CAUSES OF DISEASE

There are three factors which are responsible for the spread of a disease. These factors include agent, host and environment. These factors are known as epidemiological triad. If any one of these factors is missing then disease cannot develop. Agent, host, and environmental factors interrelate in a variety of complex ways to produce disease. Different diseases require different balances and interactions of these three components.
These three factors are described below:

1.    AGENT

Agent is the most important factor for the occurrence of disease. Generally, the agent must be present for disease to occur; however, presence of that agent alone is not always sufficient to cause disease. A variety of factors influence the occurrence of disease.

The disease agents include:

Biological agents: bacteria, viruses, fungi, protozoa, worms and insects.

Nutrient agents: carbohydrates, proteins, fats, vitamins, minerals and water. An excess or deficiency of these nutrients may cause nutritional diseases.

Physical agents: extremes of cold and heat, X-ray, y-rays, pressure, electricity etc.
Chemical agents: carbon monoxide, pesticides, fertilizers, fumes, dust, gases etc. may cause illness by inhalation, ingestion or direct contact.
Mechanical agents: motor vehicles; machinery etc. may cause injuries and fractures.

2.    HOST

Host is the person or population on which the agent acts. The host related factors includes age gender, ethnicity, socio-economic status, marital status, nutritional status, genetic, occupation, physiological or psychological state, preexisted disease and lifestyle characteristics.

Each of these factors will have an impact on the development of disease in the individual host. Man acts as a host to a number of pathogenic micro-organisms. These micro-organisms attack the host when the immunity (defense mechanism) is lost. 

The host factors are:

·   Age plays an important role in developing disease. Ex: Certain diseases like measles etc. are more common in childhood, cancer in middle age and tuberculosis in old age.

· Studies showed genetic factor played a role in the development of disease. Ex: sickle cell anemia, hemophilia, essential hypertension, Diabetes, etc are genetically transferred diseases.

·  Gender also plays a role in developing disease.   Ex: Females are more affected from cancer of various organs than males especially breast cancer. Cases of heart attacks are more in males than in females. Other illness due to gender includes Essential hypertension, diabetes, mental diseases etc.

·   Sickle cell anemia is more common in certain ethnic groups like People of African descent, including African-Americans.

·  Physiological and psychological state of host is also considered in disease occurrence. Ex: pregnancy, obesity, high blood pressure etc. 
   Stress is one of the important psychological factors in developing disease.

·  Pre-existence of diseases and immunocompetence are also key factors affecting susceptibility and resistance to diseases.

·  Nutritional factor such as Deficiency of proteins may cause kwashiorkor and other problems. Over-eating may lead to obesity and diabetes. Certain habits like smoking may cause lung cancer; open air defecation may cause soil and water pollution which ultimately causes various types of intestinal disorders.

3.     ENVIRONMENT

Environment plays a great role in the maintenance of health. A healthy environment is crucial for the health and well being of individuals and communities. Environment is the third concept inherent in the epidemiological triad in causing disease. It may be favorable to host or to agent. If the environment is favorable to agent it will cause disease. The interaction of host and environmental factors is very important in tracing the etiology of disease.

Negative environmental factors are threats to health, and controlling them is public environmental health. They include:

· Climatic and seasonal factors may determine whether it will be suitable to a particular disease or not e.g. malaria is more common in rainy season whereas common cold is more common in winter. Pollen and pollution in air leads to respiratory diseases or cancers

   Environmental disruptions like floods, droughts, storms, fires, earthquakes, volcanoes affect the health.

Sanitary conditions, provision of potable water supply, education and standard of living as well as biological environment e.g. animals, insects, rodents etc. are important factors in determining incidence of diseases.

· Release of noxious chemicals like mercury becomes poison. Create temporary, intense, life-threatening heat islands (e.g. urban heat waves exacerbated by climate change) results from nuclear, biological or chemical warfare etc.

PREVENTION OF DISEASES

Communicable or infectious diseases are infections which are transmitted from an infected person, animal or reservoir to another person. These infections can spread through direct or indirect contact. Knowledge of how infectious diseases spread can help minimize the risk of infections. Adopting disease prevention measures can reduce illness.

Disease prevention focuses on prevention strategies in reducing the risk of developing diseases and other morbidities. “Prevention is better than cure”. According to this, suitable preventive measure must be taken for the occurrence and spread of diseases. The concept of prevention of diseases includes three levels.

     A.   PRIMARY PREVENTION:

Primary prevention may be defined as” the action taken prior to the onset of disease which removes the possibility of ever occurrence of a disease”. Primary prevention is studied under two sub categories

i.              Health promotion measures

These include:

·         Maintenance of a healthy environment

·         Maintenance of personal hygiene

·         Eating adequate balanced diet

·         Provision for safe water supply

·         Provision of proper disposal of human excreta and domestic wastes

·         Provision of well managed sewer system

·         Isolation of infected persons

·         Immunization

·         Maintenance of healthy and clean sex life

·         Motivating people to avoid the use of tobacco, alcohol and drugs.

ii.            Specific protective measures

Specific diseases can be prevented by taking specific measures against these diseases. Ex: tuberculosis, diphtheria, pertussis, tetanus, polio, measles etc, can be prevented by immunization at proper age and time. Since children are more susceptible to these diseases. Hence vaccination is necessary. Few diseases like Rickets and scurvy can be prevented by administration of vitamin D and vitamin C respectively.

