The 3rd chapter of Charaka Samhitha Vimana sthana is Janapadoddhvamsaneeya Vimanam. Janapada means a community. Udhwamsa means destruction. This deals with the determination of the specific characteristics of epidemics.
In Kampilya (modern Kampil of Farokhabad District in Uttar Pradesh), the capital city of the country called Panchala, which was inhabited by the high class people, Atreya was residing with his disciples. He was taking a stroll in the woods near the bank of the Ganga during the month of Jyestha (approximately May – June). He then, started speaking to his disciple Agnivesha. 
Collection, administration of herbs
Collection of herbs before the onset of epidemics:
O! Agnivesha, some abnormalities are now appearing in the stars, planets, moon, sun, air, fire and Disha (directions). This forecasts abnormality in the coming seasons. Very soon, the earth will cease to manifest proper tastes, potency, Vipaka (after digestion taste conversion) and Prabhava (special effects). This is bound to result in the wide-spread manifestation of diseases.”
Therefore, O! Agnivesha, all of you should collect herbs before the time of destruction and before the earth loses its fertility, leading to the impairments of taste, potency, Vipaka and special effects.
Administration of herbs during epidemic disease:
We shall administer these herbs with proper taste, potency, vipaka, and Prabhava to treat diseases. It is not difficult to treat epidemic diseases, provided the herbs are collected, preserved and administered properly. 
Query about onset of epidemic disease:
Agnivesha asked Lord Atreya, “O! Lord, herbs will soon be collected, preserved and administered properly. How is it that people having dissimilar nature, diet, physical strength, congeniality, mental faculties and age, simultaneously get afflicted by the same epidemic disease? 
Factors responsible for epidemics:
Lord Atreya replied, “Agnivesha! Though there is dissimilarity in the physical constitution of human beings, there are such factors as are common to all individuals. They are – air, water, location and seasons. (Vayu, Udaka, Desha and Kala). Vitiation of these factors leads to the simultaneous manifestations of diseases having the same set of symptoms leading to the destruction of a country. 
Characteristics of pollution of air, water, land and time:
Polluted air features
Air with following characteristics is injurious to health:
Ati stimitam ati chalam – Excessive calmness or violent waves
Excessive dryness, cold, hot air, roughness or humidity
Excessive clashes among each other (wind blowing from one direction clashing with the one from the other)
Paraspara gatim atikualinam – excessive cyclones and
Presence of unwholesome smell, gases, sand, ashes and smoke
Polluted water features
Water that can cause endemic diseases:
Water having the following characteristics is considered to devoid of its normal attributes
abnormal smell, color, taste and touch
Kleda – excessive stickiness
absence of aquatic birds
Reduction in the number of aquatic animals and
unpleasantness in taste and odor
Polluted land features
Land having the following characteristics is considered harmful:
Abnormal color, smell, taste and touch
Kleda bahulam – Excessive stickiness, moistness
Abundance of serpents, wild animals, mosquitoes, locusts, flies, rats, owls, vulture and jackal
Having excess of grass and weeds
Abundance of highly branched creepers
Having a novel look
Abundance of smoke in the wind;
Presence of wild cries of birds and dogs
Bewilderment and pain in animals and birds.
Pollution of time features
Time having following characteristics is considered to be harmful:
Perversion or absence of religion, truth, modesty, manners, conducts and other qualities of the inhabitants of the land
Constant agitation and over-flow of water reservoirs
Frequent occurrence of meteorites, thunderbolts and earthquakes
Fierce look and cries in the nature
Appearances of roughness and coppery red and white colored sun, moon and stars; their appearance as if they are covered with a net of clouds
Confusion, excitement; apprehension, lamentation and darkness in the atmosphere
Presence of excessive crying noise as if the country is seized by demons
Manifestation of the characteristic features contrary to the normal conditions of the various seasons is considered to be harmful.
The above mentioned four factors along with their respective features of vitiation are considered by the wise as responsible for destruction by epidemic diseases. When these factors are having qualities opposite to above, they are congenial for human beings.
Importance of treatment
During the impairment of these Janapadodhwamsakara Bhavas (factors), if proper medicine administration is done, one need not be afraid of diseases. [7-8]
Most dangerous factor – Janapadodhwamsa kara Bhava:
Thus it is said: – We shall now explain the vitiation of land, season, air and water in the order of their importance.
Impairment of air, water, place and time are more lethal in their increasing order. (impairment of time is most dangerous).
A specialist should know that, it is easier to correct the vitiation of air, water and land, than those of time (Kala). [9-11]
Line of treatment of epidemic diseases
One does not suffer from these disease even while all these 4 vitiated factors (vitiated air, water, place and time) are at work if he is administered with medicines and treatment.
