October 8, 2008

Report: Climate Change Will Hasten Spread Of Deadly Diseases

Health experts from the Wildlife Conservation Society (WCS) released a new report on Tuesday that lists 12 pathogens that are likely to spread due to changes in temperatures and precipitation levels resulting from global warming.

The "deadly dozen" diseases will have potential impacts to both human and wildlife health and global economies, the experts said.

Entitled "The Deadly Dozen: Wildlife Diseases in the Age of Climate Change", the report was released at the IUCN World Conservation Congress, held in Barcelona, Spain.

The list includes such diseases as avian influenza, Ebola, cholera, and tuberculosis. The report's authors said wildlife monitoring to detect how these diseases are moving is the best defense in mitigating the impact of the pathogens.

"The health of wild animals is tightly linked to the ecosystems in which they live and influenced by the environment surrounding them, and even minor disturbances can have far reaching consequences on what diseases they might encounter and transmit as climate changes. Monitoring wildlife health will help us predict where those trouble spots will occur and plan how to prepare," said Dr. Steven E. Sanderson, President and CEO of the Wildlife Conservation Society.

"The term 'climate change' conjures images of melting ice caps and rising sea levels that threaten coastal cities and nations, but just as important is how increasing temperatures and fluctuating precipitation levels will change the distribution of dangerous pathogens."

The report expands on guidelines issued in a recently published paper entitled "Wildlife Health as an Indicator of Climate Change", which examined the harmful impacts of climate change on the health of wild animals and the subsequent effects on human populations.

The pathogens also have the capacity to destabilize trade and cause substantial economic damage.  For instance, several livestock diseases that have reemerged since the mid-1990s (including avian flu) have caused an estimated $100 billion in losses to the global economy.

WCS's Global Health Program currently leads an international consortium that monitors the movements of avian influenza through wild bird populations around the world. The Global Avian Influenza Network for Surveillance (GAINS) program was established in 2006 with support from the United States Agency for International Development (USAID), and now includes dozens of private and public partners that monitor wild bird populations for avian influenza around the world.

"Emerging infectious diseases are a major threat to the health and economic stability of the world," said Congresswoman Rosa L. DeLauro (D-CT3), a supporter of the program.

"What we've learned from WCS and the GAINS Program is that monitoring wildlife populations for potential health threats is essential in our preparedness and prevention strategy and expanding monitoring beyond bird flu to other deadly diseases must be our immediate next step."

"The monitoring of wildlife health provides us with a sensitive and quantitative means of detecting changes in the environment," said Dr. William Karesh, Vice President and Director of WCS's Global Health Programs.

Wildlife health monitoring provides a view of what is changing around us, and will help governments, agencies, and communities detect and mitigate threats before they become disasters."

Although monitoring initiatives have focused on many wildlife pathogens, data about how these diseases will spread in response to climate change is sparse.  Future monitoring of these diseases must be conducted in parallel with an examination of meteorological data to uncover climate-related trends.

The authors of the WCS report said their list of twelve pathogens is not comprehensive, and that subsequent studies may ultimately eliminate some pathogens from the list of those enabled by climatic factors.

The pathogens included in the report, along with their impacts, are listed below.

Avian influenza: Like human influenza, avian influenza viruses occur naturally in wild birds, though often with no severe consequences. The virus is shed by infected birds via secretions and feces. A highly pathogenic strain of the disease"”H5N1"”is currently a major concern for the world's governments and health organizations, specifically because it has proven deadly to domestic and wild birds, as well as humans, and has the potential to evolve into a strain that can spread from human to human. Current data indicate that the movement of H5N1 from region to region is largely driven by the poultry trade. However, climate changes can disrupt normal movements of wild birds and can bring both wild and domestic bird populations into greater contact at remaining water sources.

Babesiosis: Babesia species are examples of tick-borne diseases that affect domestic animals and wildlife, and Babesiosis is an emerging disease in humans. In some cases, Babesia may not always cause severe problems by themselves but when infections are severe due to large numbers of ticks, the host becomes more susceptible to other infectious diseases.  Climate factors fostered heavy infestations of ticks on wild buffalo and subsequent spill-over infection of lions, which then became more susceptible to infection.  In Europe and North America, the disease is becoming more common in humans. 

