Yahoo! News: Stinky feet may lead to better malaria traps

volunteer in foilThis foil-wrapped person is making his contribution to malaria research by adding his sweaty aroma to the collection of mosquito bait that is particularly tantalizing to malaria-carrying mosquitos. Image: Sang Tan, Associated Press, news.yahoo.com

mosquitoThe malaria-carrying mosquito Anopheles gambiae is eager to get at the aroma emitted by stinky feet. Image: James Gathany/CDC through news.sciencemag.org

mosquitoThe Anopheles stephensi mosquito is the major vector transmitting malaria to humans in the Middle East and South Asia. Scientists have now successfully infected it with bacteria that drive the malarial parasites from it. Image: CDC through www.nature.com

WolbachiaWolbachia bacteria (green) have successfully infected the ovaries of the malaria-transmitting mosquito Anopheles stephensi. Image: Zhiyong Xi/Michigan State University through www.npr.org

Can bad-smelling feet, probiotics for mosquitoes, and evolutionary presuppositions solve the problem of malaria?

Malaria—one of the oldest and most devastating illnesses to plague mankind—kills over half a million people a year despite the best efforts of modern medicine. Ancient records in China and Egypt suggest malaria was known in the ancient world, and scholars suspect some diseases referenced in the Bible were malaria. Two hopeful avenues to address this scourge have appeared in the recent news, along with a potentially troubling bit of information regarding our supposed ape-cousins.

Malaria is caused by parasitic protozoans of the genus Plasmodium. During their complex life cycle these protozoans take at least seven different forms as they inhabit various parts of a host animal’s or human’s body and the body of their mosquito vector. Mosquitoes get infected when they bite infected hosts and then transmit the infection to other hosts.

Perhaps something as innocuous as smelly feet might help researchers bridge the gap to a better tomorrow for places where malaria is endemic. Researchers at the London School of Hygiene and Tropical Medicine have found that mosquitoes carrying malaria parasites are much more likely than uninfected ones to be attracted to smelly feet.

After wearing a nylon stocking for 20 hours, entomologist Renate Smallegange offered the smelly footwear to caged mosquitoes They all loved it, but the malaria-carrying ones were three times as eager to take a stab at the sock in a fruitless attempt to find some blood.

“Smelly feet have a use after all,” says Dr. James Logan, who headed the research project. “Every time we identify a new part of how the malaria mosquito interacts with us, we're one step closer to controlling it better.” In a related experiment, sweaty smells from foil-wrapped people were collected, providing another source of mosquito-appeal.

Human body odor consists of a variety of molecules, so scientists hope that in the future they can determine what the malarial mosquitoes like best. Some cheeses, for instance, smell like stinky feet, but mosquitoes aren’t fooled. “Mosquitoes aren't attracted to cheese because they've evolved to know the difference,” Logan said. “You have to get the mixture, ratios and concentrations of those chemicals exactly right otherwise the mosquito won't think it's a human.” Timing is also important. Mosquitoes aren’t lured by human smells until about two weeks after they are infected with Plasmodium, and it takes just that long for the malarial life cycle to progress to the point that the mosquitoes’ bites will be infectious. Of course, while processes like natural selection can be involved in fine-tuning such possible adaptations, mosquitoes have remained mosquitoes without actually evolving from or into any other kind of organism.

lifecycleThe complex life cycle of Plasmodium passes through multiple locations in the bodies of its human or animal host as well as the body of the mosquito vector that carries it. Image: National Institute of Allergy and Infectious Disease www.niaid.nih.gov

Logan’s group hopes to use their knowledge of mosquito preferences to build effective mosquito traps that target mosquitoes carrying malaria. Such an approach—targeting the infected insects rather than all mosquitoes—may avoid the problem of developing resistant populations. “The only way mosquitoes could [develop resistance] is if they were less attracted to human odors,” commented University of Pennsylvania entomologist Andrew Read. “And if they did that and started feeding on something else—like cows—that would be fine.”