For those who are afflicted with these 4 factors, Panchakarma detoxification therapy is the best treatment.
Proper Rasayana therapy done with medicines that are collected before onset of epidemic disease restores physical health.
Bhoote Daya – compassion for living beings,
Dana – donation, charity,
Bali – scarifies,
Devatarchana – prayer to the gods,
Sadvrutta – good deeds,
adoption of preventive measures, tranquility, protection of the self by Mantra etc are very effective.
Devotion towards God, residence in auspicious localities, observance of Brahmacharya, service to those observing Brahmacharya is told as a remedy.
Discussion on religious scriptures, befriending great sages, who have self- control, who follow religion, who are Satvika and who are learned people.
These therapies, which when adopted during epidemic disorders, can easily save lives of individuals provided the epidemics can easily save the lives of individuals provided the death of a particular individual is not pre-determined (by destiny) [12-18]
Factors underlying vitiation of air etc
Reasons for pollution of water etc leading to epidemics:
Having heard the causes of epidemics leading to the destruction of countries, Agnivesha again inquired from Lord Atreya, Sir! What is the factor underlying the vitiation of air etc., which destroy the entire country?
Lord Atreya replied “Sins of the present life or the misdeeds of the past life are at the root of the vitiation of all these factors. Intellectual blasphemy (Prajnaparadha) constitutes the origin of both the types of sins.
Causes – Sins
For example, when the rulers of states, towns, cities and countries do not follow the righteous path and take up to sins, then their subordinates and common people of villages and cities, and merchants add further to this sinful situation.
Sinful acts make the righteous acts to disappear. Because of the disappearance of Dharma, the god’s desert the people living in these places. Such are the places where seasons get impaired. Consequently, there will not be rainfall, wind does not blow properly; there is abnormality in the earth, water dries up, drugs lose their qualities and get impaired. Then there is impairment of the country because of the impairment of food and drinks. [19-20]
Sinful act leading to war:
Similarly a sinful act is at the root of destruction of a country by armaments. Because of increased greed, anger, ego, some people may start fighting among themselves with killer intention or the enemy looking down- upon them as weak persons. They may attack the enemy or may get attacked by them. 
Sinful act leading to affliction by Rakshasas:
People also get destroyed by Rakshasas (demons, germs, viruses) and varieties of other creatures due to sins. 
Sinful act leading to curse:
Similarly the sinful act causes destruction of population by curse. Those who get on without religious duties, they wrongly behave by showing disrespect to respectable ones. Many such families get immediately destroyed by curse. Even if they do not stay together, they get simultaneously destroyed because of the predetermined effect of the curse on them. 
Attributes in different Yugas
From the beginning of creation, manifestation of inauspiciousness has been preceded by sinful acts.
During Satyuga / Krutayuga:
During Satyuga, people were energetic like the sun; They were gods, divine saints, following Dharma, Yajna as per rules, Their bodies were firm like mountains; compact and stable; they had clear complexion and senses; they had strength, motion and valor like those of the wind;
They were endowed with the good shaped organs, features, proper body measurements, happiness and nourishment;
They were endowed with truthfulness, simplicity, non-violence, charity, self-control, observance of rules, medication, fasting, Brahmacharya and religious rites, and they were devoid of fear, attachment, envy, delicious, greed, anger, grief, mental diseases, abnormal sleep, drowsiness, fatigue, exhaustion, laziness and tendency to collect things.
Because of these factors they were endowed with an unlimited span of life in the beginning of the Satyuga.
Because of the noble mind, qualities and actions of the people, the earth etc., got endowed with all the good qualities as a result of which excellent tastes, potencies, Vipaka and specific actions were manifested in food grains.
At the end of Satyuga / Krutayuga:
At the end of the satyayuga, some rich people got heaviness in their bodies due to over- indulgence. They suffered from fatigue because of the heaviness of the body. Fatigue gave rise to laziness; laziness made them to accumulate things; accumulation led to the attachment for these things and attachment resulted in greed.
During Tretayuga greed gave rise to malice; malice gave rise to false statements, arose passion, anger, vanity, hatred, cruelty, infliction of injury, fear, sorrow, grief, worry, anxiety etc. therefore, during Tretayuga, a quarter of Dharma (religious duties) disappeared.
Because of this, the lifespan of human beings reduced by a quarter. Similarly, there was reduction in the attributes of earth etc, by one quarter. Because of the reduction of these attributes there was diminution by one quarter of the unctuousness, purity, tastes, potency, Vipakas, specific actions and qualities of grains.
