Epidemiological Aspects of Feline Hyperthyroidism

Olczak J.

Conference Proceedings, (2000). Proceedings of the 9th Symposium of hte International Society for Veterinary Epidemiology and Economics, Breckenridge, CO:


A questionnaire-based case-control study involving 375 New Zealand cats was conducted to examine associations between putative risk factors and feline hyperthyroidism. Data was collected for cat and owner demography, medical history, indoor and outdoor environment and diet and feeding practices from the owners of 125 hyperthyroid case cats, 125 randomly selected control cats and 125 cats matched to cases with regard to sex and age (± 1.5 years). A range of statist ical techniques was employed to analyse the data, including descriptive analyses, univariate logistic regression for each variable and multivariate stepwise forward logistic regression. TIle multivariate unconditional logistic regression procedure for comparison ofcases with random controls revealed that cats whose bedding was regularly treated with anti-flea products appeared to be at higher risk (OR=57.6 (3.79->200)) =(Odds Ratio (95% confidence intervals)). A 6.6·fold (1.84-23.89) increase in risk was found for cats predominantly sleeping on the floor. Dental disorders were associated with 5.5 times (1.73-17.49) the risk of developing hyperthyroid ism and this was independent of tile eat’ s age. Cats whose history indicated they had a previous owner or were of unknown origin were at higher risk OR=4.1 (0.96-17.89) than cats reared from an early age by their owners. Female cats were more likely to be affected than males (OR=3.3 (1.18-9.02)) and the risk of developing hyperthyroidism increased with age for both genders. Cats eating half or more of their daily food requirement as canned commercial cat food were twice (0.33-12.93) as likely to have hyperthyroidism as cats not fed canned food. Siamese cats appeared to be at lower risk of developing hyperthyroid ism than other breeds (OR=O.O I (0.00 1-0.2)). The multivariate conditional logistic regression procedure for comparison of cases with matched controls revealed that cats with episodes of diarrhoea were 7.4 times (2.4-22.5) as likely to have hyperthyroidism. The interaction between drinking water from puddles and the regular use of organic fertilizers in the eat’s outdoor territory was a risk factor associated with a 5.3 fold (1.08-25.6 1) increase in the risk of developing disease. Disease risk was higher in cats exposed to a variety of flavours of commercial canned cat food compared to those fed only one flavour (OR=3.8 (1.5-9.61)). The risk of developing hyperthyroidism was higher with the regular use of fly sprays in the eat’s indoor territory (OR=3.3 (1. 19-9.29)). The variable ‘more than one cat in household ‘ appeared to have a protective effect (OR=0.15 (0.05-0.44) . Some of these associations may not be causal and further studies are warranted to clarify these aspects and investigate the role of breed, sex, diet and exposure to other potentially important environmental factors, e.g. insecticides.