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Why should we care if parasites go extinct?

By Elizabeth Rayne
Brugia Malayi

“You have worms.” Hearing that diagnosis is really all it takes to break out into a bloodcurdling scream, so why should we try to save parasites that invade primates like us?

Anything that feeds off your flesh or sucks your blood is instant nightmare fuel. Nobody wants to be a walking horror movie with something wriggling under their skin or gnawing at their intestines, but if endangered primates go extinct, so will their parasites. Isn’t that supposed to be a positive? Not necessarily. Not all parasites are pathogenic, and some could possibly influence medical advancements—before they vanish forever.

Researcher James Herrera is a scientist on an unlikely mission. As the program coordinator of Duke University’s Duke Lemur Center SAVA Conservation program, and based in Madagascar, which is known for its bizarre primates, he led a study about the potential effects of primate parasite extinction. It was recently published in Philosophical Transactions B.

“It might be hard to imagine, but some parasites play important roles for the regulation of host populations, akin to predators,” he told SYFY WIRE. “In that sense, they are important to stabilize populations to prevent them from exceeding the environmental carrying capacity.”

Without predators, entire ecosystems would be thrown off. Think of what happened with cane toads in Australia. They were an invasive species to begin with, brought in as what turned out to be an unsuccessful attempt at controlling cane beetles. Nothing eats them because they are too toxic. Because these toads have poison and no predators, the population has exploded, and they threaten some of the country’s endemic species. Similar things could happen to an ecosystem without parasites to keep non-endangered primate populations from blowing up.

Herrera thinks that up to 95 percent of primate parasites might have not even been discovered yet. There is another reason to keep finding them. You wouldn’t expect such maligned creatures as parasitic worms that live in the gut to prevent infections rather than create them, but before you start writhing in disgust, such species, like hemlinth worms, exist. Hemlinths can also help with autoimmune disorders. They have actually been introduced to humans with successful results, and unlike some pathogenic worms, they will not chew your guts from the inside out.

“Some parasites may indeed be going extinct before their hosts,” Herrera said. “It turns out that threatened hosts have fewer parasites than nonthreatened hosts. Some parasites that were specialized may already be gone.”

If the host species of a specialist parasite is so endangered that there aren’t too many of them to go around, that kind of fragmented population is not conducive to spreading parasites. What can happen then is that generalist parasites take over what was once the domain of those specialist parasites. That could threaten the population even more, especially if the habitat of that primate is disappearing. Endangered primates in habitats that are also degrading are the most prone to ending up with gastrointestinal infections from generalist parasites.

Parasite extinction would have an adverse effect on any ecosystem. This goes for both pathogenic and non-pathogenic types, however much some of us may want the pathogenic ones gone. There would be negative effects on biodiversity as the number of species dwindled. Host populations could also overrun an area just like cane toads, and with too many individuals and too little food to support them all, the population would cave in on itself. It is possible that endangered primates would see a benefit from fewer infections, but that is questionable.

“In theory, if threatened hosts lost their parasites which regulate populations, we might see an increase in their numbers,” said Herrera. “But then we don't know if the habitats can support more animals, again because so many are degraded habitats.”

Even pathogenic species of parasites can be beneficial for medical purposes. Whipworm* and tapeworm might make anyone cringe, but whipworm can be therapeutic for Crohn’s disease and tapeworm can alleviate symptoms of multiple sclerosis. Both of these are hemlinth worms and both disorders are autoimmune. Imagine what else might be lost if we allow parasites to go extinct. Could parasites with an extinct host possible adapt to a new one, like viruses? Viruses do have an advantage because they mutate faster, but Herrera thinks they might.

“If a new variant has a mutation that allows them to invade a new, more abundant host, that mutation would be enormously advantageous and would likely lead to fast evolution,” he said.

Human parasites don’t need to be kept alive if they are sucking the life out of you. If you suspect something you ate gave you food poisoning, get yourself to a doctor before you get eaten.

*Your friendly neighborhood author had whipworm once, and can confirm it is one of the grossest things in the known universe.

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