July 2, 2007
The bacterium in question — Anaplasma phagocytophilium — is spread by the same tick that causes Lyme disease. When the bug enters the body, it causes a sickness known as human granulocytic anaplasmosis (HGA), which is characterized by high fever, headaches, and liver damage. Anaplasma phagocytophilium, what's more, is a cholesterol addict. It can't make cholesterol from scratch but need lots for its cell membrane. Once inside the body, it steals the needed lipid from human cells.
Researchers in Yasuko Rikihisa's lab at Ohio State University in Columbus used mutant mice to study whether higher blood cholesterol levels can lead to higher rates of infection. The mice were engineered to lack a key cholesterol-processing gene (apolipoprotein E) and thus had lots of cholesterol free-floating in the blood.
The scientists studied four groups: healthy mice with a normal diet, healthy mice on a high cholesterol diet, mutant mice with a normal diet, and mutant mice with a high cholesterol diet. The mice were injected with cells infected with Anaplasma phagocytophilium, and were then monitored for levels of cholesterol and numbers of bacteria.
At the end of four weeks, the results were clear: Mutant mice who consumed high-cholesterol food had two to three times higher cholesterol levels and significantly higher bacterial counts than the other three groups. The study appears in the May 15 issue of the Journal of Infectious Diseases.
The moral of this story? People who are genetically prone to high cholesterol levels and who chow down on a cholesterol-promoting diet may be more susceptible to HGA, the scientists suggest. (The average age of HGA infection is 51, whereas for Lyme disease, it is 39. Since the same ticks carry both diseases, the new research may explain why older people, who tend to have higher cholesterol, are stricken with HGA.)
So if you're the kind who's apt to go out walking in the woods — maybe shun that burger and pick up a salad?
— Chelsea Martinez
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