Ecology of Selected Diseases in South Asia

In the space of this essay, it is possible to focus on only a few selected prevalent diseases in South Asia. Thus, smallpox, in spite of the fact that it was once a major killer disease in India, has been omitted because it has been eradicated. Likewise, although plague has some endemicity, its incidence is now very limited. Instead the focus is on diseases of high endemicity or prevalence.


Although cholera, an acute communicable disease, is not peculiar to South Asia, there are endemic areas of cholera in this region from which periodic outbreaks have occurred (see Map VII.3.1). Cholera etiology is relatively simple, since this disease is caused by the ingestion of Vibrio cholerae. Two distinct modes of cholera transmission are usually recognized (Craig 1986). In the "primary" transmission, the vibrio is ingested through vegetables and fish raised in water that is contaminated with the vibrio. The "secondary" mode is the fecal-oral transmission. In non-immunized persons with relatively lowered stomach acidity, symptoms of cholera develop rapidly, marked by frequent watery stools, vomiting, and fever. Since the vibrio is present in great quantities in the characteristic watery stools, flies may carry the germ from them to human food. Consumption of this contami

Map VII.3.1. General endemicity of cholera, malaria, and "kangri burn" cancer. (Based on Misra 1970; Hütt and Burkitt 1986.)

nated food results in the ingestion of the vibrio, thus creating a fecal-oral link, resulting in manifestation of the disease. Death occurs as a result of excessive dehydration, electrolyte imbalance, and the pyro-genic endotoxins of V. cholerae.

Cholera remains endemic in the delta lands of Ganga in West Bengal and Bangladesh. Indeed, the "cholera pandemic that scourged the world in the first half of the nineteenth century began in the Bengali basin and spread as far and as rapidly as man was then able to travel" (Cahill 1976). The reasons for cholera's endemicity have to do with a combination of physical, environmental, and human conditions. The deltaic region is characterized by heavy monsoon rainfall from June through September, resulting in frequent and often disastrous flooding. In the aftermath of rains, slow-moving water in the maze of Ganga's distributaries and stagnant water in numerous shallow pools characterize the landscape. Tanks and wells used as a resource for drinking water are filled with surface flow. Algal infestations of these ponds and tanks greatly increase the alkalinity of stagnant water, and create favorable conditions for the multiplication of V. cholerae (Jusatz 1977). Most people defecate outdoors and seek proximity to water for cleaning themselves. Thus, chances for the accu mulation of cholera germs in pools of water increase, putting at risk individuals who use this water for drinking. During the dry season, shrinking pools and tanks, owing to intense heat, become even more concentrated with the vibrio. Fish taken from these sources, and vegetables washed with this water, can transmit cholera. Since most drinking water is neither filtered nor boiled, chances for vibrio ingestion remain high. During the monsoon season, when heat and humidity are high, people tend to lose large amounts of moisture with sweating. Drinking large quantities of water greatly dilutes the stomach acidity. If vibrio-infected food or water is taken under this condition, the chances for disease manifestation multiply. This situation happens usually at village fairs, periodic markets, or other big gatherings in the open. Because the disease has a very rapid course, causing vomiting, fever, and passage of watery stools, vibrio from such body wastes can be easily conveyed by the ubiquitous flies to food items being consumed by other participants at the fair. Cholera epidemics are therefore notorious for their speed and virulence during the summer monsoon season.

From the delta region of the Ganges, cholera has often spread in epidemic forms (May 1958; Acker-knecht 1972), although today the death rate is quite

C Kotura

Malaria - (a) hyper-endemlc

(5) endemic "Kangri Burn" Cancer no dala

C Kotura

Malaria - (a) hyper-endemlc

(5) endemic "Kangri Burn" Cancer no dala low because of widespread immunization in South Asia. In the past, cholera has also been spread through the agency of pilgrims, both Hindu and Muslim (Misra 1970; Dutta 1985). Hindus visiting their sacred places in different parts of India have been exposed to cholera. The massive Kumbha bathing festivals that attract pilgrims from all over India have been the scene of cholera epidemics. Pilgrims from the endemic areas have inadvertently carried the cholera germ to sacred centers, where sanitation breakdowns have occurred, leading to the exposure of pilgrims from nonendemic areas. Muslim pilgrims on hajj to Mecca from Bengal in the past may also have been both carriers of and affected by cholera. Although these religious convergences remain a potential mechanism for the diffusion of cholera, large-scale immunization efforts and improved water supplies at these religious centers have prevented epidemics of cholera. At large pilgrimage congregations in India, pilgrims are routinely checked for certification of cholera immunization at points of entry to the designated area of religious fairs. Those without a valid certificate are inoculated on the spot before proceeding further on their religious journey.

