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Dengue: Soon to be a worldwide problem?

Experts predict dengue fever will threaten sixty percent of the world’s population, amounting to a predicted six billion people by 2080. This predicted increase can be largely attributed to two factors: urbanisation and global warming.

In India, dengue fever is endemic across all 35 states and union territories. The disease has shown a gradual increase in its prevalence over time in India as more people move to urban centres, allowing for faster transmission rates due to the more densely packed population.

In many cases, the disease has been shown to be asymptomatic — an issue that has been detected by scientists at the All India Institute for Medical Sciences (AIIMS) and postulated to be hastening the spread of the disease.

Dengue outbreak in Kerala: 18199389 - anopheles mosquito main cause of maleria and dengue in india. Copyright: signout / 123RF Stock Photo
The anopheles mosquito.

Urbanisation: A petri dish for dengue fever?

In many ways, the prediction of a global increase in dengue mirrors what has already occurred in India. Globally more and more people are moving to ever more densely populated urban metropolises in search of better economic prospects. The potential health risks are especially pronounced in low- and middle-income countries undergoing the urbanisation trend.

In many cases, the infrastructure of the cities are unable to cope with such a rapid influx of people. This results in a situation where the capacity of landfill sites are exceeded. In India, this is already taking shape. Cities with expanding populations generate 143,000 metric tonnes of solid waste every day, a mere quarter of which is properly processed. This means it is dumped at landfill sites: once these sites become overfull, refuse is often found commonly on the streets and stagnant water becomes commonplace. This situation could lead to ample opportunities for breeding populations of mosquitoes to establish themselves.

Though this study projects as far as the year 2080, similar effects are already being seen in other diseases. Los Angeles, for example, has seen huge pile-ups of refuse along its streets, coupled with a severe homelessness crisis. Resultantly diseases that were otherwise unknown in the area are showing up in local hospitals, many of which are flea-borne such as typhus. Experts have gone as far as to suggest that if the situation continues, diseases such as the bubonic plague could show a resurgence.

This is a situation occurring in one of the world’s wealthiest cities. For large cities in developing nations, the situation may become even more dire, far more rapidly. Less money is available for infrastructural adjustments to handle the tides of people. In these cases, it is a common occurrence for vast numbers of people to be densely packed into slum-like areas. This situation is an ideal environment for infectious diseases to fester.

As an example, in Delhi, slum-dwellers – accounting for more than half of the national’s capital population – have been exposed to the rapid spread of conditions such as tuberculosis and influenza. Lack of access to sanitation and waste management facilities mean vector-borne diseases have an ideal breeding ground, adding to the disease woes of these citizens.

Likewise, the interconnectivity of modern-day cities and the tendency for individuals to commute to work allows for diseases to be spread rapidly from one side of a city to the other. One individual infected with the flu may sneeze on a bus, potentially exposing, for instance, ten other individuals to the virus. These ten other individuals may go to ten places of work, or take another bus or train, exposing more and more people, exponentially increasing the number of infected individuals. In the instance of a more deadly disease, this could reap a considerable death toll.

As previously reported by Health Issues India, India is especially vulnerable to this owing to the fact that its commuter vehicles are often packed far beyond their intended capacity. This has manifest in the example of conditions such as chikungunya, which have spread rapidly in urban India in recent years in-line with a trend of increased urbanisation.


Global warming: Sending diseases north

A swiftly growing population has also been a major contributing factor to climate change. A higher population necessitates more energy production, more motor vehicles, and more building projects. All of these lead to an increased output of pollution, hastening the process of climate change.

In the context of dengue fever, this could have grave implications. India sees a surge in dengue cases during and after the monsoon season. This is due to the need for mosquitoes to breed in areas with an abundance of of stagnant water. The mosquito species that spread the virus are native to sub-tropical areas, southeast Asia being a prime example.

Climate change alters the environment of the areas in which these mosquito species are capable of maintaining breeding populations owing to the prospect of warmer temperatures. With rising temperatures worldwide, it is likely these breeding populations will begin to occur further north.

Aedes albopictus, also known as the tiger mosquito has already spread northwards into Europe, being detected as far as northern France. Though this mosquito has a reduced capacity to transfer dengue compared to other species, this opens up the possibility for European outbreaks.

Different weather patterns in these regions could lead to a disease epidemiology substantially different from what is seen in India. Where India has wet weather specifically around the monsoon season, many nations in Europe see rain all year round. This could create a situation where mosquitoes are present over a longer period of time, creating a wider window of opportunity for infection to occur.

The study predicts areas likely have endemic dengue fever in the near future include the southeastern United States, coastal areas of China and Japan, and inland regions of Australia.

The true effects of climate change are all but impossible to summarise concisely. While it is easy to think of as simply an issue of temperature, the effects extend beyond this. Disease epidemiology is likely to dramatically change. Regions of the globe will face diseases they have not yet encountered — and are therefore far more difficult to cope with due to lack of expertise and equipment. More must be done to combat the issue, or we are likely to face crises on multiple fronts.

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