Prevalence of and risk factors for feline hyperthyroidism in South Africa

Abstract

Feline hyperthyroidism is a disease of middle-aged to older cats that has shown a marked increase in worldwide incidence within the last three decades as well as a marked geographic variation in prevalence. The exact pathogenesis of the disease still remains obscure and despite a plethora of epidemiological studies, clear risk factors have not been identified. The purpose of this study was to determine the prevalence of feline hyperthyroidism in South Africa and to identify potential risk factors. Serum total thyroxine (tT4) and thyroid stimulating hormone (cTSH) were measured in 302 cats aged 9 years and older that were presented at various veterinary clinics. In a few cats, serum free thyroxine (fT4) was also measured. At the time of blood sampling a questionnaire was completed regarding vaccination history, internal and external parasite control, diet and environment. The prevalence of hyperthyroidism (tT4> 50nmol/L or tT4 between 30-50 nmol/L with cTSH < 0.03ng/ml and fT4> 50pmol/L) within this population was 7.0% with no significant difference in prevalence between healthy (5.1%) and sick (8.2%) cats. Cats ≥ 12years of age (OR= 4.3, p= 0.02) and cats with canned food in their diet (OR= 2.1, p= 0.1) were more likely to be diagnosed with hyperthyroidism. No significant relationship between vaccinations, parasite control or indoor environment and hyperthyroidism was observed. Hyperthyroid cats were more likely to present with weight loss (OR= 3.2, p= 0.01) and with a heart rate ≥ 200bpm (OR= 5, p= 0.01) than cats without the disease.The prevalence of feline hyperthyroidism in South Africa appears to be similar to that in cats in Japan and Portugal but less than that in cats in the UK and Germany. Risk factors for hyperthyroidism, previously found in other studies, specifically older age and eating canned food was present in this study population.