So I see no logical contradiction by saying "these ticks have been around since 2017" and "entire country is about to be infested".
The old math question asks, "Duckweed is spreading on a lake. It takes 1 year to double the area of duckweed. From start to end, it took 15 years to cover entire lake. Which year the duckweed covers half of the lake?"
Exponential growth has this feature that for a long time it seems fine and then suddenly it is over as it overload's the physical capacity to handle it.
And I would say 7 years to get to the current state is extremely fast rate and definitely cause for alarm in my opinion.