Prof. Dr. Gela Preisfeld / Biology
Photo: Sebastian Jarych

The bloodsucker that can smell with its legs

Prof. Gela Preisfeld about the dangers of ticks for humans and their importance for the ecosystem.

They lurk in the grass, in bushes, in the forest and in the undergrowth. Motionless and for hours they wait for their host, on which they finally bite and often suck unnoticed for several days before they drop again or are removed by force. Ticks. Hardly any other animal species is associated with as much revulsion in our climes as these little bloodsuckers. Biologist Gela Preisfeld is familiar with the dangers of these small creepy-crawlies as well as their importance for the ecosystem and says: "They fulfill a function. If you removed all the parasites, the ecosystem would collapse."

Germany's most dangerous animal

Experts consider the tick to be Germany's most dangerous animal, because no other animal causes as many cases of disease in this country as the bloodsucker. There are several reasons for this, the professor explains, because the particularly nasty thing about these animals is that we often don't notice when they bite. "They start sucking blood without us being aware of it. That's how pathogens can get into our blood system." Two diseases known in the general population that ticks can cause are early summer meningoencephalitis, or TBE, and Lyme disease. Ticks can suck on a human or animal for several days, during which time they introduce pathogens into the host through their saliva. The sophistication with which they do this is remarkable to the biologist. "They scratch our skin with their jaw claws. Then blood leaks out because they destroy the small capillaries. Normally, our blood would then immediately clot and substances would be released that would then activate our immune system. But this does not happen because the substances in the saliva of the tick prevent this process and the wound cannot close. They have a kind of proboscis in which there is a groove. On this groove then the blood flows up to the mouth. And to make sure that they really stick to us, they have two options. Either they claw with their strong legs, or they stick. When a tick bites, infected ticks then transmit pathogens such as viruses or bacteria."

Ixodida - the largest mites

"Among ticks, there are several genera with different species," the scientist explains. They belong to the so-called pine weevils (Chelicerata), a group that is considered to be arachnids. Within this group, they belong to the mites that are more likely to be found in house dust or even naturally carried on the skin. Scientifically, they belong to an order called Ixodida. There are two major groups of ticks there, the leather ticks and the shield ticks. The ticks we're dealing with here primarily belong to the shield ticks."

The main representative, which we also find on our dogs and cats, is the common wood tick. But also some other species like the alluvial tick or the taiga tick move in our country, and the immigration of other species from more southern countries - as with other groups of animals and plants, we call such organisms neobiota - of course also takes place here.

Nose on the leg

Wherever there are plants, the pests can be. In many cases, they sit on blades of grass or low bushes. "When they are hungry, they lie in wait with their front legs stretched upwards," says Preisfeld, describing the 'hunting behavior'. "They do this because on their front legs are what are called Haller's organs. These are the 'noses', i.e. the sense of smell of the animals. There they wait until someone comes along who smells of butyric acid or ammonia compounds. They even perceiveCO2 emissions through their breath. They drop and immediately claw their way in, but then look for a suitable spot because they like dark, moist or hairy areas. Once they've found that, they start to bore in." Once fully engorged, ticks can go years without feeding. The life expectancy of the common wood tick in the wild is three to five years.

Ticks pass on pathogens

"Ticks themselves become infected by ingesting the blood of already infected small mammals," the biologist explains. "Often these are mice or rats, in which viruses or bacteria multiply very well." In the case of TBE, a virological disease, the first phase of the infection proceeds like a cold and that is also the problematic thing, she says, because we often don't even notice it. Most of the time, however, it's over. "In individual people, however, and we don't know what the cause of this is, there is a second phase. In this phase, the symptoms can be quite serious, up to and including respiratory paralysis. In 1% of sufferers, this ends fatally. The older you get, the greater the risk of contracting it seriously." However, not every tick is infected per se; experts assume that about 5% are infected. Even if NRW is not a TBE region, it is important to know that these carriers also exist here. "Lyme disease, on the other hand, is a bacterial infection, a bacterium that is closely related to the one that can also trigger syphilis. Borrelia affects different organ systems, so the symptomatology is not always clear. The skin in particular, joints, but also nerves and the brain, the so-called neuroborreliosis. Borrelia manage to cross the blood-brain barrier and cause bad sequelae." Lyme disease, whose symptoms can include fever, diarrhea, nausea, fatigue and a wandering redness, but unlike TBE, is easily treated with antibiotics. Not as common in our area is babesiosis, which can be transmitted by riparian ticks. "Babesiosis is more common in dogs, which is why it's also called canine malaria," the expert explains. Moreover, in the course of climate change, other ticks, such as the Hyalomma tick from Asia and Africa, which reaches Europe through migratory birds or timber transports, could also become more important. "Rising temperatures and falling humidity allow larvae to survive here with us," Preisfeld says. Meanwhile, ticks are also active in winter in some cases, he says, simply because the climate is becoming milder.

Remove in any case

If you discover a tick on yourself or your pet, you should remove it immediately. Whether with tweezers, a tick card or your fingers, the faster it is removed, the lower the risk of infection. However, there are many false legends about removing a tick. Preisfeld says: "When removing a tick, you should always grab it at the bottom so that you can get the head out, and then pull it straight out but don't twist it. Please do not use oil or even glue, this has the opposite effect, because then once again extremely saliva is secreted."

Place in the ecosystem

Despite the ticks is so unpopular, they still play an important role in the ecosystem. "They serve primarily as food for snails, nematodes, wasps, birds and also fungi. Of course, no one likes parasites. But like all organisms, they have their place in the ecosystem. They fulfill a function. And they mean us no harm. If they harm us, they are infected themselves. They do not want to weaken or kill their host, because they need it. It's not the tick that harms us, but the germs it carries."

While it's difficult for the layperson to take anything positive away from this species, Preisfeld points to another important regulatory function of ticks that could become more important as climate change continues. "There is a hypothesis that says parasites can regulate populations. Now, when foreign organisms invade a habitat - and this happens all the time - whether it's the crayfish, the raccoon, etc., there are then interactions between the parasites and the hosts. Then a parasite could make sure that a new animal that's not yet part of that interaction can't even get a foothold there because the parasite is sitting in between." In that sense, it prevents a non-natural establishment. "In addition, a parasite also ensures that a population is not overly large, but is kept within limits. Also, the host's immune system is activated by the frequent transmission of parasites, and that can be an advantage in evolutionary biology terms, because the animals have greater fitness and thus a higher likelihood of reproducing."

Sturdy shoes and black seed oil

For nature enthusiasts, there are clear protective measures. Once out in the woods and fields, sturdy shoes and socks that can be put over pants should be worn. Back home, you examine your four-legged companion and yourself and pat out your clothes properly. If you don't want to get to grips with the creepy-crawlies using chemical preparations, the biologist recommends: "I've had good experience with black cumin oil for our dog. Two drops in the fodder, that has a tender smell, there are fatty acids and ethereal oils in it. It's healthy and you can also rub it on your skin when diluted."

Uwe Blass

Professor Dr. Gela Preisfeld studied, earned her doctorate and habilitated at the University of Bielefeld. After brief research stays in Australia and a substitute position at the Goethe University in Frankfurt/Main, she accepted the appointment to the Chair of Biology and its Didactics, Zoology at Bergische Universität in 2006.

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