Five fascinating facts about ticks

Patrik Dinnétz, senior lecturer in biology and Thérese Janzén, PhD in environmental science, study ticks and tick-borne diseases. Their research includes studying ticks in urban green spaces and identifying the environments where they thrive and those where they do not.

In her thesis, Thérese demonstrated that there is a significant risk that tick-borne diseases can also spread in urban green spaces. They are also studying how people can avoid contracting tick-borne diseases.

“Ticks are rewarding to work with,” says Patrik. “They are easy to catch and study. They also cause problems for humans – and many people have strong feelings about them, even if they are not positive ones.”

Thérese has a personal reason for studying this unpopular little organism:

“When I was growing up we had a holiday home in the Stockholm archipelago, and there were so many ticks! I’ve had people close to me who have been ill with both Lyme disease and TBE [tick borne encephalitis]. My dissertation for my Master’s in Infectious Disease Control at Södertörn University was about the risk of equine anaplasmosis. Anaplasma is a bacterium that is spread by ticks and which can also infect humans. After that, I realised that I wanted to continue with research and working on diseases transferred by ticks. I wanted to find out more about the environments in which the risk of being infected by tick-borne disease is greatest and thus perhaps help others not to be affected by TBE, for example,” she says.

Patrik and Thérese bring out a white sheet, test tube, a mop and some rubber gloves – it’s time for a tick excursion! While we’re out, they share their expertise on the pest we hope not to see this summer. And here are the experts’ five facts about ticks:

1. Ticks
   Ticks are arachnids; their closest relatives are mites. There are over twenty different species in Sweden and the most common is Ixodes Ricinus, known as the castor bean or sheep tick. If you are bitten by a tick or see a tick crawling on your body, it is almost certainly one of these, but if you are in central Norrland or further north, the tick you see could be Ixodes persulcatus, the taiga tick, which looks almost exactly the same.
2. A tick’s life stages
   In Sweden, a castor bean tick lives for two to five years. It has three life stages – larva, nymph and adult tick - and lives a very quiet life. Mostly, it sits on a blade of grass and waits for a host animal to pass by so it can have one of the two or three meals of blood in its life. Males need to feed once as larvae and once as nymphs, but as adults they do not feed at all. Instead, they focus on mating. The females, however, also need to feed on blood as adults so they have enough energy to produce around 2,000 eggs. A bonus fact is that tick larva only have six legs then, like all arachnids, they grow eight legs.
3. Any animal can be a host animal
   The castor bean tick has almost no preferences when it comes to host animals, they just attach themselves to whatever happens to pass by: birds, humans, foxes, deer, cats or dogs – even amphibians and snakes. Many species of ticks can be carried by migratory birds. This is why new species of ticks are being found in Sweden, such as the large Hyaloma marginatum, which has been found in southern Sweden over the past few years.
4. Ticks don’t only suck blood
   We often say that ticks suck blood, but this doesn’t work in the same way as for a mosquito. Once a tick has attached to a host animal, it injects it with saliva which contains enzymes that can break down the cells beneath the skin. The saliva also contains an anticoagulant, so the blood keeps flowing. Then the tick starts to eat from the soup of blood and cells that has formed around its mouthparts. Often, many ticks gather to share this cell soup, which may increase opportunities for bacteria and viruses to spread between them.
5. How diseases are transferred
   Ticks can carry around twenty different viruses, bacteria and parasites that can cause illness; the ones we in Sweden most commonly encounter are a virus that causes TBE and a bacterium that causes Lyme disease. The TBE virus is present in the tick’s saliva as soon as it bites through the skin and injects the saliva into our body. This means that a tick that is carrying the TBE virus – which only a fraction of all ticks do – unfortunately transmits the infection directly to the host animal. The bacteria that cause Lyme disease, however, are found in the tick’s gut, so they must first move to the salivary glands before the tick can transmit them to the host animal. It takes at least twelve hours for the bacteria to reach the tick’s salivary glands. Ticks also tend to regurgitate, which means that they vomit waste products from their stomachs back into the host animal. This can also transmit the bacteria that cause Lyme disease, but this also happens only after at least twelve hours. If you have been vaccinated against TBE and remove ticks as soon as possible after they have attached themselves, your risk of contracting TBE or Lyme disease is minimal.

How to avoid ticks and their diseases

Ticks attach most easily where things that are a little soft and fluffy. Hairy legs and brushed cotton are perfect for ticks! Slippery fabrics and rubber boots provide good protection. Mosquito repellent has also been proven to provide some protection. It is also clear that some people are less attractive to ticks than others – but we still don’t know why. If you do get a tick, pull it off as soon as possible with tweezers. Take hold of the tick and pull it straight out. It is a good idea to apply antiseptic to the area of the bite. Keep an eye on it and contact the health services if you see a large red ring growing around the bite. In Sweden, you can get advice about tick bites via Vårdguiden 1177. External link.