Supported by:

Emerging diseases: The human health perspective
Professor Aileen Plant
Australian Biosecurity Cooperative Research Centre for Emerging Infectious Disease, Curtin University of Technology, Perth, WA

Powerpoint presentation (500KB)

In the last three decades more than 30 new organisms have been identified, along with an increase in some infectious diseases that were previously thought to be under control. A good working definition of an emerging infectious disease is one that has increased in number or geographic spread in the preceding two decades. Today I want to leave you with the message that emerging diseases are here to stay, and that as such we need to deal with them. I will do this by considering three diseases, why they arise and what we should worry about.

Some diseases have never gone away. Diseases such as tuberculosis, malaria, cholera, and dengue once appeared to be either in control or even disappearing but have now come back and cause more problems than ever before. Antibiotic resistance appears inevitable - we see outbreaks of disease caused by methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci.

In the last few years the world has been significantly troubled by the advent of various new diseases, although some have not become significant problems from a population perspective, although there may have been individual deaths. Two viruses that have caused deaths as well as public health concern are Nipah virus and West Nile virus. Nipah caused the deaths of over 100 people in Malaysia as well as significant economic losses due to the slaughter of pigs. In total it is estimated that the outbreak cost in the vicinity of US$500 million. West Nile virus arrived in mainland USA and has since spread throughout nearly the whole country as well as Canada and Mexico, leading to many deaths of humans as well as the impact on horses and birds, and considerable economic loss. Australia also has not been immune with the occurrence of new viruses such as Hendra virus and Australian bat lyssavirus, a form of rabies. Both have caused deaths, and while these represent individual tragedies, neither disease has become a major public health problem.

In 2003 a new disease which came to be known as SARS (Severe Acute Respiratory Syndrome, caused by a coronavirus) had a major impact on health, travel and tourism. In some ways it epitomised the fears surrounding a new organism – rapid spread, apparently fairly infectious, a significant number of deaths and the helpless feeling that a new disease engenders. I will return to SARS later.

Then of course there are the diseases that have had major impacts on the world: AIDS and variant Creutzfeldt Syndrome (vCJD), the human form of the so-called ‘mad cow disease'. vCJD may not have any greater impact than it already has but at the moment, it is still too early to say. And of course influenza continues to threaten the globe.

Controlling any disease, emerging or not requires; surveillance so that we know a disease has occurred, a response mechanism, control measures and of course preparation (or prevention) for next time the disease occurs

A new disease occurred quite recently and there was extensive spread before it was noticed, a good outbreak investigation which determined multiple methods of spread; it was quickly discovered how to prevent the disease and good tests were rapidly developed. At this stage there is no vaccine but treatment, at least is some countries is improving fast. But AIDS is still a global disaster. Around the world AIDS has led to more than 20 million deaths, over 40 million people are living with HIV today and by 2010 it is estimated that more than 40 million children will have one or both parents dead from AIDS. AIDS differentially affects working aged people, and has a major impact on the economy. In some countries the impact of AIDS has lead to a major fall in the Gross National Product.

When SARS occurred in the early part of 2003, people around the globe were concerned about a potential pandemic. At that time we had no identified agent, no diagnostic assays, no defined risk factors, no specific treatment or prevention, no knowledge of the origin of the virus, and the necessary infection control practices were ill-defined.

By the end of the SARS outbreak, SARS had left in its wake 8098 cases, 774 deaths, a world wide economic impact with billions lost in airlines, and tourism, and a devastated health care system

However, within 5 months (Feb-July) the virus was identified, diagnostic tests were developed and shared around the world, and infection control practices were established. The international public health response was unprecedented with surveillance programs established, laboratory, clinical and epidemiological networks that met by teleconference were established for the sharing of knowledge, skills and data, and a global approach to control implemented. On 5 July 2003, WHO removed the last region from the list of areas with recent local transmission.

Let us now turn to the impact of avian influenza, and its implications for humans. About every 30 years there is a pandemic of influenza. There are three prerequisites for a pandemic to occur: a novel influenza sub-type must be transmitted to humans, the new virus must be able to replicate in humans and cause disease, and the new virus must be efficiently transmitted human to human.

Since 1997, the first two criteria have been met four times, mostly with the same strain of influenza (the H5N1 strain) – 1997 Hong Kong (H5N1), 2003 Hong Kong (H5N1), 2003 Netherlands (H7N7), 2004 Vietnam and Thailand (H5N1)

The outbreak in birds has been unprecedented both in terms of its size and the number of countries affected. This appears to be the first time humans have been infected directly without prior modification in mammalian host. While there is some evidence of human to human spread, at this point it does not seem to be efficient spread.

The World Health Organization has met in various fora throughout the year, aiming to improve global preparedness. This includes surveillance, especially ensuring adequate capacity in countries to identify any outbreak early, planning for appropriate public health interventions, the use and availability of antiviral drugs and the development, production and distribution of vaccines.

So what are the keys to success in controlling infectious disease. Looking at SARS first of all, one of the characteristics of countries like Viet Nam where the response was extraordinary was the importance of political leadership and the speed with which government responded. The engagement of government, including the setting up of intersectoral committees was key to rapid and effective response. Of course the global engagement and the support in terms of human and financial resources were also critical, with both the giving and receiving of assistance requiring adjustments for all involved. The importance of the media and the resultant public discussions were vital. And of course, the technical skills were a major contributor. When we look at the response to AIDS, however, the world has been very slow to respond. Some countries still try and hide their AIDS problems, and too few have access to the contemporary technologies and resources that are making such a difference in countries like Australia. And when we think of influenza, there is no doubt that there is considerable technical expertise available throughout the world. Despite the fact that when the pandemic occurs, the world will truly function as one village because of contemporary travel and trade patterns. At this point the resources for identifying and controlling the outbreak early are very mal-distributed. This puts the whole ‘village' at risk. Influenza control is far more complicated than that required for SARS. Thus far we have not seen the global collaboration necessary to deal with this major threat to humankind.

The reasons that diseases emerge are complex and diverse, but have been reasonably well categorised. Some of them include microbial adaptation and change, human demographics and behaviour, technology and industry (includes animal practice, food production), economic development and land use, international travel and commerce, breakdown of public health measures, human susceptibility to infection, changes to climate and weather, changing ecosystems, poverty and social inequality, war and famine, lack of political will, and the intent to harm.

Conclusion

In conclusion, there are undoubtedly more emerging diseases to come. In order to control them scientific approaches are essential, but while science is necessary it is not enough. There remain considerable challenges in integrating science and practice. In the meantime, dealing with the diseases we have is the best preparation for the diseases we await. What do I think will be next? I think the biggest risks are influenza, antibiotic resistance, hospital-acquired infections, possibly vCJD. And of course, something new and previously unthought of!

top of page