Fleas are small (1.5 to 3.3 mm) long, agile, usually dark colored (for example, the reddish-brown of the cat flea), wingless insects with tube-like mouth-parts adapted to feeding on the blood of their hosts. Their bodies are laterally compressed (human anatomical terms), permitting easy movement through the hairs or feathers on the host's body (or in the case of humans, under clothes).
Their legs are long, the hind pair well adapted for jumping around 200 times their own body length, making the flea one of the best jumpers of all known animals (in comparison to body size), second only to the froghopper. The flea body is hard, polished, and covered with many hairs and short spines directed backward, which also assists its movements on the host.
Some well known flea species include:
Fleas are blood-sucking insects that feed on humans, dog, cats, and other animals. Fleas do not have wings.
Fleas As Pests
Fleas are a parasite which feed on the blood of warm blooded animals, including humans. They pierce the skin, inject an anti-coagulant chemical into the host to prevent blood clotting and suck out the blood some passing straight through their rectum in order to lay their eggs. A flea bite can cause acute irritation, infection and transfer of other parasites, such as, tapeworms.
Fleas often enter a building on dogs and cats, and are commonly deposited in carpeted areas, in the garden, yard and under the building. Flea eggs can take several weeks to more than 12 months to hatch - generally during hot humid weather causing an instant infestation of plague proportions.
Diseases Caused By Fleas
Many of the species of fleas that infest domestic mammals and birds will also utilize humans as a host, although people are not the generally preferred host of these blood-sucking parasites.
The most deadly disease that can be spread to humans by fleas is bubonic plague or black death, caused by the bacterium Pasteurella pestis, and spread to people by various species of fleas, but particularly by the plague or oriental rat flea (Xenopsylla cheopis). Bubonic plague is an extremely serious disease, because it can occur in epidemics that afflict large numbers of people, and can result in high mortality rates. During the European Black Death of medieval times, millions of people died of this disease. There have been similarly serious outbreaks in other places where rats, plague fleas, and humans were all abundant. Bubonic plague is mostly a disease of rodents, which serve as a longer-term reservoir for this disease. However, plague can be transmitted to humans when they serve as an alternate host to rodent fleas during times when rodent populations are large. Plague is mostly spread to humans when infested flea feces are inadvertently scratched into the skin, but transmission can also occur more directly while the fleas are feeding, or when a host accidentally ingests an infected flea.
Another disease that can be spread to humans by fleas is known as endemic or murine flea-borne typhus. This disease is caused by a microorganism known as Rickettsia, and is passed to humans by various species of fleas and lice, but especially by the oriental rat flea. Fleas are also the vector of a deadly disease that afflicts rabbits, known as myxomatosis.
Fleas may also serve as alternate hosts of several tapeworms that can infect humans. These include Dipylidium caninum, which is most commonly a parasite of dogs, but can be passed to humans by the dog flea (Ctenocephalides canis). Similarly, the tapeworm Hymenolepis diminuta can be passed to people by the rat flea (Xenopsylla cheopis). Biting or scratching is usually the first reaction of an animal with fleas. Some animals may begin excessive grooming to try to rid themselves of the irritation, eating many of the fleas in the process. Light-haired dogs or cats who do this may develop an orange-brown discoloration due to salivary staining. These general symptoms are usually referred to as pruritus.
As the flea feeds on a cat or dog, it releases saliva to stop blood from coagulating. This saliva contains chemicals that cause an irritant reaction and pruritis (itching) in the host. Some animals have a high tolerance to flea bites and aren't disturbed by even large numbers. Other pets are more sensitive, and may show a reaction after exposure to smaller number of fleas.
Flea Allergy Dermatitis (FAD)
Recent research indicates that FAD may be caused by intermittent exposure to large numbers of fleas. Animals sensitized in this way may subsequently become intensely reactive to flea saliva. This is important as it suggests the way to prevent FAD may be to prevent repeated flea infestations. The initial reaction is usually a reddened wheal, which forms a papule or swollen nodule and crusts over. After that, several secondary changes are possible:
The itching that occurs in dogs with FAD is intense, and results in self-mutilation. Generally, clinical signs are distributed over the inner thigh and abdomen and along the spine and hindquarters. Corticosteroids are often used to temporarily relieve clinical signs. This recommendation must come from your veterinarian, but a flea control programme is needed to resolve the problem completely.
Tapeworm (Dipylidium Caninum)
This species of tapeworm uses the flea as an intermediate host in its own life cycle. Eggs deposited by the adult tapeworm are shed into the environment where they are consumed by the flea larvae. If a pet then ingests an adult flea that consumed tapeworm eggs as a larva, the tapeworm parasite is passed on. Although tapeworm doesn't usually cause serious disease in pets, they are disgusting all the same. They can usually be seen wriggling near the hind end of the animal near the base of the tail. People can also become infected with tapeworm if they accidentally ingest an infected flea.
Because fleas are blood sucking insects, a heavy infestation can produce parasitic anemia, particularly in young animals. Fleas have been reported to produce anemia in dogs, cats, goats, cattle and sheep. Severe flea infestations in young pups and kittens can cause anemia to the point of death.
Below you can find some research work done on the Fleas and diseases caused by fleas.