Parasitic Insects, Mites and Ticks: Genera of Medical and Veterinary Importance/Fleas

Fleas (Siphonaptera)

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Characters of fleas

All fleas are insects specialized as ectoparasites that feed on blood through piercing mouthparts. The adults are obligate parasites. Most species infest terrestrial mammals and often any one species of flea will readily infest several species of mammal. Fleas specialize to feed on hosts that are strongly associated with a nest, den, or other regular resting site. Some groups of fleas have adapted to feed on birds. In contrast to lice and acarines, only adult fleas are parasitic, and with some species of flea the adult can spend much time off the host between feeds.

Scanning electron-micrograph shows an adult Ctenocephalides flea that commonly infests cats, dogs, other domestic animals, and humans.

The life-cycle has a complete metamorphosis. The illustration below for Ctenocephalides shows a fully grown larva, and the pupa which metamorphoses into the adult. Larval fleas feed on organic debris, and pellets of dried blood excreted by the adults. These pellets drop into the nest or resting site of the host. Adult fleas are typically ectoparasitic blood-feeders, but at least one species penetrates into the skin of its hosts.The larvae pupate at these sites, and will hatch rapidly into hungry adults when the host returns to nest. This nest-inhabiting behavior is formally described as nidicolous.

Diagram of feeding at skin shows an adult flea sucking blood from dermal capillaries of its host (for clarity only hind-legs are drawn).

Adult fleas are laterally flattened, never develop wings, the head bears a pair of compact antennae and a pair of eyes. On their hosts fleas have a shiny brown appearance. The thorax bears three pairs of strong legs, enabling the flea to jump from nest onto host. Fleas have many strong setae which hold them against the effects of host grooming. Of diagnostic use are the distinct rows of spines. The whole row is like a comb, technically called a ctenidium. These occur on the head (genal ctenidium) and on the first thoracic segment (pronotal ctenidium) .

Glossary

• Complete metamorphosis = Process of developing from stage to stage of an invertebrate animal that involves a total change of form between immature stages and the reproductive adult stage (see diagram for two winged fly in Insects (Insecta) ).
• Ctenidium = a dense row of bristles, like a comb; occurs on head (genal ctenidium) or on thorax (pronotal ctenidium) (1 and 3 on Ctenocephalides).
• Pupa = The stage during which the change of form in a complete metamorphosis occurs (7 on Ctenocephalides).
• Meral rod = A vertical thickening of the body wall (mesopleuron part) of the thorax of fleas (4 on Ctenocephalides).
• Nidicolous = In this context this means the behaviour of insects or acarines that inhabit the nests of their hosts.
• Ocular bristle = A small bristle or seta in front of the eye (2 on Xenopsylla).

Pulex (Pulicidae)

Characters: adult, lateral. 1- Genal ctenidium is absent. 2- Ocular bristle occurs below the eye. 3- Dorsal profile of head is smoothly rounded. 4- Bristles are absent from posterior margin of head. 5- Pronotal ctenidium is absent. 6- Meral rod is absent.

Hosts: Humans, pigs, dog, cats, rats and other mammals are liable to infestation with Pulex irritans.

Symptoms and disease: Irritation and biting stress are caused by heavy infestations, but for many humans infestation with Ctenocephalides cat or dog fleas is more likely. Pulex irritans can under some circumstances transmit the causative organism of bubonic plague, the bacterium Yersinia pestis . However P. irritans does not readily feed on rats, and Xenopsylla species of flea are more important as vectors of this bacterium from its rat natural host to humans (see Xenopsylla below). Also there are various contaminative and contagious routes of transmission of Yersinia pestis.

Ctenocephalides (Pulicidae)

Characters: adult, larva, pupa. 1- Genal ctenidium has 10 or more spines (counting both sides). 2- Dorsal profile of head is smoothly rounded. 3- Pronotal ctenidium is present, usually with 16 spines (total of both sides). 4- Meral rod is present (a vertical thickening of exoskeleton on the mid thoracic segment). 5- Male posterior segments of abdomen. Also: 6- Larva. 7- Pupa.

Hosts: Ctenocephalides felis (Cat-flea) infests domestic cats and dogs. The Cat-flea is often the commonest flea infesting dogs in human domestic environments. Also in tropical and sub-tropical regions Cat-fleas infest cattle, buffalo, sheep and goats. Ctenocephalides canis (Dog-flea) is mainly restricted to dogs. Both these flea species will readily feed on humans but the domestic animal hosts sustain the populations of these fleas .

