 Let us come back to a new session on dentistry and more. So we will be continuing our session on concept of causation. So so far we have covered germ theory, epilomological triad, multifactorial causation, web of causation and iceberg of disease. So the remaining portions that is natural history of disease, risk factors and spectrum of disease. Okay, so these three topics will be covered into today's session. So let's move on to the natural history of disease. So natural history of disease is nothing but suppose what happens when a pathogen enters our body, that is before the before the stage that is pre pathogenesis state, that is when we are exposed to a place where there are chances of pathogen entry and to a state where the pathogen can cause its full on effect to our body. So in definition, we can say that a disease evolves over time from the earliest stage of its pre pathogenesis phase to its termination. Okay, so when it has shows its full effect that is this pathogen has shows its full effect. It results in either recovery, disability or death. Usually in absence of treatment or prevention, we are not doing anything. Suppose we are not doing anything to prevent that pathogen control of pathogen. What will be the course of this pathogen action? How do this pathogen react or present in our body? So that is natural history of disease. Usually when pathogen enters the symptoms arise, we go to doctor or we take treatment and it will be cured or with maybe some disability will be there. So what if we are not doing any prevention or any treatment? So it might end up recovery, disability or death. So that is a natural history of any disease. So the process begins like when we are going to a place or when we are at a risk of getting an infection. Suppose we are going to a slum where the epidemic of cholera is around or in the air. I mean the water. So we are exposed to this cholera bacteria and we are having a high chance of getting this bacteria through water or any other way. But we have not yet shown this pathogen entry, the way for pathogen entry. The pathogen is still outside the body. So that is pre-pathogenesis phase but any moment this pathogen can enter and once it enter, it starts the pathogenesis phase because pathogen enters the body and it starts replicating and it shows its effect. So that is pathogenesis and pre-pathogenesis phase. So if there is no medical intervention what happens is as I told there will be either disability or death or there will be recovery. The body immune system itself shows recovery. You will fight against the pathogen and the body will be recovered. So what happens is the pathogen exposure we are going in a place where we get exposed, pathogen enters the host body, it results in disease, there is no intervention, it may end up either death, disability or recovery. So this process is known as natural history of disease, there is no intervention here. So usually natural history of disease can be studied in a cohort study. So we know cohort study is a prospective or future looking study. It studies, study starts with a disease free person and it goes and over a future period of time the person develops a disease. So the best way to study natural history of disease is cohort study. But since we know it is very laborious and it is costly. So mostly it is done by other methods like cross-sectional and retrospective like case control study. But best way is always cohort study because we can understand that how the disease shows this clear effect because when we start the study there is no disease. So over the period we will be knowing very clearly how the disease shows this effect. But if you are doing a retrospective study the disease has already done its all effect on the people or the particular person. So we will be asking questions and trying to find out what would have done. So it is not very accurate as we get the information during a cohort study. So what physician sees in clinic is just an episode of natural history of disease. So we go to a doctor when we get symptoms, when we get fever, when we get headache or when we feel tiredness, such symptoms we go to the physician or a doctor. So that is just part of or just an episode of the natural history of disease. So natural history of disease can be studied only by an epidemiologist. So a clinician or a doctor cannot study the natural history of disease. It should be studied by an epidemiologist how it starts, how it goes and what are the symptoms it shows and how it finishes its course via recovery, disability or death. So we can divide the natural history of disease as prepathogenic and pathogenic. Prepathogenic is before the pathogen enters the body but we are at a risk of getting the pathogen. Once the pathogen enters our body, pathogenic phase starts. So prepathogenic says as I mentioned earlier we are at a condition where the disease or the pathogen can enter our body at any time but it is not yet entered. So that is the prepathogenesis phase of many communicable and non-communicable disease. So this communicable disease like cholera or foot poison, we are at a position where any time we can get the pathogen. Like we are going to a restaurant where the foot poison has been reported. Any moment we get the pathogen, we are at an area where the cholera has been reported. We get any moment the disease and the pathogen enters our body. So that is prepathogenesis phase because pathogen hasn't entered our body. So I am exposed to the risk of the disease because there is a risk of disease in all these places. So we are at a risk of disease but we are not infected with the pathogen. So next is pathogening phase. When the pathogen or organism enters our body, when this Trostridium botany that is a foot poison causing bacteria or vibrio cholera enters our body, the pathogenic phase starts. It shows symptoms. It can be clinical or subclinical because we know many people with coronavirus it's not showing any symptoms but they are under pathogenic phase. We are all now since it is a pandemic we are all living in prepathogenesis phase because everywhere there is a case present. We may get the disease from any person. So we are all under prepathogenic phase that's only a case for such pandemic diseases. Once it enters it becomes pathogenesis. So clinical or subclinical let it be but it is a pathogenic phase. So the pathogen phase decides basically the fate of the disease, how it ended up with outcome can be recovery, disability or death. So we can summarize the natural history of disease by this picture. This is a cause of this pathogen. How it shows its effect on our body and these two phases one is prepathogenesis phase and this is pathogenesis phase. So we are living in an area where anytime the pathogen can enter our body that is prepathogenesis phase. We are living in a slum or we are going to a restaurant that is prepathogenesis phase. This particular organism enters our body the pathogenesis phase starts. Once it starts it might be asymptomatic or it is symptomatic. If it is symptomatic we will go to a doctor or a physician and we get it diagnosed. So diagnosis can be done only at clinical stage. Asymptomatic stage and diagnosis is very difficult. So it may end up death, disability