Similarly industrial accidents can be prevented by using specific protective devises like goggles, gloves, shield against carcinogens, allergens and occupational hazards etc.

Primary prevention also includes prevention of chronic diseases by avoiding smoking, drinking, dietary control and physical exercise etc.

Primary prevention is less expensive, safe and more effective way of preventing diseases in comparison to secondary and tertiary prevention.

B.   SECONDARY  PREVENTION

Secondary prevention aims to detect new cases of infectious disease at the earliest possible stage and intervene in ways that prevent or reduces the risk of infection spreading further in population. Secondary prevention strategies include:

i.              Early treatment

This level of prevention involves infected (or exposed) individuals receiving early treatment to prevent the transmission of pathogens to susceptible hosts. Benefit to the individual may also result from treatment, but the aim of community health is to protect the community as a whole from further infections, rather than to aid the personal recovery of identified patients.

ii.            Education and health-related behavior modification

Secondary prevention relies partly on educating the population about signs of illness that require prompt medical appointment coupled with systematic surveillance to detect and report cases quickly and respond with effective treatment. If the disease has the potential to generate an epidemic, it is necessary to isolate (quarantine) infected individuals by educating about how they can prevent or reduce the risk of transmission to other individual.

iii.           Screening

Infected individuals can also be identified even before symptoms develop in systematic screening programmes, i.e. application of a test or an investigation to large numbers of individuals to identify who are at risk of developing a particular disease, or in case of infectious disease those who are already infected. The screening service can target groups assumed to be at high risk. Ex: TB screening.

C.   TERTIARY PREVENTION

Medical treatment to prevent the worst outcomes of a disease in an individual is known as tertiary prevention. The aim of the tertiary prevention is to reduce further complications or permanent disability in patients which includes

• Permanent disability can be prevented by immunizing the infants against polio, etc. Disability due to industrial accidents can be prevented by wearing goggles, gloves, hood etc. Surgical operations can limit the disability to the extent. Adequate treatment and physiotherapy can reduce the duration of disability.

• Rehabilitation of the handicapped patients is very important which could be brought by
  
  medical(physiotherapy), social, educational and vocational rehabilitation, sheltered workshops, colonies, selective changes in occupation, opening hostels and schools for handicapped children and attachment of artificial limbs to an accident victims etc.

The key goal for tertiary prevention is to enhance quality of life.

TRANSMISSION OF DISEASES IN A COMMUNITY

All communicable diseases transmitted from one person to another through some transmission methods and they spread from the source or reservoir of infection to a susceptible host. The source of infection may be a person, animal, object or substance from which an infection is transmitted to the host.

A reservoir may be any person, animal, arthropod, plants, substance or soil or combination of these in which an infectious agent lives and multiplies from where it can be transmitted to the susceptible host.

Ex: Reservoir for tetanus bacilli is the soil but the host is man,

Reservoir for rabies virus is an animal but the host may be animal or man.

Infectious diseases are those that are transmitted from person to person by direct or indirect contact. Viruses, bacteria, parasites, and fungi all cause infectious disease.

Modes of transmission of Infection:

Infection may be transmitted from the reservoir to the host by the following modes:

A.      DIRECT TRANSMISSION

In direct transmission infection is spreads without any intermediate host.

a)      Direct contact: some diseases spread from person to person by direct contact.

Ex: shaking hands, kissing, sexual contact etc.

Diseases spread through direct contact are diarrhoea, dysentery, cholera, typhoid, syphilis, gonorrhea and AIDS.

b)      Droplet infection:

Respiratory infections transmit through fine droplets during coughing, sneezing and talking. These droplets contain Diseases pass from one person to other through inhalation are called droplet infections. This is the common mode of transmission of diseases. Diseases spread through droplet infections are common cold, influenza, whooping cough, tuberculosis, measles, chicken pox, small pox, diphtheria, pneumococcal and viral pneumonia etc.

c)       Infected dust:

The droplets containing pathogenic micro-organisms which are expelled during sneezing, coughing, talking or laughing by the diseased person either settles down on articles like clothes, carpets, bedding's, floor or on other objects. These droplets dried up on those things and released into the air during dusting, cleaning and bed making. When the healthy person inhales these dust particles infection starts. Dust particles may also be blown by wind from infected soil.

Diseases caused by infected dust include, enteric fever, cholera, amoebic dysentery, pneumonia, tuberculosis and tetanus.

d)      Animal bite:

Some infections gets transmitted through animal bite such as dog bite, snake bite etc. diseases transmitted through animal bite includes, rabies,tularemia, plague, monkey pox, listeria, anthrax etc.

e)      Transplacental transmission:

Some diseases may be transmitted from the infected mother to the foetus through the placenta. This mode of transmission is known as vertical transmission. Examples of diseases through this transmission include hepatitis B, rubella virus, syphilis and AIDS.

