Fleas (Siphonaptera) and Classification

Fleas (Siphonaptera)

• Fleas belong to the order Siphonaptera.
• Fleas are small wingless insects adapted for jumping.
• Adult fleas are exclusively bloodsuckers, mainly mobile but some attach to the host.
• The "attached" flea species stay on their host and put their mouthparts in the host.
• Unfed adults will stay in the area of the host while waiting for a blood meal.
• Fleas are somewhat host-specific, but not as much as lice.

Classification of Flea Species

• Pulicidae family includes:
  • Cediopsylla simplex (rabbit flea).
  • Ctenocephalides canis (dog flea).
  • Ctenocephalides felis (cat flea).
  • Echidnophaga gallinacea (sticktight flea).
  • Pulex irritans (human flea).
  • Xenopsylla cheopis (oriental rat flea).
• Tungidae family includes:
  • Tunga penetrans (chigoe).
• Ceratophyllidae family includes:
  • Ceratophyllus gallinae (European chicken flea).
  • Nosopsyllus fasciatus (northern rat flea).
• Xenopsylla cheopis (Oriental rat flea) is a primary vector of urban plague and also known as X. brasiliensis in Africa, India, and South America but is more rural.
• Pulex irritans (Human flea) is an occasional epidemic plague vector.
• Nosopsyllus fasciatus (Northern Rat flea) is an epidemic plague and murine typhus vector.
• Diamanus montanus (Common Ground Squirrel flea) is an endemic plague vector in Western US.
• Ctenocephalides felis, C. canis, and P. irritans are primary pest species.

Flea Anatomy

• Fleas have pronotal and genal ctenidia (combs).
• They have an antenna, frons, eye, and maxillary palp on their head.
• The thorax consists of the pronotum, mesonotum, and metanotum.
• The abdomen has tergites (T1-T7) and sternites, as well as antesensilial setae, sensilium, and anal stylet.
• Hind legs are adapted for jumping.

Sensillum

• This sensory feature helps adult fleas in detection through air movement, vibrations, and temperature gradients.
• The sensillum aids host detection and initiating escape responses.

Flea Genitalia

• Male flea genitalia are morphologically complex.
• Major structures include paired claspers to secure the female.
• The aedeagus and penis rods are specialized structures inserted into the female genital opening.
• Major components of the female genitalia are the vagina, spermathecal duct, and spermatheca.
• Sperm is stored in the spermatheca after mating.
• During copulation, the male pushes under the female, grasping her with claspers and sucker-like discs on the antennae.

Flea Mouthparts & Alimentary Canal

• The mouthparts are well-adapted for piercing and sucking.
• Three slender stylets, or the fascicle, pierce the host skin.
• The laciniae penetrate the host skin and the tip of the epipharynx enters a host capillary.
• A salivary canal is formed by the appressed medial surfaces of the two laciniae.
• A food canal is formed at the confluence of the laciniae with the epipharynx.
• Fleas introduce anticoagulants, antiplatelet enzyme apyrase, and other salivary components.
• Sometimes flea bites introduce allergens or pathogens into the wound via the salivary canal.
• Host blood is imbibed through the food canal.
• The alimentary canal includes an anterior pharynx that leads to the elongated esophagus and then to the proventriculus at the junction of the foregut and midgut.
• The proventriculus is armed with spines to prevent regurgitation.
• The midgut expands to accommodate large blood meals but lacks distensible diverticula or caeca.
• Fleas void blood-rich feces during or soon after feeding.
• Pathogens like Rickettsia typhi can be voided in the feces.
• Four excretory Malpighian tubules radiate from the junction of the midgut with the hindgut.