or recovery. We are not doing any treatment here. This is just a natural history of disease. This diagnosis is possible under clinical stage because the patient will show symptoms. So that is all about natural history of disease. How a disease progresses without any medical treatment or any intervention or any prevention. How it goes and how it shows its full effect on the death, disability or recovery. So studying natural history of disease is very much important in prevention of disease. So natural history of disease is over. Next is the spectrum of disease. This is almost like our natural history. So it says that it is a graphic representation. So you can see that we know spectrum of color when a light enters the prism. It radiates many colors or that is why it got this name, spectrum of disease. So spectrum of disease is a graphic representation of variations in the manifestation of disease. So one disease can present various outcome. Sometimes a particular disease might be asymptomatic in a particular person. It might be symptomatic but very mild stage. Sometimes it will be in a moderate stage. Sometimes the same disease can be very fatal for that next person. So various manifestations are present for the same disease. So that is all about spectrum of disease. A healthy person, a particular disease showing various manifestations. So at one end, that is this end, the person is having positive health because that particular disease is not showing any problem for that particular patient. At one end of the spectrum are subclinical infections. Suppose if we take tuberculosis, many of the Indian population are carious. They are not showing any symptoms. Still they harbor microorganisms in their body. So they are under subclinical infection and they are not having any problems as such because positive health, better health. And the other end is death. The same disease can cause death of a person. They are very malnourished. They are living in overcrowded slum areas. The same disease can cause death of that person. So at one end it will be positive and better health. And the other extreme end it shows as a death. So at one end the spectrum are subclinical infection. And the other end it is fatal illness. So in the middle it is having illness ranging in severity. That is mild to moderate. This area will be mild to moderate. So spectrum of disease is nothing but a disease manifestations in various people ranging from positive health to death. So next we go to the iceberg we already covered. Next we go to the risk factors. Risk factors are very much important in the present scenario because all most of the diseases which were present in the past century like cholera, that contagious diseases, other contagious diseases like smallpox, plague, all are under well control because our scientific knowledge and our medical facilities have improved to a very extent that all these contagious diseases can be well controlled. So exceptions are there like corona pandemic. Still all the contagious diseases can be well controlled. But what happens is the other side of the disease that is chronic diseases or lifestyle diseases are on a increasing fashion because due to the change in lifestyle or due to change in the food habit or sedentary lifestyle the people are getting affected with many lifestyle diseases like coronary heart disease, diabetes, obesity, high cholesterol. So all these are risk factors we can say because we just cannot say we know that tuberculosis caused by mycobacterium tuberculae. In many diseases we cannot say what causes what because in multifactorial and web of causation we have seen how the chronic diseases or lifestyle diseases are exposed to. There are many factors which are intricate relationship causing the disease. So risk factors are coming into the limelight in this 21st century or the past 30, 50 years where the lifestyle of people have changed drastically. So risk factors are nothing but an attribute that significantly associated with the development of a disease that takes smoking. So this attribute has significantly associated with causing lung cancer. So it can be called as a risk factor anything which has a significant effect of producing something increased probability of causing something is known as risk factor. So it can be modified by intervention or reduce the possibility of occurrence. So we can prevent your measures, we can educate the people and risk factors can be modified and it is always modifiable. Some risk factors are not modifiable like our genetic makeup, our chromosomal abnormalities, our immune system. Such things are not modifiable risk factors but many risk factors like heating practices, sedentary lifestyle, the smoking, alcoholism. So such things can be modified and the outcome will be changed. So risk factors are suggestive but not absolute proof that is the difference between our germ theory and the recent web of causation. Germ theory says this bacteria causes this disease but in risk factors we cannot give that much assurance or absolute proof is not possible. It can give a suggestive power. It can cause this disease. Smoking can cause lung cancer. We cannot say that smoking causes lung cancer because many people with lung cancer smoking might not be a very significant factor because we don't have that much evidence, a perfect 100 percentage evidence because most of diseases are due to the web of causation. So that is the risk factors. So risk factors are many times modifiable and non-modifiable. Other modifiable are the which is coming in our daily practices and non-modifiable risk factors are also there. So risk factors are commonly associated with our lifestyle diseases. So we have covered most of the concept of causation. So I will just have a recap. So germ theory we covered epitomological triad, multifactorial natural and web of causation. These two are coming into our chronic or lifestyle diseases. Then the natural history of disease, how the disease be presented without an intervention and it has pre pathogenesis and pathogenesis phase. I spoke of disease we know what is a tip and what is under water and spectrum of disease, how the spectrum of disease showing from perfect health death and the risk factors and risk group. And risk group we know people who follows risk factors and there will be many risk groups because if we say contagious diseases we can say that the slim people or overcrowded people are mostly the risk group for getting that disease. People who are under smoking habit is a risk group for lung cancer or other emphysema such diseases. So there will be always risk group and age old people will be it is for schizophrenia, Parkinson's disease. So risk groups should be taken care of well. So this is all about concept of causation. So I covered it all the various concepts how the diseases between diseases caused from the 18th century and prior some diseases theories were there and to the very recent ones. So the present stage we are mostly seeing this risk factors and risk groups risk factors are the main thing and web of causation or multifactorial causation. So the next class I will be covering the prevention of disease the levels of prevention. So that's all about concept of causation. Thank you.