Why Animals Die

Abstract

All living things will die. Understanding the pathogenesis of diseases and conditions present at death could lead to clarity about causes of death, the disease itself, and mechanisms of aging. Aging is the culmination of a lifetime of events within a cell, tissue, organ, or organism. After conception, animals (including humans) attain a life span that is defined by genetics, environment, and accidents. Aging encompasses molecular, cellular, and organ-specific phenomena that change with exposure to life's events. As animals age, cellular and tissue degeneration and atrophy, cellular senescence and dysregulation, neoplasia, chronic inflammation, and tissue repair and scarring occur and often manifest as diseases. 7,34 Diseases may be nondegenerative age-related or degenerative age-related. Environmental exposures may modify the natural course of all these changes and include diet, composition of the air and water, exposure to toxins and other harmful materials, infectious agents, and lifestyle. Chance (replicative mutations) may also play a major role in cancer development. Each species has natural or induced subsets of genetic lines, which result in strains, breeds, subpopulations, or races. Individual life span is determined by these multiple factors. Aging research aims to define and study the causes of age-related diseases. 22,23,31,49 When an individual develops a potentially life-threatening disorder, it may be fatal more commonly in some environments depending on access to resources. Medical diagnosis and treatment can modify outcome. Some of these interactions may be initially beneficial but end up producing an adverse event. Death is the final culmination of normal or abnormal molecular, biochemical, and other pathologic events in an individual. Medically, diseases can be diagnosed by clinical history with physical examination, imaging, laboratory tests, and other techniques; together, these often result in specific diagnoses. Clinical diagnostic techniques and postmortem examinations often reveal gross and histopathologic lesions that are related to causes of death (CODs), contributing CODs (CCODs), and determinants of life span. 45 In this special issue of Veterinary Pathology, a collection of papers addresses the pathology of aging in various animal species and how some age-related lesions develop and may lead to disease and death. In addition, spontaneous and transgenic animal models of human age-related diseases are discussed. 22-24,34,49,55 References in this introduction are to these special issue papers and to others in the literature.

Multicentric lymphoma in a donkey with intestinal and bone marrow involvement

“…However, such characterizations are not as thorough in the literature regarding donkey lymphomas likely due to scarcity of cases as well as economic limitations precluding further evaluation of the neoplasm. Interestingly, although neoplasia is the most common cause of death in dogs and the second most common cause in humans (USA), it is not one of the top 5 common causes of death in the horse [ 18 ]. Interspecies comparison between donkeys and horses on common causes of mortality cannot be performed at this time as there is a lack of similar prevalence of surveys in donkeys.…”

Hypotheses on the extended phenotype of the mitochondrion: sex, mortality, and aging

“…Mice display many of the same causes of death as humans [134]. This seems remarkable given they have a much shorter lifespan.…”

“…This seems remarkable given they have a much shorter lifespan. Cancer for instance is the leading cause of death in mice and ranks second for humans [134]. That 1 year old mice frequently die from cancer while 1 year old humans rarely do strongly suggests that death from cancer is an evolutionary adaptation.…”

Histopathologic Evaluation and Scoring of Viral Lung Infection

“…Inclusion of experienced board-certified pathologists, who are specially trained to examine and interpret tissues changes, as part of the multidisciplinary team can greatly enhance the quality of tissue evaluation [22,27]. By histopathology, a skilled eye (ideally a pathologist familiar with the model) can not only define the types of inflammatory processes, but also corroborate these findings to clinical signs and/or data from other analyses [22,[27][28][29][30]. In addition, pathologists have knowledge of correct lesion nomenclature, as well as potential effects of such variables as strainrelated background lesions, husbandry, the microbiome, and diet on the interpretation of results [25].…”