There are two ways in which the environment affects human health. The first is directly—through pollutants discharged by industries into the air and the water and by automobiles. In urban areas, in particular, the current disease pattern is closely linked to the deterioration in the quality of air and water.
Human health is also affected by the quality of the environment in the place of work. Over the years, the authorities have recognised that the workers in certain occupations—such as textile mills or stone quarries—suffer from occupational diseases (tuberculosis).
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Although by law, the people running these factories and quarries are supposed to provide the workers with equipment to minimise their exposure to pollutants, in most cases such steps are not taken.
As a result, an increasing number of workers— specially those in the informal sector—suffer for years from diseases, for which they receive little or no compensation.
The World Health Organisation recognises a number of environmental factors that affect human health (Table-31.1):
The deterioration of the environment—such as the existence of stagnant pools in villages and cities—provides fertile ground for the breeding of vectors. Many such disease-carrying vectors have developed immunity to pesticides. As a result malaria, which was once thought to have been eradicated, has reached endemic proportions in many parts of the country.
What is worse, the malarial parasite has become immune to a growing number of pesticides and drugs. For instance, P. falciparum, which causes virulent cerebral malaria, is resistant to chloroquine, the drug most commonly used in the treatment of malaria. Similarly, diseases like kala-azar are difficult to eradicate because the organisms spreading it find increasing number of breeding places.
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Overcrowding and unhygienic living conditions in cities, specially in slums, have also contributed to the spread of other communicable diseases like tuberculosis and cholera. Health interventions become almost meaningless so long as such conditions prevail.
It has become abundantly clear that improving environmental conditions should form an important part of healthcare, because curative care alone will not suffice as more succumb to these diseases.
Human Diseases:
A disease is a deleterious change in the body’s condition in response to environmental factors that could be nutritional, chemical, biological and psychological.
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Diet and nutrition and infectious agents, toxic chemicals, physical factors and psychological stress all play roles in the onset or progress of human diseases.
To understand how these factors affect us, let’s look at some of the major categories of environmental health hazards (Table-31.2):
Chemicals:
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Toxic chemicals in the environment are becoming a source of increasing concern to people of industrialised countries, though human beings are often exposed to toxic substances in nature also. Chemical agents are divided into two broad categories—those that are hazardous and those that are toxic.
Hazardous substances include inflammable chemicals, explosives, irritants, sensitizers, acids and alkalies, etc.; while toxic substances include poisonous materials that are cytotoxic in nature.
In addition allergens, mutagens, teratogens and carcinogens are also quite common in nature that causes severe health hazards in communities. Physical agents like radiation also causes serious health hazards to humans.
There are many sources of toxic and hazardous chemicals in the environment. The danger of each chemical can be determined by factors related to the chemical itself, its route or method of exposure and its persistence in the environment as well as characteristics of the target organism.
Cells have mechanism for bioaccumulation, selectively absorbing and storing a great variety of molecules. This allows them to accumulate nutrients and essential minerals, but they also may absorb and store harmful substances through this same mechanism.
Subsequently, the; effects of toxins are magnified in the environment through food chains. Bio magnification occurs when ‘the toxic burden of a large number of organisms at a lower trophic level is accumulated and concentrated by a predator at a higher trophic level.
Some such toxic chemicals/compounds are very unstable and degrade rapidly under most environmental conditions. For example, DDT and other chlorinated pesticides poses a serious threat to biotic communities due to its prolong persistence.
Diet:
Diet also has an important effect on health. Malnutrition particularly poses a serious threat to the protection against infectious diseases as well as exposures to toxic substances. In addition to calories, we need specific nutrients such as proteins, vitamins and minerals in our diet. The world’s most prevalent diseases are shown in Table 31.3.
Some special categories of health problems are:
1. Water-borne pathogens;
2. Respiratory hazards due to air pollution in urban centers;
3. Climate changes and human health effects;
4. Vector-borne diseases;
5. Metal toxicity and diseases—e.g., Minamata disease; and
1. Water-Borne Pathogens:
A wide variety of human pathogens may be found in the excrement from humans as well as from other animals. Most human pathogens can be classified as either viruses, protozoans, helminths or bacterias. Both raw sanitary sewage and land runoff contain pathogenic organisms.
Approximately 20% of the reported outbreaks and illness associated with water-borne diseases were attributed to bacterial pathogens belonging to the genera Salmonella and Shigella. Cholera is another serious and acute intestinal disease which is caused by the bacterium Vibrio cholera; occurs sporadically as epidemic disease.
Numerous protozoan species normally inhabit the intestinal tract of warm blood animals, including humans Entameba and Giardia are the most common protozoan infective agents. A good number of enteric viruses were found in water which happens to infect various organs of human being.