Cholera: Cholera is a water-borne diarrheal disease that affects humans primarily in the developing world. It is caused by a bacterium Vibrio cholerae, which survives in small organisms in contaminated water sources and may also be present in raw shellfish such as oysters.  Once contracted, cholera rapidly becomes deadly. It is highly temperature dependent, and increases in water temperature correlate directly with occurrence of the disease. Rising global temperatures are expected to increase incidence of this disease.

Ebola: Ebola hemorrhagic fever virus and its closely related cousin"”the Marburg fever virus"”easily kill humans, gorillas, and chimpanzees. Currently, there is no known cure.  There is significant evidence that outbreaks are related to unusual variations in rainfall/dry season patterns. As climate change disrupts and exaggerates seasonal patterns, we may expect to see outbreaks of these deadly diseases occurring in new locations and with more frequency.

Intestinal and external parasites: Parasites are widespread throughout terrestrial and aquatic environments. As temperatures and precipitation levels shift, survival of parasites in the environment will increase in many places, infecting an increasing number of humans and animals. Many species of parasites are zoonotic, spread between wildlife and humans. The nematode, Baylisascaris procyonis, is spread by the common raccoon and is deadly to many other species of wildlife and humans. A close relative, Baylisascaris schroederi, causes death in its natural host"”the critically endangered giant panda.

Lyme disease: This disease is caused by a bacterium and is transmitted to humans through tick bites. Tick distributions will shift as a result of climate change, bringing Lyme disease into new regions to infect more animals and people.

Plague: Plague, Yersinia pestis"”one of the oldest infectious diseases known"”causes significant death rates in wildlife, domestic animals, and humans in certain areas.  Plague is spread by rodents and their fleas.  Alterations in temperatures and rainfall are expected to change the distribution of rodent populations around the globe, which would likely impact plague.

"Red tides": Harmful algal blooms off global coasts create toxins that are deadly to both humans and wildlife. These occurrences"”commonly called "red tides""”cause mass fish kills, marine mammal strandings, penguin and seabird mortality, and human illness and death from brevetoxins, domoic acid, and saxitoxins.  Similar events in freshwater are caused by a species of Cyanobacteria and have resulted in animal die-offs in Africa. Altered temperatures or food-web dynamics resulting from climate change will have unpredictable impacts on the occurrences of this worldwide phenomenon. Effects of harmful algal blooms on sea life are often the first indicators that such an event is taking place.

Rift Valley Fever: Rift Valley fever virus (RVFV) is an emerging zoonotic disease of significant public health, food security, and overall economic importance, particularly in Africa and the Middle East. In infected livestock such as cattle, sheep, goats and camels, abortions and high death rates are common. The disease can be fatal in people.  Given the role of mosquitoes in transmission of the virus, changes in climate continue to be associated with concerns over the spread of RVFV.

Sleeping sickness: Also known as trypanosomiasis, this disease affects both people and animals. It is caused by the protozoan, Trypanosoma brucei, and transmitted by the tsetse fly. The disease is endemic in certain regions of Sub-Saharan Africa, affecting 36 countries, with estimates of 300,000 new cases every year and more than 40,000 human deaths each year in eastern Africa. Domestic cattle are a major source of the disease. Direct and indirect effects of climate change on tsetse fly distributions could play a role in the distribution of this deadly disease.

Tuberculosis: As humans have moved cattle around the world, bovine tuberculosis has also spread.  It now has a global distribution and is especially problematic in Africa, where it was introduced by European livestock in the 1800s. The disease infects vital wildlife populations, such as buffalo and lions in Kruger National Park in South Africa, where tourism is an integral part of local economies. The disease also infects humans in southern Africa through the consumption of un-pasteurized milk. Human forms of tuberculosis can also infect wild animals. Climate change impacts on water availability due to drought are likely to increase the contact of wildlife and livestock at limited water sources, resulting in increased transmission of the disease between livestock and wildlife and livestock and humans.

Yellow fever: Found in the tropical regions of Africa and parts of Central and South America, this virus is carried by mosquitoes.  The disease is expected to spread into new areas as changes in temperatures and precipitation levels permit.  One type of the virus"”jungle yellow fever"”can be spread from primates to humans and vice-versa via mosquitoes that feed on both hosts. Recent outbreaks in Brazil and Argentina have had devastating impacts on wild primate populations.


Image Caption: Babesia species are examples of tick-borne diseases that affect domestic animals and wildlife, and Babesiosis is an emerging disease in humans. Courtesy Andr© Karwath - Wikipedia


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