Abbreviations ACTH: adrenocorticotrophic hormone; AIHA: autoimmune haemolytic anaemia; APACHE II: acute physiology and chronic health evaluation II; APTT: activated partial thromboplastin time; ARDS: acute respiratory distress syndrome; CNS: central nervous system; DIC: disseminated intravascular coagulation; FiO 2 : fraction of inspired oxygen; HAART: highly active antiretroviral therapy; HHV-8: human herpes virus-8; HIV: human immunodeficiency virus; ICU: intensive care unit; MAP: mean arterial pressure; MCD: Multicentric Castleman's Disease; PT: prothrombin time; SAPS I: simplified acute physiology score I. Attenuated Salmonella choleraesuis-mediated RNAi targeted to conserved regions against foot-and-mouth disease virus in guinea pigs and swine In this study, specific sequences within three genes (3D, VP4 and 2B) of the foot-and-mouth disease virus (FMDV) genome were determined to be effective RNAi targets. These sequences are highly conserved among different serotype viruses based on sequence analysis. Small interfering RNA (siRNA)-expressing plasmids (p3D-NT19, p3D-NT56, pVP4-NT19, pVP4-NT65 and p2B-NT25) were constructed to express siRNA targeting 3D, VP4 and 2B, respectively. The antiviral potential of these siRNA for various FMDV isolates was investigated in baby hamster kidney (BHK-21) cells and suckling mice. The results show that these siRNA inhibited virus yield 10- to 300-fold for different FMDV isolates of serotype O and serotype Asia I at 48 h post infection in BHK-21 cells compared to control cells. In suckling mice, p3D-NT56 and p2B-NT25 delayed the death of mice. Twenty percent to 40% of the animals that received a single siRNA dose survived 5 days post infection with serotype O or serotype Asia I. We used an attenuated Salmonella choleraesuis (C500) vaccine strain, to carry the plasmid that expresses siRNA directed against the polymerase gene 3D (p3D-NT56) of FMDV. We used guinea pigs to evaluate the inhibitory effects of recombinant S. cho (p3D-NT56/S. cho) on FMDV infection. The results show that 80% of guinea pigs inoculated with 10(9) CFU of p3D-NT56/S. cho and challenged 36 h later with 50 ID(50) of homologous FMDV were protected. We also measured the antiviral activity of p3D-NT56/S. cho in swine. The results indicate that 100% of the animals treated with 5 × 10(9) CFU of p3D-NT56/S. cho were protected in 9 days. Short interfering RNA (siRNA) are small, double-stranded RNA molecules that direct the degradation of complementary messenger RNA via a cellular process known as RNA interference. It is widely believed that RNA interference is an evolutionarily conserved mechanism within eukaryotes and that its functions include endogenous gene regulation, viral defense and the maintenance of genomic stability [14] . Because of the rapidity and specificity of RNAi, this technology could complement and improve the traditional tools available to control important animal pathogens.