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Department of Medical Entomology |  |
| Fleas |
 modified from: Kettle, D.S. (1995). Medical and Veterinary Entomology. CAB International. Wallingford |
Fleas are highly specialised bloodsucking parasites belonging to the order of insects called Siphonaptera, which means "wingless siphon". They have a formidable reputation of claiming more victims than all the wars ever fought, as a result of the "bubonic" (Black Death) plague they spread throughout the world in the 14th century causing the deaths of over 200 million people. Now, these insects are better known for their irritation and pest status worldwide.
Fleas are light brown to mahogany in colour
and roughly oval shaped. Their laterally flattened appearance enables them to quickly move
through the host's hair. Measuring
2-8 mm in length, the adults are entirely covered
with a series of bristles and combs that assists them in clinging to the host. The small
head is equipped with sawing and sucking mouthparts, and two tiny simple eyes. To aid in
the detection of a host, fleas possess two short antennae on the head that are sensitive
to stimuli including heat, vibration, traces of carbon dioxide and change in air currents
and shadows. The hind pair of legs that are well developed for jumping enable fleas to be
propelled 10-30cms, either to make contact with a host or avoid a threatening situation.
Both female and males fleas rely on blood
for their nutrition, but can survive for several months without it. When a flea blood
feeds, it will crouch low to penetrate the host's tissue with a sawing motion of the
mouthparts. A small amount of anti-coagulatant is injected with the saliva, to permit easy
siphoning of the blood. Fleas 
will bite only accessible parts of the body and
clustered bites on the lower limbs are diagnostic. Blood feeding maybe interrupted, and
fleas will often probe several times before repletion which can increase their total body
weight by 30%. Each female flea uses her blood to nourish developing eggs, and will
deposit up to 4 eggs after each blood meal; most females will lay at least 100 eggs within
a life cycle of several months. The eggs are oval, white to cream in colour and measure
0.5mm in length; they can hatch within 1 week, but this will be dependent on prevailing
conditions as larvae are extremely sensitive to desiccation. When the maggot-like larvae
emerge, they are sparsely covered in hair and have no legs but are capable of moving
rapidly in search of food, which consists mainly of skin scales or undigested blood
excreted by the adults. Within a 1-3 week period, the larvae will grow and undergo 4
moults prior to pupating in a silken cocoon which they spin. The adult fleas emerge from
the pupal case in 1-2 weeks but can remain dormant in their cocoons for several months
depending on the availability of food and conditions. Often the emergence of adults from
the pupal stage is triggered by vibrations, which occasionally happens on entering an
unoccupied home of previous pet owners.
Some fleas can attack a range of hosts, and their ability to transfer
from one host to another allows for the possible transfer of pathogens including viral,
bacterial and parasitic diseases. The main flea species that attack humans include the cat
flea Ctenocephalides felis, the dog flea C. canis, and the human flea Pulex
irritans. The latter two species are relatively rare. The common cat flea is found on
both cats and dogs, and is the species usually identified in attacks on humans and usually
responsible for flea
plagues. Cat fleas are the intermediate host for the dog and cat tapeworm (Dipylidium
caninum) which is easily transmitted to humans. The only flea-borne disease that
currently occur within Australia is murine typhus; this is transmitted from rats to humans
by particular rat fleas, typically Xenopsylla
cheopis, and although it has been widespread, it is uncommon.
The continual biting activity of fleas alone causes a great deal of irritation and distress to humans, especially during flea plagues. Reactions to the flea's saliva are often delayed, with the formation of a wheal surrounding each puncture site within 5-30 minutes of the bite, accompanied by intense itching. Within 12-24 hours each wheal may progress to a small lesion or vesicle. The onset of symptoms in sensitized individuals often develops much later, and the initial reaction may become apparent only after 12-24 hours. Fleas are the major cause of papular urticaria, particularly on the legs of children, and continual scratching may lead to secondary infections.
Identification of fleas is performed with the use of light microscopy and taxonomic keys.
With the increase in carpeted homes, central heating and number of household pets, flea control is a continuing problem for pest controllers and pet owners. The prolonged periods of warm, humid weather in the summer months provide ideal conditions for fleas to flourish. Typically, concentrations of the immature stages of fleas (eggs and larvae) will be found in areas where pets feed and rest, and control measures should be targeted at any such areas, in addition to their housing, basket, blankets and the pets themselves. Regular vacuuming of floors and washing of pets and bedding with an insecticidal preparation will aid in control. Newer products with insect growth regulators are (e.g. in aerosol "bombs") are readily available in supermarkets provide an economical means of eradication by fumigation of a home, but they should only be used as directed.Continual reinfestation of fleas in homes may indicate the source has not been detected and may require intervention by a reputable pest controller.
Identification of fleas and all other medically important arthropods is preformed through the Medical Entomology Department at ICPMR, Westmead Hospital.
See 'Contacts' for further information.
