Acorns affect our health!

By Michael Crupain, MD, MPH

I think most of us probably think that as humans we are pretty removed from what happens in “nature.”  And certainly in medical school we didn’t have any classes on how human health is dependent on the health of the ecosystem.  Despite this sentiment though, human beings are still linked to the environment and what effects nature also affects our health.  This is true whether we are talking about something as big as climate change or apparently something as small as acorns. 

Last week’s New York Times reminded us of this link in the article, After Lean Acorn Crop in Northeast, Even People May Feel the Effects.  It turns out that this year is a very bad year for acorn production.  While we don’t have much direct use for acorns, field mice, deer, and birds do.  Without these acorns the deer will wander further out of the cover of the forest and be more likely to be hit by cars.  This results in not only dead Deer, but also serious injuries for drivers. 

Acorn abundance also has an effect of the risk of humans acquiring Lyme disease and the article states that 2012 may be “the worst year for Lyme disease ever.” The reason for this has to do with the effect of acorns on the population of both mice and deer.

The acorn is one of the primary foodstuffs of the field mouse.  The field mouse, in turn, is one of the main sources of food for the tick that spreads Lyme disease and one of the primary reservoirs for the bacteria responsible for the disease.  In years of high acorn production the mouse population grows, which provides more opportunities for the tick population that carries the Lyme disease causing bacteria.

But wait, the article said that there were less acorns this year, so shouldn’t the risk of Lyme disease decrease with the decreasing mouse population?  This is where is gets a little confusing, but hopefully I can clear it up for you. 

It turns out that the lifecycle a tick is two years long from Egg to Larva to Nymph to Adult.  Most ticks get “infected” with the Lyme causing bacteria in the larval stage when they feed on the blood of a field mouse.  Development from Larva to Nymph, the stage when a tick is most likely to infect humans, takes one year. 

With that in mind lets get back to acorns.  Unlike this year, the fall of 2010 saw a bumper crop of acorns.  This excess of food led to an explosion in the population of field mice in the summer of 2011.  This increase in mice means that tick Larva were more likely to be exposed to the Lyme bacteria during this time.  Remember though, that it takes one year for the ticks to reach the Nymph stage when they are most likely to effect humans.  So now in the summer of 2012, when the Larva becomes Nymphs, there will likely be many more of them than usual in the forest to attach to humans passing by.  In addition because of the lean acorn crop in the fall of 2011, the deer we discussed earlier that will wander out of the woods to find food will also spread the infected ticks further from the forest floor.   It feels a long way off, but it will be important to be extra vigilant for ticks this coming summer.  The good news is though, that because of the low acorn yield this year, the summer of 2013 should see less Lyme disease.