Dysentery and Diarrheal Disease Intestinal infections of various types are widely prevalent in South Asia. Cholera has been the focus of much attention because of its notorious epidemics and pandemics; however, it is dysentery (both amebic and bacillary) that generally leads in morbidity in most normal years. Unfortunately, dysentery and diarrhea (due to a variety of diseases of the alimentary canal) have not been accorded the attention they deserve because they are predominant among poor rural children. Perhaps as many as 80 percent of rural India's children are infected by parasitic worms (Nyrop 1986). Tropical diarrhea, mostly a traveler's disease, has attracted far more attention in-the literature than the killer infantile diarrhea, which is linked to high infant mortality throughout India, Pakistan, Nepal, Bhutan, and Bangladesh.

The causative agent of bacillary dysentery is bacteria of the Shigella group, whereas amebic dysentery is produced by protozoa. However, both diseases manifest after ingestion of the pathogen whether by food infected by flies carrying the pathogen, by one's own infected hands, or by infected vessels, such as food containers. Thus, cultural practices, personal cleanliness, and the nature of the food available determine whether the disease will actually develop in an individual or family. The practice of using water on bare hands for cleaning the anal area after defecation increases the chances that the pathogen could be carried under the fingernails, and conveyed to food. Many middle-class South Asian families employ servants as cooks who come from poor families. Dysentery pathogens may be inadvertently conveyed to the food of these families, even though the latter may have a high standard of personal hygiene. Many edible items in stores and shops are exposed to flies and dust in spite of public health regulations. It is virtually inevitable that such items when consumed (without cooking) will carry pathogens with them. In cities, where it is easier to enforce environmental hygiene regulations, and where the modernizing consumers themselves exert sufficient pressure, store owners do respond by adopting strict hygienic practices. But most of the population of South Asia is rural, and therefore the enforcement of public health measures is highly problematic. In addition, the population - especially the adult rural population - of South Asian countries (Sri Lanka is again the exception) is mostly illiterate, and does not effectively demand hygienic practices from food vendors. Thus, dysentery, a highly preventable disease, persists.

As expected, dysentery shows marked seasonality in South Asia, because cpnditions for the multiplication of flies, a major carrier of dysentery pathogens, become ideal during and soon after the rainy season, through summer and early autumn. This is also the season when many types of melons, other fruits, and vegetables are sold in the open. Thus, even the more literate urban populations are placed at risk. Poor sections of the cities - the slums and the shanties -are particularly vulnerable because of the virtual lack of sanitation facilities that lead to a very high density of fly population. Many sanitary systems break down, and wells get polluted. The diffusion of tube wells as sources for irrigation and drinking water in the rural areas may have had some impact on the incidence of dysentery. The prevalence of dysentery in South Asia illustrates the fallacy of considering disease as only a biomedical entity. It forces us to recognize the significance of looking at the web of ecological relationships between people and their total environment.


Fevers of many types have been described in the ancient Vedic literature of India. Vedic hymns speak of fevers that cause chills and high body temperature, and torment the sufferer during summer and autumn (Filliozat 1964). An intermittent fever, takman, seems to have been particularly feared by the Aryans living in the Indus Basin. Their descriptions indicate characteristics of the fever much resembling malaria in its seasonality and symptoms.

Unlike cholera, malaria ecology is complex, since this infection depends upon the life cycles of the parasite Plasmodium and the vector Anopheles mosquito on the one hand, and human contact with the infected vector on the other. This contact has to be close enough for the infected vector to take a human blood meal and, in the process, to inject the pathogen parasite into the human bloodstream. Repeated infections are not uncommon, and once the Plasmodium parasite is in human blood, fever relapse can occur. Characterized by chills, high fever, splenomegaly, and debilitation, malaria fever has had a serious impact on economic development by affecting millions of people. Between 1947, India's year of Independence, and 1953, the year the Malaria Control Program was first launched, malaria incidence was about 75 million, of which nearly 800,000 lives were lost to this disease annually (India 1987).

Distribution. Geographic distribution of malaria, as indeed of several other diseases, has been affected by socioeconomic changes in South Asian countries since the 1950s. Before Independence, the major hyperendemic areas (spleen rates over 75 percent) included the following:

1. The narrow tarai belt along southern Nepal and northern Uttar Pradesh. Lying at the foot of the Himalaya Mountain system, this strip was characterized by tall thick grass and sal forest on a relatively thin stony soil. Rainfall in this region decreases toward the west but is generally over 60 inches per annum.

