So far we have seen that the world has become primarily urban. Therefore, it’s important to consider how cities are affected or going to be affected by climate change and how they are adapting to it.

Some of the main ways by which cities are affected by climate change is through water:

• Flooding because river basins, tanks and reservoirs are occupied by slums
• Flooding/Storm damage because of sea level rise
• Depletion of ground water
• Intense rain events overwhelming the sewerage and storm water drainage systems of a city

Other ways by which cities will be impacted by climate change is increasing heat waves and increasing susceptibility to vector borne infections.

In today’s post, let us consider the vector borne infection problem.

The only infection every one is talking about today is Ebola. So let us deal briefly with that first. How did Ebola come about? The strongest hypothesis is this: humans started consuming bush meat from monkey infected with the Ebola virus and the virus made a “species jump” into humans. Epidemics of Ebola until now have been relatively small and ended fairly quickly – why is the current one so different?

1. Travel; As the world becomes more urban and there is more travel between cities, infections that were once geographically restrained have become more widespread.
2. Crowding: as this disease has hit crowded urban centers, one infected person has the potential to infect far more people than he would have in a rural (less crowded) setting.
3. Overwhelmed medical facilities: Recently there was an article that said there was a need for 1000 beds in Monrovia in Liberia to care for Ebola patients. There were only 250 beds available. So a number of Ebola patients had to be turned away from the hospital to return home and infect more people.
4. Shared sanitation facilities: many slums in cities do not have adequate toilet facilities, so people end up sharing facilities or practicing open defecation. Ebola spreads through contaminated body fluids including feces.

So this Ebola epidemic is made worse by poorly planned urbanization not so much because of climate change.

Now, let us consider the main infection made so much worse by climate change: Dengue.

What is Dengue: Dengue is a disease caused by the dengue virus. A person contracts dengue fever when bitten by a particular type of mosquito which is a carrier of the dengue virus. Dengue is an urban disease – an infected Aedes Aegypti mosquito typically flies for a distance less than 50-100 metres – often much less. So transmission is possible only in crowded local conditions.

Dengue is a terrible illness – the patients suffer from fever and tremendous pain (the disease is also called break bone fever) and a complication – Dengue hemorrhagic fever or dengue shock syndrome – this can be fatal.

How is dengue transmission affected by climate change?

When a city’s coping mechanisms (reservoirs, tanks, sewage and storm water drains) are overwhelmed by either encroachment, increasing population or irregular but intense rainfall, water tends to stagnate. This provides a fertile breeding ground for Dengue.

Second, as the world warms, many cities that were earlier out of reach for mosquitoes. This is no longer the case as is evidenced by the spread of the West Nile Virus in the US.

PS: On a personal note, I’ve had dengue recently – it really is the worst disease I’ve ever had (and I’ve had Hepatitis A, Measles, Malaria etc.). The city I live in has been subject to increasing dengue epidemics in the last 10 years. It was not at all common before that.