Lyme Disease

Part 2

Hi – in the second part of our look into Lyme disease, we will discuss the life cycle of the deer tick and how this pertains to the spread of the disease. 

The deer tick goes through several changes in its life.  The springtime finds tick eggs hatching larvae.  The Lyme disease bacteria (Borrelia burgdorferi) live in mice, deer, and other small mammals. During the summer months, a larva will feed once on a small mammal such as a mouse.  If this little critter happens to be infected with B. burgdorferi, the tick larva can also be infected.  After feeding, the larva molts into a nymph – not necessarily the kind that might hang out with Pan – then goes dormant for the winter. Now, after wintering over, from May through July, the nymph feeds on another mammal or dog or human.  At this time if the nymph has escaped infection as a larva – it can pick the infection up from an infected animal, and it can pass the infection on as well at this stage. During late summer and fall the nymph molts and becomes an adult deer tick.  The infected female deer tick goes for bigger game – and will feed on dogs, humans or deer or a larger mammal. It should be said here that the wildlife infected seem not to become sick with the disease. She mates and lays her eggs and dies.  However, if she doesn’t feed in the fall, she will hang around till spring to find a larger host.  And so the cycle of life continues.

For the nymph or adult to transmit the bacteria, it has to be on its host for 48 hours.  If the tick is removed or dies during this time, transmission of the disease won’t happen. 

And sometimes even if a tick carries the bacteria and is on a dog for more than 48 hours, the dog may not contract the disease.  According to one reference, studies show that in all actuality only about 10% of dogs exposed to the bacteria get Lyme disease.  We know that Lyme disease is not contagious – we can’t catch it from our dogs. However, if not treated the dog can be a reservoir for ticks.  Once a tick has feasted till it is full, it will detach and not bite another animal!  One danger comes from a tick that hasn’t gotten it’s fill before being detached and goes looking for another meal.

The deer tick, alone seems to have the notoriety of spreading Lyme disease.  While other ticks and insects do get infected by the bacteria, they are considered negligible in the spread of the disease.

Despite the fact that people or dogs from all over the United States have been infected with the disease it is felt they were exposed when traveling through endemic areas. (Areas where the disease is consistently present.)  Actually, there is only a small portion of the US where the disease is present, BUT these areas have high people and pet populations. The area is also becoming larger with the advent of warmer winter seasons and areas that have not had tick populations now have them.  Most cases come from the east coast.  A much smaller number come from Wisconsin, Minnesota and California. 

So it would appear that Lyme disease and its carrier are becoming a bigger threat to people and dogs as ticks find their way into new areas.

For the final part of this series we will look at prevention, testing and vaccination.  Till then think spring!

I would like feedback on the educational material presented on the Collie College page, as well as any topics that you find interesting.  Please e-mail me directly with this information.  Pamela.e.frazier@dartmouth.edu