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Fleas are small (1.5–3.3mm), dark-coloured wingless insects adapted to feeding on
the blood of warm-blooded vertebrates, including dogs, cats, pigs, chickens, and,
unfortunately, humans. Most often, humans are bitten by animal fleas (usually cat or
dog fleas), but these fleas do not live on humans and need access to their animal host
to reproduce. Nowadays human fleas are found most often on farms. They live on
pigs, which have similar skin to humans.

Fleas have extraordinarily hard shiny bodies that are virtually impossible to crush
between the fingers or with a hard instrument. They are prodigious jumpers—their
muscular legs can launch them vertically up to 18cm and horizontally up to 33cm.
Bedbugs are an increasing problem.
Papular urticaria
This eruption, frequent in children, is caused by an allergy to bites, usually those of
cat fleas. The flea lays eggs on the cat, but these fall off into the bedding (or the sofa)
where they pupate and then hatch in about 1 month. If the cat is not available, the flea
is happy to bite another warm- blooded creature. Bites cause few symptoms, unless
the patient is allergic to the flea’s saliva. Fleas can survive for a year between meals,
and pupae can remain dormant for 2 years or more. Presentation may be particularly
dramatic if the house has been empty for a while, no cats have been in residence, and
the fleas are hungry.

What should I look for?
• Clusters of itchy papules on the ankle and legs (the fleas jump up from the carpet to
the nearest exposed skin). In crawling infants, the eruption may be more widespread.

What should I do?
• Try to convince the patient (or parent) that the problem lies with the cat (dog) and
fleas. Explain that cat fleas are virtually impossible to eradicate, even though the pet
has been treated, because the fleas are not living on the cat.
• Prescribe an antihistamine and a moderately potent topical steroid cream, such as
clobetasone butyrate, to be applied to bites bd.
• Reassure everyone that the allergy will gradually become less of a problem.
• Recommend treating carpets, furnishings, pet bedding (and the cat) with appropriate
insecticides and vacuuming frequently (but dispose of the vacuum bag afterwards).
• Recommend washing pet bedding every week, and consider moving the pet’s bed to
an area without carpets.

Human fleas (Pulex irritans)
• Itchy, dark red papules clustered in small groups round the waist or abdomen
suggest bites of human fleas.
• Hunt for the flea(s) to prove the diagnosis

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