Updated: Apr 2, 2020
The Covid-19 pandemic is no flash in the pan. New strains of pathogens are emerging every year, exposing large geographies and populations to the risk of infectious diseases. Pandemic preparedness calls for a global coordinated effort to identify potential disease ‘hotspots’ and zoonosis.
Zoonotic pathogens – those which transmit naturally between non-human animals to humans – have been the subject of extensive research for decades. These pathogens originate in a host or natural reservoir which is their natural habitat for survival and reproduction. Humans, animals and even the environment (plants, soil and water) are reservoirs of different types of pathogens (infectious agents). When a pathogen is transmitted under natural conditions to humans, the process is called zoonosis.
Over the last four decades, there has been an increase in emerging infectious diseases (EIDs) in humans, and nearly three-quarters of them have been zoonotic infections. Zoonosis is not a new occurrence; the origins of a wide range of human diseases, including plague, influenza, anthrax, yellow fever and tuberculosis, can be traced back to animals, with most of them originating in domestic animals (including livestock) and poultry. However, recent emergences of infectious diseases are frequently being traced back to wild animals. Some of these pathogens transmit directly from the reservoir to humans, while others transmit via an intermediate animal host.
EIDs are being increasingly linked to wildlife. This may be the outcome of a combination of factors such as changes in destruction of wildlife habitats, changes in human behaviour, and other environmental changes. The impact of these changes creates conditions which make it conducive for infectious pathogens to ‘spill over’ from animals to humans.
Various scientific studies have been undertaken to establish such a causality. A 2008 study analysed a database of 335 EID events (origins of EIDs) between 1940 and 2004. The researchers observed that EID events had “risen significantly over time”, with 60% of such events being dominated by zoonoses. Of these zoonotic infections, nearly 72% originated in wildlife. The analysis showed that majority of EIDs (54%) were caused by bacteria or rickettsiae, a quarter of them were caused by viral pathogens, and the remaining by fungi, protozoa and helminths.
The novel coronavirus (Covid-19) pandemic is the latest example of an infectious disease where a viral pathogen ‘jumped’ from an animal reservoir, most likely a bat, and transmitted to humans via an intermediate host, speculated to be a pangolin. For years, the scientific community had been predicting that a pandemic involving ‘Disease X’ was overdue. ‘Disease X’ has also been a permanent feature in the World Health Organisation’s (WHO) annual Research and Development (R&D) Blueprint, a list of diseases which need to be prioritised for R&D in emergency contexts.
As per the WHO, ‘Disease X’ represents “the knowledge that a serious international epidemic could be caused by a pathogen currently unknown to cause human disease. The R&D Blueprint explicitly seeks to enable early cross-cutting R&D preparedness that is also relevant for an unknown ‘Disease X’.” As of March 2020, Covid-19 features at the top of the list while ‘Disease X’ continues to feature ominously at the end.
The inclusion of an unknown ‘Disease X’ is not without basis. Since 1901, there have been several major viral outbreaks globally, of which four (including Covid-19) have been categorised as pandemics.
Changes in land use patterns due to population growth and significantly higher demand for food are leading to irreversible changes in wildlife habitats and reduction in biodiversity. Scientists have, for decades, hypothesized that conservation of wildlife can protect human health.
A 2019 study by researchers from Auburn University attempted to provide a new perspective on habitat loss and its correlation with the emergence of infectious diseases in humans. The researchers postulated that “as humans alter the landscape through habitat loss, forest fragments act as islands, and the wildlife hosts and disease-causing microbes that live within them undergo rapid diversification.” These fragmented landscapes were likely to result in a higher diversification of disease-causing microbes, thereby increasing the risk of such microbes spilling over into human populations.
The rapid pace of population growth is causing severe strain on limited natural resources, including land available for agriculture and related activities. From the current 7.8 billion people, global population is projected to reach 8.6 billion by 2030 and 11.2 billion by 2100. Mounting global population will lead to a surge in demand for food, which in turn will alter land use patterns. Forests will be cleared to divert the land for agriculture, dairy farming and rearing livestock. Many wildlife species will become extinct, and the ones which survive, especially bats and rodents, are the best at transmitting deadly viruses. Some researchers consider land-use change as the “biggest driver of risk.”
Global food production will also face significant challenges due to the impact of climate change, including extreme conditions such as drought and flooding, along with unpredictable weather patterns. With affected regions becoming too hot or wet, agricultural activities will be diverted to new areas – this will increase the likelihood of converting natural wildlife habitats into agricultural land.