Because of the reduction by a quarter of the attributes of diets and regimens there was an unusual change in the maintenance of equilibrium of Dhatus and there was vitiation of Agni (pitta) and Maruta (vata) by which, first of all, bodies of living being got afflicted with diseases like fever. Therefore the lifespan of living beings underwent gradual diminution. 
Gradual decrease in lifespan
Thus it is said: – Religious duties and qualities of living beings got reduced in quarters gradually by the passage of each Yuga. This is how the entire universe has to face dissolution. After the passage of 1/ 100th of the Yuga, the life span of living beings got reduced by one year the actual span of life specific to that age. Thus the origin of diseases in ancient times is described. [25-27]
Query about span of life:
Agnivesha enquired from lord Atreya, “O! Lord, is the span of life of all individuals predetermined or not?
Daiva and purusakara
Lord Atreya replied, O! Agnivesha, the lifespan of individuals depends upon the strength or weakness of both the Daiva (pre-determined) and Purusha (human effort).
Daiva and Purusha Kaara:
What is done during the past life is known as Daiva where the effect is predetermined and what is done during the existing life is known as Purusakaara- where the effect is based upon the human effort.
Depending upon the strength or weakness, both the types of actions described above are classified into three categories, viz, mild, moderate and strong.
Association with the effects of both these types of actions belonging to the strong category results in the long and happy life with a predetermined span.
In case of their mildness, the result is opposite and in the case of their mediocrity, the result is moderate. Hear the other cause of the predetermination or otherwise of the life-span [29-32]
Daiva and Purusakaara dominance of one over the other:
A weak Daiva (actions during the past life) get subdued by a strong Puruhsakara (action during the present life).
Similarly a strong Daiva subdues Purushakaara and because of this, some scholars hold the view that the span of life is invariably pre-determined.
Effects of a strong Daiva (actions of the previous life) are invariably manifested. The time of this manifestation is conditioned by the availability of a congenial atmosphere. [33-35]
Actions of past lives (Daiva) and present lives (purusakara) – their role in the determination of span of life:
Since the actions of past and present lives – both play their roles in the determination of the span of life, it is not correct to hold one sided view that one or the other is responsible for this.
If the lifespan is totally predetermined, then why there is need to do mantras, Aushadi (auspicious substances), Mani (wearing gems), Mangala Bali – auspicious rites, Upahara -offering, oblations, observance of religious rules (niyama), reconciliation, fasting, benedictory rites, paying obeisance, pilgrimage etc?
If the lifespan is totally predetermined, one may not be afraid of fierce and excited bulls, elephants, camels, donkeys, horses, buffaloes, harmful winds, waterfalls, rivers passing through mountains and having dangerous currents which are difficult to cross; rough fierce people and whose minds are afflicted with confusion and greed, enemies, highly inflamed fire, various poisonous animals like reptiles, over straining, regimens which are not conducive to the locality and seasons and such deeds as would enrage the king of the land.
If lifespan is totally predetermined, then those who have not taken steps to prevent untimely death, is not be afraid of it;
The instructions for initiation and discussions about the administration of Rasayana therapies would all be meaningless;
If lifespan is totally predetermined, even Lord Indra cannot kill his enemy by his Vajra (thunderbolt), even great sages cannot live as long as they like by means of meditation.
Why pre-determined lifespan theory is hoax?
The futility of the theory of predetermined lifespan can be observed even with the naked eyes. For example, thousands of people who go in for a battle and those who do not, have dissimilar spans of life.
Similarly, people whose diseases are treated immediately after their manifestation and those whose diseases are not treated in time or those who take poison and those who do not, have dissimilar spans of life. Earthen jars used as ornamental vases differ in respect of their durability.
Therefore, wholesome regimens lead to longevity, unwholesome ones to death. One should gradually resort to such actions and diets that are having qualities opposite to those of the locality, seasons and one’s own body.
He should avoid the over utilization, non- utilization and wrong- utilization of all regimens (Heena, Mithya and Atiyoga). One should give up all types of over indulgences; he is not supreme the manifested urges and he should avoid over straining. We know, we properly advise and we properly observe the above mentioned factors for the maintenance of health. 
Time of death
Agnivesha’s query about time of death
Agnivesha enquired, “O! Lord, if the span of living being is not predetermined then how is it said that some people die in the predetermined time and the rest otherwise?” 
Lord Atreya replied, “O! Agnivesha, as a vehicle with an axle endowed with all good qualities and driven on a good road gets destroyed only after the expiry of its normal life, similarly the life inside the body of an individual endowed with strong physique and wholesome regimen will come to an end only at the end of its normal span (according to the Yuga).
This is called “timely death”, the same vehicle along with its axle may subject itself to premature destruction in the event of a heavy load, uneven road, driving in places where there is no road, breakage of the wheel, defects in the vehicle or the driver, separation of the locking hook, lack of grease or an accident.