Scientists do, however, have to be concerned about other hosts. There are about 250 species of Plasmodium, the malaria-causing protozoan, and they infect a variety of animals—harming some and coexisting peacefully with others. Four species currently infect humans, but some genetically similar species have been found in apes. One group of researchers has also just identified two species of malaria-friendly mosquitoes that bite both humans and animals.1 There is precedent for transmission between animals and humans, and Plasmodium has proven adept at switching hosts, with less virulent species transferring between humans and macaques (P. knowlesi) and humans and South American monkeys (P. vivax).2

Plasmodium falciparum is by far the most deadly species, being responsible for 91% of malarial deaths. Evolutionists believe that Plasmodium protozoans evolved over millions of years and thus must assume that these parasites coevolved with animals, eventually passing to humans. It is important, however, to distinguish between zoonosis—the observable process in which some pathogens pass between animals and humans—and unobservable claims of coevolution over millions of years.

The fact that animals can act as a reservoir for pathogens in the present world makes animal research a matter of practical medical urgency. Actually, evolutionary presumptions for a time led scientists to some wrong conclusions about the source of malaria in humans. Plasmodium reichenowi is genetically similar to P. falciparum, and in 2009 it was found in a chimpanzee. Believing that humans and chimps diverged from a common ancestor, evolutionary scientists presumed that the deadly P. falciparum diverged from the chimpanzee-affecting P. reichenowi when humans and chimps diverged from an ape-like ancestor. Subsequent research demonstrated that chimpanzees, even though evolutionary scientists believe they are our closest relatives, are not the source of human malaria.2

In 2010, research suggested that the gorilla could be a source of human infection. Gorillas were found to be infected by a form of Plasmodium not just similar but genetically indistinguishable from P. falciparum. This was a great surprise because P. falciparum was thought to be specific to humans.2 Since that time, P. falciparum and other species affecting humans have been found in a variety of apes. Did gorillas act as a reservoir from which humans “caught” the deadliest form of malaria? Scientists think this likely but are not sure at this point.2 The comparatively “small genetic diversity observed within the current human P. falciparum isolates (compared to the one observed in gorillas)”2 is more consistent with a scenario of gorilla-to-human transmission at some point in the recent past than with a tale of coevolution with diverging ape-like ancestors millions of years ago.3 The importance of this epidemiological question lies in the way Plasmodium is able to adapt itself to various hosts, leaving open the possibility that additional virulent varieties could emerge from an animal reservoir to further afflict humanity.

While researchers typically refer to the importance of tracing the evolutionary history of Plasmodium, we should note that they are tracking the path of varieties of Plasmodium, not seeing Plasmodium protozoans evolve from or into some other kind of microbe. Such a devastating pathogen also raises the question among some as to how Plasmodium could exist in the perfectly good world that God originally created.

We know from Exodus 20:11 and other verses that God completed His work of creation in six days. Therefore, Plasmodium and even mosquitoes must have been part of the original creation. God said that all He had made was very good, however, so Plasmodium and mosquitoes must have behaved very differently in that world unmarred by sin and death. Mosquitoes today pollinate goldenrod, grasses, and orchids.4 Only female mosquitoes consume blood today; male mosquitoes subsist on plant juices. A type of hemoglobin molecule is produced in leguminous plants today, suggesting a way that female mosquitoes’ nutritional needs could have originally been supplied by plants. Mosquitoes in the original creation were likely pollinators able to derive the nutrients needed to reproduce from plants without consuming blood.

But what about the malaria-causing parasite before “the Fall”? The apicoplast, an organelle inside Plasmodium, offers a clue to the original nature of Plasmodium. The apicoplast is similar to the chloroplast, an organelle in plants and algae that makes food through photosynthesis. The apicoplast cannot perform photosynthesis. It is quite possible that Plasmodium was originally an algae that through mutations lost its ability to manufacture its own food, becoming parasitic sometime after sin’s Curse entered the world. Many microbes in today’s world function symbiotically with other organisms large and small. Evidence suggests the original Plasmodium may have filled symbiotic niches in the original creation.4

Recent discoveries in the area of malaria control reveal that microbiological manipulation of infected mosquito populations may be effective even for the deadliest strains. This supports the view that in the original creation, as in today’s world, an organism and the microbes that live on it or in it form a microbiome to keep microbial populations in balance, direct the development of immune systems, and otherwise contribute to the complex interwoven relationships between organisms and “the chemically rich but inert physical environment.”5

