The plague of infected ticks is an alarming development which has attracted lots of public attention in recent years. The number of disease-carrying ticks in Poland has increased over tenfold since the early 1990s. What has caused this dangerous phenomenon? What are its consequences and the prospects for the future?
A walk in the meadows, a country bicycle ride or jogging through the woods are generally considered pleasant and relaxing experiences. Few people would associate these activities with serious health hazards. However, doctors and scientists have been warning against the danger posed by ticks – tiny slow-moving arachnids that feed on human and animal blood. Currently, every third tick carries Borrelia – bacteria causing Lyme disease. Though curable in over 90 percent of cases, the disease can result in a number of very dangerous complications, some of which can even develop after successful treatment. Why has this cosmopolitan species, which has lived in Poland for ages, now become such a serious threat?
Abundance of acorns? Watch for ticks!
The number of infected ticks is linked to... the number of acorns. This apparently absurd statement is based on the scientifically proven correlation between the oak acorn crop and Lyme disease incidence in a given year, which can be explained by the fact that acorns are one of the favourite foods of many forest animals, including mice, whose fur provides an attractive “feeding ground” for ticks. So, the more acorns are produced by oaks, the more rodents come to forests to eat them. It’s the presence of mice in the woods that poses the greatest threat. The newly hatched ticks are free from Borrelia, even if their mother was the carrier of Lyme disease. Almost none of the larvae carry the bacteria, until they get them from their rodent hosts.
The abundance of acorns contributed to the great increase in the population of mice, which stocked up much more food for the winter and, consequently, started to breed not only during summer, but throughout the year. In turn, the greater number of rodents led to the increase in the population of tick species feeding on mouse blood, which acquired Borrelia from their hosts.
The worse still to come
The most obvious question is: what has caused the increased seed production by oaks? For these trees the mast year, that is, the year when they produce most fruit occurs once every 5-8 years. How do all the trees ‘agree’ to simultaneously bear more fruit? There are several hypotheses, but no definite answer to this question. The fact is that the oak mast year two years ago led to the tenfold increase in the number of rodents last year (2018). The population of Borrelia-infected ticks is expected to reach its peak two years later (2020), which means that the worse is still to come.
The second contributing factor is... the global warming, resulting in milder winters and increased air humidity, which allows more ticks to survive the winter period and get infected by wood rodents.
What doesn’t kill you... will kill your grandchildren
Some may think that the easiest way to cope with the tick threat would be to cut down oaks or kill off forest mice. Yet, such interferences often have catastrophic consequences for the ecosystem (like the extermination of sparrows in China). Nature is extremely stubborn and doesn’t like being manipulated. Elimination of one species could only lead to its substitution by something else. Such a change would carry unpredictable implications and, obviously, great risks for the future.
So how could we protect ourselves from this dangerous plague? The biggest problem is that ticks have no natural enemies in the ecosystem, as they aren’t eaten by any known creatures. They can only be effectively exterminated by a long and very cold winter. Unfortunately, due to the climate change, such winters are long gone and shouldn’t be expected to return in the following years. Hence, until scientists develop an effective method of eliminating ticks or preventing the harmful effects of their presence, caution is the only way of protecting ourselves from Lyme disease.
Photo in the upper left corner: California Department of Public Health
Original text: www.nauka.uj.edu.pl