Causes of Demodectic Mange
Demodicosis in dogs is caused by tiny parasitic mites of the species, Demodex canis. These mites live deep inside the hair follicles and sebaceous glands of the skin of host dogs. Demodex canis mites are considered to be part of the normal flora of the skin of dogs and typically are present in small numbers without causing any noticeable symptoms. In fact, almost all puppies acquire these mites directly from their mothers within the first few days of life. The immune systems of healthy dogs usually suppress excessive proliferation of the mites, which in turn prevents any obvious adverse reactions from their presence. However, dogs with weakened immune systems can develop clinical signs of demodectic mange, because the mite population gets out of control. In other words, the immune system does not respond properly to the normal presence of the Demodex mites. It is thought that genetic influences play a strong role in a dog’s development of demodicosis. This theory is supported by the fact that purebred dogs from certain breeds and bloodlines are more likely to develop demodectic mange than are other dogs.
In most cases, demodicosis is localized, meaning that it causes patchy, non-itchy hair loss on only a few areas of the dog’s body. However, demodicosis can also become generalized, with hair loss and lesions (sores) across most or all parts of the dog. Generalized demodectic mange can be a very serious medical condition that unfortunately often is resistant to treatment.
Prevention of Demodectic Mange
Many authorities recommend not breeding dogs that have been affected by either localized or generalized demodectic mange, because of the suspected hereditary component to its cause. Vaccinations, heartworm infection, administration of corticosteroids and estrus (going through a heat cycle) have all been reported to potentially exacerbate Demodex infections, probably because they suppress dogs’ immune systems for a period of time.
The precise mechanism that permits Demodex mites to proliferate in some dogs but not in others is unknown. Certainly, it is thought that genetics play a role. Adult dogs that develop generalized demodicosis usually have some underlying systemic disease that suppresses or weakens their immune system, allowing the mites to reproduce without control. In puppies, the localized form is much more common and usually resolves over time.