A 42-year-old man presents with an intensely pruritic eruption affecting both ankles for approximately 2 weeks. He is active in sports and spends ample time outdoors. He also does yard work on his property on weekends. He has 3 cats that spend time outdoors in the daytime and on occasion share his bed at night. Examination reveals scattered excoriations of both ankles.
Submit your diagnosis to see full explanation.
One evening, the patient discovered a tiny black insect traversing his ankle, and magnification confirmed the diagnosis of cat fleas. Anti-flea treatment was administered to the cats, the carpets were cleaned, and the condition resolved.
Cat fleas (Ctenocephalides felis) are miniscule wingless insects that take up residence in birds and mammals, burrowing under their feathers or fur to access blood.1 Their coloration ranges from rust to black, and they have a streamlined body with backward-pointing bristles that enhance navigation to the skin surface. The fleas are approximately 2 mm in length and have mouthparts for piercing and sucking blood. Fleas do not fly but are prodigious jumpers. They do not live on humans but will bite when the opportunity arises. Flea bites occur most commonly on the ankles.2
Fleas are the most common ectoparasites on domestic dogs and cats worldwide.3 Flea-bite dermatitis is an allergic reaction caused by substances in flea saliva.4
Cat fleas not only engender discomfort but they can also spread disease. Transmission of rickettsial illness is well documented.5 Horizontal transmission of Rickettsia occurs in many ways, including cofeeding, mating, and contact with contaminated feces.6
Ridding a home of cat fleas entails treating pets, washing bedding, and vacuuming carpets.1 Spraying baseboards with insecticide is also advocated.
Stephen Schleicher, MD, is an associate professor of medicine at the Commonwealth Medical College in Scranton, Pennsylvania, and an adjunct assistant professor of dermatology at the Perelman School of Medicine at the University of Pennsylvania in Philadelphia. He practices dermatology in Hazleton, Pennsylvania.
- Ridge GE. Cat flea. The Connecticut Agricultural Experimental Station. http://www.ct.gov/CAES/cwp/view.asp?a=2815&q=376710. Updated November 3, 2010. Accessed February 24, 2016.
- Lee SE, Johnstone IP, Lee RP, Opdebeeck JP. Putative salivary allergens of the cat flea, Ctenocephalides felis felis. Vet Immunol Immunopathol. 1999;69(2-4):229-237.
- Slapeta J, King J, McDonell D, et al. The cat flea (Ctenocephalides f. felis) is the dominant flea on domestic dogs and cats in Australian veterinary practices. Vet Parasitol. 2011;180(3-4):383-388.
- Youssefi MR, Ebrahimpour S, Rezaei M, Ahmadpour E, Rakhshanpour A, Rahimi MT. Dermatitis caused by Ctenocephalides felis (cat flea) in human. Caspian J Intern Med. 2014;5(4):248-250.
- Thepparit C, Hirunkanokpun S, Popov VL, Foil LD, Macaluso KR. Dissemination of bloodmeal-acquired Rickettsia felis in cat fleas, Ctenocephalides felis. Parasit Vectors. 2013;6:149.
- Hirunkanokpun S, Thepparit C, Foil LD, Macaluso KR. Horizontal transmission of Rickettsia felis between cat fleas, Ctenocephalides felis. Mol Ecol. 2011;20(21):4577-4586.