No wildlife charity campaigns to save parasites. But they should

We tend to think of parasites as harmful, itchy, nasty, creepy crawlies. But these strange, beautiful creatures have many uses – and they need our help

Until very recently, the skies of North America played host to one of the largest birds on earth: the Californian condor (Gymnogyps californianus). Weighing in at 12 kg with a wingspan of three metres, these remarkable birds were almost lost to us until efforts were made in 1987 to round up the last remaining 27 individuals of the species for captive breeding efforts at San Diego Zoo.

However, these birds were not alone. Nestled amongst their feathers was another species on the brink of extinction: the Californian condor louse (Colpocephalum californici). Regrettably, within weeks of entering San Diego Zoo for conservation efforts, a species went extinct. When an animal is taken into captivity to prevent its extinction zookeepers are quick to treat each individual with anti-parasitic drugs. The condor louse became a victim of this all too common practice.

Today we stand at an ecological crossroad. The scientific community has established that we are in the throes of Earth’s 6th mass extinction event, this time caused by human activity. If we stand idly by, we will doom countless species to extinction. If we act now we may be able to halt this crisis and save many strange and beautiful species integral to the functioning of our ecosystems and our own survival. Organisations like the International Union for the Conservation of Nature (IUCN) and the World Wildlife Foundation (WWF) are strong advocates for the survival of our planet’s species, but if you look a little closer you will not see many invertebrates in the lists of animals they hope to save. You will certainly not see any parasites. The public is enraptured with big enigma animals like tigers and rhinoceros but care little for the more humble species: the plants, insects and parasites. These are the small things that run the world and it’s time we took notice of them.

When we hear the word “parasite” our minds quickly turn to the itchy image of head lice or the stomach-churning intestinal worm. We think of the diseases they cause and the incalculable damage they have wrought on humanity. So why save parasites at all?

Parasites are one of the most species-rich groups on Earth. When we speak of them we generally include the arthropods such as lice, fleas and tick; helminths such as tapeworms, roundworms and flatworms; and protozoa such as giardia. Parasites have been recorded from almost all animal species, and although parasitologists haven’t yet checked every species in detail, it’s common for many host species to have multiple parasites – many of which are species-specific and cannot be found on any other type of animal but their main host. They are diverse, strange and quite extraordinary and many are in need of conservation efforts owing to the fact that their main hosts are also often threatened with extinction, a status known as co-endangered.

An obvious argument for the conservation of any species is intrinsic value. This is the idea that a species should be allowed to exist for its own sake. Proponents of this view feel that a species should not have to benefit humanity in some to warrant its conservation or survival. While this argument is commonly made for much-loved icons of conservation like pandas and polar bears, it can equally be applied to parasites. Although perhaps less cuddly or cute, botflies, lice and tapeworms have a right to share this earth with us too, don’t they? However, most people outside the realm of bioethicists tucked away in dusty offices in the basements of universities would view this as a fairly weak argument. Many believe that species should provide some benefit, some incentive for us to protect and preserve them.

Perhaps a more practical reason to conserve parasites is their utility as conservation monitoring tools. As the number of individuals in the population of an endangered animal decline so too does the ease with which researchers can track individuals in the population and monitor it for disastrous events like inbreeding or sudden population declines. This is where parasites come in very handy. Researchers have previously used leeches to locate populations of rare mammals by looking at the DNA in the blood the leeches have ingested. Through this, researchers can identify the DNA signature of rare species which the leeches can locate but which the researchers cannot.

Parasites have also been used to track inbreeding and the loss of genetic diversity in their hosts’ populations. Populations of intestinal worms live within the guts of populations of larger animals such as tigers. If the tiger population declines and inbreeding increases, so too will inbreeding increase in their parasitic worms. Therefore, instead of having to track all the tigers in a population and take their DNA, researchers can compare the genetic variation by collecting tiger poo, extracting DNA from the worms within and using levels of inbreeding the worm population as a proxy for the tiger population.

The prevailing idea in biology regarding parasites is that they cause serious damage to their hosts. Scientific findings are beginning to challenge this long-held dogma, and we are beginning to realise that parasites may be more crucial to our health and the health of wildlife than we previously recognised. In humans, ideas like the hygiene hypothesis are beginning to gain traction in the scientific world. The hygiene hypothesis suggests that we need to encounter infectious organisms like intestinal worms in our younger years for our immune systems to learn the correct way of fighting infection so that it doesn’t overreact, as occurs in the case of allergy or autoimmune diseases. This may also be the case in wildlife, which like us may require parasites like lice and intestinal worms to help train their immune systems to better fight off disease. Although at first sight it may seem like a juxtaposition, the health benefits of parasites may be a great reason to warrant their conservation.

Ecological services are the roles certain species play within the ecosystem that allows it to function normally. It should be no surprise that parasites play a large role in ecosystems and that their loss could have catastrophic consequences and even lead to a tropic cascade where by an ecosystem collapses due to the loss of important species. There is evidence to suggest that parasites play a crucial role in controlling the distribution and population size of their hosts and in doing so prevent overgrazing by herbivores and overhunting by carnivores. If we are to maintain our fragile ecosystems we will need to consider the role parasites play in them and what may occur if we lose them from systems through extinction.

Perhaps the most attractive reason to protect and conserve parasites is their utility as reservoirs of new medicines. Bioprospecting is the increasingly popular practice of searching for new drugs and commercially valuable substances within the living world. Parasites are ideal candidates for bioprospecting research as they live so closely with other species that they have honed their ability to modulate their hosts over evolutionary time. For example, many intestinal worms can produce compounds which down-regulate parts of our immune system: essentially turning them down a bit. These compounds could be crucial for people suffering autoimmune diseases where the immune system is up-regulated and gets so “trigger happy” it attacks the body. Some parasites such as botflies produce painkillers so that their hosts do not notice them as they burrow beneath the skin. Those compounds could be used as local anaesthetics during surgery or other medical procedures. Some intestinal worms have also been shown to bioaccumulate heavy metals from their hosts. Understanding this process could lead to new treatments for heavy metal overdoses.

In short, parasites need us and it’s becoming increasingly clear that we need them a lot more than we realised. So perhaps it’s time for us to look beyond the fierce and fluffy conservation icons we cherish and instead embrace the creepy, strange and beautiful parasites that call our wild places home and so desperately need some public love.


Mackenzie Kwak

The GuardianTramp

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