Incidence and risk factors of heat‐related illness in dogs from New South Wales, Australia (1997–2017)

Abstract

Heat Related Illness (HRI) in dogs is expected to increase as heatwaves surge due to global warming. The most severe form of HRI, heat stroke, is potentially fatal in dogs. The current study investigated the incidence and risk factors for HRI in dogs in NSW, Australia, from 1997 to 2017. We identified 119 HRI cases during this period, with a fatality rate of 23%. Dog breeds at elevated risk of HRI were Australian Stumpy Tail Cattle Dog, British Bulldog, French Bulldog, Maremma Sheepdog, Italian Greyhound, Chow Chow, Airedale Terrier, Pug, Samoyed, English Springer Spaniel, Labrador Retriever, Golden Retriever, Cavalier King Charles Spaniel, Border Collie, Staffordshire Bull Terrier, and pooled non‐Australian National Kennel Council breeds (which included the American and Australian Bulldog) when compared with cross breeds (i.e., the reference variable). As expected, HRI cases were more likely in December and January, during the Australian summer and during hotter years (e.g., 2016). There were no differences in the risk of HRI between males and females nor between desexed or un‐desexed dogs; but older dogs were at increased risk of HRI. These findings underscore the need for data collection that will enable the incidence of HRI in dogs to be monitored and to better understand canine risk factors particularly as temperatures will continue to rise due to global warming. The risk of mortality from HRI underpins the need for education programs focussed on prevention and early identification of HRI so that owners present affected dogs to their veterinarian as promptly as possible.

Epidemiology of heat‐related illness in dogs under UK emergency veterinary care in 2022

“…Many of the mild‐grade cases of canine HRI that occurred out‐of‐hours may have been treated at home rather than presented for emergency veterinary care to avoid the associated financial and logistical costs 30 . A primary veterinary care study in Australia reported an overall HRI event fatality rate of 23.00%, with higher rates during heatwave years 10 . Previous smaller studies from referral populations 7,11,12 reported even higher HRI fatality rates of 36%‒50% but tended to include only more severe, hospitalised cases, whereas the current study included all grades of HRI presented for first‐opinion emergency veterinary care.…”

“…The risk factor analysis used multivariable logistic regression modelling conducted in SPSS v29 (IMB Inc.). Model specification used information theory 24 based on previously reported risk factors associated with HRI—breed type, sex/neuter status and age—with an alternative model using skull shape and bodyweight to replace breed type 9,10 . A chi‐squared test was used to compare HRI event fatality rates during and outside the UK heat periods.…”

“…Brachycephalic breeds and dogs over 50 kg were also at increased risk. Research within VetCompass Australia identified similar HRI risk factors and highlighted increased case numbers during heatwave years across a 20‐year period (1997‒2017) 10 . Multiple studies have identified exertion as the most common trigger of HRI in dogs 7,11–14 and have found that brachycephalic breeds are at particularly high risk 7,9,10,12,13 …”

“…Previous VetCompass research on HRI reported an estimated annual incidence risk of 0.04%, with an event fatality rate of 14.18%, in dogs under primary veterinary care in the UK in 2016 9 . The significant risk factors for HRI identified in various studies include breed, heavier bodyweight relative to the breed/sex mean and being over 2 years old 7,9,10,11 . Brachycephalic breeds and dogs over 50 kg were also at increased risk.…”

“…Previously, canine HRI studies have presented case series from referral populations focusing on more severe, hospitalised cases 7–8 . HRI is now recognised as a progressive condition, 1 and more recent studies have taken this into account, including studies of dogs with less severe stages of HRI in their risk factor analysis 9,10 . Previous VetCompass research on HRI reported an estimated annual incidence risk of 0.04%, with an event fatality rate of 14.18%, in dogs under primary veterinary care in the UK in 2016 9 .…”