Covid-19 pandemic has caused daunting public health challenges across the world and in India. Studies reveal that the ecological and socio-economic conditions of human host have significant role in the emergence of pandemics. This review article highlights the role of convergence of demographic size, urbanisation, mobility, nutritional status and co-morbidities to have heightened the public health challenge in India amid Covid-19 pandemic. The public health interventions by the governments have reasonably reduced the likely catastrophic outcomes of the pandemic in India. However, in view of prevalence of Covid-19 as an endemic, efforts must be made to enhance nutrition, reduce co-morbidities and develop adequate health infrastructure along with massive vaccination drives for all to minimise the future Covid-19 induced mortalities.

The human population has always been confronted with pathogens since prehistoric time (Diamond, 2002; Krause, 1992; Dobson & Carper, 1996, Wolfe, et al., 2007). Nevertheless, the occurrence of pathogens and emergence of pandemics have become more frequent since the advent of agricultural revolution around 8000 BC (Diamond, 2002; Diamond, et al., 1997; Dobson & Carper, 1996; McNeill, 1976), and with the beginning of industrialisation in 18th century (Patz, et al., 2004; Neiderud, 2015). Pathogen transmission largely depends upon ecological, environmental and socio-economic conditions of host population (Morens, et al. 2004; Smolinski, et al., 2003; Binder, et al, 1999; Daszak, et al, 2000; Taylor, et al., 2001; Patz, et al., 2004; Weiss & McMichael, 2004; Morse, 1993; Jones, et al., 2008; Dobson & Carper, 1996). The rapidly changing demographic and economic set up, the emerging infectious diseases (EIDs) are causing significant pressure on economies and public health (Morens, et al., 2004; Smolinski, et al., 2003; Binder, et al, 1999). The initiation of sedentary economic lifestyle, increased global movement, and urbanisation and monotones food systems has aggravated the pathogens to become pandemics in the modern times (Dobson & Carter, 1996).

Coronavirus disease (SARS-CoV-2), termed as Covid-19, is an infectious disease caused by a newly discovered coronavirus (WHO, 2020). The genomic analysis revealed that SARS-CoV-2 is phylogenetically associated with SARS viruses, and bats could be the possible primary source of Covid-19 (Chakraborty & Maity, 2020). The socio-economic contexts have contributed to the shifting of global ecology of vector transmission enabling Covid-19 to emerge worldwide, by severely uniting the human hosts, vectors and pathogen (Su, et al., 2020). Various studies have shown significant associations between different socio-economic and demographic determinants and prevalence of Covid-19 (Wortham, 2020; Jordan, et al., 2020; Lighter, 2020; Chen, 2020; Zheng, et al. 2020; Chaudhry, 2020; Shaw, et al, 2021). The demographic size, socio-economic characteristics, poor nutrition and associated co-morbidities in India have been serious concerns for long. The emergence of Covid-19 pandemic poses a serious public health challenge in India. In view of this, the understanding of the associated conditions to have caused public health challenge during Covid-19 pandemic has become urgent. This article may have relevance for public health policy interventions as well as for future research in the field for our preparedness for future similar occurrences of disease outbreaks.

Convergence of Demography, Urbanisation, Mobility and Covid-19

Human population growth and economic structure have closely associated with the spread of diseases and public health (Narayan, 2017; McLafferty, 2010). Many of the early pathogens emerged from the diseases of domesticated animals (Dobson & Carper, 1996). The increased population concentration and subsequent mobility among early towns around 5500 BC led to the population threshold to sustain the bacterial and viral infections (Dobson & Carper, 1996). The influenza epidemic in 16th century in Europe and few Asian countries became highly contagious as a result of high population concentration in medieval towns (McNeill, 1976). The majority of the world, including India, until 1950, had experienced low life expectancy and high mortality in the absence of improvements in food production, nutrition, sanitation and hygiene. Nonetheless, along with the expansion of Indian economy, demographic size increased from 360 million in 1950 to 1360 millions in 2019 (United Nations, 2019), causing high population density (382 persons/Km², 2011) (GOI, 2011) (see table 1). Studies reveal that high density of population is positively associated with Covid-19 infection rate (Rocklöv & Sjödin, 2020; Ahmadi, 2020; Copiello, 2020).

