EPIDEMIOLOGICAL ANTHROPOLOGY: Infectious diseases, Non-Infectious diseases, and Malnutrition

Epidemiology is often defined as the study, distribution, and determinants of disease and injuries in the human population. Human growth occurs along a genetically destined trajectory but is influenced by environmental factors consequently affecting its longevity and health status. We need to consider not only the man’s physical environment but also his social, cultural, and psychological circumstances. For instance, environmental components of causation lie in lung cancer and degenerative arterial disease as in tuberculosis and smallpox.

INFECTIOUS DISEASES:

There exist a competitive interaction between man and environment. Man has been able to control his nearby environment or at least mitigate its worst effects by various adaptive mechanisms.  On one hand, this struggle may be against unalterable and passive opponents, e.g. physical and climatic factors, and on the other hand, the biological environment which is in itself capable of adaptive responses. Therefore, in the context of eradication of infectious diseases, appropriate steps must be adopted to ensure the adaptation of individual and mal-adaptation of disease-causing agents to the environment.

The ecological aspects of the disease can be revealed in two ways:

=> Physical environment: It is a direct and immediate source of injury and ill health. There is consequently a clear geographical distribution of pathology manifested as a consequence of extreme climatic effect e.g. heat stroke (desert), mountain sickness (high altitude), and rodent ulcer (ultra-violet light). In recent years, air pollution due to smoke and associated substances has become an important environmental hazard in many countries.

=> Biotic component of the environment harbors pathogenic organisms (viruses, bacteria, protozoa, fungi) dangerous animals as well as poisonous plants and insects. In addition, nutritional disorders arise due to improper utilization of food sources - animals and vegetables.

Besides, environmentally produced diseases, some illnesses make their overt appearance due to maladjustment of metabolic and regulatory functions during growth but manifest completely in response to the external environment. The genetic defect may refer to an inability of the individual to support him, while psychological disorder is an inability to apprehend and respond to external events and demands.

Hunting-gathering practices, deforestation, swamp drainage, and other activities have enabled man to dispose of his major competitors for space and food. This struggle for existence has even lead to the extermination of many species. Indeed, a readjustment of ecological balance and enlightened policy of conservation is urgently necessary if numerous species are to be saved from total extinction.

The geographical background is the prime single factor governing the abundance of a specific type of parasites and pathogens in a region. Micro-organisms may be water-borne, air-borne, or carried by insects and other animals. The host-parasitic relation often takes a complex course depending on the number of stages and factors involved in a life cycle of parasite- vector, intermediate host, and one or more reservoirs. Analysis of the locality eventually reveals that ecological relationships are strongly influenced by physical features such as wind, rainwater, drainage, temperature, and humidity. The pathogen itself may have limited environmental tolerance. 

The ecological relations are complex. A relatively few out of the thousands of kinds of human parasites characterize any given locality. Thus, the ecological relations of most micro-organism disease will be unraveled only by specific regional analysis. For instance, Yaws, a microbial disease has a strong relationship to climate. 80 percent of the yaws affected areas have the 80 F mean annual isotherms.

The characteristic housing structure and settlement pattern of man may introduce favorable factors to the spread of particular diseases. Human settlement may require deforestation which may provide conditions favorable for the propagation of infectious diseases. Deforestation of the hills of Ceylon led to frequent pool formation during a dry spell and successively to mosquito-breeding. In Malaya, certain rats capable of carrying tick disease are very rare in the natural forest but after deforestation, they occur in great numbers.

BIOLOGICAL RESPONSES:

There are two-fold responses to infectious diseases: 

> immediate which depend on the adaptive flexibility of the individual and 

> long-term responses that become evident after a long period but are action-specific.

If a disease is widespread or severe in nature then it may act as an efficient selective agent. Individuals who are able to combat the disease will survive while others are eliminated. Such resistance may be due to increased physiological adaptability, enhanced immune response, or both. Many of the infectious diseases occur during the pre-reproductive and reproductive phases of life, thereby increasing their selective significance.

NON-INFECTIOUS DISEASES:

In non-infectious diseases, the whole complex of environmental factors and biological responses (inborn and acquired) must be considered to account for regional variation. Many diseases have been accorded a ‘racial pathology’ but the distribution was entirely related to environmental peculiarities. Primary cancer of the liver, common among Africans seems to be a sequel of the widely prevalent liver cirrhosis. It is caused by the consumption of diet chronically low in animal protein and rich in carbohydrates since infancy. Striking ‘racial’ differences in the incidence of coronary disease is associated with diets high in fat.

