1b. disease dilemmas - there is a relationship between phyiscal factors and the prevalence of disease which can change over time.

How climate affects patterns of disease

• Major control because pathogens and vectors survive best within particular temperatures and moisture ranges.

• Warm temps and high precipitation favour many vector-borne diseases.

• Malaria and yellow fever- mosquitoes breed rapidly where rainfall leaves stagnant water and air temperatures remain high for long periods.

Effect of relief/precipitation on patterns of disease

• Matters because lower, warmer and more humid lowlands often have higher disease risk than cooler uplands.

• Ethiopia - malaria is common in lowlands but absent from the central highlands because temperatures low mosquito and parasite development.

Effects of water sources on patterns of disease

• If water comes from an unsafe/contaminated surface sources, communities face much higher risks of water-borne diseases

• Guinea worm - linked directly to stagnant water containing infected water fleas so its distribution it dependant on unsafe drinking water sources rather than on human to human transmission.

What is a vector

Organism that carried disease from one host to another. Mosquitoes, ticks, fleas and freshwater snails are all major disease vectors

When does vector abundance rise

Example

• When temperatures are high enough for breeding and where humidity prevents desiccation. Water sources are especially important because they provide breeding habitats.

• Dengue fever - around 400 million infections are estimated globally each year and about 25,000 deaths, with outbreaks especially likely where temperatures exceed 32degrees and humidity is very high.

Which areas are most vulnerable to prevalence of mosquitoes

• Areas close to ponds, marshes, irrigation channels, rice paddies and monsoon pools

• They allow vectors to reproduce quickly.

what does winter influenza show?

• Not all diseases are tropical. Viral transmission is more efficient at lower temperatures (why flue peaks during cooler months).

• Wider point is that physical conditions shape where vectors can live, how quickly they breed, and how long the transmission season lasts.

How does climate change provide the conditions for emerging infectious diseases to spread to new places and hosts?

• Climate change acts as a risk multiplier because warmer temperatures, shifting rainfall patterns and longer warm seasons create more favourable conditions for vectors and pathogens.

• Rising temperatures allow vectors to survive at higher latitudes and altitudes than before so the diseases once confined to tropical regions can spread into new areas.

• Longer warm seasons also increase the length of the transmission window, allowing more breeding cycles and a greater chance of infection

Example of climate changes impact on infectious disease is spreading to new areas

• The West Nile virus was first identified in Uganda in 1937 it is transmitted by Culex mosquito and has since spread far beyond its original range.

• Climate change may lengthen tsetse fly and take seasons, increasing the population exposed to vector-borne disease.

• Tens of millions more people could be at risk from disease diseases such as sleeping sickness by the end of the century.

• Climate change does not directly cause disease but it changes the environment in which vectors, hosts, and pathogens can survive and interact.

What is a zoonotic disease, what can intensify risk of this.

• Disease that passes from animals to humans. They become more likely where humans and animals live in close and repeated contact.

• Live animal markets, intensive farming and global livestock movement increase the chance that pathogens will cross the species barrier and then begin circulating in human populations.

• Urbanisation can intensify risk by creating habitats for animals such as rats, dogs, foxes, raccoons, and bats in close proximity to people

What can intensify the spread of zoonotic diseases

• Poor sanitation, poor hygiene, and weak regulation of diseases animals all raise the risk of transmission. Rabies risk rises where feral dog populations are poorly controlled and pet vaccination coverage is limited.

• Bird flu - prolonged close contact between humans and infected poultry increases the likelihood of transmission

• Once a zoonotic disease adapts to human to human spread the challenge becomes much greater because the outbreak is no longer controlled by animal movement alone