Saturday, May 31, 2008

A Twist of Lyme

My dear husband, Smintheus, came home earlier this week looking less than his usual robust self. He soon spiked a fever. Since he had been camping and morel hunting in a Lyme endemic area the two previous weekends, I took him to the clinic for some doxycyline. Although he didn't have a documented tick bite, several in his party did, and the ticks are so small at that stage, they would be easily missed. The doctor agreed that it would be prudent to treat the disease as Lyme, since the blood test is often inconclusive and early treatment can prevent serious long-term consequences.

"Here she goes again," you say. "Another off-topic post."

Stay with me.

Lyme (not Lyme's) disease was named for the town in Connecticut where it was first identified. It is caused by the bacterium Borrelia burgdorferi, transmitted to humans by the black-legged tick, also known as the deer tick. This tick (Ixodes scapularis) has a complex two year life cycle. From the common name of the tick, you would expect to find them associated with deer, and they are.

But they also feed on mice, and it is the mice that are the source of the infection.

The ticks only take a blood meal two or three times in their lives. The first, which is usually from a mouse, allows it to mature from a larva to a nymph. It is the nymphal stage that is most likely to bite humans, especially in the late spring and summer. The second blood meal (which can be from a variety of animals, including humans) allows the nymph to mature into an adult tick. The female takes a third blood meal from a deer so that she can lay eggs.

Deer are important for the life cycle of the ticks and for carrying them around and spreading them through the environment, but they aren't infected by the Lyme bacterium.

It's our friend the mouse, specifically the white footed deer mouse (Peromyscus leucopus), that is the major reservoir. Up to 90% of mice in some areas are infected with the Lyme bacterium.

Here is a fascinating discussion of the ecology of Lyme disease and how the prevalence and transmission are affected by deer, mice, weather, acorns, and human behavior. Here is a paper (and a more user-friendly press release) about mouse vaccination as a way to interfere with the transmission of Lyme disease.

Tuesday, May 27, 2008

Ear Worm

I know this is off-topic, but I have this tune I can't get out of my head. Maybe if I blog about it, I'll be rid of it.

I'm working on a piece on collagen and I keep thinking of that ad for College Inn chicken broth, you know:

"Homemade soup with collagen..."

It always struck me as a rather unappetizing commercial. I know there's collagen in soup, but it's not something you'd want to advertise.

Thursday, May 15, 2008

You are what you eat (from)

It's not just food that makes us fat.

In studies presented yesterday at the 16th European Congress on Obesity in Geneva, Switzerland, researchers have shown that exposure to certain chemicals early in life can promote obesity.

Three groups of researchers presented findings on the effects of endocrine disruptors, chemicals that mimic the effects of hormones, on the development of mice.

The chemicals include:
  • Bisphenol A (BPA), used in polycarbonate plastics, like plastic containers, plastic wrap, and the linings of food cans
  • Perfluorooctanoic acid (PFOA), a greaseproofer used in food containers, like microwave popcorn bags and pizza boxes
  • Tributylin, used in plastic food wrap
These chemicals can leach into food and has been found in the blood of people living in developed countries.

The researchers, from Tufts University, the EPA, and UC-Irvine, demonstrated that mice exposed to these chemicals in utero and early in life were fatter as adults than control mice, even when their food intake and activity level were the same. The exact mechanism of action is unclear, but the investigators noted differences in the ways these mice regulate glucose and respond to insulin, and in levels of the hormone, leptin. The effects were not seen when mice were exposed only later in life.

I was told as a new mother that bottle-fed babies have a greater chance of becoming obese than breast-fed babies, probably because they don't learn to regulate how much they eat. "Just finish this bottle, and we'll be done, sweetie." Or maybe it was because of certain ingredients in commercial baby formula. These studies make me think that it's not just what's in the bottle, or how much they drink from the bottle, but the bottle itself that predisposes to obesity.