Will we be able to predict the next zoonotic pandemic?

In a new Lancet Series, leading experts discuss the ecology, drivers, and dynamics of zoonoses, while also addressing how we might predict the next zoonotic pandemic, and reduce the potentially catastrophic human and economic cost of such an outbreak.

In the first Series paper, an international group of experts led by Dr William Karesh of the EcoHealth Alliance in New York, USA, warn that as global trade and travel expand, zoonoses pose an increasing concern for the global medical community. Zoonoses develop in complex ecological conditions, depending not just on the macro-environment in which organisms spread and develop, but also the internal micro-environment of the organisms which they infect. The spread of zoonoses is strongly affected by human activities, particularly global travel, changes in land use, and animal agriculture, but despite this, not enough is known about the ecology of zoonoses, and more effective collaboration between clincians, public health scientists, ecologists and disease ecologists needs to drive research in this area.

Human processes that infringe upon previously uninhabited areas, such as road building, agricultural expansion, and extractive industries, such as logging and mining, all have the potential to profoundly affect our exposure to zoonoses, yet the authors point out that health assessments around these industrial activities rarely take account of principles of disease ecology, which would inform knowledge of whether a certain process carries a risk of zoonotic outbreak. New guidelines for these industries are urgently needed if we are to insure against the next zoonotic outbreak coming from development activities and changes in the way people utilise and interact with our natural resources.

Vector-borne zoonotic diseases – pathogens which can infect humans but which are spread primarily by an arthropod vector – are on the rise, with many vector-borne pathogens appearing in new regions in the last two decades (eg, recent outbreaks of West Nile Virus in the US), at the same time as certain endemic vector-borne pathogens have started to spread locally in some regions. In the second Series paper, Professor A. Marm Kilpatrick, of the University of California Santa Cruz, USA, and Sarah Randolph of the University of Oxford, UK, describe how environmental changes (such as habitat change) and social changes (such as poverty and conflict) have increased incidence of endemic local pathogens, while the increased speed and ease of travel in recent decades has contributed to the spread of vector-borne pathogens to new regions.

The authors point out that population growth and changes in land use can exert selective evolutionary pressures on vector-borne pathogens, leading to more efficient transmission by vectors and in humans and a consequent increase in pathogen incidence. The authors contrast the different dynamics of vector-borne zoonotic disease outbreaks, with increases in endemic or long-established pathogens generally showing sustained rises, while newly introduced pathogens often show a large initial epidemic, and then fewer cases in most years thereafter.

Despite the enormous impact on global public health, no zoonotic pandemic has ever been successfully predicted before infecting human beings. In the third Series paper, a group of experts led by Professor Stephen Morse, of the Mailman School of Public Health at Columbia University, New York, USA, show that recent developments in modelling and technology mean that we could be on the verge of being able to predict the next zoonotic pandemic. However, serious deficiencies remain – in disease surveillance, in our understanding of the key groups of animals that spread zoonotic disease, and in our ability to use the latest molecular screening methods to identify which bacteria, viruses or fungi are going to cause the next pandemic, and which are harmless.

According to Professor Morse, "There is no question of whether we will have another zoonotic pandemic – the question is merely when, and where, the next pandemic will emerge. The challenge now is to establish whether and how researchers can intervene before a pathogen reaches the human population and develop appropriate triggers for action. Zoonotic diseases, by definition, should be a key mission of human health agencies, agricultural authorities and producers, and natural resource managers, all working cooperatively. However, in reality, the current situation leaves much to be desired, and we need substantial investments in each of these areas if we are to have any hope of ameliorating the effect of the next zoonotic pandemic."

In a Comment accompanying the Series, Dr Peter Daszak of the EcoHealth Alliance in New York, USA, highlights the role that industrial processes may play in exposing humans to zoonoses, stating that, "Pandemics are a product of our economic development – they emerge when we domesticate new species, open up new trade routes, build roads into forests, or expand air travel networks. Perhaps these industries should insure themselves against the rare but devastating pandemics their activities can sometimes cause."

In another Comment, a group of medical anthropologists, led by Dr Craig Janes of Simon Fraser University in Burnaby, Canada, point out that since human behaviour and activities play a dominant role in how zoonotic pandemics arise and spread, there needs to be much more effective collaboration between social scientists, biomedical researchers, and public heath scientists. "To achieve prediction and control, we should better recognise and account for the fact that parasites and pathogens travel within and between human bodies that are linked in complex but patterned relationships", says Dr Janes.

The Lancet Series is published ahead of a special 20th Anniversary Symposium to be held on December 11th – 12th, 2012 in Washington, DC, and hosted by the Institute of Medicine's (IOM) Forum on Microbial Threats. The symposium will take a retrospective look at the Institute of Medicine's seminal reports on Emerging Infections (1992) and Microbial Threats to Health (2003) as well as reflect upon the Institute of Medicine's creation of the Forum in 1996.