Tick bites do not trigger Alzheimer’s disease

Health and Wellness 30. nov 2019 2 min MD, PhD Lars Omland Written by Kristian Sjøgren

New Danish research using more than 30 years of data on tick bites in Denmark shows that Lyme neuroborreliosis does not increase the risk of developing Alzheimer’s, Parkinson’s and other diseases of the nervous system.

Tick bites are unpleasant, and many people experiencing them can be infected with Borrelia bacteria, which can end up in the nervous system and the meninges and cause the debilitating disease Lyme neuroborreliosis.

Many people who develop Lyme neuroborreliosis are concerned about whether it increases their risk of developing diseases such as Parkinson’s, Alzheimer’s and dementia, but Danish researchers have now rejected this hypothesis.

They are not associated.

The research results were published in Clinical Infectious Diseases.

“This is a negative result, and these rarely get much attention, but the finding is important anyway, because it should eliminate the concern of the people who have Lyme neuroborreliosis or know someone who does. There have been many rumours about possible links between Lyme neuroborreliosis and diseases of the nervous system, but we have not been able to demonstrate that this is a problem,” explains a researcher behind the new study, Lars Omland, PhD and doctor, Department of Infectious Diseases, Rigshospitalet, Copenhagen.

Patient advocacy organizations spread false rumours

The rumours about a possible association between Lyme neuroborreliosis and an increased risk of developing diseases of the nervous system stem mainly from various web forums and patient advocacy organizations, which think that Lyme neuroborreliosis can cause a wide range of disorders.

According to Lars Omland, the probable reason for this misconception is that people automatically link infections of the nervous system with Alzheimer’s, Parkinson’s, dementia and epilepsy, although no association has been proven.

“When there is infection in or around the central nervous system, ruling out a biological association is difficult, which is why examining this in a major study such as ours is important,” says Lars Omland.

2067 have had Lyme neuroborreliosis in the past 30 years

Lars Omland and his colleagues examined various databases to identify all cases of Lyme neuroborreliosis in the past 30 years in Denmark, totalling 2067 people.

Then the researchers linked the cases of Lyme neuroborreliosis with cases of Parkinson’s, Alzheimer’s, dementia, epilepsy and Guillain-Barré syndrome using data from the Danish National Patient Registry.

The researchers compared the results with similar linked data from 20,670 control subjects.

“We matched the people with Lyme neuroborreliosis with the control subjects in terms of age, sex and other characteristics, so if the risk of developing these diseases of the nervous system was increased, we would have been able to see this,” says Lars Omland.

No elevated risk

The long-term results show that 12 people with Lyme neuroborreliosis developed Alzheimer’s, 7 developed Parkinson’s and 33 developed dementia.

For the control group, the numbers were 108, 76 and 326, respectively, the same proportions as the people with Lyme neuroborreliosis.

“The people with Lyme neuroborreliosis are at all ends of the spectrum. Some were young when they developed neuroborreliosis, whereas others were older. Some were infected recently, and others were infected 30 years ago. Although the spectrum is broad, we still think that we have enough data to declare that we did not find any increased risk of developing diseases of the nervous system in the long term,” says Lars Omland.

Slight increase in the risk of developing epilepsy around the time of diagnosis

However, the new research results show a slight increased risk of developing epilepsy and Guillain-Barré syndrome within the first year after Lyme neuroborreliosis was diagnosed.

Within 1 year after diagnosis, 8 people with neuroborreliosis (0.4%) developed epilepsy, a much higher percentage than in the control group, in which only 20 developed epilepsy (0.1%).

Similarly, 11 people with neuroborreliosis developed Guillain-Barré syndrome (0.5%) versus 0 in the control group.

In the long term, however, the risk of developing these diseases was not increased.

“We speculate that people with Guillain-Barré syndrome, for example, often get a spinal fluid test, and if they have Lyme neuroborreliosis or have had it before, the test will show it. We therefore imagine that the association does not reflect increased risk but simply that Lyme neuroborreliosis is being detected among people with newly diagnosed Guillain-Barré syndrome,” says Lars Omland.

Lars Omland thinks that the research results clearly show that people with Lyme neuroborreliosis should not worry about any increased risk of developing Parkinson’s, Alzheimer’s, dementia, epilepsy or Guillain-Barré syndrome.

Risk of neurological disorders in patients with European Lyme neuroborreliosis. A nationwide population-based cohort study” has been published in Clinical Infectious Diseases. The Novo Nordisk Foundation awarded a grant in 2018 to Thomas Benfield, Professor, Hvidovre Hospital for the project Shortened Antibiotic Treatment in Community-acquired Pneumonia: A Nationwide Danish Randomized Clinical Trial.

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