Demodicosis is a parasitic skin disease often occurring over a very long time and in at least fifty species of mammals, including monkey, ox, horse, dog or cat. In humans, the first description was in 1842, and in dogs the first description was made two years later. It was not until 1859 that we met the parasite in dogs and it was called/named Demodex canis.
Currently, three species of Demodex have been identified in dogs. The most common is Demodex canis, which lives in hair follicles and sebaceous glands (oil glands). The male mite is 40 to 250 microns which is smaller than a full stop. The full stop at the end of this sentence is 600 microns, so that just goes to show how small they are.
Females are 300 microns for long, which is half the size of a full stop. In the 80's, a species much shorter called Demodex cornei, began to be observed. It is about half as long as Demodex canis, with the abdomen (middle bit) being much shorter. By analogy to what is known about Demodex gatoi which is the short form observed in cats, it is believed that this species also lives in the stratum corneum. This species is regularly observed with Demodex canis, one wonders if now would not be a mutant of the latter. In other words they found a mite in cats that looks like a smaller version of the dogs mites. Are they ancient cousins in evolution?
In 1997, a new species much longer than Demodex canis (dog mite), Demodex called injai has been described. This species also is localized to the hair follicles and sebaceous areas by and large, but it is essentially isolated at the thoracolumbar region (the back and bum). This species is about twice as long as Demodex canis (the dog mite). The life cycle takes place entirely on the dog's body, and it takes 20 to 35 days to live and die.
On the skin of the animal, we can find eggs, six-legged larvae, and pupae and adults with eight legs. Exceptionally, these mites can be found in the lymph nodes, spleen, liver, or blood, urine and faeces…..Basically these suckers get everywhere!!!
Demodex are passed from mother to pups in the first three days of life. If the puppy is born by caesarean section, and it is not breastfeeding thereafter, there is no transmission of the parasite, because it does not pass the placental barrier (It can‘t get through the umbilical cord). Transmission from mother to pups is the only presently known mode of transmission under natural conditions. If it was experimentally possible to transmit between Demodex adult dogs, it has consistently been followed by spontaneous resolution of any injuries occurred. In other words, dogs only really pass the mites to other dogs if they bite them.
Mites of the genus Demodex mites are commensals of the dog and often hop between humans and pets easily. You could infect your dog, or they could infect you. Many animals can be carriers throughout their lives and never develop Demodicosis or any ill effects.