Large-scale deforestation, which has an immediate potential to disrupt ecosystems in tropical and temperate regions, is associated with a significant loss of biodiversity. Critical elements of ecosystems, including soil & water conditions and micro-climates, are impacted by forest clearings.
The correlation between deforestation and emergence of infectious diseases has not been completely established, with related research still in its early stages. However, since deforestation results in the transformation of entire ecosystems, it can have far-reaching impacts on disease transmission. The global rate of tropical deforestation appears to be increasing with maximum losses being recorded in Brazil and other nations in the Americas. In parts of Africa, the rates of deforestation are nearly 1% per year. Logging in North America, Russia and Europe is leading to an increase in deforestation in temperate regions.
Past research has found a direct link between deforestation and human diseases, both vector-borne and viral. Human vector-borne diseases such as malaria, Lyme disease, cutaneous leishmaniasis and severe onchocerciasis have increased or been impacted by deforestation and forest fragmentation. The emergence of viral pathogens such as SARS, Ebola and other bat-related viruses have been linked to deforestation. Loss of habitat affects migratory patterns and timings of avian populations – these changes may lead to “altered flyways” and increase contact among different avian species, which exposes human populations to novel pathogens.
This devastating impact has been superbly articulated by David Quammen, author of Spillover: Animal Infections and the Next Pandemic: “We invade tropical forests and other wild landscapes, which harbour so many species of animals and plants – and within those creatures, so many unknown viruses. We cut the trees; we kill the animals or cage them and send them to markets. We disrupt ecosystems, and we shake viruses loose from their natural hosts. When that happens, they need a new host. Often, we are it.”
Pandemic preparedness calls for a global coordinated effort to identify potential disease ‘hotspots’ and zoonoses before their large-scale emergence. A simultaneous and equally critical activity involves conserving natural wildlife habitats and taking immediate steps to stop biodiversity loss.
The Covid-19 pandemic is not the first, and neither will it be the last. However, the frequency with which EIDs have been increasing are cause for deep concern. It necessitates a global coordinated effort to identify emerging disease hotspots in high-risk areas which include tropical Africa, Latin America and Asia. Due to the significant threat of zoonoses from wildlife, there is a critical need to detect new, potentially zoonotic pathogens in wildlife populations. This has to be a long-term, coordinated effort which needs to be backed and funded by governments, possibly under the aegis of the WHO.
One such initiative had been undertaken by the U.S. Agency for International Development (USAID) which established its Emerging Pandemic Threats (EPT) program. The EPT program comprised four projects: PREDICT, RESPOND, IDENTIFY, and PREVENT. The PREDICT project was concerned with the “detection and discovery of zoonotic diseases at the wildlife-human interface.” Under the PREDICT projects, research was carried out in geographic ‘hotspots’ with a focus on wildlife – animals such as bats, rodents and nonhuman primates – with a high likelihood of carrying zoonotic diseases. Despite its critical role with regard to research on pandemic preparedness, the PREDICT project was shut down in October 2019 after its 10-year funding cycle ended.
A key element of preventing the next epidemic or pandemic is to understand how to keep Nature’s protective effects intact. A 2010 study found that a 4% reduction in the Amazon rainforest was associated with a 48% increase in the incidence of malaria in 48 Brazilian districts. It may be possible to predict the region from where the next disease can emerge by monitoring encroachment into forests and natural habitats. This could mean going to remote village areas which can be potential ‘interfaces’ between humans and wildlife, places where mines have recently opened up, or areas where new roads are being constructed.
While the immediate priority is protecting the global population from Covid-19, the long-term priority involves protecting biodiversity and preventing loss of habitats. Inger Andersen, executive director of the UN Environment Programme, stated in a recent interview, “Never before have so many opportunities existed for pathogens to pass from wild and domestic animals to people. Our continued erosion of wild spaces has brought us uncomfortably close to animals and plants that harbour diseases that can jump to humans.”
“It’s almost always a human behaviour that causes it and there will be more in the future unless we change,” said Prof. Andrew Cunningham, of the Zoological Society of London. The Covid-19 pandemic has made it clear that viral pathogens do not differentiate based on country, social ranking, affluence levels or the colour of one’s skin. It has affected royalty and commoners alike. Instead of resorting to blame-games, countries must awaken from their slumber and work in a coordinated manner to pre-empt the next pandemic.
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