Vaccines for malaria and other human protozoal diseases could benefit from animal research
The June article of the month from Parasitology is “Successful vaccines for naturally occurring protozoal diseases of animals should guide human vaccine research. A review of protozoal vaccines and their designs.” Parasitology 141: 624-640, an open access article by Milton McAllister. Dr McAllister, from the University of Adelaide, discusses here the implications of the research.
“Pathogenic protozoa are responsible for some of humankind’s most notorious diseases. Despite much research, there are still no vaccines for malaria, Chagas’ disease, African sleeping sickness, kala-azar, cryptosporidiosis, giardiasis, or any other protozoal disease of humans. The prevailing explanation is that, because of the complexity of these pathogens, malaria and other protozoal diseases require novel strategies that move beyond the old concepts of attenuated or killed organism vaccines. But this explanation is not consistent with evidence in veterinary medicine.
A recent review article, published in Parasitology, highlights the magnitude of discordance between veterinary and human vaccines for protozoal diseases. Indeed, there are effective vaccines for many protozoal diseases of livestock, including several types of vector-borne haemoparasites of cattle and sheep that resemble malaria. These vaccines universally depend upon cultivation of organisms instead of more technologically advanced research methods such as transfection vectors, recombinant proteins, or DNA. This observation should influence future malaria research to seek improved methods for organism cultivation and attenuation. Other approaches for vaccine development remain legitimate goals but continue to face a high risk of failure.
A second issue has contributed to the persisting emphasis upon novel malaria vaccine designs. Artificially-adapted animal models of malaria behave in a “winner-takes-all” manner that does not closely resemble naturally evolved malaria relationships. In these artificial host-parasite relationships, relatively minor treatments may cause a radical shift between the only two major outcomes – death or complete recovery with sterile immunity. Many researchers have received false hope when experimental vaccines have protected lab animals against highly lethal challenges.
A third issue has been the worry that live protozoal vaccines for people carry unacceptable risks, whilst development of veterinary vaccines has benefitted from greater risk tolerance. The author suggests that new emphasis should be placed upon the development of novel methods to improve the safety of live malaria vaccines, which can reasonably be expected to be effective.
Science has not yet created a highly effective recombinant antigen or DNA vaccine for any protozoal disease, so it is premature to expect these approaches to work well for human malaria. Human health could reap long-term benefits from embracing a One Health approach to research funding. Many protozoal diseases of animals would be appropriate for investigation of highly novel and potentially transformative vaccine designs, including bovine babesiosis, toxoplasmosis in rodents and livestock, and avian malaria, to name a few. Novel vaccines that are effective against natural host-parasite relationships should have high predictive value and excellent potential for translation into similar vaccines for people.”
Read the full article here
In this video Professor McAllister talks more about his research in this area.
Read the press release from The University of Adelaide here