Not every one exposed to disease agent develops disease. Disease results from a complex interaction between man, causative factor and environment. If we closely study the Natural History of Medicine & the levels of prevention, we can successfully apply Homoeopathy at different levels as a mode of Intervention & minimize the sufferings in the world.

There are two phases of development of disease-

1. Prepathogenesis Phase:

Prepathogenesis phase refers to the period preliminary to onset of disease. During this phase the factors which favour the interaction of causative agent with the man already exist but disease process has not yet begun. Potentially most of us are in prepathogenesis phase of many diseases, both communicable & non communicable.

2. Pathogenesis Phase:

During this phase interaction between the host, disease cause & environment occurs to initiate the disease process. In presymptomatic stage, there is no clinical manifestation; & in clinical stage, recognizable signs & symptoms pathognomonic to disease appear. Variation in the onset of disease & its outcome in an individual depends on varying degree of host's reaction.

The goals of medicine are to promote health, to preserve health, to restore health when it is impaired, to minimize suffering and distress. These goals are embodied in the word "prevention".

On the basis of the evolution of the disease there can be three levels of Prevention:

1. Primary Level of Prevention:

It is defined as action taken prior to the onset of disease which removes the possibility that a disease will even occur. It lays emphasis on prevention of the emergence or development of risk factors. It signifies intervention in the Prepathogenesis phase.

In epidemiologic terminology, host is referred to as soil & disease cause as seed. No disease can develop until favorable soil is present for it. Similarly, all individuals exposed to similar disease agent do not develop disease.

Dr. Hahnemann  gives the answer for this variation in Aphorism 31 of Organon Of Medicine:

" The inimical forces, partly psychical, partly physical, to which our terrestrial existence is exposed, which are termed as morbific noxious agent, do not possess the power  of morbidly deranging the health of man unconditionally; but  we are made ill by them  only when our organism is sufficiently disposed & susceptible to the attack of morbific cause that may be present, and to be altered in its health, deranged and made to undergo abnormal sensations and functions- hence they do not produce disease in every one nor at all times".

An organism is made sick only if it has got sufficient susceptibility to the disease cause. Susceptibility in an organism, mental or bodily, is equivalent to state. State involves the attitude of organization to internal causes and to external circumstances.  Morbid susceptibility can be regarded as a negative or minus condition - a state of lowered resistance. Behind this morbid susceptibility lies some fundamental cause. Therefore, the active (fundamental) cause lies within and the apparent cause (exciting or maintaining cause) lies without. This fundamental intrinsic cause can be discovered in its latent form by studying the attributes which represent its existence - constitution of the patient, his mind, his will & desires, his moral and intellectual character, his sensations, his social and domestic relations, and his sexual functions. By giving proper constitutional remedy, the disposition to certain diseases and morbid susceptibility can be altered and the health of the individual can be preserved.

2. Secondary Level of Prevention:

Secondary prevention can be defined as "action which halts the progress of disease at its incipient stage & prevents its complications". The specific interventions are early diagnosis and adequate treatment. It attempts to restore health-(i) by seeking out unrecognized disease (ii) arrest the disease process and treating it before irreversible pathological changes have taken place (iii) reverse communicability of infectious diseases.

From homoeopathic point of view we can say that this level of intervention is required when functional changes start setting in. The body expresses its need for external aid by exhibiting symptoms & signs. In aphorism 18, Dr. Hahnemann writes-

"From this dubitable truth, that besides the totality of symptoms, with consideration of the accompanying modalities nothing can by means be discovered in disease where with they could express their need for aid , it follows undeniably that the sum of all the symptoms and conditions in each individual case of disease must be sole indication, the sole guide to direct us in the choice of a remedy."

It is necessary to know sickness, not from pathology, not from physical diagnosis, no matter how important these branches are, but by symptoms, the language of nature. Pathology gives us the results of disease, and not the language of nature. The science of Homoeopathy teaches us how each disease expresses itself in language and appearance and sensations.

Therefore, by carefully perceiving the changes in  the health of body and mind  (morbid phenomenon, symptoms ,sensations  & functions) patient can be screened  earlier , before the full fledged development of  pathognomonic symptoms  take place and the laboratory tests specific  for the diagnosis of the disease become positive. Homoeopathy can thereby help to seek out and treat the disease in pathologically presymptomatic stage and alter the progress of disease.

As far as clinical stage of the disease is considered, there is no better alternative than homeopathic medication to check the disease before any irreversible changes take place in the body. In aphorism Dr. Hahnemann says:

"Now, as diseases are nothing more than the alteration in the state of health of the health individual which themselves by morbid signs, and the cure is also only possible by a change to the health condition of state of health of  the diseased individual, it is very evident that medicines could never cure diseases if they did not possess the power of altering man's state of health which depends on sensations and functions ; indeed, that their curative power must be owing solely to this power the possess of altering man's state of health".

To reverse the communicability of infectious diseases, genus epidemicus can be of great help. Each  epidemic is of a peculiar, uniform character common to all the individuals attacked, and when this character is found in the totality of the symptoms common to all, it guides us to the discover of the homoeopathic (specific )remedy suitable to all the cases and preventable for new cases.

3. Tertiary Level of Prevention :

It signifies intervention in the late pathogenesis phase. Tertiary prevention can be defined as "all measures available to reduce or limit impairments and disabilities, minimize suffering from existing departures from good health and to promote patient's adjustment to irremediable conditions".

Practically speaking this is the stage when patients turn to Homoeopathy with the hope of miracles. Though miracles are not possible and cure can not take place at this stage, homoeopaths too have to revert to palliative mode of treatment as gross pathological changes have taken place. Allopath has the means of putting the patient under the influence of strong drugs and making them imagine that something is being done to their benefit, whereas injury is being done whenever the are patched by strong drugs. But homeopathy provides a better alternative even in this stage. If a short acting single homoeopathic remedy is applied on symptom similarity basis, further progress of the disease process can be checked upto some extent .The patient starts feeling mentally and emotionally better and his highest functional ability can be maintained. Homoeopathic medication can help to minimize the impairments and disabilities and can help the patient lead a better life.