Fleas

INSECTA PARASITES

Siphonaptera Introduction

Fleas are wingless insects that are laterally flattened so can move rapidly through hair and fur. Their hind legs are adapted for jumping. They are of major significance to veterinary practice and will be seen almost on a daily basis at most general practices.

Adult fleas are blood sucking ectoparasites which can cause pruritis, annoyance and anaemia if present in large numbers. Flea allergic dermatitis can also occur where the animal becomes allergic to the antigens in the flea saliva triggering a hypersensitivity reaction when the flea bites.

Fleas can also act as intermediate hosts and vectors.

The terms ctenidia and combs can be used interchangably for spines on the head/thorax. Spines on the cheeks are referred to as genal and spines on the thorax are called pronotal combs. The presence and location of the chitinous spines are important in differentiating between the different flea species. The chitinous anal struts are also used for identification and help the flea larvae with vigorous motility.

Species of Veterinary Importance

Ctenocephalides felis

• Most common flea on cats and dogs

• Most important flea of veterinary medicine

• Commonly called the 'cat flea'

• Can bite humans and other animals

• Both genal and pronotal commbs present

• Similar length genal combs

• Sloping nose

Ctenocephalides canis

• Not very common

• Commonly called the 'dog flea'

• Host specific

• Both genal and pronotal commbs present

• Irregular length genal spines

• Rounded nose

Ceratophyllus gallinae

• Commonly called the 'poultry flea'

• Bites humans and other animals

• Pronotal combs only

Pulex irritans

• Commonly called the 'human flea'

• No combs

• Head rounded anteiorly

Spilopsyllus cuniculi

• Commonly called the 'rabbit flea'

• Both genal and pronotal combs present

• Genal comb obviously oblique

• Behaviour synchronised with the reproductive cycle of the rabbit
  • Adults spend most of their time off the host taking occasional blood feeds
  • Shortly before the doe gives birth the adult fleas attach to the ears of the rabbit and feed producing a lot of faeces
  • After parturition the adult fleas move onto the kittens where they feed, mate and lay eggs
  • The new adult fleas emerge from the pupa before the kittens leave the nest

Other important flea species

• Fleas of wildlife can sometimes infect domestic animals

• Other species of importance are found in America
  • E.g. Tunga penetrans or 'Jiggers' which burrows into the skin of man (also called the 'sand flea' or 'chigoe flea')

• Nosopsyllus fasciatus
  • Rodents
  • 18-20 spines in pronotal ctenidium

• Echisnophaga gallinacea
  • Poultry
  • Frons (forehead) angled anteriorly
  • Also called the 'sticktight' flea

• Archaeopsylla erinacei
  • Hedgehogs
  • 1-3 short spines on genal ctendium
  • 1 short spine on pronotal ctenidium

Life-Cycle

In order to advise owners of adequate treatments to control fleas on their animals, the life cycle of the flea must be understood

• The time for the egg to develop into the adult flea takes 3-4 weeks in summer

• The life cycle can be faster or slower depending on temperature

1. The adult

• Uses changes in light intensity, warmth and carbon dioxide to locate host

• Once on host, the flea will usually remain
  • With animals in close contact there may be a small degree of transfer between hosts
  • The majority of adult fleas are aquired from the environment

• The adult flea takes frequent blood meals

• Flea dirt (faeces) are produced in large quantities

• The life span of the flea is determined by the grooming activity of the host
  • Usually the adult flea lives for between 7 and 10 days

2. Eggs

• The adults lay eggs 1-2 days after locating a host

• Approximately 15 eggs are layed in the pelage (coat) per day

• Eggs are ivory white and oval, approxiamtely 0.5mm long

• The eggs drop to the ground within hours
  • In reality this usually happens when the animal jumps of the sofa or makes sudden movements. Flea eggs will cluster in hot spots around the house particularly in places the animal often rests in and this should be considered when control methods are thought about.

3. Larvae

• Larvae are small, about 2-5mm in length

• Larvae are yellow/white (look like maggots) and are covered in bristles

• Chitinous mouthparts and anal struts (useful for identification)

• Larvae are negatively phototropic so try to move away from light sources
  • E.g. under furniture, into thick mats or carpet

• Larvae feed on skin debris from other animals, flea dirt and other organic debris

• High humidity is needed to survive

• Freezing temperatures will kill larvae

4. Pupae

• The larvae pupate forming pupae of 5mm in length

• Silken cocoon surrounds pupae
  • Slightly sticky so small particles adhere to it
  • Camoflaged in the environment

• Methoprene the juvenile development hormone coordinates the growth of the immature stages
  • Activates genetic switches
  • Determines the sequence of tissue and organ development

• Newly emerged adults do not leave the cocoon straight away
  • The pupal window is the time that it takes for the adult to emerge
  • Temperature determines when the adult fleas emerge
  • Some fleas may wait several months before emerging

• Newly emerged unfed adults can survive days without feeding but once they have fed, if they fall of the host they can only survive hours

Links

Internal

• Flea allergic dermatitis (FAD)

• Fleas acts as intermediate hosts for Dipylidium tapeworms

• Fleas act as vectors for myxomatosis in rabbits

External

• Wikipedia- Fleas