2. The hills of eastern India up to a height of about 5,000 feet. These forested and poorly accessible areas have been thinly populated by tribal people who practiced considerable slash-and-burn agriculture. Rainfall in these areas is very heavy and is highly concentrated during the months of June through September.

3. The Chota Nagpur Plateau and the Eastern Hills region of the Indian Peninsula. Covered by forests, these regions have poor reddish soils and marginal agriculture carried on by tribal people. Rainfall is well over 40 inches and occurs mostly in the months of June through September.

4. A narrow forested strip along the crest of the western Ghats. This region receives heavy rainfall during the monsoon season, but the rest of the year is quite dry.

5. The western part of the Ganges Delta, and parts of the Coromandel coastal region of peninsular India. The Ganges Delta, of course, has the typical monsoon rainfall regime, but the Coromandel coastal region is an area of mostly autumn rainfall. These are densely populated, dominantly agricultural areas.

In addition to these areas of hyperendemicity, most of India, with over 40 inches of rainfall, was considered endemic for malaria. Moderate malaria endemicity also was found in the plains of Punjab, especially along the rivers and the irrigation canals. The rest of India, with rainfall of less than 40 inches, suffered from periodic, but severe, epidemics of malaria. Especially intense "fulminant" epidemics occurred in the western Ganga Plains and the adjoining Punjab Plains.

Malaria Resurgence. A. T. Learmonth (1957,1958), A. K. Dutt, R. Akhtar, and H. Dutta (1980), and later Learmonth and Akhtar (1984) have added significantly to our knowledge of malaria ecology in India. In a series of maps, they bring out the story of malaria resurgence from 1965 to 1976. Through the efforts of the government of India, aided by the World Health Organization (WHO), and the active support of the state governments, malaria seemed to have been brought under control. The success of the Malaria Control Program, consisting mostly of the spraying of DDT, encouraged the government of India to convert this program to malaria eradication, which showed spectacular success until about 1965. In that year, malaria incidence had declined to 100,000 as compared to 70 million in 1947. But two India-Pakistan wars (1965 and 1970-1), the war of Bangladesh's liberation, and later the oil crisis resulted in massive disruption of the campaign against malaria. In addition, both the Anopheles vector species and the pathogen Plasmodium have developed resistance to antivector and anti-Plasmodium chemicals and drugs, respectively. Thus, hopes of malaria eradication were replaced by the stark reality of its recrudescence. From a low of about 100,000 cases in 1965, a resurgence of malaria developed, with over 5 million cases in 1975. In spite of further malaria control efforts, there were still 2 million cases in 1979, only marginally declining to about 1.6 million by 1985. A similar resurgence has occurred in several other countries (Development Forum 1988).

Geographically, as Learmonth and Akhtar (1984) have showed, by 1965 most of India had a low annual parasite index (API) (see Map VII.3.2). An API of

Annual parasite index rale per 1.000

Map VII.3.2. Malaria: annual parasite index (API), per 1,000 population, for selected years. (Based on Learmonth and Akhtar 1984.)

Cambridge Histories Online © Cambridge University Press, 2008

over 5 per 1,000 existed in the hyperendemic region of Eastern Hills, parts of Chota Nagpur Plateau and northeastern peninsular India, western Vindhyan Range, the marshlands of Kachch and western Gujarat, and the foothill zone of western Uttar Pradesh. Relative inaccessibility is a major common attribute of all these areas. Their rainfall and soil characteristics vary widely, but all these areas have a high proportion of "scheduled tribes." It needs to be stressed that these people have a somewhat different genre de vie than do the nontribal populations of India. Formerly much more widespread, the tribal peoples now occupy "refuge areas" of marginal agricultural productivity. Malaria control - eradication programs of the government of India - seemed to have been ineffective in these poorly accessible areas. Thus, these areas remained highly endemic malarial time bombs. Slackening of the eradication programs, due to diversion of the national resources to two major wars in the subcontinent, in 1965 and again in 1971, meant a partial reassertion of the pre-Malaria Control Program pattern of malaria epidemics. From these focal points, malaria spread again to virtually all parts of India, although as a result of antimalarial drugs and greater availability of medical facilities, mortality is now minimal. A virtually similar process of malaria resurgence occurred in Bangladesh (Paul 1984). Malaria had been beaten back to the remote tribal areas of Chittagong Hills, from which it has reasserted itself.

