Flea Bites

Bites by fleas, mainly the cat flea Ctenocephalides felis (also the dog flea, human flea Pulex irritans and rat flea Xenopsylla cheopis). Fleas live on pets and in carpets, bedding and furniture, and jump up to 30 cm onto the lower legs.

• Adult fleas feed on blood several times a day. Larvae develop in the environment, and pupae can lie dormant for months, so infestations explode when a house is reoccupied or vibration triggers emergence.
• The reaction depends on sensitisation to flea saliva. Non-sensitised people have little reaction. Sensitised people, particularly children, develop papular urticaria.
• Fleas transmit Rickettsia typhi (murine typhus) and R. felis (flea borne spotted fever), Bartonella henselae (cat scratch disease), Yersinia pestis (plague) and the tapeworm Dipylidium caninum (when fleas are swallowed, mainly by children).
• Tungiasis, caused by the burrowing sand flea, is a separate disease.

• Groups or lines of small, intensely itchy red papules, often with a central dark puncture point or haemorrhagic punctum, on the ankles and lower legs. Sometimes clusters of three ("breakfast, lunch and dinner").
• Other sites are the waist, axillae, groin, and the antecubital and popliteal fossae. In heavy infestation the trunk and arms are affected.
• Bullae occur on the lower legs of children. Weals occur in highly sensitised people.
• Chronic or repeated bites cause papular urticaria (crops of papules in children aged 2 to 10 years), excoriation, prurigo nodules, post-inflammatory pigmentation and sleep loss.
• Systemic features suggest transmitted disease:
  • Murine typhus: fever, headache, myalgia, and a maculopapular rash on the trunk about 4 to 7 days after the fever begins (fever starts 7 to 14 days after the bite).
  • Cat scratch disease: a papule at the bite site, then tender regional lymphadenopathy 1 to 3 weeks later, with fever.
  • Plague: sudden fever, chills and a painful swollen lymph node (bubo), in endemic areas.
• Differential diagnosis: bed bug bites, mosquito bites, scabies, chigger bites, folliculitis, contact dermatitis, varicella and dermatitis herpetiformis.
• Complications: secondary impetigo and cellulitis, iron deficiency anaemia in heavy infestation (infants and animals), and disease transmission.

• Clinical, based on the distribution (lower legs), the grouped papules, pet ownership, and other household members and pets affected.
• Confirm infestation by white sock test (walk through the area in white socks and look for jumping fleas), flea comb on pets, sticky light traps, and inspection of bedding and carpets for flea dirt (black specks that turn red when wet).
• Exclude scabies (burrows, finger webs) in itchy papular eruptions.
• Swab infected lesions. In fever after bites, test for murine typhus (PCR or serology), perform blood cultures, and in endemic areas with a bubo urgently aspirate for plague and call for infectious disease advice.

• Treat the person:
  • Mometasone furoate 0.1% or betamethasone valerate 0.1% cream once daily for 3 to 7 days (hydrocortisone 1% for the face or in young children).
  • Menthol 0.25 to 1% or calamine lotion for itch.
  • Cetirizine 10 mg orally once daily (child 2 to 5 years 2.5 mg, 6 to 11 years 5 mg). Hydroxyzine 10 to 25 mg at night in adults helps sleep.
  • Prednisolone 0.5 mg/kg per day for 3 to 5 days for extensive bullous reactions.
• Secondary infection: mupirocin 2% ointment 3 times daily for 5 to 7 days, or flucloxacillin 500 mg orally 6 hourly for 7 days (child 12.5 to 25 mg/kg 6 hourly).
• Treat the source, which is essential:
  • Treat all pets with a veterinary flea product (for example fipronil, imidacloprid, selamectin, nitenpyram or an isoxazoline tablet), following veterinary dosing, and repeat monthly for at least 3 months to break the life cycle.
  • Wash bedding, pet bedding and clothes at 60 C. Vacuum carpets, upholstery and floor cracks daily for 2 weeks, and discard the bag.
  • Treat the home with an insecticide containing an adulticide plus an insect growth regulator (methoprene or pyriproxyfen), or use professional pest control. Treat outdoor resting areas for pets.
• Murine typhus: doxycycline 100 mg orally or IV 12 hourly (child under 45 kg 2.2 mg/kg 12 hourly), for 7 days or for 48 hours after the fever resolves. Use azithromycin 500 mg once daily for 3 days in pregnancy.
• Cat scratch disease: usually self-limiting. For marked lymphadenopathy give azithromycin 500 mg on day 1 then 250 mg daily for 4 days (child under 45 kg 10 mg/kg on day 1 then 5 mg/kg for 4 days). Severe or disseminated disease needs specialist treatment with doxycycline 100 mg 12 hourly plus rifampicin 300 mg 12 hourly for 2 to 4 weeks.
• Plague is an emergency: start gentamicin 5 mg/kg IV once daily or streptomycin 15 mg/kg IM 12 hourly (maximum 1 g), or doxycycline 100 mg 12 hourly, for 10 days, with respiratory isolation for pneumonic disease, and notify public health authorities.
• Dipylidium caninum: praziquantel 5 to 10 mg/kg orally as a single dose.
• Special groups:
  • Children: weight based antihistamine, mild steroid, short nails. Treat siblings and pets together, since reactions vary by person.
  • Pregnancy: calamine, mild steroid, cetirizine or loratadine, with azithromycin for rickettsial infection.
  • Immunosuppression: treat infection early.
• Follow up: lesions settle in 1 to 2 weeks, but new bites continue until the infestation ends. Review if lesions persist beyond 3 weeks, if fever or lymphadenopathy appears, or if the household has continuing bites. Refer to dermatology for prurigo nodularis or persistent papular urticaria.