Many diseases and malformations are known to have a genetic basis; the afflicted individual is usually homozygous for the recessive gene, though dominant genes are also involved in some conditions. Genetic diseases are very rare. However, certain populations have a high frequency of such diseases. 

ECOLOGY OF MALNUTRITION:

The nutritional status of individuals and populations span a broad range from extremes of deficiency to excess. Malnutrition refers to a cellular imbalance between the supply of nutrients and energy and the body’s demand for them to ensure growth, maintenance, and specific function. It is more prevalent among developing nations, primarily those undergoing urbanization. Severe malnutrition is frequent during the war. Protein-caloric malnutrition is the most common form of undernutrition. It includes Kwashiorkor(second-child disease) and Marasmus(withering or wasting).

Kwashiorkor and Marasmus represent extreme examples of malnutrition and growth retardation. Lack of specific nutrients in the diet may lead to a less severe form of malnutrition and other health risks.

Obesity refers to excess fat accumulation which may unfavorably affect the health of an individual leading to reduced life expectancy and increased health problems. An adult with BMI > 30kg/m² is said to be obese while a child is considered obese when his or her body weight is 20 percent greater than that for his sex and age-specific weight-for-height standard. Obese children mature earlier.

DISTRIBUTION OF DEFICIENCY DISEASES:

American Geographical Society has provided an eminent image of the distribution of nutritional deficiency diseases in different parts of the world. Protein deficiency is predominantly found in the South American, African, Indian, and South-East Asian populations. Mineral deficiencies predominate in the Northern American continent, the upper part of South-East Asian countries, and some African populations. The incidence of multi-vitamin deficiencies is rampant in Africa, the Middle-East, and some islands of the Pacific Ocean.

EFFECTS OF NUTRITIONAL STRESS:

=> Infant Mortality and Childhood Death: Infant mortality rate in India is very high, computed as 80/1000 live births. Prolonged nutritional stress, specifically during infancy and preschool age is a major, although indirect factor leading to infant and early childhood mortality. For instance, diarrhea usually occurs during the weaning period due to the combined effect of infection and low food intake.  

=> Undernutrition and Learning Abilities: The period of active growth of the human brain extends from the 30th week of gestation to the end of the second year of life. Undernutrition during this period appears to adversely affect the development of the brain. In recent years, intensive investigations have focused on the relationship of nutritional deprivation in early life and subsequent development of the brain and cognitive abilities. Evidence have been derived either from the association of malnutrition in early infancy with the poor mental performance later in childhood or with the retarded brain growth or size as observed in autopsy specimens. 

NUTRITIONAL STRESS IN MODERN SOCIETY:

Prior to middle age, rice was used in South East Asia and some parts of the Indian subcontinent, maize in Central America, potatoes in South America, wheat in South West Asia, and millets in Africa and parts of China. However, during middle age, long voyages undertaken by several groups of people led to the worldwide dispersion of new domestic crops and animals. Rice cultivation was brought to Africa. The potatoes were also spread to many parts of the world. Horses, donkeys, cattle, sheep, etc. were introduced into America that provided essential nutrients to many native populations.

Disruption of traditional diets and the introduction of new foodstuffs caused nutritional stress in many societies. The estimate of such stress in earlier times is not known completely but by the beginning of 20th-century epidemics of goiter, pellagra and beriberi were evident. In urban areas, the movement of people into the cash economies decreased the supply of proteins, making it costlier. Poorer sections of society in urban areas thus became victims of Kwashiorkor.

Though nutritional stresses are declining in contemporary society, infectious diseases are being replaced by non-infectious diseases. Increased genetic heterosis is also indicated. Children in modern society are growing faster and taller. They are maturing sexually at an earlier age. However, in many third world countries, nutritional deficiency diseases are still found on a large scale.

Conclusion:

Epidemiological Anthropology confers to the determination, manifestation, and distribution of certain diseases and disorders in human communities spread all over the globe. The spectrum of disease-causing factors ranges from genetic to environment. Socio-cultural background also exhibits an influential role as human settlement patterns enhance the spread of diseases. The epidemiological aspects consider two kinds of diseases namely, infectious and non-infectious. Malnutrition is another contributory factor for the affliction of certain diseases. Nutritional stress is frequently observed during infancy and early childhood consequently causing infant and childhood mortality. Nowadays, nutritional stress is incident in different developing countries and affects different communities to a varying degree.