Natural History

Group 1

Fleas

Natural History

·  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.

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·  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.

Clinical Presentation

·  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.

Bug Facts - Fleas

Physical Characteristics

·  There are about 2,250 species of fleas.

·  Fleas are small, wingless, brown to black, blood sucking insects.

·  Fleas have flattened bodies with spines that are aimed backwards. This enables them to move rapidly and efficiently through the body hair of an animal.

·  They have piercing-sucking mouth parts that are somewhat like a "siphon".

·  Fleas can jump 7"- 8" vertically and 14"- 16" horizontally which is 20 times their own height. The equivalent of a 6 foot man jumping 120 feet.

·  Flea larvae have been observed to burrow to a maximum depth of 1/2 inch.

·  Flea larvae will crawl several inches to reach cover and escape bright light and feed on dried faecal blood.

·  The adult flea will spend 99% of its life on a host animal but eggs fall off and thereby spread infestation. Fleas resting in their cocoons come out in response to vibration from vacuum cleaners, people or pets moving about.

Reproductive Facts

·  The flea’s life cycle is; egg, larvae, pupae, adult. The time required to complete a cycle depends on temperature, humidity, and the food available to the developing insect.

·  The female flea can lay 300 to 500 eggs in her lifetime. Flea eggs are about 1/50th of an inch in length.

·  Flea eggs hatch in 1 - 6 days and fleas can develop from egg to adult in 17 - 21 days.

·  The female mates only once, she lays her eggs loose on the host animal and must have a blood meal before she can lay fertile eggs.

·  The adult flea can live up to 20 weeks in the pupa case.

Feeding Habits

·  Flea larvae stay very near the surface to be close to their food supply-adult flea faeces and other animal derived material.

·  Flea larvae primary food is faeces of the adult flea, but will feed on other materials such as pet dander, flea eggs, injured larvae, and proglottids- the shed body segments of the dog and cat tapeworm.

·  Adult fleas can live for months without food.

Disease Factors

·  Fleas can carry Bubonic Plague and Murine Typhus. Some fleas, especially those from squirrels in the Sierras, still carry "The Plague."

·  About 75% of fleas are associated with rodents.

·  Dog and cats can get tapeworms from the flea.

·  The egg containing proglottids exit the host's body via the anus, These tiny egg packets dry to form what looks like sesame seeds.

·  Flea larvae chew into them, swallowing tapeworm eggs. These eggs hatch in a flea larva and form a cyst within its muscles.

·  Here the tapeworm waits for the larva to metamorphose, and the adult flea to be eaten by the cat or dog during grooming. When the dead flea is digested the tapeworm is released.

The Oriental Rat Flea: Xenopsylla cheopis

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Family: Pulicidae
Order: Siphonaptera
Genus: Xenopsylla
Species: cheopis

·  Fleas are blood sucking parasites. They have the potential of spreading dangerous diseases to humans and other animals.

·  It is possible the first flea was native to Africa and travelled by boat on the back of a rat to different destinations around the world.

·  Even though there are many different types of fleas, they all have similar body parts; eyes and legs help them survive the dangers of their life.

·  A flea undergoes four different life cycles to become an adult. The Black Death, also known as the Bubonic Plague, is one of the deadly diseases that the flea can spread to man and animals.

Body Parts

·  The rat flea has two eyes, yet it can only see very bright light.

·  On the very tip of its head is a genial comb. Right behind the eyes are two short antennae.

·  Behind the antennae is the pronotum and behind that lays the protonotal comb.

·  A flea's mouth has two functions: one for squirting saliva or partly digested blood into the bite, and one for sucking up blood from the host.

·  This process mechanically transmits pathogens that may cause diseases the flea might have.

·  Fleas smell exhaled carbon dioxide from humans and animals and jump rapidly to the source to feed on the newly found host.

·  A flea is wingless so it can not fly, but it can jump long distances with the help of small powerful legs.

·  A flea's leg consists of four parts. The part that is closest to the body is the coxa. Next is the femur, tibia and tausus. A flea can use its legs to jump up to 200 times its own body length. It can also jump about 130 times its own height.

·  The flea's body is only about one tenth of an inch. A flea's body is constructed to make it easier to jump long distances.

·  The flea's body consists of three regions: head, thorax, and abdomen. The head and the thorax have rows of bristles (called combs) and the abdomen consists of eight visible segments.

Life Cycle

·  There are four stages in a flea's life.

·  The first stage is the egg stage. Microscopic white eggs fall easily from the female to the ground or from the animal she lays on. If they are laid on an animal, they soon fall off in the dust or in the animals bedding.

·  If the eggs do fall immediately on the ground, then they fall into crevices on the floor where they will be safe until they hatch one to ten days later (depending on the environment that they live in, it may take longer to hatch).

·  When they finally hatch, the flea is a larva. The larva looks very similar to a worm that is about two millimetres long. It only has small body and a mouth part. (No arms or legs)

·  At this stage, the flea does not drink blood; instead it eats dead skin cells, flea droppings, and other smaller parasites lying around them in the dust.

·  When the larva is mature it makes a silken cocoon around itself and pupates.

·  This is when the flea spins a white, silken cocoon for itself. The flea stays in this stage from one week to six months changing in a process called metamorphosis.

·  When the flea emerges, it begins the final cycle, called the adult stage.

·  A flea can now suck blood from host and mate with other fleas. A single female flea can mate once and lay eggs every day with up to fifty eggs per day.

·  Fleas like to live in an environment that is warm, where they can live up to a year.