There are many known causes of dementia. One of these causes are bacteria. Bacteria are usually ignored despite its historical and current significance in dementia research. A hundred years ago it was well known that syphilis—a bacterium—was the only known cause of dementia. The bacteria interferes with the nerves until it reaches the brain where it destroys the brain from the inside. In the end, the expression of long-term syphilis is dementia—Neurosyphilis. Alois Alzheimer wrote his post-doctoral thesis (Habilitationsschrift) entitled “Histological studies on the differential diagnosis of progressive paralysis.” on neurosyphilis before his supervisor Emil Kraepelin propelled him into the history books by defining Alzheimer’s disease as a new disease in 1911. 
Neurosyphilis was very common in the 1900s. Between one in four to one in ten people in mental institutions were there because of neurosyphilis. Eventually syphilis kills its victims. Before the introduction of penicillin in 1943, syphilis was a common killer. In 1929, among men, the death rate from syphilis was 28.3 per 100,000 for Whites and 97.9 per 100,000 for Blacks . The similarities between syphilis and dementia were addressed repeatedly in the early literature in Alzheimer’s disease . Because syphilis can now be treated easily and cheaply, it has nearly been eradicated. But there is a new bacterium threat emerging—one that can also cause dementia.
Today, the main bacterial threat to acquiring dementia comes from Lyme disease—a bacterium borrelia burgdorferi. Lyme disease is transmitted to humans mainly through the bite of infected blacklegged tick. These ticks are themselves infected by feeding off mainly diseased birds, which bring the infection from across the globe. Worldwide there are 23 different species of ticks that can carry Lyme disease or diseases that are similair to Lyme disease (e.g. Borrelia bissettii.)
Lyme disease is the most common disease carried by animals in the northern hemisphere and it is becoming an increasingly public health concern . Not only because Lyme disease is a debilitating disease, but because eventually Lyme disease has been shown to cause dementia—Lyme dementia . Science has not identified the mechanism for the development of Lyme dementia, but Judith Miklossy has some interesting leads. The American psychiatrist Robert Bransfield has been documenting some of its neurological expressions, but so far there is a lack of emphasis in the research community on exploring these clinical features.
Ernie Murakami, a retired physician, has been monitoring the spread of Lyme disease across the world. With more than 65 countries that have the blacklegged ticks which transmit Lyme disease, this is a worldwide pandemic.The prevalence of Lyme disease reporting varies dramatically. Canada reporting the lowest cases in the world, with 1 case per million, while Slovenia reports 13 cases per 10,000. In the United Sates the Centers for Disease Control and Prevention reports that more than 329,000 people are likely to be infected every year in the U.S. alone. Only one in ten cases are reported since clinicians are not looking for Lyme disease. This estimated number of annual infections is higher than hepatitis C, HIV, colon cancer, and breast cancer. Lyme disease accounts for more than 90% of all reported cases of diseases carried by animals (vector-borne illness).
With any good public health strategy there needs to be a two pronged response. One is to address the clinical effects of the disease and the other is to address the underlying cause. In the United States, although research funds to examine and explore cures for Lyme disease are minimal, this avenue is likely to see the most significant increase. But this would be folly without addressing the underlying cause of the disease. Addressing these underlying causes will however be challenging.
Harvard Medical School Center reports that areas suitable for tick habitation will quadruple by the 2080s. But there are more pressing changes that will happen in our lifetime. Deforestation and climate-induced habitat change are affecting insect which carry diseases like malaria and Lyme disease. Slow climate change, urban growth in areas next to forests, reforestation following the abandonment of agriculture, and increases in the deer, mice and squirrel populations (among many others) which harbor these ticks.
Malaria and Lyme disease are both projected to increase. Even taking a more conservative estimate (all of the USA, most of Canada, all of Europe, Middle East and China), more than half the world’s populations are likely to be exposed to Lyme disease. A proportion of these populations will become infected with Lyme disease and eventually some will develop dementia. Pure Lyme dementia exists and reacts well to antibiotics . Is public health ready to address this? 
© USA Copyrighted 2017 Mario D. Garrett
 Garrett MD (2015) Politics of Anguish: How Alzheimer's disease became the malady of the 21st century. Createspace. USA.
 Hazen H.H. (1937). A leading cause of death among Negroes: Syphilis. Journal of Negro Education, 310-321.
 Pearson S. (2014). Recognising and understanding Lyme disease. Nursing Standard, 29(1): 37-43.
 Blanc F., Philippi N., Cretin B., Kleitz C., Berly L., Jung B., ... & de Seze J. (2014). Lyme Neuroborreliosis and Dementia. Journal of Alzheimer's Disease, 41(4): 1087-93.
 Miklossy, J. (2015). Historic evidence to support a causal relationship between spirochetal infections and Alzheimer’s disease. Frontiers in aging neuroscience, 7.
 Garrett MD, & Valle R (2015) A New Public Health Paradigm for Alzheimer’s Disease Research. SOJ Neurol 2(1), 1-9. Accessible for free from: https://sites.google.com/site/mariodrmariogarrettcom/GARRETT_VALLE_NEUROLOGY.pdf?attredirects=0
Miklossy J (2017). Handbook of Infections and Alzheimer's disease. IOS Press.