Flea Bite Reaction

Flea bite reactions result from bites by Ctenocephalides felis and C. canis (cat and dog fleas), human fleas (Pulex irritans) and rat fleas (Xenopsylla cheopis). Bites are intensely itchy and cluster on the lower legs and ankles.

• Source: pets, rodents, carpeting, bedding, animal shelters, poor sanitation.
• Reaction severity depends on sensitisation.
• Fleas transmit murine typhus, Bartonella, tapeworm, and plague in endemic foci.

Pruritic grouped red papules, often three in a row, with a central punctum or small blister, on the ankles, calves, waist, axillae and areas where clothing is tight.

• Sensitised people develop bullae and persistent urticarial papules.
• Differential diagnosis: bedbug bites, papular urticaria, scabies, tungiasis (Tunga penetrans, painful nodule with black dot on foot), mosquito bites, folliculitis, cheyletiellosis, chiggers (trombiculid larvae), contact dermatitis, dermatitis herpetiformis.
• Complications: secondary infection, impetigo, post inflammatory pigmentation, anaemia in severe infestation, transmission of murine typhus or plague, tapeworm in children who ingest fleas.

Clinical, with exposure history and identification of fleas on pets or in the home.

• Flea dirt (black specks that turn red on wet paper) in pet fur or bedding.
• Swab if infected; full blood count in heavy infestation.
• Where fever and tender lymph node follow exposure in an endemic plague area, urgent evaluation is needed.

Treat the skin and the environment.

• Supportive: wash bedding at 60 degrees Celsius, vacuum carpets, furniture and cracks regularly and discard bags outdoors, treat all pets in the home with a veterinary approved flea treatment, rodent control, insecticide on floors and bedding when needed, wear socks and long trousers outdoors in infested areas.
• Pharmacological: hydrocortisone 1 percent or mometasone furoate 0.1 percent cream once or twice daily for 5 to 7 days; calamine lotion; oral cetirizine 10 mg daily (children 2 to 5 years 2.5 mg twice daily, 6 to 11 years 5 mg daily); secondary infection with fusidic acid 2 percent cream three times daily or flucloxacillin 500 mg four times daily for 7 days. Murine typhus: doxycycline 100 mg twice daily for 7 days. Suspected plague: doxycycline 100 mg twice daily, or gentamicin 5 mg/kg IV daily, after urgent referral.
• Procedures: surgical extraction of embedded sand fleas (tungiasis) under sterile technique if present.
• Special groups: pregnancy, cetirizine and topical steroid acceptable, avoid doxycycline and use gentamicin 5 mg/kg IV daily if plague is suspected; children under 8 years, avoid doxycycline except for life threatening disease; immunosuppressed, treat infection early.
• Red flags: fever with painful lymph node swelling (plague), generalised rash with fever (murine typhus), spreading cellulitis, anaphylaxis, black eschar.
• Follow-up: review at 1 to 2 weeks; recheck environment and pets after 2 weeks.