Science - November 18, 2010

Bacteria make bugs tick

Ticks seem to benefit from the bacteria responsible for Lyme disease.

Infection with Lyme bacteria through tick bites is on the rise.
Borrelia bacteria are very nasty. Not only do they cause Lyme disease, they could also make the ticks which transmit this disease to humans extra dangerous. This is the conclusion of Fedor Gassner in his thesis 'Tick Tactics' which he will defend on Monday in the Aula.
Ticks infected with Borrelia are a bit bigger, more active, have more fats, better endurance power and are less susceptible to dehydration. As such, they can lie in wait longer before having to replenish themselves in mulch. Such manipulation gives the bacteria a bigger chance - it is not known how - to reach a new victim. Gassner offers an explanation from a human point of view: 'Perhaps the chances of getting bitten by an infected tick are relatively higher than getting bitten by an uninfected tick.'
The numbers of recorded Borrelia infections continue to rise in the Netherlands. Gassner suspects that this is not just the result of paying more attention to Lyme disease, but actual increases. 'It's obvious to conclude that infected ticks are increasing in numbers, and this hypothesis is elucidated in my thesis. The numbers of infected ticks vary greatly from month to month and from place to place, ranging from zero to more than fifty percent. In fact, we don't know why more people are falling sick. What we see is just the tip of the iceberg; most of the pathogens are found in the nature.'
Underestimated problem
To learn more about this concealed enemy, Gassner studied tick ecology in depth. His research reveals that there is a connection between half open forests and the thickness of the mulch covering. It has also become clear that ticks thrive in the neighbourhood of small rodents and birds, major hosts for baby ticks. On the other hand, grazing in nature areas puts the parasites at a disadvantage, probably because cattle kill the undergrowth, damage the mulch layer and chase away small rodents with their big hoofs. That could account for the difference of several percent in tick bites in people on foot, says Gassner. 'Every bite less helps. Lyme disease is an underestimated problem; prevention of tick bites needs to be as natural as looking left and right before crossing a road.'
Gassner will continue to carry out this conviction after his graduation, such as by working for Natuurkalender (Nature's Calendar). In addition, he is writing a new research proposal with his promoter, Willem Takken. 'The ticks aren't rid of me yet.'  
What makes someone tick
Fedor Gassner knows what he's talking about. His record: fourteen tick bites in one summer. 'My father always gets them too, while my mother, who has a similar lifestyle, has never had a tick bite before. Obviously, not everyone is equally attractive. The same can be observed in mice: 20 percent of the animals have 80 percent of the ticks.

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