Greenpeace: CLIMATE CHANGE AND GLOBAL INFECTIOUS DISEASE THREATS

Climate Change and Emerging Infectious Diseases

The current diversity of infectious disease threats facing humanity is unprecedented.* Over the last two decades, malaria, dengue, cholera and tuberculosis (TB) have resurged, and human immunodeficiency virus (HIV), viral haemorrhagic fevers and hantavirus pulmonary syndrome have appeared unexpectedly in new populations.** William Forge, the former director of the US Centers for Disease Control and Prevention (CDC), coined the term "global infectious disease threats" because international interdependence, modern transportation, trade and changing social patterns ensure emerging infections are a global threat, from which no country is sufficiently remote or disconnected to assume that its populations are safe.***

The recent emergence of a Equine morbillivirus (which killed two horse trainers) in Queensland,Ý the increasing geographic spread of Barmah Forest virus,ÝÝ the emergence of a lethal frog iridovirus in southeast Queensland,ÝÝÝ and the first reported case of Japanese encephalitis in Australian territoryý serve as a reminder that Australia can fall prey to the emergence of indigenous or foreign microbes.

The IPCC human health author groupýý and othersýýý have forewarned that global climate change will exacerbate and accelerate the tempo of contemporary infectious disease emergence, particularly for those diseases transmitted by an intermediate host, or vector.

Researchers have long appreciated the role climate plays in vector-borne disease distribution,*ý and the combined effects of the projected increases in temperature and rainfall (Table 1.) suggest an expansion of favourable habitats for many vector-borne diseases, regional changes from seasonal to perennial transmission (or vice versa), and the migration of vectors into areas currently disease free, such as to higher altitudes.*ýý

Modelling studies of climates suitable for vector-borne diseases under enhanced greenhouse conditions suggest a significant increase in the areas suitable for vector-borne disease transmission.*Ý (Figure 1.) High risk analysis by Martens and colleagues suggests that an additional 620 million people could be at risk from malaria in developing countries by 2050.*ÝÝ By 2100, the number could grow to around one billion.

Climate change scenarios for Australia*Ýý (Table 2.) suggest conditions that would significantly increase arbovirus activity, including Ross River virus, and Barmah Forest virus, and Murry Valley encephalitis virus.*ýÝ Vectors for dengue, yellow fever and malaria already exist in Australia; pessimistic scenarios suggest the (re)establishment of these diseases as climate change increases the favourableness of vector environments and increasing numbers human viremic travellers enter the country. Irrespective of whether or not this occurs, climate change is likely to favour localised epidemics of imported diseases.*ý* Under future climate conditions, the heavily populated southeastern regions of the country may be at risk.*Ý*

Humanity's ability to adapt via changes in culture, technology, migration and personal behaviour could, at least in developed counties, to an extent mitigate the impacts of climate change.*** The elimination of malaria from Australia, for example, was a direct result of proactive public health action. Both climate change-related and non-climate change-related factors will influence Australia's vulnerability to emerging infections, including:

Demographic changes, such as an aging population, escalating migration to coastal tropical areas and increased drug dependence and chronic illness.#ýÝ
The introduction of microbes and vectors by escalating and unprecedented transboundary movements of people.**ý
Expanding prevalence of drug-resistant pathogens and pesticide-resistant vectors.**Ý
A potentially uncontrollable influx of millions of refugees from Southeast Asia and the Pacific, displaced by climate change and sea level rise.ý* These refugees would at best strain health systems or at worst overwhelm them, spreading diseases into populations with no immunity.ÝÝ

The climate and ecosystems interact in a non-linear fashion and projected climate changes lie outside human experience. There is therefore considerable scope for "surprises" in the future.ý** For example, pathogens go undetected around us and, as in the climate-related emergence of hantavirus pulmonary syndrome in the southwest US in 1993,ýÝ could emerge as environmental change favours infected vertebrates or arthropod vectors.ýÝÝ As animals and humans attempt to migrate in response to climatic changes, new species will be exposed to new arthropod vectors and currently "silent" wildlife transmission cycles.*** Disease carriers may begin to mix and for some viruses, this "ecological overlap" would favour the gene swapping between pathogens and emergence of novel strains.ýÝ*

A change in the distribution of infective agents and their carriers may be among the first biological indicators of climate change.ý*Ý Recent disease emergence, attributed or partially attributed to climatic factors, suggests that such indicators may be beginning to appear:

In the North West Frontier Province of Pakistan, a regional increase in annual mean temperature of 0.5oC since 1978 has contributed to the increase in malaria (Plasmodium falciparum) cases from a few hundred in the early 1980s to 25,000 in 1990.ý*ý An extended season of malaria and dengue activity has also been observed in Argentina.ýÝý
Epidemic malaria has occurred at high altitudes over the last decade in Rwanda,ýý* Zambia, Swaziland, Ethiopia, and Madagascar.ýýÝ Increased temperatures and/or rainfall, have acted alone or in concert with increased drug resistance to promote these epidemics.Ýý One epidemic in highland Madagascar in 1988 killed more than 100,000 people.Ýýý
Dengue has appeared at higher altitudes than previously reported in Costa Rica (at 1,250m),Ý* and in Colombia and India (at 2,200m).Ý** The previous range was temperature limited to approximately 1,000 metres above sea level. In Mexico, the dengue vector (Aedes aegypti) has been detected at 1,600 metres; transmission of dengue was unknown above 1,200m before 1986.Ý*ý The above cases lie near or above the altitude or latitude limit of transmission and would be vulnerable to the small increases in temperature that have occurred across these regions.
Other examples of climate-related changes in the prevalence or distribution of pathogens and their vectors include the resurgence of Mediterranean spotted fever in Spain and Italy,Ýý* the recent epizootic of African horse sickness in Iberia,ÝýÝ the resurgence of plague in parts of southern Africa,Ý*Ý increased incidence and geographic spread of algal blooms,ÝÝý outbreaks of opportunistic infections among seals,ÝÝ* and the spread and establishment of pathogens and vectors in Switzerland.#

Recent changes in climate throughout Australia are not inconsistent with projections of climate change.## (Table 2.) In response to successive mild winters and heavy rains, the buffalo fly (Haematobia irritans exigua) has spread southwards into northern NSW from central Queensland,### and in recent years, relatively large climate-related arbovirus epidemics have occurred.#Ý In South Australia, high rainfall and temperatures between August 1992 and February 1993 led to the proliferation of Ross River virus vectors and a subsequent epidemic of the disease. More than 800 cases were reported, compared to the average annual number of cases of less than ten. Smaller outbreaks occurred in 1984 and 1989, 136 and 155 cases respectively.#ý

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