Flea Life Cycle

• Fleas have a holometabolous life cycle.
• The flea life cycle goes from egg to larva to pupa to adult and takes 18 days to 20 months.
• Eggs: Deposit 3-18 at a time in several batches.
• Larvae: Require high humidity, with 9-15 days being optimal.
• Pupa: Lasts from 7 days to 1 year.
• Adult: Live up to 4 years.
• Adult females lay approximately 40 eggs each day

Flea-Transmitted Pathogens and Parasites

• Viruses transmitted by fleas:
  • Myxoma virus (Myxomatosis, spread by Spilopsyllus cuniculi to Rabbits).
• Bacteria transmitted by fleas:
  • Bartonella henselae (Cat scratch disease).
  • Rickettsia felis (Cat flea rickettsiosis).
  • Rickettsia typhi (Murine typhus, spread by Xenopsylla and Ctenocephalides to mammals).
  • Yersinia pestis (Plague, spread mainly by Xenopsylla to humans, rodents, cats).
• Protozoa transmitted by fleas:
  • Trypanosoma lewisi (Murine trypanosomiasis, spread by Nosopsyllus and Xenopsylla to Rats).
• Cestoda transmitted by fleas:
  • Dipylidium caninum (Double-pored tapeworm, spread by Ctenocephalides to Dogs, cats, and humans, but is an intermediate host).

Tunga Penetrans

• Known as the chigoe flea or jigger flea.
• The species' distribution is mainly in tropical regions.
• It will not transmit any disease-causing agent.
• Size is small and very compressed.
• Females burrow into the skin resulting in tungiasis

Flea Bites

• Flea bites can cause intense irritation for several days.
• Bites are characterized by a tiny purplish spot, or purpura pulicosa, surrounded by slightly swollen skin called roseola pulicosa.
• Most flea bites experienced by humans result from cat fleas.
• Cat fleas generally attack humans on the ankles, but other body parts may be affected.
• Women tend to be bitten more than men, possibly due to attraction to female hormones.

Murine Typhus

• Also called Flea Typhus or Endemic Typhus.
• Rickettsia typhi causes murine typhus.
• The primary vector is Xenopsylla cheopis (oriental rat flea).
• The reservoir is the roof rat and Norway rat.
• Murine typhus is distributed in the USA, Mexico, Europe, Australia, and Port areas.
• Transmission happens through flea feces.

Plague

• Plague has a long and brutal history.
• The pathogen is a gram-negative coccobacillus.
• Xenopsylla cheopis (oriental rat flea) serves as the primary vector.
• The reservoir is Rattus rattus (the roof rat).
• Plague is present worldwide, in both urban and rural environments.
• Transmission occurs through regurgitation and crushing the flea.
• Signs and symptoms include "bubos".
• The two common forms are primary bubonic and primary Pneumonic.
• Treatment is available.
• Plague, caused by Yersinia pestis, is treatable with antibiotics.
• The Black Death also refers to plague.
• Symptoms include buboes (swollen and tender lymph nodes), fever, chills, headache, and extreme exhaustion.
• Symptoms develop 2 to 6 days after infection.
• The disease has very rapid development and can be misdiagnosed.
• It is important to treat the plague effectively early.
• A high mortality rate of 90% occurs when the plague becomes Pneumonic

Urban Plague

• The pathogen is Yersinia pestis.
• Domestic rodents, especially Rattus rattus (the roof rat), serve as reservoirs.
• Xenopsylla cheopis (oriental rat flea) is the primary vector.

Rural Plague

• The pathogen is Yersinia pestis.
• Numerous flea species can vector the disease.
• Numerous reservoirs, including wild rodents: filed mice, deer mice, pack rats, chipmunks, ground squirrels, tree squirrels, prairie dogs, and cottontails.
• Pets can bring fleas into homes.
• Cats are highly susceptible.

Flea Control

• Sanitation and environmental clean-up are essential for destroying harborage for eggs, larvae, pupae, and adults.
• Apply Chemical Insecticides to cats and dogs and spray rodent-infested environments.
  • Flea collars are not very effective.
  • Topical application of insecticides are absorbed through the skin.
• Use Insect Growth Regulators, such as topical application on animals and fumigation of affected rooms.
  • Effective as an ovicidal as well as an insecticidal application.
• Metal guards on ship hawsers can prevent rat access, helping to enforce plague control related to shipping.