Tips from the journals of the American Society for Microbiology

Scientists are looking at a novel strategy to prevent the spread of pandemic avian influenza. They have developed a vaccine that protects ducks, a known natural reservoir for the virus. They report their findings in the November 2008 issue of the Journal of Virology

Waterfowl are considered to be the natural reservoir of influenza A viruses due to the isolation of all subtypes from these hosts. Current research indicates that influenza A viruses are continuously evolving within their natural environment and can be transmitted to a variety of animals, including humans. H5N1 avian influenza A viruses are now endemic in domestic poultry in many Asian countries and ducks are believed to be the primary source of infection. Reducing the spread of H5N1 in ducks could play a key role in minimizing the risk of a pandemic outbreak.

In the study researchers first identified dominant pathogenic strains of H5N1 influenza A viruses circulating in Asian poultry and found that four caused symptomatic illness in domestic ducks, but not all were lethal. In addition the researchers reversed the genetics of the viruses in domestic ducks to develop three different inactivated oil emulsion whole-virus H5 influenza vaccines. Following one round of inoculation with the vaccines ducks were completely protected when challenged with a lethal dose of the H5N1 virus.

"The vaccines provided complete protection against the lethal challenge of the homologous and heterologous H5N1 avian influenza A virus with no evidence of morbidity, mortality, or shedding of the challenge virus," say the researchers. "The complete protection offered by these vaccines will be useful for reducing the shedding of H5N1 avian influenza A viruses among vaccinated agricultural avian populations."

(J.K. Kim, P. Seiler, H.L. Forrest, A.M. Khalenkov, J. Franks, M. Kumar, W.B. Karesh, M. Gilbert, R. Sodnomdarjaa, B. Douangngeun, E.A. Govorkova, R.G. Webster. 2008. Pathogenicity and vaccine efficacy of different clades of Asian H5N1 avian influenza A viruses in domestic ducks. Journal of Virology, 82. 22: 11374-11382.)

A new study suggests that darkling beetles and their larvae can transmit harmful food-borne pathogens to chicks in broiler houses in successive rearing cycles. The researchers from Wageningen University, Wageningen, The Netherlands and Research Centre, Lelystad, The Netherlands report their findings in the November 2008 issue of the journal Applied and Environmental Microbiology.

Salmonella and Campylobacter are two main sources of human food-borne disease and many of the reported cases can be directly linked to the handling or consumption of contaminated chicken meat. Although exact contamination routes of broiler flocks are not fully understood, certain insects that are persistent in these environments are common reservoirs of zoonotic bacteria such as Salmonella and Campylobacter.

The darkling beetle (Alphitobius diaperinus) and its larvae are known to inhabit broiler houses and are believed to survive between rearing cycles by eating their way into insulation materials and hiding under floors. In the study researchers artificially contaminated several groups of beetles and their larvae with a mixture of Salmonella enterica Serovar Paratyphi B Variant Java and three Campylobacter jejuni strains and fed them to housed chicks either the day of inoculation or one week following to mimic an empty week between rearing cycles. All the broiler chicks that were fed insects contaminated on the same day showed Campylobacter and Salmonella colonization levels of 50 to 100%. Insects that were fed a week after infection resulted in transfer of both pathogens as well, but at lower levels. Naturally infected insects collected at a commercial broiler farm and fed to chicks also resulted in colonization but at lower levels.

"In conclusion, the fact that Salmonella and Campylobacter can be transmitted via beetles and their larvae to flocks in successive rearing cycles indicates that there should be intensive control programs for exclusion of these insects from broiler homes," say the researchers.

(W.C. Hazeleger, N.M. Bolder, R.R. Beumer, W.F. Jacobs-Reitsma. 2008. Darkling beetles (Alphitobius diapernus) and their larvae as potential vectors for the transfer of Campylobacter jejuni and Salmonella enterica Serovar Paratyphi B Variant Java between successive broiler flocks. Applied and Environmental Microbiology, 74. 22: 6887-6891.)

A new study shows that the current tuberculosis vaccine induces protective immunity against nine strains of the bacteria in mice indicating that strain-specific resistance may be uncommon. The researchers report their findings in the November 2008 issue of the journal Infection and Immunity.

Tuberculosis (TB) is one of the world's most challenging infectious diseases to date and is responsible for approximately 2 million deaths per year. An attenuated vaccine incorporating Mycobacterium bovis BCG has been used for over 50 years, however, high mortality rates have persisted and researchers attribute multiple factors to its varying effectiveness including that the anti-TB protective immunity induced by the vaccine may be strain-specific.

W-Beijing lineage strains are among the most prominent associated with worldwide outbreaks of TB. In the study researchers investigated the strain specificity of Mycobacterium bovis BCG vaccine-induced antituberculosis protective immunity responses by inoculating mice with the vaccine and challenging them 2 months later with one of nine Mycobacterium tuberculosis strains, four from the W-Beijing lineage, four non-Beijing isolates, and one control. Organ bacterial burdens and lung pathology were examined in vaccinated and naïve mice the day of infection as well as at 4, 12, and 20 weeks postchallenge. Four weeks following an aerosol challenge with each of the strains, results showed the bacterial growth in the lungs and spleens were much lower and lung pathology significantly improved in all vaccinated animals when compared to controls. Animals infected with six of the nine strains exhibited reduced organ bacterial burdens after 12 weeks and lung inflammation in all immunized animals was measurably lower at 20 weeks postchallenge.

"These data demonstrate that BCG vaccination protects against infection with diverse M. tuberculosis strains in the mouse model of pulmonary tuberculosis and suggest that strain-specific resistance to BCG-induced protective immunity may be uncommon," say the researchers.

(B.Y. Joen, S.C. Derrick, J. Lim, K. Kolibab, V. Dheenadhayalan, A.L. Yang, B. Kreiswirth, S.L. Morris. 2008. Mycobacterium bovis BCG immunization induces protective immunity against nine different Mycobacterium tuberculosis strains in mice. Infection and Immunity, 76. 11: 5173-5180.)