High Cholesterol Levels Increase the Severity of Tick-borne Diseases
11 September, 2007 08:17 (CST)
Clinical Mind - Individuals with high cholesterol levels are more likely to get infected by disease spread by ticks. A recent study published in the Journal of Infectious Diseases, indicates that the likelihood of developing Human Granulocytic Anaplasmosis (HGA) is higher in people with high cholesterol levels. The study was conducted by Yasuko Rikihisa and her team on two groups of mice. Rikihisa is the lead author of the study and a professor of veterinary biosciences at Ohio State University.
The research involved infecting mice with a bacterium Anaplasma phagocytophilum. This bacterium is responsible for causing HGA with symptoms similar to the flu. The level of bacteria was 10 times higher in mice with an inherited tendency for high cholesterol levels. It was also high in mice supplied with a cholesterol-rich diet.
The findings revealed that the bacterium thrives on cholesterol stores of its host. This implies that persons with higher cholesterol levels are more likely to develop HGA.
Unfortunately, due to its flu-like presentation, it is very difficult to correctly diagnose HGA. Symptoms include high fever, chills, muscle aches, and headaches. An incorrect diagnosis can often lead to a fatal situation in patients suffering from the disease.
Rikihisa says that young people do not seem to develop any severe symptoms of the disease. However, if the disease goes undiagnosed in elderly people, it could prove fatal to a person with an impaired immune system. This takes place when the immune system weakens gradually and the blood cholesterol levels rises as we grow old.
Incidence of HGA is rising rapidly in the United States. The study estimates that 400 to 1,000 people get infected with the disease every year. Besides causing HGA, ticks also spread Lyme disease, which is carried by Deer ticks. The disease is common in the upper Midwest, parts of the mid-Atlantic States, New England, and northern California. Lyme disease attacks granulocytes, type of immune cells.
The study investigated two groups of mice. The first group of mice had a deficiency of protein called apoliprotein E. This protein plays an important role in maintaining normal blood cholesterol levels. Mice in the second group had normal levels of apoliprotein E present in their bodies.
The scientists fed one group of mice with a cholesterol-rich diet for a period of one-month. The other group was given a diet with a normal level of cholesterol. Scientists then infected some of the mice from each group with A. phagocytophilum. Blood samples of each infected mouse were collected after 10 days of infection. The researchers also harvested the spleen and liver of each infected mouse.
They found that the level of infection varied with the amount of bacteria obtained in each tissue. The researchers expected to find higher levels of bacteria in the liver and spleen, because both organs filter blood, with liver also manufacturing and storing cholesterol.
The research indicated that level of A. phagocytophilum was 10 times higher in mice with a genetic tendency for higher blood cholesterol levels. It was also high in mice who were given cholesterol-rich diet as compared to the other group, which had normal-cholesterol diet, but were genetically prone to develop higher cholesterol levels.
The tests revealed that level of bacteria was highest in the blood and the spleen of mice, and was fairly low in the liver of all mice. The study further showed that cholesterol levels increased 4 times in mice with high-cholesterol diet and also in mice predisposed to high cholesterol. But, the cholesterol levels were found normal in the mice with cholesterol predisposition but having diet with normal cholesterol levels.
Scientists say that some individuals undergo mutations in the apoE gene, which controls the production of apoE. This leads to an imbalance of blood cholesterol levels. In humans, the mutation is likely to increase blood cholesterol levels if a person has a high intake of cholesterol-rich diet.
``A high-cholesterol diet really boosted infection levels in the mice without apoE. The findings suggest that humans may be more susceptible to HGA if they eat a high-cholesterol diet and if they are otherwise prone to high blood cholesterol levels,'' Rikihisa said.
The research performed by other scientists indicates a direct relationship between older age and an increase in A. phagocytophilum infection. According to one such study, the average age of infected patients was 51 years, while it was 39 years for those infected with Lyme disease.
Rikihisa said that individuals who suspect they have been bitten by a tick must seek immediate professional health care and possibly receive a quick antibiotic therapy. In addition, the infected person should aim at lowering the cholesterol levels by following a healthy diet along with an effective medication. This will help minimize the risk of developing HGA and also reduce the severity of the disease. The research was sponsored by the National Institutes of Health.
Source: Ohio State University
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