Sarcoptes scabiei var. canis, the mite of sarcoptic mange, an intensely pruritic, transmissible skin disease, is a frequent parasite of dogs, and to a lesser degree, cats and humans in Singapore (S. scabiei var. cuniculi, the rabbit scabies mite, is also endemic here). The mites prefer lightly haired regions, and are most common on the elbows, hocks, ears, chest and abdomen. The disease spreads rapidly, and the entire body may be colonised by mites. The female mite tunnels through the skin, depositing eggs as she goes. Once these ova hatch, the larvae burrow to the surface where they browse and feed. The larval stage then rests in a "moulting pocket" and develops to the nymph stage. These also graze the skin surface before returning to moult to the adult stage. The life-cycle is completed in approx. 3 weeks. Transmission occurs mostly through direct contact with an infected animal.

MANGE:

Initially the pruritis is mild until the host develops a hypersensitivity to the mite, usually 3 to 4 weeks post-exposure. At this time, the itching becomes intense - hence the common name "scabies" from the French scabere "to scratch" - leading to self-induced traumatic wounds that exude serum, forming crusts.

However, the presenting signs of sarcoptic mange can be varied and misleading, some dogs never developing "classical" lesions. Secondary pyoderma (bacterial infection) and alopecia are common signs, and may be confused with atopic (allergic) dermatitis, food allergies or Staphylococcal pyoderma. Microscopic demonstration of the mites from a skin scraping establishes the diagnosis, although in some cases a response to therapy is needed for confirmation.

Sarcoptes mites are quite species-specific, and usually cannot complete their life cycle on a non-definitive host. Nevertheless, this does not prevent opportunistic infection of cats, humans and other species. In such situations, while the clinical signs may be severe, the infection is usually self-limiting with spontaneous regression of lesions once contact with the infected animal ceases. However, if exposure is prolonged or repeated, or if many mites are transmitted, lesions may persist for lengthy periods.

Mites

More than 50 species of mites live on or in domesticated mammals and birds of North America. These include the parasitic mange and scab mites, ear mites, and internal-living mites. Mites are quite small, most species being either microscopic or under 1 mm in length. The legs are provided with claw-like hooks or suctorial cups.

The life cycle of the mite usually begins with laying of the egg, from which a six-legged larva emerges. After feeding, the skin is shed and the eight-legged, sexually mature nymph appears. Following several skin molts, the mature adult male is formed.

Sarcoptes scabiei causes sarcoptic mange or itch. The fertilized females work their way deeply into the epidermis, forming tunnels where they deposit their eggs. Close proximity to nerve endings causes intense puritis. The skin thickens and dense crusts form. Frequently, secondary bacterial infection with Staphylococcus or other pathogens occurs.

Infection is common in the laboratory dog, and is particularly a problem in young, short-haired breed dogs. The disease is characterized by a papular dermatitis with subsequent rupture and crusting of lesions, puritis and automutilation. The skin becomes dry, rough, and thickened, with generalized alopecia. Dogs which become infected with secondary bacteria, or who have severe, generalized lesions, may become cachectic and die. Histologically, hyperkeratosis, parakeratosis, crusting, and presence of parasites are observed.

Diagnosis is made by skin scraping and identification of the organism. Control is through supportive nutrition, clipping, bathing and weekly application of medications to affected areas. Many different insecticides have been used to control the infestation.

Direct transmission to man can occur. Human infections are mild and self-limiting.

Notoedric mange mites resemble sarcoptic mites but are smaller. Notoedres cati mange is fairly common in cats. Lesions are first noticed on the face and other areas of the head. Later, lesions spread to various parts of the body, particularly the forelegs. Advanced lesions can give cats an "old age" appearance, caused by the wrinkling of the skin of the face. There is persistent pruritus, alopecia, and self-inflicted trauma. Transient dermatitis in man can occur

Otodectes cynotis, the cause of ear canker in the dog, cat, and other carnivores is extremely common. In the United States, 27-100% incidence has been reported in various areas.

The mite is usually found deep in the external ear, but sometimes foci of infestation occur on the feet and tip of the tail. Intense irritation occurs, with inflammatory exudates, cerumen and mites accumulating at the external canal. The infestation is usually bilateral. The host shakes its head and scratches violently at the ears. Ulceration of the auditory canal is common, and auricular hematoma, otitis media with torticollis, circling, and convulsions sometimes occur. Otodectic mange is thought to be the most common cause of seizures in the cat. More than 50% of otitis externa cases in the dog can be traced to infestation with Otodectes.

As in the rabbit, the ear mites can be readily observed with an otoscope, but when otoscopy fails, microscopic examination of ear contents should be performed. Control is based on eradication by treatment. All newly acquired dogs and cats should be examined on receipt, and periodic examination of colony animals should be performed. Treatment includes removal of cerumen and debris followed by treatment with a mineral oil/insecticide combination. Cesarean derivation will eradicate the disease

Demodex canis (Family: Demodicidae) is the common follicle-inhibiting mite of the dog and is the cause of demodectic (red) mange. It occurs worldwide and affects all breeds. Most normal dogs carry the organism without showing clinical signs. The disease is most common in short-haired breeds under 1 year of age.

The mites are found in the hair follicles and sebaceous glands. The mode of transmission is unknown; experimental attempts to transmit by direct contact have failed. Neonatal transmission is probable. Its precise role as primary disease agent is unknown, as the organism can frequently be present without lesions being present. Intestinal parasites, malnutrition, or immunologic insufficiency are potentiating factors toward development of demodectic mange. There are 2 types of cutaneous lesions which can occur: squamous or pustular. Both types can occur concurrently. Localized alopecia, dry, scaly dermatitis, and mild induration are typical in the squamous form. Early lesions are seen on the head and on other parts of the body. Frequently, in puppies, lesions are first observed just above the eye.

The pustular form occurs as a primary condition or as a sequelae to the squamous type. It is generally associated with secondary bacterial infection and is characterized by chronic, moist dermatitis and purulent exudate. The term "red" mange is applied to a generalized hyperemia with little or no pustule formation.

Numerous treatments have been tried, but often dogs recover without therapy. On the other hand, some animals are refractory to treatment and euthanasia is the eventual outcome.

Top

(Note:  many pet owners are finding relief for their animals by bathing them with Lice R Gone and cleaning the environment with Safe Solutions' Enzyme Cleaner)