History dictates that with a changing population structure there is a parallel mirror process affecting health. The theory behind population change is called the demographic transition, while the historical change in mortality is called the epidemiological transition [1]. Epidemiological transition piggybacks on an established mathematical theory that argues that populations go through a cycle of high death and high birth rate, followed by declining death rate and declining birth rate. Finally reaching a stage characterized by very low birth rate and low but fluctuating death rate. The epidemiological transition posits that throughout this cycle mortality changes from infectious diseases to chronic disease. Finally reaching a stage of delayed chronic diseases. Unlike the distinct definitions of fertility and death rate that determine the demographic transition, the cut-off between an infectious disease and a chronic disease has become blurred.
In the United States, according to the Centers for Disease Control and Prevention (USA-CDC) more than seventy percent of all deaths are due to chronic diseases [2] . Chronic diseases are characterized by Alzheimer’s disease, heart disease, diabetes and cancer. Since the causes of chronic disease was argued to be a combination of genetic, environmental, or lifestyle factors, public health was relegated as unimportant in dealing with chronic diseases. Public health is something that concerns only developing countries, until this year.
When an accountant managed water quality in Flint, Michigan, we very quickly saw a public health disaster enfold. Resulting in tainted water that marred the lives of a countless number of children for the rest of their lives. We created a chronic problem from a public health disaster. So perhaps we need to revisit the epidemiological transition, since infectious diseases might also contribute to chronic diseases. Especially since we are finding that chronic disease may apparently be infectious after all. If we can show that chronic diseases are infectious then the epidemiological transition becomes irrelevant.
An increasing number of chronic diseases are coming under scrutiny as possibly caused by infections. There are multiple examples to support the view that chronic diseases are in fact infectious diseases with a delayed expression. However, the search for bacterial, viruses, or environmental toxicity causes is difficult. Primary difficulty lies in detecting and replicating the causative agents in the laboratory. In most cases there are lags between the infection and the expression of the disease. Sometimes by the time the symptoms of the chronic disease appear, the causative agent is no longer present. But there are already strong signs that the three main chronic diseases have elements of infections: Alzheimer’s disease, cancer and heart disease.
Alzheimer’s disease
The initial infection that starts Alzheimer’s disease is unknown. As a chronic disease most of the research focuses on genetic mechanisms. But there is growing evidence that other, more relevant mechanisms exist, especially if we look at Alzheimer’s disease as a public health concern. These mechanism are: viral (HIV/AIDS, herpes simplex virus type I, Varicella zoster virus, cytomegalovirus, Epstein-Barr virus), bacteria (syphilis and Lyme-disease/borrelia), parasites (toxoplasmosis, cryptococcosis and neurocysticercosis), behavior (Alcohol, cigarette smoking, recreational drugs, concussion/mild/severe brain trauma) environmental elements (possibly aluminum), infections (possibly prions such as in Cretchfeldt-Jakobs disease), vascular causes (stroke, multiple-infarct dementia hydrocephalus, and injury or brain tumors, and emotional trauma. There are numerous studies that correlate all of these factors with Alzheimer’s disease, but surprisingly none of these factors appear in the federal “guidelines” for Alzheimer’s disease. [3]
As an example of the likely bacterium connection to Alzheimer’s is Lyme disease. Alois Alzheimer—who identified the disease in 1907—was primarily interested in syphilis. For centuries, other than just old age, syphilis was the main and only known cause of dementia. Although neurosyphilis is rare today, another bacterium gaining interest is Lyme disease. Lyme dementia has become a greater concern because it is the most common vector-borne disease in the northern hemisphere. Since there is no cure the expectation is that more patients will develop Lyme dementia in the near future [4].
Cancer
Other example where an infectious or an environmental substance contributes to chronic diseases is cancer. Viral causes of cancer are common enough that we call viruses that can cause cancer an oncovirus. These include human papillomavirus (cervical carcinoma), Epstein-Barr virus (B-cell lymphoproliferative disease and nasopharyngeal carcinoma), Kaposi's sarcoma herpesvirus (Kaposi's Sarcoma and primary effusion lymphomas), hepatitis B and hepatitis C viruses (hepatocellular carcinoma), and Human T-cell leukemia virus-1 (T-cell leukemias).
