Question

What role does climate change play in emerging disease?

Answer 1

Role of climate change play in emerging disease are:

Climate can influence pathogens, vectors, host defenses and habitat. Diseases carried by mosquito vectors are particularly sensitive to meteorological conditions. These relationships were described in the 1920s and quantified in the 1950s. Excessive heat kills mosquitoes, but within their survivable range, warmer temperatures increase their reproduction and biting activity, and the rate at which pathogens mature within them. At 20 °C falciparum malarial protozoa take 26 days to incubate, but at 25 °C, they develop in 13. Anopheles mosquitoes (carriers of malaria) live only several weeks. Thus warmer temperatures permit parasites to mature in time for the mosquito to transfer the infection.

Temperature thresholds limit the geographic range of mosquitoes. Transmission of Anopheles-borne falciparum malaria occurs where temperatures exceed 16 °C .

The range of yellow fever (with a high rate of mortality) and dengue fever (characterized by severe headaches and bone pain, with mortality associated with dengue hemorrhagic fever and dengue shock syndrome), both carried by Aedes aegypti, is restricted by the 10 °C winter isotherm. Freezing kills Aedes eggs, larvae and adults. Thus, given other conditions, such as small water containers, expanding tropical conditions can enlarge the ranges and extend the season, with conditions allowing transmission. Warm nights and warm winters favor insect survival. Fossils from the end of the last Ice Age demonstrate that rapid, poleward shifts of insects accompanied warming, especially of these minimum temperatures. Insects, notably Edith’s checkerspot butterflies today, are superb ’paleothermometers’, outpacing the march of grasses, shrubs, trees and mammals in response to advancing frost lines. In addition to the direct impacts of warming on insects, volatile weather and warming can disrupt co-evolved relationships among species that help to prevent the spread of ’nuisance’ species.

Today, one-half of the world’s population is exposed to malaria on a daily basis. Deforestation, drug and pesticide resistance and inadequate public health measures have all contributed to a recent resurgence.Warming and extreme weather add new stresses. Dynamic models project that the warming accompanying the doubling of atmospheric CO2 will increase the transmission capacity of mosquitoes some 100-fold in temperate zones, and that the area capable of sustaining transmission will grow from that containing 45% of the world’s population to 60% ; though recent statistical modeling projects less of a change. Notably, all these analyses rely on average temperatures, rather than the more rapid changes in minimum temperatures being observed, and thus may underestimate the biological responses. In addition, historical approaches to understanding the role of temperature and infectious disease have argued that the relationships do not hold for periods such as the medieval Warm Period and the Little Ice Age. It is important to note, however, that the change of CO2 and temperature (and their rates of change) over the 20^th century are outside the bounds of those observed during

the entire Holocene (the last 10 000 years); indeed, the previous 420 000 years. Some of these projected changes may be under way. Since 1975 several VBDs have reappeared in temperate regions. Anopheline mosquitoes have long been present in North America and malaria circulated in the US earlier this century. But by the 1980s, transmission in the US was limited to California, after mosquito control programs. Since 1990, however, small outbreaks of locally transmitted malaria have occurred during hot spells in Texas, Georgia, Florida, Michigan, New Jersey, New York, and in Toronto . Malaria has returned to South Korea, parts of southern Europe and the former Soviet Union. Moving southward, malaria has re-colonized the Indian Ocean coastal province of South Africa, while dengue fever has spread into northern Australia and Argentina.

These changes are consistent with projections, though one author has stressed alternative explanations for these changes . Land clearing, population movements and drug and pesticide resistance have all played parts. But a set of changes occurring in tropical highland regions are internally consistent, indicative of long-term warming