Understanding Demodicosis in Dogs and Cats: Pathogenesis and Predisposing Factors

Demodicosis is a parasitic skin disease of dogs and cats associated with the proliferation of Demodex mites, which are considered part of the normal cutaneous fauna in many animals¹. Under normal conditions, these mites inhabit hair follicles and sebaceous glands without inducing clinical disease. However, an imbalance between the host and the mite population may result in clinically apparent dermatological lesions. 

Pathogenesis 

The pathogenesis of demodicosis is closely linked to defects in cell-mediated immunity, which may allow uncontrolled mite multiplication¹. This immune dysfunction may be transient, particularly in younger animals, or more persistent in cases associated with systemic disease. 

Juvenile-onset demodicosis is often associated with an immature immune system, whereas adult-onset disease may be linked to underlying disorders or immunosuppression². However, not all cases have an identifiable cause, and clinical presentation may vary. 

Demodex Species 

Different Demodex species are implicated in dogs and cats¹: 

• Demodex canis is most commonly identified in dogs 

• In cats, Demodex cati and Demodex gatoi are recognized 

D. canis and D. cati are typically considered commensal organisms, whereas D. gatoi may be associated with contagious transmission in some feline populations. 

Predisposing Factors¹ 

Several factors may increase susceptibility to clinical disease: 

Age 

Juvenile animals are more frequently affected, possibly due to developing immune competence. Adult-onset cases may warrant further investigation. 

Genetic Susceptibility 

Certain dog breeds appear predisposed, suggesting a hereditary component. A genetic influence on immune response has been proposed, and breeding from affected animals is generally discouraged. 

Underlying Disease 

Adult-onset demodicosis may be associated with: 

• Endocrine disorders 

• Chronic systemic illness 

• Neoplasia 

A comprehensive clinical evaluation may be considered in such case. 

Immunosuppressive Therapy 

Administration of glucocorticoids or other immunosuppressive agents may contribute to mite proliferation and disease expression. 

General Health and Stress 

Nutritional status, concurrent infections, and environmental stressors may influence disease development, although their exact contribution may vary. 

Clinical Relevance 

Understanding the underlying pathogenesis and predisposing factors is important for guiding diagnostic workup and treatment planning. Identification and, where possible, management of contributing factors may improve therapeutic outcomes and reduce recurrence risk. 

References  

1. Mueller RS, Rosenkrantz W, Bensignor E, Karaś‐Tęcza J, Paterson T, Shipstone MA. Diagnosis and treatment of demodicosis in dogs and cats: Clinical consensus guidelines of the World Association for Veterinary Dermatology. Veterinary dermatology. 2020 Feb;31(1):4-e2. https://ebvminpractice.org/wp-content/uploads/2025/09/veterinary-dermatology-2020-mueller-diagnosis-and-treatment-of-demodicosis-in-dogs-and-cats.pdf  

2. Souza CP, Schissler JR, Contreras ET, Dow SW, Hopkins LS, Coy JW, Rosychuk RA, Hawley JR, Lappin MR. Evaluation of immunological parameters in pit bull terrier‐type dogs with juvenile onset generalized demodicosis and age‐matched healthy pit bull terrier‐type dogs. Veterinary dermatology. 2018 Dec;29(6):482-e162. https://www.researchgate.net/profile/Clarissa-Souza-2/publication/327205423_Evaluation_of_immunological_parameters_in_pit_bull_terrier-type_dogs_with_juvenile_onset_generalized_demodicosis_and_age-matched_healthy_pit_bull_terrier-type_dogs/links/5b860f65299bf1d5a72eae6c/Evaluation-of-immunological-parameters-in-pit-bull-terrier-type-dogs-with-juvenile-onset-generalized-demodicosis-and-age-matched-healthy-pit-bull-terrier-type-dogs.pdf