Demodectic mange is caused by a tiny mite, Demodex canis, too small to be seen with the naked eye. Nearly all dogs acquire mange mites from their mother during the first few days of life. These mites are considered normal skin fauna when present in small numbers. They produce disease only when an abnormal immune system allows their numbers to get out of control. This occurs primarily in puppies and in adult dogs with lowered immunity. A high incidence of mange in certain bloodlines suggests that some purebred dogs are born with an inherited immune susceptibility.
Demodectic mange occurs in localized and generalized forms. The diagnosis is made by taking multiple skin scrapings and looking for the mites. Demodectic mites are usually easy to find.
Localized Demodectic Mange
This disease occurs in dogs under 1 year of age. The appearance of the skin is similar to that of ringworm. The principal sign is thinning hair around the eye- lids, lips, and corners of the mouth, and occasionally on the trunk, the legs, and the feet. The thinning progresses to patches of ragged hair loss about 1 inch (2.5 cm) in diameter. In some cases the skin becomes red, scaly, and infected.
Localized mange usually heals spontaneously in six to eight weeks, but may wax and wane for several months. If more than five patches are present, the disease could be progressing to the generalized form. This occurs in approximately 10 percent of cases.
Treatment: A topical ointment containing either benzoyl peroxide gel (OxyDex or Pyoben), or a mild topical preparation used to treat ear mites can be massaged into affected areas once a day. This may shorten the course of the disease. The medication should be rubbed with the lay of the hair to minimize further hair loss. Treatment may cause the area to look worse for the first two to three weeks.
There is no evidence that treating localized mange prevents the disease from becoming generalized. The dog should be checked again in four weeks.
Generalized Demodectic Mange
Dogs with the generalized disease develop patches of hair loss on the head, legs, and trunk. These patches coalesce to form large areas of hair loss. The hair follicles become plugged with mites and skin scales. The skin breaks down to form sores, crusts, and draining tracts, presenting a most disabling problem. Some cases are a continuation of localized mange; others develop spontaneously in older dogs.
When generalized demodectic mange develops in dogs under 1 year of age, there is a 30 to 50 percent chance that the puppy will recover spontaneously. It is uncertain whether medical treatment accelerates this recovery.
In dogs older than 1 year, a spontaneous cure is unlikely but the outlook for improvement with medical treatment has increased dramatically in recent decades. Most dogs can be cured with intense therapy. Most of the remaining cases can be controlled if the owner is willing to commit the necessary time and expense.
Treatment: Generalized demodectic mange must be treated under close veterinary supervision. Therapy involves the use of medicated sham- poos and dips to remove surface scales and kill mites. Shave or clip hair from all affected areas to facilitate access to the skin.
The FDA protocol involves first bathing the dog with a medicated benzoyl peroxide shampoo (OxyDex or Pyoben) to remove skin scales. Allow the shampoo to remain on the dog for 10 minutes before rinsing it off. Completely dry the dog.
Amitraz (brand name Mitaban) currently is the only miticide approved by the FDA for use on dogs. Make up an amitraz dip by adding Mitaban to water, according to the directions on the label. Be sure to treat the dog in a well- ventilated area and wear rubber or plastic gloves to keep the chemical off your skin. Sponge on the dip over a 10-minute period, allowing the dog’s feet to soak in the rinse. Allow the dip to dry on the dog. Repeat every two weeks, or as directed by your veterinarian. Try to keep the dog from getting her coat and feet wet between dips. Continue this protocol for 60 days beyond the day when skin scrapings first became negative.
Side effects of Mitaban include drowsiness, lethargy, vomiting, diarrhea, dizziness, and a staggering gait. Puppies are more susceptible than adults to these effects. If such a reaction occurs, immediately remove the miticide by thoroughly rinsing the coat and skin.
If the FDA protocol is not completely effective, your veterinarian may suggest an alternative treatment. Oral milbemycin and ivermectin have been used as off-label treatments, and require close cooperation between your veterinarian and you since they are not officially approved for treating this problem.
Secondary skin infections should be treated with antibiotics, based on culture and sensitivity tests. Corticosteroids, often used to control severe itching, lower the dog’s immunity to the mites and should not be used to treat this disease.
Because of an inherited immune susceptibility, dogs who recover from generalized demodectic mange should not be bred.