They aren’t only bloodsuckers. Ticks can also be dangerous, transmitting serious diseases like Lyme disease and tick-borne encephalitis (TBE). The biologist Christiane Hönicke examines which land-use patterns influence the existence of these parasites and their being infected with Lyme disease spirochetes. She concentrates on utilized agricultural areas because they cover a majority of Germany.
Finding the animals Hönicke seeks is not easy, but, wielding a big white flannel cloth, the biologist tracks down the little mites. She adeptly glides the tick flag across the meadow. “The transitional areas between shrubs and meadows are their favorite places,” the biologist explains. And indeed, after a few meters, two black spots are crawling over the white cloth. These ticks have eight legs – they are adults. One is black; the other has a reddish-brown edge. “The black one is male, and the auburn one is female,” Hönicke explains. Female ticks pose a particular danger to humans, sucking their hosts’ blood for days or even for over a week to satisfy the extensive amount of blood necessary to lay their eggs and reproduce, and they can transmit Lyme disease. Male ticks suck only for a few minutes and do not transmit Lyme disease.
Hönicke has gathered more than 2,500 ticks over the past three years, traveling regularly to the Uckermark region to do so. The Leibniz Centre for Agricultural Landscape Research (ZALF) is examining a test area of 450 km2 around the research station in Dedelow an area used for agriculture. This presents no problem for Hönicke’s research, on the contrary: “My study takes place in an agrarian landscape. Considering the fact that a large part of Germany – up to 60 percent depending on the calculation method – is used for agriculture, we clearly see what influence it can have on the ecosystems,” Hönicke says. This is the aim of the ZALF project Agro ScapeLabs (Agricultural landScape Laboratories), with which Christiane Hönicke’s research is associated. The size of the test area allows the researchers to not only examine small, individual areas but also entire landscape areas and to consider complex interactions. The PhD student is supervised by scientists from the University of Potsdam, the Technische Universität Braunschweig, and ZALF. The biologist investigates how land-use patterns affect tick populations and their hosts as well as which environmental parameters support or impede transmission dynamics of Lyme disease spirochetes.
Hönicke has been to over 100 places with her tick flag – hedges and other transition areas in arable fields, forests, embankments, and meadows. She has also caught mice in live traps. The small mammals are important hosts for the parasites. The number of ticks on the mice provides information about the size of the tick population. The biologist released all the mice, but brought the ticks back to the laboratory to examine them molecularly biologically. If she was able to verify parts of the pathogenic genome in the isolated DNA, the tick was infected by borrelia. This was the case in about 10% of the ticks. The scientist also distinguished between types of borrelia because not all of them are dangerous to humans. “After DNA detection, I used DNA sequencing to identify the respective type of borrelia in databases,” Hönicke describes the procedure. Out of the seven Lyme disease spirochetes native to Germany, five can cause clinical symptoms in humans.
“Larval ticks cannot transmit Lyme disease,” Hönicke explains, because the larva must first ingest a blood meal from an infected animal, usually a small rodent like a mouse. The larva then molts and becomes a nymph already capable of transmitting borrelia. When the infected nymph then draws in blood from another animal or human, the pathogens move from the midgut to the salivary glands and into the host’s skin via the mouthparts. This happens only after 24 hours. “It is, therefore, extremely important to remove the tick as soon as possible,” Hönicke point out.
After her work in the field and laboratory, the scientist is now statistically analyzing the relationship between landscape patterns and tick prevalence and the extent of borrelia infestation. “What is the influence of the type of cultivation and size of arable land – this question is the starting point of my study.” The biologist has already identified big differences within small areas. “In one spot we may find ticks infected with spirochetes, and just 10 meters away the ticks are uninfected.” She tries to analyze what is the reason for this. “It surely depends on many factors like wind, vegetation, humidity, and the host animals,” Hönicke says. She uses the collected data to develop a mathematical model able to identify the factors that most influence the occurrence of ticks and borrelia. “Of course, we also want to make predictions about landscape patterns that increase or reduce the infection risk for humans,” Hönicke explains.
Scientists now know that the type of land-use can decisively influence the infestation of ticks with borrelia. “Deer, goats, sheep, and cattle are not susceptible to borrelia infestation,” Hönicke says. These animals, in fact, are even free from borrelia if bitten by an infected tick, but the reason remains unclear. “The exact mechanism is being researched,” the biologist says. “We actually find fewer borrelia-infected ticks on pastures. Unfortunately, pasture farming has often disappeared,” she adds. “This example clearly demonstrates how our use of land can have an influence.”
The Project
AgroScapeLabs (Agricultural landScape Laboratories) is a pilot project researching the effects of land-use on biodiversity and functions of the ecosystem.
Participating: Leibniz Centre for Agricultural Landscape Research (ZALF), University of Potsdam, Technische Universität Braunschweig
The Scientist
Christiane Hönicke studied biology in Halle (Saale). In 2011 she began her doctoral studies at the University of Potsdam, which she has continued at the Leibniz Centre for Agricultural Landscape Research (ZALF) since 2013.
Contact
Universität Potsdam
Institut für Biochemie und Biologie
Maulbeerallee 1
14469 Potsdam
E-Mail: christiane.hoenickeuuni-potsdampde
Lyme Disease
Lyme disease is named after the American town Old Lyme, Connecticut, where the disease pattern was first described in 1975. The pathogens of the disease belong to a species of bacteria and are transmitted by tick bites. They cause various symptoms in humans. Erythema migrans – a circular, outwardly expanding rash – occurs at the site of the tick bite about one to two weeks after the infection. Patients may later experience fever, arthritis, palsy, and even inflammation of the nervous system. There is no vaccination for Lyme disease.
Text: Heike Kampe, Online-editing: Agnes Bressa, Translation: Susanne Voigt
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