26 June 2020

Animals, Land Use and Disease

Welcome back. One of the daily science news websites I monitor usually announces one or two new funding awards. I was particularly interested in one awardee’s grant because I’d been hemming and hawing about reviewing a recently published study on the topic. That was the shove I needed.

The grant was from the National Institutes of Health to Kansas State University to establish a Center on Emerging and Zoonotic Infectious Diseases. Zoonotic refers to a zoonosis, a disease that can be transmitted from animals to humans.

A young pangolin in Namibia—pangolins in China are one of the animals suspected of transmitting the coronavirus (photo by Alex Strachan from www.pressenza.com/2020/03).
The study that I’m going to tell you about was by researchers affiliated with the UK’s Exeter and Southampton universities.

Zoonotic Disease Review Background
The researchers completed a systematic review of the effects of anthropogenic (i.e., human-induced), land-use change on emerging, zoonotic diseases originating in mammals. If any of that slipped by you, here’s the longer version:

- Emerging infectious diseases are newly recognized or reappearing diseases that are rapidly increasing in prevalence or geographic range.

- Three-quarters of emerging human pathogens are zoonotic; zoonoses account for nearly two-thirds of emerging infectious diseases.

- Zoonotic diseases range from A for anthrax to W for West Nile fever and include HIV, Ebola, SARS and, probably, COVID-19.

- The majority of zoonoses originate in wild animals, and mammals are particularly important disease hosts.

- Incursions into wild habitats expose humans to new pathogens if they come in contact with animals or hunt, butcher and consume wild meat.

- Land-use changes that alter the local environment and human-wildlife interactions can be a major source of zoonotic diseases; they remove or reduce the natural habitats and ranges of many species, forcing them to live closer to humans.

- Land-use changes, such as urbanization, agricultural intensification, deforestation and habitat fragmentation, are expected to increase with expanded population and increased demand for resources.

The Systematic Review
To highlight the most important mammalian hosts and pathogens and identify avenues for future research, the researchers compiled 276 studies on zoonotic diseases and anthropogenic land-use change, published between 1990 and 2019. Nearly half of the studies (136, 49%) focused on mammals and 42% lacked a specific host.

Of the mammal studies, 24% were global, 20% were conducted in each of South America and Asia, and about 10% in each of Europe, Africa and North America.

The most frequently studied mammalian taxa were rodents (27%), livestock (25%) and carnivores (24%); the remaining studies focused on non-human primates (13%), bats (10%) and other wild mammals (10%).

Studies of anthropogenic land-use change and mammalian zoonotic diseases--(left to right) proportion of papers on different host taxa, land-use change categories and pathogens (from onlinelibrary.wiley.com/doi/full/10.1111/mam.12201).
The mammal studies were mostly empirical (63%), on rodents (34%) and urbanization (53%); while the majority of non-host specific studies were reviews (72%), on livestock (54%) and agricultural intensification (54%).

Significant associations were identified between land-use change and mammals. Livestock were studied more in the context of agricultural intensification, carnivores with urbanization, bats with deforestation and primates with habitat fragmentation.

The most common pathogens and parasites studied in conjunction with anthropogenic land-use change and mammals were bacteria (33 studies, 24%), viruses (16%), helminths (parasitic worms) (16%) and protozoa (15%). Bats were studied more with viruses, carnivores with helminths and primates with protozoa. A quarter of mammalian studies reviewed did not focus on a specific pathogen.

Associations between (a) mammalian taxa and land-use change, (b) pathogens and land-use change and (c) mammalian taxa and pathogens, based on the percentage of studies on each category; the number of studies is shown above each bar (from onlinelibrary.wiley.com/doi/full/10.1111/mam.12201).
Wrap Up
Research into specific animal reservoirs has increased our understanding of how anthropogenic land-use change affects the risk of spillover to humans and spread of zoonotic diseases.

Improved prediction requires more empirical and data synthesis studies that link host ecology and responses with pathogen ecology and disease spread. The COVID-19 pandemic highlights the urgency of meeting that need.

The timing is right for Kansas State University’s new center. Thanks for stopping by.

Announcement of NIH grant to Kansas State University: www.ksnt.com/news/local-news/k-state-veterinary-research-team-receives-federal-grant/
Example articles on zoonoses:
Study of emerging zoonotic diseases in Mammal Review journal: onlinelibrary.wiley.com/doi/full/10.1111/mam.12201
Article on study on EurekAlert! website: eurekalert.org/pub_releases/2020-06/w-hdl060120.php

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