An unusual zoonosisBMJ 2005; 331 doi: https://doi.org/10.1136/bmj.331.7527.1255 (Published 24 November 2005) Cite this as: BMJ 2005;331:1255
As a general practitioner and pet owner, I treated my scratching Abyssinian guinea pigs' nits with subcutaneous ivermectin. A few days later, I experienced intense pruritus of the forearms with raised papules surrounded by a histamine-like response. Assuming that the lesions were mosquito bites from warm, humid evening dog walks, I attempted to suppress the irritation with mometasone, but with only partial success. As the days progressed, excoriations developed, without a history of injury, that did not penetrate the epidermis. At last, the penny dropped—burrows. I had scabies. But from where?
I had seen a case recently but had never before caught a parasite from a patient in 25 years of practice. Out came the veterinary textbook to see whether guinea pigs can harbour scabies. The nits had obviously been a red herring (coinfestation). Apparently, the sarcoptic mite Trixacarus caviae, which causes guinea pig mange, has zoonotic potential. The family Sarcoptidae also includes Notoedres cati (cat mange), Notoedres muri (rat ear itch), Sarcoptes scabiei (species-specific varieties in dog, squirrel, fox, etc). The cavie species can also cause scabies in humans, but this rarely occurs.
The life cycle begins as the adult female lays its eggs while burrowing into the skin. The eggs hatch to release larvae, which moult into nymphs. Larvae and nymphs are found in short burrows called moulting pouches. Mating occurs after a male penetrates the moulting pouch of an adult female. Impregnated females extend their moulting pouches into burrows, laying eggs as they go; and so on. Transmission is by person to person and fomites, such as bedding and clothing. Mites are predominantly found between the fingers and on the wrists. Rashes may occur on the abdomen, axillae, pubic area, knees, ankles, buttocks, elbows, and between the shoulder blades. Mites hold onto the skin using suckers attached to the two most anterior pairs of legs.
After making the diagnosis, I visited our local pharmacist, who handed me a bottle of malathion at arm's length.
Since fairly prolonged contact is required to spread scabies, the risks to my patients must be close to zero. It may, however, be worth doctors questioning their patients about small pets if similar unexplained itching occurs.
As for myself, the pruritus persists but is no doubt iatrogenic or, more probably, psychogenic.