New nasal vaccine blocks parasite transmission to mosquitoes

Malaria is one of the most significant infectious diseases affecting developing countries and is often prominent in children. Mortality and morbidity levels are high and although antimalarial drug chemotherapy and insecticide-treated bed nets have somewhat reduced the number of malaria infections, additional prevention and treatment methods such as vaccines are needed for local elimination and ultimately complete eradication. Prior studies show that the ookinete-to-oocyst phase in the malaria life cycle, when the malarial parasite is fertilized in the mosquito's body, is one of the most vulnerable stages making it an ideal target for anti-transmission vaccines.

In the study, researchers developed a nasal vaccine based on ookinete-surface proteins (OSPs or also known as parasite antigens) and intranasally vaccinated mice infected with malaria. When given in conjunction with the cholera toxin adjuvant vaccinated mice developed a robust antibody response and completely prevented transmission of the parasite to mosquitoes that were allowed to feed on them after infection.

"To our knowledge, this is the first time that mucosal vaccination has been demonstrated to be efficacious for directly preventing parasite transmission from vaccinated animals to mosquitoes, and the results may provide important insight into rational design of non-parenteral vaccines for use against human malaria," say the researchers.

(T. Arakawa, M. Tachibana, T. Miyata, T. Harakuni, H. Kohama, Y. Matsumoto, N. Tsuji, H. Hisaeda, A. Stowers, M. Torii, T. Tsuboi. 2009. Malaria ookinete surface protein-based vaccination via the intranasal route completely blocks parasite transmission in both passive and active vaccination regimens in a rodent model of malaria infection. Infection and Immunity, 77. 12: 5496-5500.)