Ticks: what are they for? What is their role in the ecosystem?

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In ecology, an ecosystem is formed by a community of living beings interacting with the environment, the components of which form a dense network of dependencies, exchanges of energy and information that allows life to be maintained and developed. True carriers of pathogens for humans, ticks are difficult to imagine useful in nature. However, parasites play an important role in the regulation of the living world.

Ixodida (or mites colloquially) is an order of spider mites with 896 classified species, 41 of which are found in France. The largest of the ticks, the tick, has an oval body and a snout that allows it to cling to its host. Indeed, it is a hematophagous parasite that feeds on the blood of another organism in order to survive, and can transmit diseases to it.

During its life (up to 3-4 years), the tick takes only three meals, each time lasting several days. Each meal symbolizes a new stage in her life: the transition of the larva-nymph, the transition of the nymph-adult, reproduction and laying eggs. From the first meal, a tick can infect itself with a bacterium, parasite, or pathogenic virus present in the host it feeds on. It can then be infected throughout its life and transmit the pathogen at the next meal through saliva.

Thus, about half of these ticks are carriers of one or more pathogens. As accidental hosts, humans can be infected with ticks, the most well-known pathologies in Europe being Lyme disease and tick-borne encephalitis.

Annual cycle of ticks. © INRAE

Soon tick saliva in our medicines?

Even if a tick is not a priori man’s best friend, fifteen years of research highlights the pharmacological interest of its saliva. Admittedly, the latter contains a wide range of physiologically active molecules that are critical for host attachment or pathogen transmission, but it will also be rich in anticoagulant and anti-inflammatory molecules. Thus, the protein found in tick saliva can prevent blood clots and prevent stroke or even pulmonary embolism.

More recently, researchers have synthesized proteins from tick saliva to further study its beneficial properties. In some cases, it is helpful to know that the inflammatory response caused by an attack on the body can also get carried away and get out of control. “A hallmark of many inflammatory diseases is the overexpression of chemokines, leading to an inadequate recruitment of white blood cells,” the researchers wrote in their study. “Therefore, inhibition of chemokines is recognized as an interesting strategy for the development of anti-inflammatory agents.”

However, it appears that hematophagous mites produce sulfated proteins in their saliva called evasins that can inhibit the host’s inflammatory response by binding to its chemokines. Thus, tick saliva proteins have interesting anti-inflammatory properties, for example, against pulmonary fibrosis, intestinal inflammation, and also against complications of COVID-19. What about tick saliva as an anti-inflammatory agent?

Ticks help control wildlife demographics

Although they have been around for 140 million years, the role of mites in the ecosystem has not yet been clearly defined. However, it is reliably known that these mites are not only pests, but also a source of food for other animals. Many species of reptiles, birds and amphibians feed on them, especially when they are full of blood.

The absence of mites would certainly cause an imbalance in our ecosystem (as in any living creature), and some scientists even use these hematophagous as an indicator of the stability of the ecosystem! Indeed, ticks help control wild animal populations. Biologist Claude Combs, who specializes in parasitism research, gives Liberation an example: “An antelope in the savannah carries between 5,000 and 10,000 ticks. She spends 30% of her time grooming, that is, controlling tick demographics. What happens if we rid all the antelopes of their ticks? They will have an immediate advantage: they will spend more time eating, they will grow and reproduce more. The lions would be happy… They would have more food and multiply more, especially since the larger antelopes would run slower. Who will benefit from the death of ticks? Lions? To the antelopes? What is certain is that the balance between prey and predators will change.”

Parasitism is of interest to the ecosystem

Thus, the mite is beneficial to certain animal species and is also, more broadly, a parasite. The authors explain that if the species affected by parasitism is a predator, then in some cases we can observe a population explosion of prey normally regulated by this predator. Thus, more prey can disrupt the ecosystem and have a negative impact on biodiversity.

“A prime example of this phenomenon is the epizootic of sarcoptic mange (a skin infection caused by the mite Sarcoptes scabiei) that has decimated fox populations in Scandinavia,” they write. “As a result of the decline in the populations of these predators, the populations of prey (rodents) that these foxes used to consume have been greatly reduced.”

According to another example, the myxomatosis virus in the UK caused a rapid decline in rabbit populations, which caused a modification of the vegetation, and then the invertebrates and vertebrates of the respective biotopes. Also in the UK, grafiose, which attacks elms and acts through a fungus carried by insects, has destroyed many trees. Although the habitat of many birds has been destroyed, the abundance of dead trees has allowed for large numbers of beetle larvae to be used as resources by other bird species.

A group of Japanese researchers also showed that trout use nematomorphic worms to feed themselves more. In fact, the worms push their hosts (grasshoppers, crickets, locusts, etc.) to jump into the water, thus getting into the trout’s mouth. “Save the pests,” says an article in The Atlantic, which also reported that “when wolves were stripped of butterflies and reintroduced to Yellowstone Park, they became more vulnerable to viruses.”

Thus, mites and, more broadly, parasites participate in natural selection, playing a role in the evolution of the living world. The recent explosion in their population and associated diseases is certainly the result of imbalances in ecosystems caused by human activities.

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