When scabies infection goes to the dogs

February 1, 2007

Humans can contract canine scabies from direct contact with animals such as cats, dogs, foxes, cows, pigs and other mammals.

"These are very unusual and rare cases that dermatologists need to be able to recognize," says Joseph Bikowski, M.D., director of the Bikowski Skin Care Center in Sewickley, Pa., and a clinical assistant professor of dermatology at Ohio State University, Columbus, Ohio.

"Diagnosis is the challenge. It can be confused with conditions such as eczema, human scabies and drug reactions. Once you know the correct diagnosis, then you know what is the appropriate treatment strategy."

Humans can contract canine scabies from direct contact with animals such as cats, dogs, foxes, cows, pigs and other mammals, Dr. Bikowski tells Dermatology Times.

In animals, the condition is known as Sarcoptic mange. The causative organism is a mite, called Sarcoptes scabiei var canis.

The mites live off of the host for up to 21 days. A rash will manifest within 24 to 96 hours in a human who has had direct contact with an affected animal. The rash may be similar to that which is produced from the human scabies mite, with the exception that, in canine scabies, there are no burrows.

Fortunately, the condition is not transmitted between humans, and the organism does not replicate on humans. It lasts on humans about 14 to 21 days unless repeated contact with the affected animal occurs.

Some of the signs of canine scabies in humans include severe total body pruritus, a generalized polymorphous eruption, a conspicuous absence of burrows, positive wet preparation for mites and papulovesicular lesions on the hands and wrists that measure about 1 mm in diameter, according to Dr. Bikowski.

"A wet prep mount of a skin lesion, demonstrating the mite, is necessary for absolute confirmation of the diagnosis," Dr. Bikowski says.

Dr. Bikowski describes canine scabies as not a major public health problem, but notes it is a diagnosis that a board certified dermatologist should be able to make.

He notes that a presumptive diagnosis can be made in the face of a negative wet prep when a person suffers from a generalized eczematoid eruption, intractable pruritus and a history of contact with an animal that has mange. Indeed, it's a diagnosis that requires an elevated degree of suspicion, Dr. Bikowski notes.

The condition is very rare, with Dr. Bikowski noting that he has seen only a handful of cases in 30 years of practice. Many dermatologists may not see a case in their careers, he says.

Because of its rarity as a condition, there has not been much research in canine scabies affecting humans, with virtually no new treatments being available, Dr. Bikowski says.

Case histories

In his own practice Dr. Bikowski came across a case of a middle-aged husband and wife, each presenting with a six-week history of total body rash and itch.

The couple had two lap dogs that had intractable itch and a scaling rash for the same period of time. The patients reported that their itch measured 10/10 in severity and awoke them from sleep at night. None of their relatives or acquaintances experienced this itching and there was not a known community outbreak of human scabies.

Both patients had diffuse secondarily excoriated eczematous eruption and multiple, crusted erythematous 2 mm to 5 mm papules of the neck, torso, upper and lower extremities, hands and feet. There were no burrows present. On magnified examination, vesicles measuring 1 mm in diameter were present on the wrists and in the interdigital web spaces. A wet prep from one of the wrist vesicles was positive for a mite. A similar mite was isolated from the scaling rash of each dog.

One case series of 22 patients, both treated and untreated, published in 1967, found treatment resulted in a shorter duration of symptoms.

Kicking the canine bug