Cancer in Wildlife: Understanding the Connection between Wildlife and Human Health | Slides Pathology

The prevalence and variety of neoplastic diseases in wild-

life are likely under-reported and are certainly understud-

ied. Phenotypically similar forms of cancer exist across

disparate species, underscoring the universal nature of

cancer. A better understanding of both shared and unique

aspects of cancer across wildlife species will undoubtedly

shed light on potential mechanisms of oncogenesis. This

comparison may even untangle some of the complexities

regarding human cancer. Certainly, the large number of

animal populations inhabiting distinct environments pro-

vide many natural ‘experiments’ such as that examined

by Mǿller etal.1, where cancer in a broad spectrum of

bird species was shown to be tightly linked to the natu-

ral history and immunity of each species. Wild animals

are profoundly influenced not only by selective pressures

within their own species but also by their interface with

humans. Information gained from monitoring diseases in

free-ranging wildlife is of paramount importance, as we

often occupy the same habitat. A growing human popula-

tion places increasing demand on many shared resources.

For example, globally, water resources are being limited by

both access (human development) and a shrinking sup-

ply, so that the demand for adequate wastewater treatment

will become increasingly important over the coming dec-

ades (Fig.1). Furthermore, an increasing human popula-

tion will usher in global changes that wildlife already face,

such as crowding, mixing of subpopulations and increased

environmental complexity. How these changes modulate

the pathophysiology of cancer in wildlife species will also

be extremely important to identify, as the implications for

wildlife and human health are likely to be similar.

This Review describes some of the cancers affecting

wildlife populations and what we know about the role of

infectious agents, environmental toxins and reproductive

or metabolic disturbances in contributing to the onco-

genic processes (Table1). Although neoplasia occurs in

nearly all multicellular organisms2, this Review primarily

addresses instances of such disease in wild vertebrates.

We also describe new examples of spontaneous cancers

that have been identified in both captive and wildlife spe-

cies since the potential impact of cancer on wildlife was

first reviewed by McAloose and Newton3. Such diseases

are an increasing concern for protected and endangered

species and are a unique frame of reference for pressures

that drive neoplastic transformation.

Pathogen-driven cancer

Infections in humans are considered causal for approxi-

mately 15% of the global cancer burden2. Owing to a lack

of vigilant screening, which is often applied to human

cancer, the number of wildlife cancers caused by infec-

tion is not known, nor has it been possible to determine

whether the number of cancers associated with patho-

gens is similar in humans and wildlife. However, there

Cancer in wildlife: patterns of

emergence

PatriciaA.Pesavento1*, DalenAgnew2, MichaelK.Keel1 and KevinD.Woolard1

Abstract | Cancer is ubiquitous in wildlife, affecting animals from bivalves to pachyderms and

cetaceans. Reports of increasing frequency demonstrate that neoplasia is associated with

substantial mortality in wildlife species. Anthropogenic activities and global weather changes are

shaping new geographical limitations for many species, and alterations in living niches are

associated with visible examples of genetic bottlenecks, toxin exposures, oncogenic pathogens,

stress and immunosuppression, which can all contribute to cancers in wild species. Nations that

devote resources to monitoring the health of wildlife often do so for human-centric reasons,

including for the prediction of the potential for zoonotic disease, shared contaminants, chemicals

and medications, and for observing the effect of exposure from crowding and loss of habitat.

Given the increasing human footprint on land and in the sea, wildlife conservation should also

become a more important motivating factor. Greater attention to the patterns of the emergence

of wildlife cancer is imperative because growing numbers of species are existing at the interface

between humans and the environment, making wildlife sentinels for both animal and human

health. Therefore, monitoring wildlife cancers could offer interesting and novel insights into

potentially unique non-age-related mechanisms of carcinogenesis across species.

1Department of Pathology,

Microbiology, and

Immunology, School of

Veterinary Medicine,

University of California,

Davis, CA, USA.

2Veterinary Diagnostic

Laboratory, Department of

Pathobiology and Diagnostic

Investigation, College of

Veterinary Medicine,

Michigan State University,

East Lansing, MI, USA.

