Urban Animals And Cancer: What We Know
A significant number of wild animals live in urban environments, among humans and our buildings, vehicles, and infrastructure. This number will only grow in the future, as more areas urbanize and expand into once-wild environments. As animal advocates, we should understand the effects of this change in environment on the health of animals, and possibly make changes to live more harmoniously with them.
This analysis reviews literature currently available on the effects of urbanization and the urban environment on cancer rates in wild animals. It focuses on four main consequences of urbanization: change in diet, habitat changes, exposure to physical pollutants, and light and noise pollution.
Humans, unsurprisingly, eat differently than most animals. In recent decades, processed foods have come to play a major role in our diets – things like deli meat, candy, boxed mac and cheese, and potato chips. These foods are generally considered to be unhealthy, and often contain high amounts of sugar and/or sodium, saturated and/or trans fats, and preservatives. Since they play a major role in our diets, these foods eventually make their way to our dumpsters, garbage cans, and streets, where they’re often consumed by urban animals.
High consumption of these foods is somewhat linked to cancer in humans, though the authors note that no notable studies have been conducted on this phenomenon in wild animals. Greater access to food of all kinds has other effects on wild animals, both positive and negative. Animals are less likely to starve to death in urban environments due to the high availability of food. However, animals are also more likely to become obese, which is one of the leading factors correlated with cancer in humans.
In terms of habitat, urbanization often has a fracturing effect on animals, creating tightly-packed pockets of population with little interaction between them. This can contain the spread of disease, but it also increases the likelihood of an epidemic within one of these pockets. Some animals are able to move from one pocket of population to another, which can lead to the introduction of new diseases and parasites.
In humans, infectious agents are linked to several kinds of cancer – HPV is correlated with cervical cancer, for example. This has also been found to be true in some captive animals, such as the relationship between Feline Immunodeficiency Virus and tumor growth. Currently, most studies on urban animal diseases focus on non-oncogenic (not cancer-causing) diseases, and the authors recommend more research in this field.
In terms of pollution, urban animals are generally exposed to more pollutants than non-urban animals, in various forms. Pollution can cause mutations and birth defects which in turn increases the risk of cancer. It can also compromise animals’ immune systems, which allows for the spread of cancer-causing pathogens. There are some studies on pollution’s effects on cancer rates in captive animals, but the authors were unable to find any focusing on wild urban animals.
Pollution comes not only in the form of harmful chemicals, but in the light and noise that are a part of every urban environment. In humans, a high amount of artificial light at night is linked to the growth of certain cancers, possibly due to disruption of sleep and suppression of certain hormones. In animals, this phenomenon has not been adequately studied. Noise pollution is also a problem in many cities, and can serve as a stressor for animals within. This is tenuously linked to some cancers in humans, and has been shown to have potential to cause cancer-linked inflammation in lab rats. Sparrows raised in noisy environments have been shown to have some cancer-linked traits, but no formal studies on the effects of noise pollution on wild animal cancer rates exist.
It’s worth noting here that urbanization may “increase” cancer rates in animals simply by reducing or eliminating other causes of death. Starvation and predation are less of a concern for most urban animals, enabling them to live to an older age. Urban animals may have higher cancer rates simply because they are more likely than non-urban ones to live to an age where cancer is a serious threat. Moreover, the authors note that urban environments may reduce some risks of cancer – urban animals are more likely to concern themselves with self-upkeep as opposed to quick reproduction, which may result in better overall health. However, no studies of this phenomenon exist; the authors suggest a comparative study of rural and urban animal cancer rates.
The main takeaway from this analysis is the absence of sufficient studies on the relationship between urbanization and wild animal cancer rates. We have a responsibility to make our cities safe and healthy places to live for everyone, including their non-human residents. We should be investigating whether our activity is causing cancer rates to increase in wild animals; we can’t know how to help if we don’t know what the problem is.
As most of us know, untreated cancer is often an excruciatingly painful way to die for humans, and it’s unethical to subject wild animals to this pain simply because they happen to live around us. As animal advocates, we need to first push researchers to study our impact on wild urban animals more thoroughly, and then advocate for whatever solutions they find.