Rats around the rosie: a dance of urbanization and disease

From hantavirus to the plague, rats have long since been reservoirs for a whole host of nasty infectious diseases. They live in our cities and feed off our garbage, sharing with us their fleas, ticks, and pathogens as a thank-you. With more urban development comes more rats and more potential for zoonotic diseases, making the dynamics between urbanization, rats, and their pathogens of particular interest to infectious disease specialists. With two thirds of the world expected to live in urban areas within the next 50 years, understanding how we shift the disease landscape with our city planning is vital to protecting our health.

A recent study by Blasdell et al examined the impact of urbanization on rat and pest diversity in a developing area of Malaysian Borneo. This area was chosen due to the uniquely high impact of urban rat populations on tropical areas– the combination of high temperatures and informal infrastructure offers ample resources for rats and the ideal growth conditions for the pathogens they carry– and the lack of information about rodents in these vulnerable areas. The researchers  found that across urbanization gradients, the ecology of reservoirs (rats), vectors (ticks), and pathogens changes quite drastically.

Rat diversity decreases with increasing urbanization, with the number of rat species dropping from ten to two between urban and rural areas. Urban areas in particular favor the invasive “urban exploiter” species Rattus rattus and the native “urban adapter” Sundamys muelleri. Urban exploiter refers to a species which is capable of immigrating to and establishing in a variety of urban environments, using the unique landscape to colonize new areas and establish a population, often becoming an invasive species in the process. An urban adapter, meanwhile, refers to a native species uniquely suited to urban environments who can survive and thrive when its habitat becomes increasingly urbanized. Both species were strongly associated with the presence of important disease vectors and pathogens– R. rattus carried a high diversity of zoonotic pathogens while S. muelleri was associated with important tick genera Amblyomma, Haemaphysalis, and Ixodes in urban greenspaces. Upwards of 75% of rats sampled in urban spaces were infested with ectoparasites (mites, fleas, and ticks), implying a possible route for pathogens to enter and thrive in urban spaces. Further research by the study team found that medically-relevant ticks were found in significantly higher numbers in urban spaces than rural ones. The elevated disease risk in more urbanized areas sheds light on the specific types of zoonotic diseases that can threaten cities, enabling more targeted approaches to minimizing disease risk.

Pathogenic analysis of urban rats found evidence of coronaviruses, mammarenaviruses, orthohantaviruses, orthohepeviruses, and paramyxoviruses, some of which were only present at the urban locations and not the rural ones. With an increased focus on disease transmission from animal vectors after the COVID-19 pandemic, studies such as this show how the way we plan our cities can be as impactful as our healthcare in promoting– or stopping– the spread of disease across the world.

 

Read More:

Blasdell, K., Morand, S., et al. (2022). Rats and the city: Implications of urbanization on zoonotic disease risk in Southeast Asia. Environmental Sciences, 119, 39.

 

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