New and emerging infectious diseases pose a major threat to humanities health. In the current world we live in today, humanity faces many challenges that are more often than not, a direct consequence of our own doings. The relevance of discussing new infectious diseases and the role man plays in promoting them, is more important now than ever before as emerging infectious disease, are presenting large losses to human and animal life, and large costs to society. The World Health Organisation (WHO), defines an infectious disease as- “any disease caused by pathogenic microorganisms, such as bacteria, viruses, parasite and fungi”. The transmission and occurrence of disease in this discussion, touches on two main focal points; anthroponomic (human to human) and zoonotic (animal to human) infection. Posing the question of humanities role in the increasing occurrence of new and emerging infectious diseases, is one that is multi-faceted and highly complex. Topics in this discussion will merge together to present a network of complex factors that will conclusively reveal one common denominator- humanity as a collective species, greatly contributes to the success of new diseases. Man’s susceptibility to outbreaks of new diseases, correlate to features of modern lifestyles and routines. On a superficial level, we can consider the use of the wide variety of travel/transport options available on a micro and macro scale, the expanding sector of globalisation, and the importance of practicing good hygiene. However, on a more serious note, we can consider the repercussions of major driving forces such as deforestation, urbanisation and population density. New infectious diseases can differ in classification, mode of transmission and survival potential. Broadly, they can range from fungal, viral to bacterial, be vector-borne, water-borne, direct and indirect.
WHO defines urbanisation as “changing the social and environmental landscape on every continent. It is the result of population migration from rural areas in addition to natural urban demographic growth”. Predictions from the UN highlight that urban populations around the world will double from 3.3 billion in 2007 to 6.3 billion by 2050 meaning that inevitably, the world is transitioning into urbanisation. As urban populations continue to expand, factors such as the greater demand for food, inadequate water sanitation and waste disposal will pose major threats to public health and greatly diminish the conditions of environments and ecosystems. Closely linked to urbanisation, population density is one of the major contributors to disease outbreak for our species. Infections that transmit anthropogenically, depend on the rate of indirect and direct contact between vulnerable and infectious individuals. Densely populated cities should hence be of great concern for emerging diseases as they are essentially the breeding grounds for rapid transmission and development (Lienhardt, 2001). Increasing urbanisation and population affects more than just human-human spread of infectious disease, but also raises issues related to changing land use, and the intensification of agriculture. The SARS (severe acute respiratory syndrome) epidemic is a prime example of how closely-knit population groups support the speed and severity of viral infectious disease transmission. Spread mainly via droplet transmission in the air through both indirect and direct contact, SARS saw 8273 cases and 775 fatalities in southern China between November 2002 and July 2003. With the majority of cases in Hong Kong, the population in 2002 totalled 6.74 million granting easy pathways for transmission with the city’s urban limits (Taylor, Latham, Woolhouse, 2001). Additionally, food and water-borne infections are extremely common in urban populations and insufficient sanitation of drinking water, are primary forces that lead to diarrhoeal infections and diseases such as cholera (Guévart et al. 2010). Approximately 137 million individuals living in urban areas that are densely populated have limited access to clean drinking water (Getaz, 2011). Currently, food and water-borne pathogens are the major drivers of illness in many urban populations (McDermott, Grace 2012). Nigeria is an example of a country that raises great concern as only 3% of its inhabitants are provided with access to piped water systems (Satterthwaite, 2010). Growing urban populations result in growing issues with adequate waste management. In most rural areas, waste is often reused and recycled as compost, or is burnt. However, in urban cities waste is often managed by municipal services so when these services are lacking, waste is left in large heaps on street sides and empty lots, being exposed in soil, air and sewerage systems where the potential for parasitic and diarrhoeal infections further increase, as well as the proliferation of rodents as carriers of disease (Moraes, 2007). Conversely, not all the impacts of urbanisation are negative. Urbanisation can significantly support our growing economy and is generally a positive factor in reducing worldwide poverty. Considering the determinants of health may be a useful method to assess the benefits of urbanisation (Berkman, Kawachi, 2000). The socioeconomic and sociocultural status of individuals relates to their education, income, culture and lifestyles, all of which contribute largely to quality of life and simultaneously health. Metropolitan cities provide many individuals with the opportunity to seek better jobs and attract higher salaries. Pathogens that infect via food and water vectors, are often a result of poor hygiene practices which derive from a lack of quality education. Thus, improving these determinants of health will in turn provide individuals and families with greater access to health services as well as education on ways to practice good hygiene, reducing the prevalence of infectious disease transmission and contraction.