The history of malaria control holds a major lesson for all concerned. That lesson is that a disease with a complex ecology deserves a multipronged approach. It is necessary to have a well-orchestrated plan of action by specialists in various pertinent fields of science and bureaucracy, but it is imperative that the political leadership exercise wisdom. Malaria control, let alone eradication, is possible only under conditions of political stability, permitting an uninterrupted commitment of national resources. Current interethnic conflicts in Punjab, eastern Indian states, Bangladesh, and Sri Lanka will surely affect malaria control programs adversely.


Leprosy (Hansen's disease) has been known in South Asian countries since antiquity. Called kustha in the Hindu medical literature, it was considered to be transmittable to the child from parents "when a woman and a man have (respectively) the blood and sperm vitiated by leprosy" (Filliozat 1964). During the British rule in India, the Census of India (1913) collected data on four types of disabilities for each decade since 1881: insanity, deaf-muteness, blindness, and leprosy. The last disease is usually of two types - tuberculoid and lepromatous. Tuberculoid leprosy is usually self-limiting, whereas the lepromatous form is progressive. The causative pathogen of leprosy is the bacillus Mycobacterium leprae. Lepromatous leprosy is the classic dreaded disease in which, in advanced cases, loss of digits and other deformities occur. The pathogen is usually thought to enter the body through the mucous membrane of the upper respiratory tract, or through repeated and close skin contact, but there is controversy among leprologists as to the exact mode of transmission (Cahill 1976; Sutherland 1977). The incubation period is long - 1 to 5 years - making research, early detection, and understanding of the diffusion process very difficult.

Persons with advanced stages of leprosy are frequently found begging at the railway stations, at the bus stations, and especially at the holy places all over South Asia. Even though legislation against begging has been frequent, the problem is far from solved. Likewise, the stigma attached to leprosy has made early treatment very difficult by discouraging patients to seek appropriate treatment. Since the disease is considered the greatest misfortune, sufferers from it arouse pity rather than understanding. In general, leprosy sufferers are isolated from the society either because of their own voluntary response or as a result of government policy. India has in place a national leprosy control program under which 434 leprosy control units along with 6,784 survey, education, and treatment centers, 721 urban leprosy centers, and 46 leprosy training centers have been developed (India 1987). In neighboring Nepal, the National Leprosy Control Program was established in 1975; now the Leprosy Service Development Board, it provides treatment and rehabilitative services for leprosy patients.

Geographic Distribution. South Asian countries have a medium rate of leprosy, but the very large total population base results in a correspondingly large absolute number of sufferers. In India alone, the prevalence rate of 5.7 per 1,000 population in 1986 suggests that the number of leprosy patients exceeds 4 million, according to government data (India 1987). Areas of high leprosy prevalence in India (over 10 per 1,000) include the following: (1) a belt of coastal districts of Tamil Nadu, Andhra Pradesh, and Orissa, which continues into most of West Bengal and adjoining southern Bihar; (2) western Maharashtra and the adjoining eastern Andhra Pradesh,

a substantial part of which was once the princely state of Hyderabad (all of this area lies in the interior section of the Deccan Plateau); (3) isolated areas in other parts of India, including the tarai region of Uttar Pradesh and the far eastern parts of India. Surprisingly, Bangladesh reported only 110 cases of leprosy in 1979; Pakistan, 3,269; and Sri Lanka, 751 (WHO 1981). The longitudinal river valleys of Nepal apparently show a high prevalence of endemic leprosy - over 10 per 1,000 population.

Problems of Leprosy Control. Because leprosy is prevalent in both flat coastal areas and hills and valleys, and in areas of low and high rainfall, any relationship with broad physical environmental factors seems only tenuous at best (see Map VII.3.3). Secrecy surrounding earlier phases of the disease and the victims' fear of social ostracism in the latter stages make control and curative efforts difficult to implement. Slow progression of the disease and the necessity for prolonged treatment compound both the preventive and curative problems. It has been found in Nepal that people do not necessarily use the treatment facilities located nearest to them, for fear of being stigmatized in their local community. Patients seem deliberately to seek treatment at distant facilities (Pearson 1988). This trend has major implica-

Map VII.3.3. Leprosy: prevalence rate percentage, 1974—5. (Based on Pearson 1984, 1988.)

tions for the diffusion of leprosy. With increasing mobility, the disease could spread without notice. As Kevin Cahill (1976) observed, in the "meagerness of our knowledge of the clinical, the bacteriological and the pathological course in the incubational phase of leprosy lies the primary reason for the failure of international control and eradication programmes." Peoples along traditional routes of commerce - for example, the river valleys in Nepal - could be especially at risk (Pearson 1984). In spite of the argument that leprosy is not easily communicable, intrusive tourism does place the visitors at risk of carrying the disease from the traditional endemic areas to other parts of the world.