These are namely Poliovirus, Hepatitis A, Reovirus, Adenovirus and Rotavirus, etc. A variety of helminth diseases were found to occur as human being whose cysts were found to be present in the waste water contaminated water bodies. Among the helminths, Ascariasis and Taenia infections were most prevalent.
A summarised accounts of water related infections is given in Table 31.4:
2. Respiratory Hazards:
Due to rapid rise of air pollution problems, respiratory hazards increase day by day. Over past couple of decades, urban air pollution problems enhanced the variety of respiratory hazards ranging from bronchitis to pneumonia. The extent of hazards altered markedly in different seasons (Table 31.5).
3. Climate Change and Human Health:
Over the years, global climate has changed severely—particularly with respect to temperature. Such a change leads to serious health impact, particularly with respect to allergy, vector-borne diseases and also communicable diseases.
A schematic presentation of such diseases is shown in Fig. 31.1:
4. Vector-Borne Diseases:
There are a large number of vector-borne diseases found in the tropics. These are Malaria, Kala-azar, Dengue, Encephalitis, and Yellow fever, etc. These diseases are spread by the various categories of mosquitoes.
The incidence of mosquito-borne diseases increased significantly during past six (1950-2010) decades in various tropical countries. Due to rapid deterioration of sanitation and health-care systems influencing the gradual rise of mosquito-borne diseases (Fig. 31.2).
5. Metal Toxicity:
In general, a good number of heavy metals have toxicity symptoms. Among them toxicity caused by lead, mercury and arsenic are considered to be noteworthy. Minamata disease is one such metal toxicity disease.
Arsenicosis:
Arsenic is one of the most important environmental global toxicants that cause acute and chronic adverse health effects, including cancer. Millions of people around the world have been exposed to arsenic through geologically contaminated drinking water. Epidemiological studies conducted since 1960s indicated that ingestion of inorganic arsenic is linked to internal cancers in lung, liver, skin, bladder and kidney of man.
The evidence of health risk from arsenic contamination is so compelling that since 2000 WHO/EPA (USA) recommended lowering of the maximum contaminant level of arsenic from 50 to 10 µg/ lit.
In addition to cancer induction due to arsenic toxicity, cardiovascular disease, neurogenic effects, diabetes mellitus, hearing loss, fibrosis of lung and liver, anaemia and other hematological effects are seen as an effect of arsenic toxicity.
The exposure pathways of arsenic could be inhalation of dusts containing arsenic, ingestion of food and drinks containing arsenic and also through dermal contacts. The potential role of carcinogenic effects of arsenic are considered as altered DNA/chromosomal abnormalities and/or through oxidative stresses.
Various clinical cases of arsenic affected patients are reported in West Bengal viz., cancer of skin and kidney, keratosis, raindrop pigmentation, dry gangrene, hepatomagaly, splenomagaly, polyneuropathy, anaemia, dyspepsia etc.
Fluorosis:
High fluoride level (above 1.5 mg/lit) in ground water led to fluorosis in several area of India, China and Thailand. Excess fluoride in drinking water over the years lead to dental and skeletal fluorosis (bony deformities). Around 90 districts of India have fluorosis problems. Several thousand population suffers from fluorosis, which needs to be treated with supply of fluoride free drinking water.
Goiter:
Deficiency of iodine in water and diets leads to thyroid dis-function. As a result thyroxine hormone level is very low. During such hypothyroidic condition, goiter is seen. The sign of goiter is shown as swelling below the throat along with lack of proper assimilation. Thyroxine deficiency goiter often seen in foot hill region Iodized salt is often prescribed as remedy of goiter protection.
6. Radiation Damage:
It is well-known that radiation causes short and long-term damages to various body organs. Both cosmic rays and UV-radiation has detrimental effect on human health. One of the major health hazards as induced by radiation at low level persistent exposure is induction of cancer at various organs.
The frequency of risk of different types of cancer varies widely with respect to dose of expose and also racial criterion.
An overall example of cancer risk of human organs is shown in Fig. 31.3:
Health Impact Assessment:
In genera] there are five major categories of health hazards viz., communicable diseases, non-communicable diseases, malnutrition injury and mental disorders (Table 31.6). The pattern of health impact assessment in any of these depends on types of health hazards, their causative and size of the population examined. However, a broad scheme for assessment is shown in Table 31.7.
As of now, most environmental management programmes are restricted to sanitation and hygiene. The network of primary health centers are geared only to control traditional illness. The health morbidity data due to pollution-related problems are very scarce. The health laws, as they exist now, relate only to occupational safety and chemical safety.
The existing environmental impact assessment procedures do not rigorously analyse the health and social impacts of developmental projects. Consequently, health continues to remain an extrinsic factor in all environmental analysis.