The world is rapidly urbanising (4.2 billion) (UN, 2018), and about 29% urban population live in slums (World Bank, 2018). The rising urbanisation is associated with the rise of co-morbidities (Hotez, 2017) and contamination of the environment with pathogens (Coyner, 2002) and has serious implication for public health (Neiderud, 2015; Knowlton 2001; Schmidt & Ostfeld 2001; Patz et al, 2004; WHO, 2010; Alirol, et al, 2011; Saravanan, 2016; Dobson & Carper, 1996). McLafferty (2010) found that rapid industrialisation and poor living and working conditions have neutralized the positive effects of economic development in many developing countries. The rapid growth of cities and consequent increased demand of industrial livestocks have intensified the risk of the emergence and spread of flu pandemic (Davis, 2005). Moreover, the demographic pressure induced land use changes have disrupted local ecologies and escort to increased pathogens and increase human exposure to disease (Mayer, 2000). The spread of the Covid-19 virus and resultant high death rates have been observed in hyper dense megacities across the world (Simon, 2020). The unplanned and haphazard urbanisation (377.1 billion in 2011) in India is highly vulnerable to pandemics (Patidar & Chothodi, 2020; Biswas, 2020; Gani, et al., 2011; Kumar & Quinn, 2012). The rural migrants in urban India live in dilapidated and poverty conditions in (Nova, 2020), poor sanitation (Singhal, et al., 2020). The rising air pollution in the urban areas increase the incidence of lung infection with respiratory diseases such as Pneumonia, Asthma and Chronic Respiratory Disease (CRD) (Phosri, 2019), and Covid-19 infection (Zhu, 2020; Contini, 2020). The global data of Covid-19 pandemic have also made it evident that people with weak respiratory conditions are found to be more susceptible (WHO, 2020). Contrary to the established positive association between urbanisation and pathogens, the rural people, in historic time, also experienced high mortality due to low level of immunity to pathogens (McNeill, 1976) as spread of pathogens reach to rural areas at later age of infection causing high pathogen-induced mortality. The large scale infections and death during second wave of Covid-19 can be attributed to the lower immunity to the Covid-19 in rural India.

Table 1: Population size, growth, density and urbanisation in India, 1901 to 2011

Source: Computed from Census Tables from 1901 to 2011, Census of India (GOI).

In the rapidly transforming economic structure, the global flows of people and goods have expanded and resultantly the potential for the spread of infectious diseases have been amplified (Tatem, et al., 2006; Li, 2005). Human mobility has increased thousand times since 1800 in high income countries (Wilson, 1995). As per UNDESA (2020), 281 million people (3.6 percent of the world population) migrate across international borders each year. The travellers are turned into interactive biological entities to carry microbial genetic substances at different places and times (Wilson, 2003). The hub and spoke structure of the modern transportation networks are becoming a conduit for the transmission of human pathogens (McLafferty, 2010). Covid-19 virus emerged in Wuhan of China's Hubei Province and spread to other parts of the world including India through air travellers (Chaudhry, et al, 2020, Keni, et al., 2020). The travel restriction and lockdowns have slowed down spread of Covid-19 in USA (Paez, 2020; Badr, et al., 2020), U.K. (Hadjidemetriou, et al., 2020), China (Fang, et al., 2020; Kraemer, et al., 2020) and India (Praharaj & Han, 2020). India have nearly 450 million migrants (GOI, 2011) with major share from rural areas who are largely livelihood insecure (Jonathan, 2017; Patidar, 2019) and move to urban areas and constitutes nearly 47 percent of urban population in India (GOI, 2011). The rural to urban migratory linkage is critical determinant of the spread of Covid-19 in urban areas (Biswas, 2020; Patidar, 2020) and in rural areas through reverse migration as evident by (Sharma, 2020).

Figure 1

Source: World Tourism organization (WTO), Yearbook of Tourism Statistics, Compendium of Tourism Statistics and data files, 2021.

Nutrition and Covid-19

In the disease ecology, nutrition of the host may influence the immune system and its susceptibility to viral infection (Gorji & Ghadiri, 2021). The level of nutrition among maternal and children has been decreasing since the Mesolithic period (Lukacs, 2003) due to reduced diversity in diet from a mixture of grains, meat and fruits to a diet dominated only by grains (Cohen & Armelagos, 1984). Micronutrient deficiencies affect nearly 2 billion people worldwide (Allen, et al, 2006) and weaken the immune system and help in developing more virulent strain (Beck, 1997, Beck & Metthews, 2000). The immune system is affected by the specific nutrients or nutrient combinations through the cell activation, alteration in the production of signalling molecules, and gene expression (Valdés-Ramos, et al, 2010). An adequate intake of iron, zinc, and vitamins A, E, B6, and B12 is predominantly vital for the maintenance of immune function (Gleeson, et al., 2004). The protective dietary intakes of key food and nutrients, associated with at least one disease endpoint, have been very limited in India (See table 2). Micronutrient deficiencies decrease the ability to resist infections and are a major public health challenge in developing countries (Katona & Katona, 2008; Samaras, et al. 2013). Studies pointed out the increase in susceptibility of various viral infections among nutritionally deficient individuals (Beck & Matthews, 2000; Ferrari, et al. 2019; Manios, et al, 2018; Kehoe, et al., 2019) including Covid-19 (Naja & Hamadeh, 2020; Calder, 2020; Gorji & Ghadiri , 2021). James, et al (2021), highlighted the importance of adequate nutrition and prevention of obesity and type-2 diabetes to reduce the high risk of Covid-19 outcomes.

Table 2: Dietary intakes of key foods and nutrients in adults aged 25 years and over in India, 2020

Source: Global Burden of Disease, the Institute for Health Metrics and Evaluation, 2020
Note: TMREL: theoretical minimum risk of exposure level (TMREL) represents the optimal dietary intake that minimises risk from all causes of deaths combined.

