H5N1 influenza viruses in Lao People's Democratic Republic

A prospective surveillance program for influenza viruses was established in Lao People's Democratic Republic (PDR) in July of 2005. We report isolation of H5N1 virus genetically distinct from H5N1 circulating in 2004, which indicates reintroduction of H5N1 into Lao PDR after its disappearance (i.e., no virologic or serologic evidence) for 2 years.     

Immune response to influenza vaccination in community-dwelling Chinese elderly persons

We investigated the immune antibody response to influenza vaccine in community-dwelling Chinese elderly persons in Hong Kong. One hundred and twenty-eight subjects were recruited in a single-blind, randomized, and placebo-controlled trial. There was no significant baseline difference between the vaccine and placebo groups regarding the seroprotection rates (PR) (haemagglutination inhibition [HI] titre>or=1:40) and geometric mean titres (GMT) of the HI antibody titers. The PR, GMTs and serological response rates increased significantly in the vaccinated versus placebo groups in A-H1N1 at both weeks 4 and month 6. The GMTs and serological response rates but not the PR for A-H3N2 and influenza B increased significantly in vaccinated versus placebo group at week 4 and month 6 post-vaccination. Multivariate logistic regression analyses of the seroconversion rate for A-H3N2 within the vaccinated group showed that gender, coronary heart disease and the serum albumin level were significant predictors (p=0.018, 0.009 and 0.025, respectively). Influenza vaccination provoked a protective HI antibody response in community-living Chinese elderly persons. The mean number of unplanned hospital admissions per subject over 6 months was significantly lower in the vaccinated than in the placebo groups. Hospitalized elderly persons had poorer nutrition, 4-week post-immunization HI antibody titres and lower mini-mental state examination (MMSE) score than non-hospitalized elderly persons. Logistic regression analyses showed that chronic obstructive airway disease significantly increased the risk of hospitalization while the serum albumin level and 4-week A-H3N2 PR (HI>or=40) were independent predictors of a decreased risk of hospitalizations.     

The development and characterization of H5 influenza virus vaccines derived from a 2003 human isolate

The pandemic threat posed by highly pathogenic H5N1 influenza A viruses has created an urgent need for vaccines to protect against H5 virus infection. Because pathogenic viruses grow poorly in chicken eggs and their virulence poses a biohazard to vaccine producers, avirulent viruses produced by reverse genetics have become the preferred basis for vaccine production. Here, we investigated two key characteristics of potential H5 vaccine candidates: the hemaggutinin (HA) cleavage site sequence and its modification to attenuate virulence and the choice of background virus to provide a high-growth rate. We produced recombinant (6:2 reassortant) viruses that possessed a series of modified avirulent-type HA and neuraminidase genes, both of which were derived from an H5N1 human isolate. The other genes of these recombinant viruses were derived from donor virus strains known to grow well in eggs: the human strain A/Puerto Rico/8/34 (PR8) or an avian strain. All of the recombinant viruses grew well in eggs, were avirulent in chicks, and protected animals against infection with a wild-type virus. However, one of the recombinant viruses with an avian virus background acquired a mutation in the HA cleavage site sequence that conferred virulence potential to this virus. Moreover, vaccine candidates with the avian virus background were more virulent than those with the human virus background. We conclude that 6:2 recombinant viruses with a PR8 background are more suitable than those with an avian virus background for vaccine development and that the HA cleavage site sequence must be modified to minimize the potential for a vaccine virus to convert to a virulent form.     

The role of diffusion barriers in determining the excitability of peripheral nerve

The excitability changes occurring in normal isolated peripheral nerves of rats have been studied during exposure to hypoxic and anoxic conditions before and after the administration of insulin. The changes observed have been explained in terms of the dynamics of K' equilibrium in the periaxonal spaces, and attention is drawn to the importance of the relative impermeability of the periaxonal diffusion barrier in determining this equilibrium. Isolated peripheral nerves from alloxan-diabetic rats, studied under similar conditions, show significant differences in the sequence of their excitability changes. It has been shown that the rate of change of excitability in these nerves is slower than those of control nerves. These results have now been interpreted in terms of the K' changes in the periaxonal space. It is concluded that these slower excitability changes are due to an increase in the permeability of the diffusion barrier of the diabetic nerve to potassium.     

Looking for avian influenza in remote areas. A case study in Northern Vietnam

Epidemiological surveys of avian influenza infections rarely focus on backyard poultry systems in remote locations because areas with low levels of poultry production are considered to have little influence on the emergence, re-emergence, persistence or spread of avian influenza viruses. In addition, routine disease investigations in remote areas often are neglected due to the lower availability and relatively high cost of veterinary services there. A bank of avian sera collected in 2005 from ethnic minority households in Ha Giang province (Northern Vietnam), located on the Chinese border, was analysed to estimate the seroprevalence of avian influenza virus (AIV) during a H5N1 epidemic and to identify potential risk factors for infection. The results suggest that the chicken population had been exposed to AIV with a seroprevalence rate of 7.2% [1.45; 10.5]. The H5 and H9 subtypes were identified with a seroprevalence of 3.25% [2.39; 4.11] and 1.12% [0.61; 1.63], respectively. The number of inhabitants in a village and the distance to the main national road were the most influential risk factors of AIV infection, and high-risk clusters were located along the road leading to China. These two results suggest a virus spread through commercial poultry exchanges and a possible introduction of AIV from southern China. Remote areas and small-scale farms may play an under-estimated role in the spread and persistence of AIV.