Perhaps we won't have to rely on this cheesy evolutionary fix much longer though, as there is great news on the fight against malaria. A new study of an experimental vaccine has shown that it reduces incidence of malaria in children by about 55% [STORY]. This is the first vaccine to be used against a eukaryotic parasite. In general, fighting eukaryotic diseases can be tricky. For example, it is often easier to clear a bacterial infection than a fungal infection. Why? Evolutionary principles! Eukaryotes are more closely related to us, so they share more of our molecular machinery. Consequently, it's easy to kill a fungus, but it may be hard to kill a fungus without killing us in the process.
The way the vaccine was made also seems pretty slick, a quote from the science article:
It contains an engineered protein that combines a protein fragment from the malaria parasite, Plasmodium falciparum, and a protein from the Hepatitis B virus that helps trigger a strong immune response.Even though 55% reduction isn't great by vaccine standards against bacteria and viruses, this is a spectacular development which could save many, many lives around the world.
Could the parasite evolve resistance to the vaccine? It's certainly seems possible. I don't know what the protein they used does in a normal parasite, or how conserved or variable it is in natural populations. Normally, vaccines that are highly effective knock down the population so low so that there is little to no genetic variation for the disease-causing agent, and no possibility for evolution of resistance. But this works mostly for diseases that are restricted to humans. For example, vaccines against polio are effective for this reason. However, since this vaccine only protects part of the population, and the fact that malaria infects many, many species of vertebrates, means that such an effort is unlikely to happen, and we will probably never get rid of malaria completely. However, there is a silver lining to this. I would venture to guess that humans make up only a very small portion of the hosts used by most of the world's malaria parasites. Because of this, losing us as a host probably doesn't affect fitness that much, and wouldn't be that much of a selection pressure to the parasite itself. Consequently, it might be possible that resistance wouldn't evolve so easily. I suppose even if the disease did mutate and develop resistance, we could do something like what we do for the flu virus and produce a new vaccine every year for the most common strain. This is all speculation on my part based on some pretty cursory examination of the latest news. I'm sure my friends who know more about disease ecology could talk more cogently on this!