Just as harmless bacteria colonize our bodies, so Wolbachia bacteria can live inside insects, including mosquitoes. These unusual bacteria can in some cases even be passed on to offspring and thus may, by promoting behavior that offers a selective advantage, contribute to speciation. Because Wolbachia renders the Aedes aegypti mosquito resistant to the dengue fever virus, scientists have already used this microbiological engineering to their advantage in Australia. After releasing Wolbachia-infected mosquitoes into the environment, “Over a very short period of time, the Wolbachia was able to invade the wild mosquito population until close to 100 percent of all mosquitoes had the Wolbachia infection—and so we presume, greatly reduced ability to transmit dengue between people,” explained Monash University professor Scott O’Neill.6

Wolbachia infection in Anopheles mosquitoes does seem to crowd out the Plasmodium protozoans. Efforts to get Wolbachia-infected Anopheles mosquitoes to pass on Wolbachia to their offspring are proving difficult. But after a decade of effort, microbiologists have finally managed to get infected Anopheles stephensi mosquitoes, the major malaria vector in South and West Asia, to lay infected eggs. Unfortunately, only about half hatch, but scientists are hopeful that they’ll find a solution so that the Wolbachia-infected Anopheles will be able to compete with wild populations.

“You could just release large number of infected females and establish Wolbachia in a mosquito population. Gradually it would convert a malaria-spreading population to a non-spreading one,” explains Johns Hopkins Malaria Institute’s George Dimopoulos. “The bacteria is very effective blocking the parasite in the mosquito. But this is sort of a prototype. The system needs to be optimized before it can be tested in the field.”6

Much research remains to be done as scientists try to learn how to eradicate the scourge of malaria, preferably without opening up an ecological niche for something worse. The answers will not come from evolutionary presumptions but from experimental science. Many changes have happened in the natural world since death and degeneration entered as a result of man’s rebellion against God, but nothing in science has ever demonstrated that upward evolution can occur. Read more about malaria and the design evident even in today’s degenerate forms of mosquitoes and malaria-causing parasites, as well as a detailed comparison of the evolutionary and creationist explanations of the origin of Plasmodium, in “The Genesis of Malaria.” (Thanks to Dr. Gillen for providing this excellent resource, which provided much background information for this article.)

And Don’t Miss . . .

  • Another week of non-evolution: we first learned of our non-ancestor, then how language didn’t develop, and then how sturgeons evolved into, well, sturgeons. Be sure to check back next week to see how mucus and viruses are good for you and to see some interesting ideas about how turtles got their shells. And who knows what else will be in the News?

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Footnotes

  1. www.sciencedaily.com/releases/2013/05/130503094708.htm Back
  2. www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1001283 Back (1) Back (2) Back (3) Back (4) Back (5)
  3. Authors reviewing the data on the origin of malaria, while trying to correlate it with the presumed milestones of hominid evolution in which they do have confidence, admit the limitations of molecular clock estimates. They write: “We advise readers to be cautious with time estimates and to give a second thought as to how these dates were obtained. In the absence of fossil calibration, one way to date the divergence between species is by using estimates of mutation rates. The principle is that the time separating two sequences from a common ancestor (T) is a simple function of the substitution rate (r, which is equal to the mutation rate for neutral sites) and the observed divergence between sequences (d): T=d/2r. However, it is not easy to get good estimates of mutation rates. Ideally, they should be obtained from all the genes under study and for each species in the phylogeny because substitution rates may vary from one gene to another as well as among species.” (www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1001) Even within the evolutionary model, they acknowledge the danger of drawing conclusions based on molecular clock estimates. The fact is, the dates assigned to the fossil record, the saga of molecules-to-man evolution in general, and the story of human evolution from ape-like ancestors in particular are equally built on unverifiable worldview based assumptions. Back
  4. The Genesis of Malaria Back (1) Back (2)
  5. The Organosubstrate of Life Back
  6. www.npr.org/blogs/health/2013/05/08/182339563/using-bacteria-to-swat-malaria-inside-mosquitoes Back (1) Back (2)