogenic H5N1 virus. Not only the viruses, but bacteria can also expand their host range: a new disease, streptococcal toxic shock syndrome, caused by human Streptococcus suis serotype 2 infection, has been observed in China with 52 human fatalities in two separate outbreaks (1998 and 2005, respectively). Additionally, enterohaemorrhagic Escherichia coli O157:H7 infection has increased worldwide with severe disease. Several outbreaks and sporadic isolations of this pathogen in China have made it an important target for disease control. A new highly pathogenic variant of porcine reproductive and respiratory syndrome virus (PRRSV) has been isolated in both China and Vietnam recently; although PRRSV is not a zoonotic human pathogen, its severe outbreaks have implications for food safety. All of these pathogens occur in Southeast Asia, including China, with severe consequences; therefore, we discuss the issues in this article by addressing the situation of the zoonotic threat in China.

Figure 1.

Phylogenetics of the H5N1 HA of the currently circulating strains. The representative viruses' HA sequences were downloaded from NCBI influenza virus resource (Bao et al. 2008). The classification is according to WHO's definition and human-infected viruses are labelled in red.

Figure 2.

Adapted from Wang et al. with permission. The potential routes of migratory birds from 2005 to 2006 and the occurrence of H5N1 are shown. Three flyways are shaded in green, blue and pink. The red and blue dots illustrate the H5N1 occurrence. The arrows in red, green and purple denote the directions of the migratory birds. The coloured shadows are the ranges of different flyways. The grey arrow in Europe represents the cold weather. The cartoon birds highlight the congregation area of the wild birds from three different flyways.

Figure 3.

Phylogenetics of H9N2 HA. The tree was rooted with A/turkey/Wisconsin/66 (H9N2). The human strains are in red, and those strains mentioned in the text are in blue.

Figure 4.

Map of China with EHEC outbreaks and isolations from animals. Stars represent the large-scale outbreak in 1999 in Eastern provinces, Anhui and Jiangsu. Triangles represent human infections. Diamonds represent animal isolation.

Figure 5.

Phylogenetics based on PRRSV whole-genome alignment. All Chinese strains belong to Type II (North American Type). Strains circulated in China before 2006 (blue), in 2006 (green), and in 2007 (red) and in Vietnam in 2007 (pink) are shown.