At one time it was hoped that the disease could be eradicated because human beings are known to be the only significant reservoirs of the leprosy pathogen (Lechat 1988). That this has not occurred seems reason for less optimism, at least in the foreseeable future. However, "multidrug therapy" (MDP), early identification of cases and at-risk populations, social and cultural sensitivity toward the patient, long-term commitment of the governments, and immunologic and epidemiological research, can together make a major impact. Immunologic advances, based upon the cultivation of large quantities of M. leprae bacilli in armadillos, and advances in molecular

Map VII.3.4. General distribution of filariasis and goiter. (Based on May 1961; Misra 1970; Schwein-furth 1983; and India, a reference annual 1987.)

genetics seem to promise positive results, but large-scale confirmatory results are awaited from field trials (WHO 1985).


Filarial infections, caused by worms such as Wuche-reria bancrofti and Brugi malayi, are widespread in the tropical climates of Africa, Southeast and South Asia, and the Caribbean. In India alone, over 15 million people suffer from filariasis, and over 300 million are at risk (India 1987) (see Map VII.3.4).

Filariasis is endemic in the entire Konkan and Malabar coastal areas of western India, the coastal areas of Tamil Nadu, Andhra Pradesh, and Orissa. Its incidence declines rapidly toward the interior and the northwestern parts of India. The lowest incidence is found in the Himalaya region. Sri Lanka's major endemic area of filariasis is in the hot, humid, and high rainfall areas of the coastal southwest (Schweinfurth 1983). Filariasis is found in both the rural and urban areas of this coastal region, although there are significant differences in the implicated pathogen of the two settings.

Microfilariae of the worm pathogens entering the human bloodstream through mosquito bites, circulate in blood, develop into larvae and, under suitable conditions, into adult worms. Filariasis leads to fe ver, lymphadenitis of the groin, and epididymitis. As the worms multiply, reach adulthood, and die, conditions such as hanging groins and elephantiasis of the legs develop. The high prevalence rate of elephantiasis of legs on the Malabar coast of India has led to the nomenclature "Malabar legs."

The essential components of the filaria ecology in South Asia are the pathogens W. bancrofti and B. malayi, several species of the mosquito vectors (Culex, Anopheles, Aedes), a hot and wet climate with high humidity, moist and warm soil, availability of stagnant pools of water, and a population of predominantly poor people. Culex and Anopheles mosquitoes, both abundant in all parts of South Asia, but especially in the high rainfall regions, pick up microfilaria through a blood meal from infected human beings, which reach the larva stage in the mosquito. These larvae are then introduced to other human beings through repeated mosquito bites. Filarial larvae reach adulthood in from 1 to 3 years, and may produce swarms of microfilariae. Most of the pathological symptoms are due to larvae and adult worms (Cahill 1976).

More than women, men are susceptible victims because of their outdoor agricultural activities and relatively less protective clothing. There is increasing concern that filariasis is becoming an urban disease as well. This is happening primarily as a result of the migration of rural males to large cities in search of jobs. Many of these poor migrants must live on the outskirts of the cities, where there is an abundance of stagnant water pools as a result of construction activity. These pools serve as breeding grounds for the urban mosquitoes, which, in turn, become intermediate hosts of the pathogen between new immigrants and the established city populations. Thus, a disease that at one time was thought to be primarily rural is on its way to becoming an urban phenomenon as well. U. Schweinfurth (1983) provides a very interesting case study of filariasis infections at the University of Peradenya in Sri Lanka. The beautification of the campus also provided a very good habitat for the breeding of Culex vector. Students attending this university from infected areas were the carriers of W. bancrofti in their blood. In the beautified university campus, they became the source of the pathogen for the mosquito that also found the university campus environment conducive for breeding. The vector mosquitoes in turn introduced the disease to students from non-endemic areas as well.

Difficulty of detection of the disease (microfilariae show no pathogenic symptoms) at the early stage makes preventive measures difficult as well. Sadly, filaricidal and larvicidal treatment is available to only about 10 percent of the population in the endemic areas of India (WHO 1984). Efforts to introduce larvivorous fish in pools of water where mosquitoes breed may be helpful as part of a comprehensive filaria control program. This strategy, however, may be ineffective in the periurban areas where pools of water quickly become polluted and filled with urban waste. These pools are useless for fish culture, but do invite mosquitoes to breed.

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