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Tips from the Journals of the American Society for Microbiology

American Society for Microbiology

Combined Immunization Methods May Offer Long-Term Protection Against H. pylori Infection

New immunization methods offer long-term protection against H. pylori in humans and may contribute to a possible ulcer vaccine in the future say researchers from the University of California, Davis. They report their findings in the July 2007 journal Infection and Immunity.

Helicobacter pylori is a bacterium that colonizes the digestive tract of 50% of the world's population. Infection commonly occurs in early childhood and can lead to chronic gastritis, peptic ulcer disease and gastric cancer throughout the life of its host. Antibiotics are currently used against H. pylori infection, however increasing resistance as well as high treatment costs and recurrence of infection emphasize the need for an effective, long-lasting vaccine.

In the study mice were immunized in four groups: orally alone, intramuscularly alone, orally followed by intramuscularly, and intramuscularly followed by orally and then challenged orally with H. pylori after three months. Results showed that mice receiving intramuscular immunization alone or a combination of oral and intramuscular vaccinations had significantly reduced bacterial loads and no detectible H. pylori in the intestinal tract. Mice immunized orally alone or intramuscularly followed by orally were not protected and had decreased antibody responses.

"This study demonstrates the ability to induce long-term immunity against H. pylori, provides correlates of protection, and illustrates the crucial role of the immunization route(s)," say the researchers.

(J.M. Taylor, M.E. Ziman, J. Fong, J.V. Solnick, M. Vajdy. 2007. Possible correlates of long-term protection against Helicobacter pylori following systemic or combinations of mucosal and systemic immunizations. Infection and Immunity, 75. 7: 3462-3469).

New Ferret Model May Measure Pandemic Potential of H5N1 Influenza Viruses in Humans

Researchers from the U.S. and abroad used a contact ferret model to evaluate transmissibility of influenza viruses in humans and found that some strains currently circulating throughout the world may transmit better than others in mammals. The researchers report their findings in the July 2007 issue of the Journal of Virology.

Transmission of H5N1 influenza viruses is of great concern worldwide as their geographic and host ranges continue to expand. Currently transmission to humans has been inefficient. Although there is limited knowledge of potential routes and determinants required for transmission, researchers predict genetic reassortment and mutation during adaptation in the host to be the two most likely avenues.

In the study experimental groups consisting of one inoculated ferret and two contact ferrets were used to monitor the transmissibility of four human H5N1 viruses isolates collected in Hong Kong (A/Hong Kong/213/03), Vietnam (A/Vietnam/1203/04 and A/Vietnam/JP36-2/05) and Turkey (A/Turkey/65-596/06) between 2003 and 2006. The selected isolates differed in their pathogenicity and affinity for "avian-like" and "human-like" receptors. Results showed that one contact ferret developed neutralizing antibodies to A/Hong Kong/213/03 but did not exhibit clinical signs or virus shedding. In two of the groups two contact ferrets had detectable virus following 6 to 8 days exposure with the A/Vietnam/JP36-2/05 virus-inoculated ferrets. Infected contact ferrets displayed severe clinical signs despite little or no virus detection in nasal washes. The absence of secondary transmission among ferrets housed together was attributed to minimal virus shedding. The effect of viral pathogenicity and receptor binding specificity on transmissibility showed that both Vietnam "avian-like" viruses caused neurological symptoms and death in ferrets while the Hong Kong and Turkey "human-like" viruses caused only mild non-lethal symptoms.

"Here we demonstrated a useful animal model system to evaluate the transmissibility of H5N1 viruses," say the researchers. "We propose that future selection of H5N1 vaccine candidates among new antigenic variants should take into account the transmissibility of the virus."

(H.L. Yen, A.S. Lipatov, N.A. Ilyushina, E.A. Govorkova, J. Franks, N. Yilmaz, A. Douglas, A. Hay, S. Krauss, J.E. Rehg, E. Hoffmann, R.G. Webster. 2007. Inefficient transmission of H5N1 influenza viruses in a ferret contact model. Journal of Virology, 81. 13: 6890-6898).

Defense Mechanism Found in Infected Ticks May Protect Against Harmful Parasite

A defense molecule isolated in ticks infected with the Babesia sp. parasite may protect animals and humans against infection. Researchers from the U.S. and abroad report their findings in the July 2007 issue of the journal Infection and Immunity.

Babesiosis is a well-recognized disease worldwide and recently gained increased attention as an emerging zoonosis. Transmitted to animals and humans by ticks infected with the Bebesia sp. parasite, symptoms may include fever, fatigue and hemolytic anemia. Antimcrobial peptides are defensive molecules found in the innate immune system of animals. Less toxic and more effective against multi-drug resistant bacteria, they are showing promise as a better choice for treatment of some bacterial and fungal infectious diseases.

In the study researchers identified a novel parasiticidal peptide named longicin from the tick species Haemaphysalis longicornis and tested its ability to inhibit infection. It showed a remarkable ability to inhibit the blood stage of equine Babesia equi by killing the parasites and resulted in reduction of parasitemia in animals with the zoonotic and murine Babesia microti. RNA analysis also demonstrated that longicin is capable of killing the canine strain, Babesia gibsoni.

"Here we report a defensin peptide, longicin, from the tick H. longicornis that exerts a babesiacidal effect," say the researchers. "Theoretically, longicin may serve as a model for the development of chemotherapeutic compounds against tick-borne disease organisms."

(N. Tsuji, B. Battsetseg, D. Boldbaatar, T. Miyoshi, X. Xuan, J.H. Oliver, Jr., K. Fujisaki. 2007. Babesial vector tick defensin against Babesia sp. Parasites. Infection and Immunity, 75. 7: 3633-3640).


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