Covid-19 highlights role of urbanisation and climate change in public health crises

Covid-19’s sudden emergence not only reminds us of our fragility as a species, it reveals serious structural vulnerabilities that allow diseases like this to spread. As new diseases become more infectious and more frequent, healthcare systems around the world are struggling to keep up, not just with vaccines and treatments but with patient care.

There are several factors that contribute to the success of an infectious disease, including its ability to mutate and its infectivity. Influenza, for example, is an incredibly successful virus, because it mutates quickly and is highly infectious. In addition, it is not so deadly (usually) that it kills its host before it can infect another. Sometimes, as was the case with the catastrophic 1918 Flu Pandemic, diseases mutate in such a way that makes them unusually fatal and/or infectious.

However, the ideal conditions for the mutation and spread of infectious diseases that we are seeing currently are manmade, directly and indirectly. As climate change and deforestation alter and disturb natural environments around the world, the rate at which diseases like Covid-19 are spreading and mutating is increasing significantly.

Mosquitoes and global warming

Urbanization and human migration are also expected to result in the spread of mosquitoes as both create mini-habitats ideal for mosquitoes. Unfortunately, the increasingly large habitats of disease-spreading mosquitos are not the only point of concern. A recent study by the China Agricultural University, the University of Bath and the University of York found a positive correlation between the rates of evolution in mosquitoes, rising temperatures and atmospheric carbon dioxide.

Needless to say, denser and more widespread populations of mosquitoes, which are evolving faster as a result of climate change, will certainly increase their threat to humans and increase the transmission of deadly disease in areas previously considered safe.

In some developed countries, the existence of mosquitoes during the warmer months of the year is little more than an annoyance, requiring nothing more than the purchase of a citronella candle and a can of bug spray. We tend to forget that in many regions, mosquitoes spread disease and cause the death of millions of people each year.

According to National Geographic, there are 3,000+ mosquito species, but only three can be blamed for the majority of disease transmission:

• Anopheles - Malaria
• Culex – Encephalitis, Filariasis, West Nile virus
• Aedes – Yellow Fever, Dengue, Encephalitis, Zika virus

Mosquitoes thrive in areas where stagnant, standing water can be easily found and used for breeding. Some mosquito species are even able to lay eggs in snow melt. As flooding increases due to climate change and as global temperatures rise, mosquitoes are expected to migrate to previously inhospitable areas and their populations are expected to grow. Aedes albopictus, for example, is spreading at a rate of around 93 miles per year in Europe.

Animal migration and zoonotic diseases

Approximately 60% of human diseases are zoonotic, meaning they spread between animals and humans. The Center for Disease Control and Prevention (CDC) reports that a suspected six out of ten known infectious diseases are zoonotic and three out of four new or emerging infectious diseases originate in animals.

Covid-19 falls into this category. It is widely thought to have jumped from animals to humans in a live animal market in Wuhan, China, where humans and animals (both living and dead) were in close contact. Researchers suspect infected bats passed this novel coronavirus to an intermediary species, which then passed it along to humans who are now passing it to each other.

Similar to mosquitoes, as environments change as a direct and indirect result of climate change, animals will migrate into new regions. When species move into new environments, they are often exposed to diseases they do not have immunity to. The introduction of new species into regions previously unknown to them provides diseases with yet another opportunity to mutate and spread.

However, environmental changes are not the only factor that will cause animal migration. Humans are also actively contributing to animal migration, which can again result in the spread of infectious disease.

For example, deforestation encourages the spread of zoonotic diseases by displacing wildlife and pushing animal populations into ever closer contact with humans. Zoonotic diseases, which have largely been limited to animal populations, are now spreading from animals to humans at levels previously unseen.

After the rapid deforestation of a large area in Indonesia in 1997, displaced fruit bats carrying Nipah virus travelled to and settled in Malaysian orchards near pig populations. Both pigs and pig farmers fell ill. Of the 265 people that developed severe brain inflammation as a result of this new virus, 105 died.

According to National Geographic, malaria transmission in Brazil has increased in line with forest clearance and agricultural expansion. Deforestation in Brazil has created conditions favourable to mosquitoes. Anopheles darlingi, in particular, like pooling, stagnant water near human settlements. Diseases known to have spread more widely in humans as a result of deforestation include but are not limited to leptospirosis, malaria, dengue fever, yellow fever, and Zika.

Human-to-human transmission

Climate change is happening and continues to intensify. Without proactive planning and preparation, cities and regions around the world will feel the stress of maintaining enough housing and safe infrastructure to meet the needs of their new residents.

We don’t have to guess what happens when people live on top of each other in unsanitary conditions. According to the World Health Organisation (WHO), infectious diseases like dengue fever, cholera, malaria, hepatitis, pneumonia, and tuberculosis thrive in urban slums where overcrowding and substandard housing is a fact of life.