National Policy and Programme of Vector-Borne Diseases:
1. While the public health system has to play a critical role through institution of preparedness and early warning mechanisms as well as a rapid containment capacity, comprehensive management of VBDs warrant a broad multi-sectoral response and social mobilization for full involvement of the community.
2. A medium-to long-term strategic plan, with allocation of adequate resources, should be developed including public health, environmental and legislative measures needed to prevent and control vector-borne diseases.
Vector control or prevention of vector borne diseases should be among the healthy public policies, to ensure that before any developmental activity is planned or implemented, the public health concerns are taken into consideration.
3. Partnership building and enhancing the role of various sectors such as education, public works, tourism, industry, the private sector, NGOs, etc. is critical. Each sector should be sensitized about its role in the prevention and control of vector-borne diseases.
Taking locally acceptable measures to prevent such diseases must receive a high priority. Active participation of inter-sectoral partners is needed, right from the programme planning stage to its implementation and evaluation.
4. Operational research on disease transmission and risk factors as well as on the health and socioeconomic impact of dengue are urgently needed. Data from outbreak investigations on disease distribution and determinants can also provide valuable information for formulating appropriate control measures.
In addition, such data can help us in better understanding the epidemiology, as well as the pathogenesis of disease, clinical manifestations and response to management in Indian settings. The results of such studies can be gainfully employed in revising the policies and strategies.
Surveillance and Outbreak Response:
5. The present surveillance system for VBDs need to be strengthened to make it more practical; therefore a standardized passive and active laboratory-based surveillance system of DF/DHF, with emphasis on the early warning predictive capability should be developed urgently and implemented during the epidemic and inter-epidemic periods.
The surveillance data should be effectively used to prevent vector-borne disease outbreaks or to take a preemptive epidemic response.
6. Standard case definitions of various VBDs such as dengue fever, chikungunya, etc., should be developed and, used for reporting purposes as a part of surveillance and during outbreak investigation.
7. Vector-borne diseases are mainly a rural phenomenon but dengue and chikungunya has assumed greater importance over the past few years due to their high epidemic potential and to development activities leading to mosquito breeding in urban areas.
In urban areas, surveillance requires that the multiplicity of health care providers must report regularly to a central agency using a standard case definition. In rural areas, dengue fever and vector surveillance should be a part of the Integrated Disease Surveillance Project (IDSP) and provide for an early warning system.
8. Vector surveillance including monitoring the presence and density of vector species and their breeding sites and the effectiveness and efficiency of vector control interventions should be carried out in each locality on an on-going basis in order to ensure better planning and implementation of vector control strategies.
Laboratory capacity building and networking within and outside the country are areas that require urgent attention.
Prevention through Social Mobilization:
9. A prerequisite for prevention of vector-borne diseases is scaling up the most effective interventions including integrated vector management in the form of insecticide residual spray, bed nets and other personal protection measures. Sources reduction and measures to control the vector population are integral components of disease prevention and outbreak response.
10. Intensified efforts towards creating public awareness and mobilizing the community regarding the preventive measures they can take and regarding the early seeking of medical attention by those suffering from vector-borne disease are crucial.
Communication messages using the mass media as well as interpersonal approaches can help bring about a change in the behaviour of the population. The services of a communications expert may be employed to formulate effective risk communication strategies.
Similarly, school children can be involved in prevention activities through school health programmes.
11 Population groups such as Residents Welfare Associations and Housing Societies can play an important role in encouraging and enforcing preventive activities in their respective areas. Targeting these groups with risk communication can lead to a cascading preventive effect amongst many people.
12. The management of dengue and chikungunya can be enhanced through holding a dry day every week when all residents would dry up their coolers once a day in a week for only half day (preferably forenoon). This should be supported by a legal framework to ensure compliance.
In residential areas, the dry days could be observed on Sundays and in offices or educational institutions on a weekday, i.e., Tuesdays. A sanitation day, as envisaged by the Govt. of India, in a year (i.e., 2nd October) should be observed throughout the SEA Region in order to create awareness regarding sanitation and hygiene for disease prevention and control.
Case Management:
13. Standard case management is critical for reducing morbidity and preventing mortality due to dengue hemorrhagic fever (DHF). For example, health care workers should ensure appropriate and rational use of platelets for case management.
Development of standard guidelines, their dissemination and extensive training of physicians at all levels of the health care system are key elements to ensure good clinical practices. Since transfusion of platelets in DHF saves life, availability of safe blood products warrant strengthening the capacity of blood transfusion services to respond effectively during outbreaks.
14. Laboratory support for diagnosis and case management is not widely available. Access to quality reagents is limited. Forging a network of laboratories can assure quality and enhance access to diagnostic tools.
15. Emphasis should be placed on programmes to educate physicians, nurses and others in the medical community in dengue fever/dengue hemorrhagic fever, its diagnosis, management, prevention and control.