Multiple morbidities in companion dogs: a novel model for investigating age-related disease

Abstract

The proportion of men and women surviving over 65 years has been steadily increasing over the last century. In their later years, many of these individuals are afflicted with multiple chronic conditions, placing increasing pressure on healthcare systems. The accumulation of multiple health problems with advanced age is well documented, yet the causes are poorly understood. Animal models have long been employed in attempts to elucidate these complex mechanisms with limited success. Recently, the domestic dog has been proposed as a promising model of human aging for several reasons. Mean lifespan shows twofold variation across dog breeds. In addition, dogs closely share the environments of their owners, and substantial veterinary resources are dedicated to comprehensive diagnosis of conditions in dogs. However, while dogs are therefore useful for studying multimorbidity, little is known about how aging influences the accumulation of multiple concurrent disease conditions across dog breeds. The current study examines how age, body weight, and breed contribute to variation in multimorbidity in over 2,000 companion dogs visiting private veterinary clinics in England. In common with humans, we find that the number of diagnoses increases significantly with age in dogs. However, we find no significant weight or breed effects on morbidity number. This surprising result reveals that while breeds may vary in their average longevity and causes of death, their age-related trajectories of morbidities differ little, suggesting that age of onset of disease may be the source of variation in lifespan across breeds. Future studies with increased sample sizes and longitudinal monitoring may help us discern more breed-specific patterns in morbidity. Overall, the large increase in multimorbidity seen with age in dogs mirrors that seen in humans and lends even more credence to the value of companion dogs as models for human morbidity and mortality.

The companion dog as a model for human aging and mortality

“…These phenomena allow researchers not only to study the pathologies that influence mortality, but also to understand different comorbidities and multiple chronic conditions that canines exhibit. In previous work, we showed that multimorbidity in the dog increases with age (Jin, Hoffman, Creevy, O'Neill & Promislow, 2016), similar to patterns seen in humans. As we discuss here, the domestic dog could be a useful model to understand how comorbidities, both as cause and consequence, are associated with aging in humans.…”

“…Our multimorbidity analysis suggests that companion dogs have the potential to be an excellent model to better understand the causes and consequences of multiple chronic conditions as we age. Similar to previous results reported by our laboratory (Jin et al., 2016), multimorbidity (total number of diagnoses recorded at the time of death) increases with age in the dog as is seen in human populations (Fortin, Bravo, Hudon, Vanasse & Lapointe, 2005). In addition, comorbidities vary significantly among different chronic conditions in the dog (Figure 3).…”

“…Finally, our canine analysis makes the assumption that all dogs are drawn from the same pool and does not look at the effects of breed and size variation. Previous research has shown that even within a size class, breeds can differ in their multimorbidity (Jin et al., 2016) and mortality patterns (Fleming et al., 2011). Taken together, these limitations point to the need for more detailed data from canines representing the full diversity of ages, breeds, comorbidities, and environments.…”

“…For this analysis, multimorbidity was defined as the total number of diagnoses recorded at the time of death (Jin et al., 2016), and comorbidity was defined as the number of diagnoses recorded for a dog with a specific morbidity of interest, excluding the specific morbidity of interest. Each diagnosis was weighted equally in our calculation of comorbidity or multimorbidity, regardless of the relative severity of each particular diagnosis.…”

“…Using the canine VMDB dataset, we first determined how the number of diagnoses changed with age across both sexes using a generalized linear model (GLM), where the dependent variable, multimorbidity, was assigned a negative binomial distribution (Jin et al., 2016). We modeled the impacts of sex and age on morbidity score as fixed effects.…”