Bacterial infection may also increase the risk of cancer, as seen in Helicobacter pylori-induced gastric carcinoma. Parasitic infections strongly associated with cancer include Schistosoma haematobium (squamous cell carcinoma of the bladder) and the liver flukes, Opisthorchis viverrini and Clonorchis sinensis (cholangiocarcinoma.)
The human papillomavirus, for instance, causes more than 90 percent of cervical cancer cases and is one of the most common cancers in the world especially in Asia. With childhood immunization programs, including the hepatitis B vaccine, this cancer will become less prevalent. Hepatitis C virus causes cirrhosis, end-stage liver disease, and liver cancer. Human herpesvirus 8 causes Kaposi’s sarcoma, a malignant complication of AIDS. Helicobacter pylori, a spiral-shaped bacterium, is the agent of peptic ulcers and gastric cancer and has an important story of resistance, although not biologically but politically.
In 2005, two Australians, Barry Marshall and Robin Warren were awarded the Nobel Prize in Physiology for their pioneering work identifying the bacterium Helicobacter pylori as the cause of peptic ulcer disease. Overnight peptic ulcer disease was no longer a chronic disease but an infectious disease that can be cured by a short regimen of a pair of antibiotics. But despite evidence, it took more than ten years to persuade the scientific community. At the end, it took the primary author, Barry Marshall to infect himself with the bacteria to prove his point to a disbelieving scientific community. The long held view that peptic ulcer disease was a chronic disease wrestled against any competing views that it might be infectious.
Heart Disease
The relationship between heart disease and bacteria/virus is still sparse and interpretation of results is limited by potential biases. A large number of studies have reported on associations of human coronary heart disease and certain persistent bacterial and viral infections. One concluded that the relationship of heart disease with H pylori is weak, while for C pneumoniae, the evidence of association is stronger but still uncertain [5]. Endocarditis is a disease characterized by inflammation or infection of the inner surface of the heart usually caused by a bacterial infection from the mouth that enters the heart.
And there are already evidence for the efficacy of an approach that looks at chronic disease as caused by infections. At the 2016 annual meeting of the American Association for the Advancement of Science, Stanley Riddell with Seattle's Fred Hutchinson Cancer Research Center, announced how T-cell therapy can help the human immune system fight off cancer cells the way it would attack foreign bacteria or a virus. This finding joins the arsenal of some vaccines to prevent cancer.
Such associations have been difficult to expose because the path from exposure of an infection to the expression of the chronic disease is usually not linear. There are other mediating or/and moderating factors. For example, the role of infection mediated through chronic inflammation is then associated with a variety of chronic diseases such as multiple sclerosis, rheumatoid arthritis, lupus, and other autoimmune diseases. But the pharmaceutical industry, despite their advantage at being able to “cure” chronic disease has been reticent in accepting the full force of this implication. It is not a clever economic strategy to cure diseases, only to manage them.
What we need is a broader approach to look at cancer, heart disease and Alzheimer’s disease more as a public health concern. Looking at chronic disease as a long-term assault from an external agent, whether this agent is a bacterium, virus or some toxic element. By re-addressing our priorities in research, perhaps this is the way out of this research cul-de-sac we find ourselves in. It is such radical thinking that is needed to hopefully start finding cures that have evaded us so far.
References
[1] Omran, A.R (2005. First published 1971), "The epidemiological transition: A theory of the epidemiology of population change" The Milbank Quarterly 83 (4): 731–57, doi:10.1111/j.1468-0009.2005.00398.x
[2] Centers for Disease Control and Prevention. Death and Mortality. NCHS FastStats Web site. http://www.cdc.gov/nchs/fastats/deaths.htm. Accessed December 20, 2013.
[3] Garrett MD, Valle R (2015) A New Public Health Paradigm for Alzheimer’s Disease Research. SOJ Neurol 2(1), 1-9.
[4] Blanc F,Philippi N,Cretin B,Kleitz C,Berly L,Jung B,de Seze J. Lyme Neuroborreliosis and Dementia. Journal of Alzheimer’s Disease 2014; 41(4):1087-1093.
[5] Danesh, J., Collins, R., & Peto, R. (1997). Chronic infections and coronary heart disease: is there a link?. The lancet, 350(9075), 430-436.
© USA Copyrighted 2016 Mario D. Garrett
No comments:
Post a Comment