B.      INDIRECT TRANSMISSION

When the transmission of diseases from diseased person to healthy person occurs through substances like milk, water, insects or fomites it is known as indirect transmission.

a)      Vehicle borne:

The common vehicle through which the disease is transmitted are water, milk, food, blood, blood products, tissues and organs. The diseases which are spread through water, food or blood are known as water borne, food borne or blood borne diseases respectively.

Water borne and food borne are the common infections include enteric fever, cholera, diarrhoea, dysentery, hepatitis, food poisoning etc.

Milk borne infections include bovine tuberculosis, diphtheria, sore throat, enteric fever, and dysentery.

Disease transmitted through infected blood is hepatitis B (serum hepatitis).

b)      Vector borne:

A vector is defined as an arthropod or any living organism that transfers the infectious agent to the susceptible host. Examples of such arthropods include mosquito causing malaria, rat flea causing plague, louse (typhus fever), flies etc.

Vector borne disease transmission is simply a mechanical process as the house flies carry the disease agent from one place to another on their body, wings and legs. Vector borne diseases includes malaria, filariasis, dengue, plague, leishmaniasis, schistosomiasis, etc.

c)       Fomite borne:

Fomites are the inanimate articles which are capable of absorbing, retaining or transferring infections from one person to another.

The articles which comes in direct contact with the patient will easily gets contaminated with disease agent and can spread disease to the healthy persons when they come in contact with these infected articles.

Examples of fomites are clothes, towels, handkerchiefs, bedding, spoons, drinking glasses, utensils, pen, pencil, books, toys, removed dressings, toys etc. these articles plays an important role in indirect transmission of infections.

COMMUNITY HEALTH

Community: A community is a group of people who have common characteristics. Communities can be defined by location, race, ethnicity, age, occupation, interest in particular problems or results or other common connections.

Community Health:

Community health is a field of public health a discipline which concerns with the study and improvement of the health characteristics by protecting and improving the health of communities through education, promotion of healthy lifestyles, diseases and prevention methods. 

Community health professionals analyze the effects on health of genetics, personal choice and the environment in order to develop programs that protect the health of your family and the community. 

Fundamentals of Community Health

·         The fundamentals of community health include:

·         History of community health practice

·         Factors affecting community and population health and

·      The tools of community health practice. These tools include epidemiology, community organizing, health promotion, disease prevention, planning, management, and evaluation.

Community health is studied under three broad categories:

1.    Primary Healthcare

Primary healthcare denotes the first level of interaction between individuals and families with the health system which includes family planning, immunization, prevention of locally occurring endemic diseases, treatment of common diseases or injuries, provision of essential facilities, health education, provision of food and nutrition and adequate supply of safe drinking water. Primary Healthcare is provided through Sub centers and in rural areas, whereas in urban areas through Health posts and Family Welfare Centers.

2.    Secondary Health Care

Secondary Healthcare refers to a second level of health system, in which patients from primary health care are referred to specialists in higher hospitals for further treatment. The health centers for secondary health care include District hospitals and Community Health Centers at block level.

3.    Tertiary Health Care

Tertiary Health care refers to a third level of health system, in which specialized counseling care is provided usually on referral from primary and secondary health care. These includes Specialized Intensive Care Units, advanced diagnostic support services and specialized medical personnel on the key features of tertiary health care. Under public health system, tertiary care services are provided by medical colleges and advanced medical research institutes.

Factors that Affect Community Health:

The factors that affect the health of a community include:

Physical factors: related to geography (parasitic diseases), environment (availability of natural resources), community size (overcrowding), and industrial development (pollution).

Social and cultural factors: beliefs, traditions, and prejudices (smoking in public places, availability of ethnic foods, racial disparities), economy (employee health care benefits), politics (government participation), religion (beliefs about medical treatment), social norms (drinking in a college campus), and socioeconomic status (number of people below poverty level).

Community organization: available health agencies such as (local health department, voluntary health agencies) and the ability to organize with solving problem (city council).

Individual behavior: personal behavior includes exercising, getting immunized, and recycling wastes.

Community Diseases:

A disease is the condition of an organism experiencing impaired function often with detrimental symptoms. A symptom is the body’s response to a disease and often is an indicator to diagnose the type of disease.

A disease outbreak is the occurrence of disease in surplus of what normally be expected in a defined community, geographical area or season. An outbreak may occur in a restricted geographical area, or may extend over several countries. It may last for a few days or weeks or for several years too.

The amount of a particular disease that usually present in a community is referred to baseline or endemic level of the disease. The disease may continue to occur at this level indefinitely. Thus, the baseline level is often considered as the expected level of disease.

Several factors like genetics, age, nutrition or pathogen (microorganisms) can lead to disease occurrence in humans.

Communicable or infectious diseases are often transmitted by pathogens and are easily spread from one person to another through contact and proximity. They spread through the air, water or soil or animal intermediates.

Non-communicable diseases are known as chronic diseases which are not transmitted from person to person. They are of long duration and generally slow in progression. The main types of non-communicable diseases are cardiovascular diseases (heart attack and stroke), cancer, chronic respiratory diseases (chronic obstructed pulmonary disease and asthma) and diabetes.