In the newly published paper, O’Day and Catalano investigated whether areas with the highest level of Lyme disease also had significantly higher levels of deaths due to Alzheimer’s disease compared to areas with a low incidence of Lyme disease. They found no statistically significant correlation between the two and actually found that the thirteen states with the highest number of deaths from Alzheimer’s were different from those with the highest incidence of Lyme disease.
Problems with this Study
Of course, correlation is not always a good indicator of the true picture and it may be that states with higher numbers of deaths from Alzheimer’s tend to have an older populace that is less likely to be exposed to Lyme disease through outdoor activity. Conversely, states with more Lyme disease cases may simply have a younger population with a lower rate of AD deaths due simply to age. Additionally, reporting of Lyme disease cases varies significantly across the US with some states still lagging way behind when it comes to following national reportage guidelines.
Other factors that may skew the results of a simple correlation include climate, lifestyle, and medical provision; for example, older people may choose to live in warmer states where there are fewer ticks, while younger people may spend more time in states where ticks are more common. In addition, it is important to note that Lyme disease was only recognised in the 1980s and that many cases are never diagnosed or reported.
An accurate analysis of any correlation with Alzheimer’s deaths may simply be impossible given the quality of current data and, as people with Alzheimer’s disease are living longer with the illness it may be that deaths, rather than disease incidence, do not accurately reflect any connection between LD and AD. Still, the lack of correlation is stark and will prompt other researchers to reconsider the proposed connection between the two conditions.
Alzheimer’s Disease a Result of Infection?
A paper in 2006 was one of the first to note the possibility of Alzheimer’s disease manifesting after Lyme disease. Rather, McDonald noted that the neurofibrillary tangles (NFT) seen in Alzheimer’s disease are identical to those seen in the childhood illness Subacute Sclerosing Panencephalitis (SSPE). This condition is caused by infection with atypical measles virus which causes damage to infected neurons.
McDonald also noted that in a study in monkeys where the animals received injections of Borrelia (the Lyme disease bacteria) into their skin the monkeys were later found to have Borrelia in their brain neurons. The recognition of neuroborreliosis clearly supports the notion that this bacteria can enter the brain and cause damage but the idea that this damage may play a role in Alzheimer’s disease has been dismissed by many physicians. McDonald reported on ten cases of Alzheimer’s disease seen at the McLean Hospital Brain Bank of Harvard University where 70% tested positive for infectious DNA.
How Lyme Disease Could Cause Alzheimer’s Disease
The idea is, then, that chronic infection in human neurons is responsible for Alzheimer’s disease by way of neurofibrillary tangles developing in a similar way to in SSPE. McDonald proposed that the nerves pass the infection onto one another, causing disease progression over time.
It certainly seems possible that untreated Lyme disease infection could cause significant damage to neurons and predispose a person to premature cognitive decline. Whether or not a direct link can be established between Lyme disease and Alzheimer’s disease remains to be seen however. The types of antibiotics used to treat Lyme disease may not always permeate the blood-brain barrier and thus low grade neurological infection may continue unchecked and lead to neurodegenerative changes that look like Alzheimer’s disease in later life.
Supporting the Theory
The difficult is that a sample of brain tissue would be needed to test for active infection in those displaying symptoms of Alzheimer’s disease, and in cases where patients’ deaths are recorded as being due to Alzheimer’s disease it is unlikely that an autopsy will test for infection with Borrelia. Additionally, patients who die from other disease are also unlikely to be tested for neuroborreliosis even if it is revealed at autopsy that they had early signs of neurofibrillary tangles.
The evidence thus far does not, then, support the idea of a connection between Alzheimer’s disease and Lyme disease but we should be aware that this may simply be due to a dearth of quality evidence either way.
MacDonald AB. Plaques of Alzheimer’s disease originate from cysts of Borrelia burgdorferi, the Lyme disease spirochete. Med Hypotheses. 2006;67(3):592-600. Epub 2006 May 3.
MacDonald AB. Alzheimer’s neuroborreliosis with trans-synaptic spread of infection and neurofibrillary tangles derived from intraneuronal spirochetes. Med Hypotheses. 2007;68(4):822-5. Epub 2006 Oct 20.
O’Day DH1, Catalano A2. A Lack of Correlation between the Incidence of Lyme Disease and Deaths due to Alzheimer’s Disease. J Alzheimers Dis. 2014 May 19. [Epub ahead of print]