Climate Change Culprit in Emerging Infections

Internal Medicine World Report, November 2007, Volume 0, Issue 0

ID Expert Sounding the Alarm about New Threats

ID Expert Sounding the Alarm about New Threats

By Sarah Pressman Lovinger, MD

CHICAGO—Did human-induced climate change pave the way for Chikunguya virus to thrive in Europe and infect more than 250 people in Italy this past summer? Anthony McMichael, PhD, an infectious disease expert with the Australian National University in Canberra, says it is difficult to attribute any single infectious disease outbreak to climate change, such as the appearance in Europe of a virus previously detected only in Africa and Asia, but he firmly believes that global warming provides an increased opportunity for zoonotic viruses to pass to humans.

The arrival of West Nile virus in North America just 8 years ago is another example of how changes in climate can promote infectious disease outbreaks, said Dr McMichael, acknowledging that climate change is a new issue for infectious disease experts. "It's significant that this topic is even on the agenda," said Dr McMichael. "I think you would agree that 5 or 10 years ago we would not have even been talking about this topic."

Without delving into the political ramifications, Dr McMichael agreed with the evidence that the earth is warming, and that human activity is leading to rising temperatures. He noted that even if reasonable caps on carbon dioxide emissions can be put in place globally, we are likely to witness an average temperature increase of 4?C by 2070.

Dr McMichael called on physicians to become more aware of the relationship between climate change and infectious disease outbreaks, and be alert to seeing unfamiliar conditions. Developing a more ecological prospective on how the spread of infectious diseases can help the international medical community devise ways to arrest this spread.

Climate change "has implications for public health surveillance," said Dr McMichael.

Dr McMichael and colleagues use modeling of empirical data sets to determine the relationship between climate change and communicable diseases.

Vibrio parahaemolyticus

N Engl J Med.

The report of outbreak of in Alaskan oysters ( 2005;353:1463-1470) was speculated to be affected by the warming of the Pacific Ocean.

Experts suspect that changes in the distribution of many infectious diseases can be attributed to climate change.

Increased outbreaks of such viral illnesses as Dengue fever, West Nile virus, the tick-borne enchepalitides, and Nipah virus have all been linked to climate change. Warmer weather may also increase outbreaks of bacterial illness, including Lyme disease, Cholera, and Salmonella. Although it is difficult to predict the disease burden that might result from climate change, the World Health Organization is trying to determine the impact that projected temperature increases could have on communicable diseases worldwide.

Aedes aegypti

mosquito, a vector for the spread of the Chikungunya virus.

Climate change has already opened up new avenues of disease transmission from animals to humans, according to Dr McMichael. Nipah virus, first recognized in 1999 in Malaysia, apparently spread from fruit bats to pigs, after pig ranchers cleared forests that would normally have provided nourishment to the bats. Dry conditions that experts believe resulted from climate change then led to forest fires, and the bats, deprived of their normal food source, started to eat fruit from orchards near pig farms. Pigs fed on the bat droppings and became infected with Nipah virus, which they then passed on to humans. Now Nipah virus is found not only in Malaysia, but also in Australia, the Philippines, and Indonesia.

Tropical Virus Arrives in Italy

If you or your patients are planning a visit to the Italian province of Ravenna, along with your guidebook and walking shoes, pack some mosquito repellant. Chikungunya fever, a mosquito-borne viral illness, has historically affected millions of people in India, Southeast Asia, and Africa. For the first time, epidemiologists noted an outbreak in Europe during the summer of 2007.

World Health Organization officials report that 254 cases of potential Chikungunya fever have occurred in the Emilia Romagna region of Italy.

Chikungunya virus causes severe and sometimes debilitating arthralgias that last for 5 to 7 days. Other symptoms include fever, headache, myalgias, and rash. It is not considered life-threatening, but 1 elderly Italian man with other comorbidities died from complications of the virus.

Aedes albopictus

Although Europeans have previously imported the virus to their continent after visiting endemic regions of the world, this outbreak marks the first incidence of Chikungunya transmission in Europe. Spread by a bite from the mosquito, the virus could potentially travel to other European countries via this widespread insect.

Did global climate change pave the way for the arrival of this tropical virus in Europe? Experts cannot make this claim with absolute certainty, but as more unusual viruses spread from tropical regions to temperate countries, a warmer world could certainly be one of the causes.