Climate Change and the Ecology of Infectious Disease

Climate Change and the Ecology of Infectious Disease Craig Loehle NCASI

Will Warming Increase Disease? • IPCC AR5 says yes • Focus on vector borne disease • Malaria, dengue fever examples • Water borne infections • This talk provides perspective, covers biology of disease

Historic Killers • How big were/are they? • Were/are they restricted to tropics? • Related to climate?

Black Death/Plague • Originated central Asia • Yersinia pestis bacterium • Killed 30-60% of Europe in mid-1300s • Globally reduced population 20% • Rats/fleas implicated as carriers • Vanished on its own, but some residual infections today

Smallpox • Earliest records from Egypt, India • Spread to China, Europe, then globally • Devastated Indians in Americas • 300-500 Million deaths globally during 20th Century • Eliminated by vaccine

Influenza • Constantly changing global disease • 250,000 to 500,000 deaths/yr globally • More in pandemic years • 1918 pandemic 10 to 100 Million deaths (poor records most of world)

Malaria • Amoeba spread by mosquitos • Endemic in Russia, Scandanavia late 1800s • Declined even before DDT • Why? • Mosquito depends on rain barrels • Modern water supply eliminated barrels & similar • Screens in windows • Reduce transmission rate below 1, dies out

Malaria • Recent tropical resurgence blamed on climate change • But coincides with reduction of DDT spraying and with chloroquine resistance • DDT, screens, netting, clean water would mostly eliminate malaria • Dengue fever same behavior as malaria

TB • 19th Century TB huge killer in Europe • Declined with rising health in Europe, US • Global extent, still a menace • Reduced by vaccines, healthier population

STDs/AIDS • Obvious transmission path • Global • 5.4% global disease deaths (WHO) • NOT related to region/climate

Lyme Disease • “vectors” theory: deer tick • Rise linked to increasing deer populations

Water Borne Illness • Bacteria, virus, other • IPCC claim: • Warmer water will increase risk • Increased flooding will increase risk

Water Borne Examples • Cholera • Bacterium—vaccine now available • Spread in dirty water • 100-130k deaths/yr • Diarrhea (3.2% of disease deaths,mostly children) • Other • Almost entirely cured with sanitation

Tropical Parasites • Gives impression that tropics are disease-ridden • Big problem Africa • Ex: River Blindness, Rift Valley fever • Due to living outdoors, poor sanitation • Still only 0.2% global mortality due to disease according to WHO

Summary • Causes of disease • High population: transmission • Poor sanitation • Standing water (rain barrels) • Poor health (susceptible)

Summary • Major diseases devastated the world in past • No major communicable disease shows any climate preference • Today biggest killers have been tamed • Vaccines • Sanitation • Health • Even with this reduction in total disease, tropical diseases are minor part of total disease mortality

Summary • The few diseases that might spread represent a tiny percent of total global disease mortality • Most burden of tropical disease/parasites due to sanitation • Development would do 100x more to reduce disease than would preventing a 1 deg rise in temperature

Climate Change and the Ecology of Infectious Disease