Wednesday, February 29, 2012

Lyme Disease- Mice or Deer?

Deer are commonly thought to be a major factor in Lyme disease, harboring the organism until it infects ticks which transfer it to humans.  It may be that deer are getting a bad rap.  An article in nativeplantwildlifegarden.com suggests that it is more a story of mice and men.

Dr. Richard S. Ostfeld of the Cary Institute of Ecosystem Studies has been doing research into the  factors that have contributed to the rapid increase in Lyme disease cases.  As the article says,
"Ostfeld and his team have found that the primary culprit in the skyrocketing increase in Lyme disease cases is the reduction of biodiversity due to habitat fragmentation and destruction and its impact on the number and composition of host species for ticks.  Perhaps deer are not the primary villains in the Lyme disease story as we’ve been lead to believe.
Dr. Ostfeld has found the number of infected ticks is directly related to the diversity of host mammals, including white-footed mice, chipmunks, squirrels, catbirds, opossum, fox and deer, that the ticks can feed on which is directly related to habitat biodiversity.
The risk of exposure to Lyme disease is lower in a large forested area than it is in a fragmented habitat like a small wooded lot or our own back yards. That’s because small mammals that thrive in large numbers in these fragmented habitats – mainly white-footed mice – seem to infect a large number of ticks with the Lyme disease pathogen.
Mice encounter lots of ticks. In addition, they do a poor job of grooming off ticks so they have a high rate of permissiveness and a high propensity to infect those ticks that remain with the Lyme disease pathogen, or what Ostfeld calls reservoir competence. As you can see from this table, white-footed mice, and to a lesser degree chipmunks, are apex hosts for Lyme disease."
The tables and a more complete description are available at nativeplantwildlifegarden.com. For more in-depth information, there is also his lecture Biodiversity Loss and the Rise of Emerging Infectious Diseases on youtube.com.
Addendum
This mouse-deer connection is also an excuse to work in a totally unrelated true story.  This sounds like a tall tale by our friend Buck, but this one is true.
Pregnant mouse deer

We had the privilege of seeing a mouse deer during a night hike in Kalimantan Province of Borneo years ago.  Finding my picture would require an archeological expedition into the frightening "closet of  shoe box negatives," so I had to use this one from the article below.  For those of you who don't know what a negative is, I would recommend Googling "Kodak extinct species."

Mouse deer are members of the ancient ruminant family Tragulidae.  They are the smallest of all ungulates, standing a maximum of 14" tall and weighing in at less than our miniature schnauzers.  More incredibly, they not only swim but dive a under water to escape threats as described  in this BBC story.  More at http://www.squidoo.com/mousedeer.

Postscript
The earliest case of Lyme disease has been discovered.  Oetzi, the Iceman, a by now famous 5,300-year-old body discovered frozen in the Eastern Alps in 1991was found to have the Borrelia burgdorferi bacteria which causes Lyme disease.   

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