Signs and symptoms: Infestation leads to irritation, pruritus, anemia and frequent grooming. The quality of the host's hair-coat declines. The blood excreted by adult fleas (for the benefit of the larvae in the host's nest or bedding) can be detected as dry pellets that will turn red if combed out onto a damp towel or paper.

Disease: Heavy infestations of cats and dogs cause considerable biting-stress and often lead to flea-bite hypersensitivity. Massive infestations of goats when confined at night in the same enclosures have been reported as the direct cause of death of some goats . These fleas act as intermediate hosts of the dog tapeworm, Dipylidium caninum .

Echidnophaga (Pulicidae)

Characters: adult, lateral. 1- Mouthparts are long and project conspicuously from the head. 2- Genal ctenidium is absent. 3- Dorsal profile of head is distinctly angular, forming a pentagonal shape. 4-Pronotal ctenidium is absent. 5- Abdomen is short.

Hosts: Echidnophaga gallinacae (Sticktight-flea) is predominantly a parasite of poultry and other birds but it will feed opportunistically on mammals.

Signs and disease: The Sticktight-flea is conspicuous because adults remain at the same place on the skin of their host between feeds. The favored feeding site is on the head, also on areas of bare skin; large groups of adults cluster together. In moderate to heavy infestations this type of feeding causes severe biting-stress, can damage the head of the bird and greatly reduce productivity of the birds .

Distribution: Most common in tropical and sub-tropical regions.

Tunga (Pulicidae)

Characters: female, lateral. 1- Mouthparts are long and project conspicuously from the head. 2- Genal ctenidium is absent. 3- Dorsal profile of head is angular, forming a triangular shape. 4- Pronotal ctenidium is absent. 5- Abdomen of feeding female expands greatly.

Hosts: Tunga penetrans (Jiggers, Chigger-flea, Chigoe-flea, Sand-flea, but avoid confusion with names of trombiculid mites) infests pigs, and many other species of mammals. Dogs are often badly affected. Humans are readily infested when they walk with bare skin of feet exposed .

Signs, symptoms and disease: This flea is usually seen as it is feeding, resident in its host. An unfed female rapidly burrows head first deeply into skin of its host. There it continues to feed, expanding its abdomen enormously as it produces eggs continuously. On humans a single infesting flea appears like a brown boil with a small opening to the exterior. Eggs are laid from the part of abdomen which protrudes slightly from the host’s skin. In an early infestation this brown spot may be the only sign. A single infesting flea causes pruritus followed by pain. Infestations can accumulate, and the site of inflammatory reactions to the fleas can become bacterially infected. Removal of these burrowing parasites may require surgical methods. When accidentally transported from South America to Africa these fleas have caused great problems to people and their domestic animals living in Africa.

Distribution: Tunga penetrans is a parasite of tropical and sub-tropical regions.

Ceratophyllus (Ceratophyllidae)

Characters: female, lateral. 1- Genal ctenidium is absent. 2- Dorsal profile of head is smoothly rounded. 3- Pronotal ctenidium has 24 spines (total of both sides). 4- Meral rod is present. 5- Abdomen is elongated.

Hosts: Ceratophyllus gallinae (European chicken-flea) commonly infests poultry and other birds and will also opportunistically feed on domestic cats and dogs, and on humans .

Signs and disease: Irritation, restlessness, and allergic dermatitis are caused; also anemia results from in heavy infestations.

Distribution: Ceratophyllus gallinae occurs in Europe and some regions of Asia, but has also spread to some parts of North America. Ceratophyllus niger occurs in Canada and USA.

Xenopsylla (Pulicidae)

Characters: adult, lateral. 1-Genal ctenidium is absent. 2- Ocular bristle is present below the eye. 3- Dorsal profile of head is smoothly rounded. 4- Bristles occur as a row on posterior margin of head. 5- Pronotal ctenidium is absent. 6- Meral rod is present.

Hosts: Rats principally, but these fleas will also readily feed on humans if its natural host dies and humans are available as alternative hosts in domestic housing.

Disease: The Oriental Rat-flea, Xenopsylla cheopis is the main transmitter of the bacterium Yersinia pestis, which causes bubonic plague in humans. This flea species also transmits to humans Rickettsia typhi, the causative bacterium of murine or endemic typhus (contrast with epidemic typhus in relation to Pediculus lice) .

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