Pulex, Xenopsylla and Ctenocephalides
- Parasite
- Exam priority: medium
Small jumping insects that feed on blood. Their bites itch, and some carry plague and flea-borne typhus or a dog tapeworm.
Also called: fleas, pulgas, human flea (Pulex irritans), oriental rat flea (Xenopsylla cheopis), cat and dog fleas (Ctenocephalides)
Quick facts
- Type
- Parasite · Arthropod vectors
- Gram / shape
- Brown body flattened from side to side
- Spread
- Plague · Flea-borne typhus · Dipylidium
- Causes
- Plague · Flea-borne · Dipylidiasis in young children
- Treatment
- Does not apply to the insect itself
At a glance
- Shape
- Brown body flattened from side to side, long jumping hind legs; Ctenocephalides has comb-like spines on the head
- Family
- Pulicidae
- Type
- Wingless blood-feeding insects (Siphonaptera); ectoparasites and vectors
- Size
- About 1–4 mm
Morphology
- Side-to-side flattening lets the flea move between hairs; backward spines anchor it.
- Xenopsylla has no combs; Ctenocephalides has head and thoracic combs; Pulex has none and a rounded head.
- Adults of both sexes feed on blood; larvae are blind, legless and do not bite.
Transmission
- Plague: a flea that fed on an infected rodent has its gut blocked by Yersinia pestis and regurgitates bacteria into the next bite.
- Flea-borne typhus: Rickettsia typhi is passed in flea faeces (flea dirt) rubbed into the bite or other skin breaks, or onto mucosa.
- Dipylidium: a child swallows an infected flea while playing with a dog or cat.
- Fleas jump from animals or infested floors onto people; there is no person-to-person spread of these infections by contact.
Reservoir: Rats and wild rodents (plague, flea-borne typhus); Cats, dogs and opossums (cat flea); Human dwellings with earthen floors and animals (human flea)
Vector: Xenopsylla cheopis is the classic vector of plague and flea-borne typhus; the cat flea Ctenocephalides felis also carries R. typhi and is the intermediate host of Dipylidium caninum.
Isolation precautions
What the care team adds to standard precautions.
- Standard
Life cycle
- The female lays eggs on the host; they fall off into bedding, carpets, nests and soil.
- Larvae hatch in days and feed on organic debris and the dried blood in adult flea faeces.
- After moulting twice, the larva spins a cocoon and pupates.
- The adult waits in the cocoon until vibration, warmth or carbon dioxide signal a host, then emerges.
- Adults feed on blood within hours; cycle length depends on temperature and humidity, from weeks to months.
- Flea larvae that eat Dipylidium eggs carry the cysticercoid into adulthood.
Virulence factors
- Flea saliva causes itchy papules and hypersensitivity reactions (pulicosis, papular urticaria).
- Gut blockage by Y. pestis makes the flea hungry and bite repeatedly, spreading plague.
- Fleas stay infected with R. typhi for life.
- Cocooned pupae survive empty houses for months, so infestations return when people move back in.
Diseases it causes
- Plague (Yersinia pestis) Plague →
- Flea-borne (murine) typhus (Rickettsia typhi) Rickettsial infections (spotted fever) →
- Dipylidiasis in young children (Dipylidium caninum)
- Pulicosis: itchy bites and papular urticaria
- Tungiasis is caused by another flea, Tunga penetrans Tungiasis and furuncular myiasis →
Clinical picture
- Groups of itchy red papules, often on the ankles and lower legs, sometimes with a central bite point.
- Papular urticaria: recurrent crops of itchy papules in children sensitised to flea bites.
- Flea-borne typhus: fever, headache and body aches; rash in about half of patients; few remember a flea bite.
Diagnosis
- Identifying fleas from pets, bedding or rodents by combs and head shape.
- Flea dirt (dark specks that turn red on wet paper) on pets or bedding.
- Flea-borne typhus: serology for R. typhi; treatment starts without waiting for results.
- Dipylidium: rice-like moving proglottids in a child's stool or nappy, with egg packets.
Treatment
Does not apply to the insect itself. Bites are treated with topical corticosteroids and oral antihistamines; flea-borne typhus with doxycycline; plague with aminoglycosides, fluoroquinolones or doxycycline started early; dipylidiasis with praziquantel.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Treat pets with veterinary flea-control products and wash their bedding.
- Vacuum floors and furniture often to remove eggs, larvae and pupae.
- Rodent control and keeping wildlife away from homes; do not handle dead rodents without gloves.
- Repellents during outdoor work in plague or typhus areas.
Test yourself
Think of the answer, then tap the question to see it.
How does a flea transmit plague?
Y. pestis blocks the flea's gut, so when it bites it regurgitates bacteria into the wound; it also bites more often because it stays hungry.
How is Rickettsia typhi passed from flea to person?
In flea faeces that are rubbed into the bite or other skin breaks, or reach the eyes or airways.
How does a child acquire Dipylidium caninum?
By swallowing a dog or cat flea that carries the cysticercoid, usually while playing with pets.
Which flea is the classic vector of plague?
The oriental rat flea, Xenopsylla cheopis.
Connections
← Back to the group: Arthropod vectors
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Plague | Plague | CDC (CDC, 2024); About Flea-borne Typhus (CDC, 2025); CDC - DPDx - Dipylidium caninum (CDC, 2024).
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Representative model, for educational purposes only.