Co-morbidities and Covid-19

The medical advancement (anti-biotic, immunisation, etc.) have drastically reduced maternal and child death rates from communicable diseases, especially in Lower and Middle Income Countries (LMICs) (Hogan, et al. 2010; You, et al., 2015; Byass, 2016). Six out of the top ten risk factors for mortality worldwide are cardio-metabolic risk factor (high blood pressure, high blood glucose, overweight and obesity, high cholesterol) which are related to lifestyle and behaviour associated with economic development (Narayan, et al., 2010). Over the past few decades, many countries have experienced the increase in average Body Mass Index (BMI), obesity, glucose level and type 2 diabetes (Lukacs & Pal, 2010). The recent research indicated that patients with pre-existing medical conditions especially heart disease, lung disease, diabetes, cancer, and people 60 years and older are more likely to have high severity of coronavirus infection than others (WHO, 2020, WHO, 2019; Yang, 2020; Statista, 2020; Gorji & Ghadiri, 2021; Khan et al., 2021). Studies also indicated that obesity (Jordan, et al., 2020; Lighter, 2020; Chaudhry, et al., 2020; Hajifathalian, 2020; Docherty, et al., 2020) CVD and hypertension (Jordan, et al., 2020; Chen, et al. 2020) are important determinant of Covid-19 infection rate. In addition, male patients with heart injury, hyperglycaemia and high-dose corticosteroid use may have a high risk of Covid induced death (Li, et al, 2020). Nevertheless, children may be less vulnerable to Covid-19 due their more active immunity, stronger respiratory tracts, less exposure to pollution (Lee, et al., 2020) fewer medical disorders, milder disease progression and better prognosis (Ludvigsson, 2020). However, WHO reported that refugee and migrant children, children with deprivation, disabilities, and without parental care and proper shelter are the most vulnerable to Covid-19 (Ludvigsson, 2020). The International Diabetes Federation estimated nearly 73 million diabetes cases (10.4 percent prevalence) between the ages of 20 years and 79 years in 2017 in India (Cho, et al., 2018; IDF, 2019). Half of this population might be unaware of their diabetes status. The undiagnosed diabetes with higher proportions under 50 years of age pose a serious stress on the healthcare system (Tripathy, et al., 2017). Table 3 shows the cases of Diabetes, Asthma, Cancer and Heart Disease among sampled men and women in India. Diabetes is the ninth leading cause of death in India (India Health Metrics, 2015). The recent studies reported that Covid-19 patients had the high prevalence of co-morbidities (Li, et al. 2020; Yang, 2020; Emami, et al. 2020; Hu, et al., 2020; Chen, et al., 2020; Wang, et al., 2020; Singh, et al 2020). Singh & Misra (2020) found that co-morbidities such as hypertension, diabetes, obesity, CVD, CVA, chronic obstructive pulmonary disease, asthma, chronic kidney disease and malignancy are often associated with increase in severity and mortality in patients with Covid-19 in developing countries including India. The diabetes prevalence is the highest in Indian Covid-19 patients compared to other countries (Singh & Misra, 2020). In India, CVD and associated risk factors, including type 2 diabetes, hypertension, and obesity characterize a major and increasing burden of death and disability (Patel, 2011).

Table 3: Health Problems (Self Reported) in India, NFHS- 2015–2016

Source: IIPS and National Family Health Survey, India: Key Findings, 2015–2016

Conclusion

Pandemics emerge, spread and controlled through a complex mix of ecological, environmental and socio-economic systems. The population size, urbanisation, mobility, nutrition and co-morbidities and resultant change in ecological set up have heightened the potential for the spread of pandemics. The recent public health challenges caused by the Covid-19 pandemic have caused an urgency to revisit the ecological and pathogenic structure for disease transmission and prevalence. This article aims to highlight the complex association of demographic size, urbanisation, mobility, nutritional status and co-morbidities for their role in the transmission and prevalence of Covid-19 in India. It is found that the convergence of these intertwined issues have aggravated the public health challenges in India during the pandemic. The demographic size, rapid urbanisation, global and local mobility for livelihood, inadequate nutrition and the burden of co-morbidities has undoubtedly heightened the risk of Covid-19 infection and morality. The public health interventions by the governments have reasonably reduced the likely catastrophic outcomes of the pandemic. Nonetheless, Covid-19 is now considered to be an endemic (Phillips, 2021) and in such case it is likely to reappear as an outbreak in future, therefore, there must be an immediate need to enhance nutrition, reduce co-morbidities and develop adequate health infrastructure along with massive vaccination drives for all. The future severity of Covid-19 will depend upon the state’s health monitoring and surveillance, and the future public health response.

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(Hemant Patidar, Assistant Professor, Department of General & Applied Geography, School of Applied Sciences, Dr. Harisingh Gour Vishwavidyalaya, Sagar (M.P.) India)

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