Similarly, in the event of excess strain, eating in excess, irregular meals, irregular body postures, excessive sex, association of urges which should be suppressed, affliction with evil spirits (germs), poison, wind and fire, exposure to injury and the avoidance of food and medicines, the life of an individual may soon come to an end. This is called “premature death”; when diseases like fever etc are not properly treated, they also lead to premature death. 
Hot water in fever
Query about prescription of hot water to patients suffering from fever:
Agnivesha enquired, O! Lord, why do physicians advise patients suffering from fever to take hot water in preference to cold water when the Dosha involved in the pathogenesis of this disease is is ideal for cooling therapies? 
Rationale behind administering hot water:
Lord Atreya replied, “Keeping in view physical advise the patient suffering from fever to take hot water so that the immaturely formed Doshas which are responsible for the disease may get matured. The site of origin of fever is Amashaya (stomach).
For the treatment of disease originated from the stomach, usually Pachaka (digestive), as well as emetic (Vamana) and Apatarpana (depleting) drugs are administered. It is because of this that the physician advises the patient suffering from fever to take hot water.
If hot water is taken, this results in a downward movement of Vata (flatus), stimulation of Agni (digestive enzymes), easy digestion (the hot water itself gets easily digested) and drying up of Kapha. Even then, hot water is not given to those patients with excessive vitiation of Pitta or if there is burning sensation, dizziness, delirium and diarrhea. Hot things, lead to the burning sensation, giddiness, delirium and diarrhea. Only cold food and drinks are helpful in this situation. 
Read more hot water benefits as per Ayurveda
Thus it is said:- enlightened physicians administer cold things to cure diseases caused by hot things. For diseases caused by cold things , hot drugs are useful. 
Santarpana and Apatarpana
Nourishing and depletion therapies: Santarpana and Apatarpana:
Similarly, the treatment of other disease involve the administration of therapies as are antagonistic to their causes. For example, diseases caused by the depletion of Dhatus cannot get cured without nourishing therapy; similarly diseases caused by over-nourishment cannot be cured without depletion therapy.
Apatarpana – Depletion therapy is of three types, viz,
Langhana-pachana (fasting and administration of such medicaments as would help I burning out the maturity of doshas) and
Doshavasecahna (elimination of Doshas).
Langhana (fasting) is suitable when the vitiation of Doshas is mild. By fasting, there is aggravation of Agni (power of digestion) and Vata, as a small quantity of water gets absorbed by heat and wind similarly Doshas get subsided by the aggravation of Agni and Vata due to fasting. Read more about benefits of Langhana therapy
Langhana Pachana (fasting and administration of such medicaments as would help in bringing out the maturity (paka) of Doshas) is suitable when the vitiation of Doshas is moderate. As exposure to sun rays, wind and sprinkling of ashes and dust dry up water in moderately vitiated. If the aggravation of Doshas is very strong, then it is necessary to eliminate them. Without breaking the boundary wall, it will not be eliminate to dry up a pond. Similar is the case when the doshas are exceedingly vitiated. 
Patients unsuitable for treatment
Even though required, as per state of the disease, elimination therapies, other forms of depletion therapies and nourishing therapy is not be administered to such patients who are
Anapavada Pratikara – have not been absolved of the allegations against them, those who are incapable of meeting their expenditure, those who pose themselves as physicians, those who are given to violent behavior and envy, those who draw pleasure from vicious acts, those whose strength, flesh and blood have undergone excessive diminution, these who are suffering from incurable diseases and those who are having symptoms of imminent death. If the physician takes such patients under his treatment, then he is defamed because of sinful acts. [ 45]
Thus it is said:-
If an action produces inauspicious results immediately or in the long run, then according to wise persons, one should not resort to such type of work.
Different kinds of places
Jangala or arid type of country is characterized by scarcity of water and trees, and plentiful of air and sunshine. It causes minimum number of diseases.
Anupa or marshy land is characterized by abundance of water and trees and scarcity of air and sunshine. It causes many diseases.
Sama or moderate type of country is characterized by moderation in the above mentioned factors. [46-48]
To sum up:-
Premonitory signs , causative factors in general, characteristic features and management of epidemics which destroy countries, source of the causative factors, origin of diseases in ancient times, process of the reduction in the span on life, determination of the timely and premature death of living beings, cause of premature death, appropriate medicine, selection of therapy for success, reasons for which a particular patient is not be treated- all these topics are described by lord Atreya to Agnivesha in this chapter on “ Janapadodhwamsa.” [49-52]
Thus ends the third chapter on the Determination of the Specific Characteristics of epidemics of the Vimana section of Agnivesha’s work as redacted by Charaka.