More than 7.8 billion humans currently occupy the Earth and almost every corner is covered by man either indirectly or directly (Blooms, 2011). A focal point in this discussion, is analysing aspects of human lives that make us more susceptible to new infectious diseases and undoubtedly, the topics of transport and globalisation are major contributors in this issue. Today, transportation ranges on a micro to macro scale ranging from UBERs to aeroplanes and is easily accessible by the general public. Many individuals living in urban areas, resort to various modes of public transport such as bus, train, ferry and trams on a daily basis in order to fulfil their routines. Globalisation is a heavily relied upon system that ensures interconnectedness between countries, through means of trade, travel, business and economy to name a few. In the past, humans across the world have been reasonably isolated and it was only until the late 1990s that there was contact between the old and new world (Diamond, 1998). Initially, infectious diseases only had the potential to spread the distances that man could walk, but the advancement of transportation saw new diseases develop into potential pandemics faster than ever before. Individuals are at greater risk of developing infectious diseases as the efficiency and ease of modern-day transport networks increases their exposure to familiar or unseen diseases (Guimera et al. 2005). The influenza virus often raises great concern due to its genetic variability and capacity to spread rapidly (Ferguson et al. 2003) and was the main infectious disease to portray pandemic behaviour influenced by global transport system during the 20th century (Cox and Subbaro, 2000). Public transport systems in place for local urban communities, are highly effective vectors in ensuring communicable disease success. When an individual sneezes, large droplets of saliva and mucous exit the mouth and drop to the ground fairly quickly. However, a smaller cloud of droplets containing saliva and mucous can travel eight meters in the air. Similarly for a cough, the cloud can travel for up to six meters in the air and stay suspended for 10 minutes- more than enough time for the particles to travel from one side of a train carriage to the other and reach the heating and air conditioning ventilation (HVAC) systems (Bourouiba, 2016). A more relevant disease to discuss, is the emerged novel coronavirus (SARS-Cov-2). This disease is ranked the third most highly pathogenic human coronavirus with 3.35 million confirmed cases worldwide as of February 12th 2020 (Kampf, 2020). With an incubation period of two to ten days, spread often occurs through droplets, contaminated hands, and surfaces. The survival of SARS-CoV outside a host body, varies depending of the type of surface. For example; on plastic SARS-CoV can last for up to nine days at room temperature, and on glass and metal which is often found on most transportation vehicles, it can last for four to five days at room temperature. Although the data for transmissibility from surface to hands is not yet available for this virus, it is said to be similar to influenza A which has a transmission time of five seconds where just over thirty percent of the viral load is transmitted (Bean et al. 1982). Despite often unwittingly placing ourselves in situations where the risk of exposure is increased, measures such as washing hands often, covering our mouths and nose when we cough or sneeze or staying home when ill, will greatly improve the health of individuals and the wider public. We can see that the relationship between global and local transport network expansions and increased human movement has greatly facilitated the transmission of infectious diseases. For travel times that can range from five minutes on the bus or twenty-four hours on an aeroplane, the opportunity for disease spread, contraction and transmission is very high and should be of great concern.
When considering man’s impact on the world, one of our greatest crimes is the rapid clearing of forests and land through deforestation. With forests covering thirty percent of our planet, the speed of degradation and destruction of forest habitats should raise major concerns as future pandemics may emerge from what lives within them. A primary risk factor arises from the human encroachment of animal habitats, increasing the rate of interaction between human and wildlife and as a result, supports to potential for pathogens to cross species barriers (Lo, Rota 2008). Land use for human benefit, is a key driver of emerging diseases and transmission of infections (Patz et al. 2004). Amy Vittor, an epidemiologist at the University of Florida’s Emerging Pathogens Institute, postulated that the clearing of forests subsequently creates the ideal living conditions for the mosquito Anopheles darlingi- a major transporter of malaria in the Amazon. Vittor’s research highlights a strong correlation between the abundance of malaria vectors and anthropogenic land use, concluding that deforestation as a product of man’s actions greatly impacts the breeding, abundance and species composition of mosquitoes. With malaria being one of the deadliest vector-borne diseases killing over one million individuals annually, deforestation in the Amazon has displayed a strong link to the rise in the prevalence of the disease (Sawyer et al. 2006). Altering forest structures changes the vegetation and hydrology of land, creating shaded pools of water behind debris where trees no longer stand, simultaneously altering the species composition of Anopheles darlingi creating ideal habitats for reproduction. An estimated ten percent annual increase in forest destruction, saw a three percent incline in malaria cases between 2003 and 2005, thus it can be seen that cases of malaria rise in parallel to rapid forest decline (MacDonald, 2019). It should be noted that multiple viruses exist innocuously with their host in forest habitats due to co-evolution, but humans often become oblivious hosts for pathogens when they enter forests or change habitats. More than this, mosquitoes are not the only vectors that should be of concern. Nearly sixty percent of all new infectious diseases such as the Human Immunodeficiency Virus (HIV), Ebola and Nipah virus, originate and transmitted via forest-dwelling wildlife (Jones et al. 2008). Although the products of deforestation are often drastic, they are not irreversible. In attempts to counteract the effects of deforestation, we can alter habits by planting more trees to replace those removed, better manage forest resources, and encourage agricultural techniques that avoid destroying fragile soil.