The ticks that can infect people with Lyme disease have expanded their range northwards in North America and Eurasia as the climate warms. Now a study has found that the bacteria that cause Lyme disease may aid this expansion by boosting the survival rate of overwintering ticks.
鈥淭his infection helps them get through some of these difficult winters,鈥� says at Dalhousie University in Halifax, Canada. 鈥淚t really has a big punch in terms of population numbers.鈥�
In people, Lyme disease usually . If untreated, it can lead to serious long-term problems.
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Over three winters, Adamo鈥檚 team collected deer ticks (Ixodes scapularis) in Nova Scotia, Canada, and put them in tubes, covering the ends with mesh to stop them getting out. The tubes were put in leaf litter 鈥� where ticks usually overwinter 鈥� in forests or dune grasslands. In spring, the researchers collected the tubes and tested the living and dead ticks for infection with Borrelia burgdorferi, the bacterium responsible for Lyme disease in North America.
Uninfected ticks had a 51 per cent risk of dying during the winter, while the risk of death for infected ticks was just 22 per cent.
The team calculated that this effect could have a big difference on tick populations. 鈥淚n some ways climate change can make it harder for them because you get bigger fluctuations in temperature,鈥� says Adamo. Such fluctuations would wipe out non-infected ticks in marginal areas but infected ones can survive. 鈥淥nce you get a heavy prevalence of infection, you never lose them,鈥� she says.
A previous study by Girish Neelakanta at Yale University and his colleagues showed that ticks infected by a different bacterium , and that this boosted cold survival in labs.聽It just so happens that IAFGP is also an anti-freeze protein.
If ticks infected by B. burgdorferi also produce more IAFGP to counter the infection, this might explain the higher survival rate.
This raises the question of why uninfected ticks don鈥檛 produce higher levels of IAFGP to boost winter survival. Adamo thinks it is probably because this comes at the cost of producing fewer eggs.
The finding suggests that people need to be particularly careful in early spring, as ticks that have survived the winter are more likely to be infected. 鈥淚n the very early spring, people are not usually thinking of ticks,鈥� says Adamo. 鈥淚t could be a time where maybe people are not as vigilant as they need to be.鈥�
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