*e-mail: papesavento@

ucdavis.edu

https://doi.org/10.1038/

s41568-018-0045-0

www.nature.co m/nrc

Reviews

646

OCTOBER 2018

vOlumE 18

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The prevalence and variety of neoplastic diseases in wild-

life are likely under-reported and are certainly understud-

ied. Phenotypically similar forms of cancer exist across

disparate species, underscoring the universal nature of

cancer. A better understanding of both shared and unique

aspects of cancer across wildlife species will undoubtedly

shed light on potential mechanisms of oncogenesis. This

comparison may even untangle some of the complexities

regarding human cancer. Certainly, the large number of

animal populations inhabiting distinct environments pro-

vide many natural ‘experiments’ such as that examined

by Mǿller et al.^1 , where cancer in a broad spectrum of

bird species was shown to be tightly linked to the natu-

ral history and immunity of each species. Wild animals

are profoundly influenced not only by selective pressures

within their own species but also by their interface with

humans. Information gained from monitoring diseases in

free-ranging wildlife is of paramount importance, as we

often occupy the same habitat. A growing human popula-

tion places increasing demand on many shared resources.

For example, globally, water resources are being limited by

both access (human development) and a shrinking sup-

ply, so that the demand for adequate wastewater treatment

will become increasingly important over the coming dec-

ades (Fig. 1). Furthermore, an increasing human popula-

tion will usher in global changes that wildlife already face,

such as crowding, mixing of subpopulations and increased

environmental complexity. How these changes modulate

the pathophysiology of cancer in wildlife species will also

be extremely important to identify, as the implications for

wildlife and human health are likely to be similar.

This Review describes some of the cancers affecting

wildlife populations and what we know about the role of

infectious agents, environmental toxins and reproductive

or metabolic disturbances in contributing to the onco-

genic processes (Table 1). Although neoplasia occurs in

nearly all multicellular organisms^2 , this Review primarily

addresses instances of such disease in wild vertebrates.

We also describe new examples of spontaneous cancers

that have been identified in both captive and wildlife spe-

cies since the potential impact of cancer on wildlife was

first reviewed by McAloose and Newton^3. Such diseases

are an increasing concern for protected and endangered

species and are a unique frame of reference for pressures

that drive neoplastic transformation.

Pathogen-driven cancer

Infections in humans are considered causal for approxi-

mately 15% of the global cancer burden^2. Owing to a lack

of vigilant screening, which is often applied to human

cancer, the number of wildlife cancers caused by infec-

tion is not known, nor has it been possible to determine

whether the number of cancers associated with patho-

gens is similar in humans and wildlife. However, there

Cancer in wildlife: patterns of

emergence

Abstract | Cancer is ubiquitous in wildlife, affecting animals from bivalves to pachyderms and

cetaceans. Reports of increasing frequency demonstrate that neoplasia is associated with

substantial mortality in wildlife species. Anthropogenic activities and global weather changes are

shaping new geographical limitations for many species, and alterations in living niches are

associated with visible examples of genetic bottlenecks, toxin exposures, oncogenic pathogens,

stress and immunosuppression, which can all contribute to cancers in wild species. Nations that

devote resources to monitoring the health of wildlife often do so for human-centric reasons,

including for the prediction of the potential for zoonotic disease, shared contaminants, chemicals

and medications, and for observing the effect of exposure from crowding and loss of habitat.

Given the increasing human footprint on land and in the sea, wildlife conservation should also

become a more important motivating factor. Greater attention to the patterns of the emergence

of wildlife cancer is imperative because growing numbers of species are existing at the interface

between humans and the environment, making wildlife sentinels for both animal and human

health. Therefore, monitoring wildlife cancers could offer interesting and novel insights into

potentially unique non-age-related mechanisms of carcinogenesis across species.

1 Department of Pathology,

Microbiology, and

Immunology, School of

Veterinary Medicine,

University of California,

Davis, CA, USA.