The most extreme changes will occur in areas neighbouring current high-risk areas at both higher altitudes and latitudes. In these regions, a temperature increase could convert an area that is malaria-free into an area that suffers seasonal epidemics. The affected populations would frequently have little or no immunity, so high levels of sickness and death would be the norm.
Recent disease outbreaks are consistent with model projections. Mosquito-borne diseases are being reported at higher elevations than in the past in parts of Asia, Central Africa and Latin America. In the summer of 1999, an outbreak of encephalitis claimed three lives in New York City and necessitated widespread pesticide spraying. Experts have identified the West Nile virus, transmitted by mosquitoes that feed on infected birds, as being responsible. Encephalitis had not been previously recorded anywhere in the Western hemisphere, occurring primarily in the late summer or early autumn in temperate regions, but year-round in milder climates.
Diseases carried by mammals, particularly rodents, may also be affected by climate change. A recent study found a 60% rise in human plague cases in New Mexico following wetter than average winters and springs. Plague has only existed in New Mexico since the 1940s, but a large increase in per capita cases occurred in the 1970s and 1980s associated with wetter than normal conditions. The increased precipitation apparently enhances food resources for small mammals that serve as hosts for infected fleas. The moister climate may also encourage flea survival and reproduction. The study notes that if future climate conditions become more favourable for reproduction and survival of either wild mammal populations or their flea populations, the probability of human infection via animal-flea-human contact will almost certainly increase.
Climate change will also have an impact on diseases of plants and animals, and could lead to significant population declines or even the extinction of endangered species. Climate change has been implicated, for example, in the emergence and spread of marine diseases. This happens because the range of hosts and pathogens change, because stress brought on by warming can lower disease resistance and because contaminant input from terrestrial sources increases due to run-off from heavy rainfall. Higher sea surface temperatures, for example, increase the stress on corals, increasing susceptibility to infection. Forests and agricultural crops are susceptible to the spread of pathogens, especially following droughts and floods.
The disproportionate warming at night and during the winter can allow destructive insects and pathogens to invade forests at higher latitudes from which they are now excluded.
C Read the passage again and answer the questions.
For questions 1–3, complete the sentences with words taken from the passage. Write NO MORE THAN TWO WORDS for each answer.
1. ____________ of disease could become more frequent and more intense due to rising temperatures.
2. Vector organisms will exist in places where they previously did not and they will be ____________ for longer.
3. In poor areas, disease will spread quickly because there are insufficient ____________.
For questions 4–10, complete the notes with words taken from the passage. Write NO MORE THAN THREE WORDS OR A NUMBER for each answer.
Mosquitoes
Sensitive to temperature Malaria mos. – (4) ______________ too cold / (5) ______________ too hot Dengue mos. – (6) ______________ too cold Warmer and wetter weather = higher numbers of active mos. + (7) ______________ will incubate more quickly Mos. could operate in wider (8) ______________, increasing number of malaria cases Areas most at risk – those closest to existing (9) ______________ Areas now (10) ______________ could be hit by epidemics – many deaths
106 Pathway to IELTS 6.0
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