Fleas

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Fleas

  • small wingless, obligate blood-feeding insects
  • 95% ectoparasites of mammals, rest of birds 
  • dark brown 1-6mm in length, female larger than male
  • third pair of legs much longer than the others - for jumping 
  • head and first segment of thorax (pronotum) may bear ventral (genal) or posterior (pronotal) rows of dark spines called ctenidia or combs - important in identification 
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Importance

  • feed every day or every other day
  • females require significantly more blood than males 
  • may cause inflammation, pruritis, or anaemia 
  • may act as vectors of bacteria, protozoa, viruses and tape worms
  • most veterinary importance because of cutaneous hypersensitivity reactions 
  • flea allergic dermatitis (FAD) - allergic reaction to the saliva in the flea - if repeatedly exposed in short periods 
  • most important in dogs, cats and poultry - can parasitise humans (VPH)
  • ruminants, horses and pigs do not have their own species of fleas 
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Ctenocephalides felis (cat flea) - Description

  • dark brown/black, wingless insects with laterally compressed bodies 
  • female - head is twice as long as high and pointed anteriorly 
  • male - head is as long as wide but also elongated anteriorly 
  • genal ctenidium consists of 7-8 spines and pronotal ctenidium of about 16 spines
  • first genal spine is as long as the second 
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C. felis - Epidemiology

  • most common species of flea found in domestic cats and dogs in North America and northern Europe 
  • significantly more cats are infected with fleas than dogs 
  • numbers tend to increase around late spring and early autumn - conditions favourable to larval development 
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C. felis - Life Cycle (Eggs)

  • only adults are parasitic, becomes a permenant resident once on host
  • within 24-48 hours of first blood meal the females oviposit - may be laid on ground or on host
  • average lifespan probably about a week
  • rate of oviposition highest early morning and late afternoon (when animals at rest) - flea eggs are concentrated at host resting sites 
  • eggs cannot survive below 50% relative humidity 
  • hatching occurs in 2 days to 2 weeks 
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C. felis - Life Cycle (Larvae)

  • creamy, yellow, larvae are elongate, slender and maggot-like - segments carry ring of bristles 
  • last abdominal segment has hooked anal struts 
  • chewing mouthparts, feed on debris and faeces of adult fleas - contain blood
  • negatively phototactic and positively geotactic - under carpets
  • moults twice 
  • 24C and 75% RH duration of 3 larval stages is about 1 week 
  • mature 3rd stage spins silk cocoon - vertical surface 
  • larvae pupates in cocoon (not killed by insecticides)
  • 24C and 75% RH duration of pupal stage is about 8-9 days 
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C. felis - Life Cycle (adults)

  • emerge from cocoon when fully developed 
  • at cool temperatures may remain in cocoon for 12 months 
  • emergence triggered by mechanical pressure, vibrations or heat 
  • feed as soon as they are on the host can survive several days without feeding (if RH is above 60%)
  • within 36hrs females mate with several males 
  • egg laying begins by 48hrs 
  • within 10 minutes of feeding faeces is produced 
  • faeces dry into reddish black pellets known as 'flea dirt' 
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C. felis - Pathogenesis

  • intermittent flea exposure encourages the development of flea allergy - continued exposure or exposure at an early age seems protective 
  • both immediate and delayed hypersensitivity can be observed, with individuals varying in strength and proportion of each type of sensitivity they express 
  • response to flea bite is a raised, slightly inflamed wheal on the skin associated with mild pruritis  
  • flea-bite allergy - severe clinical signs - hypersensitivity reaction to components of dflea saliva released into the skin during feeding 
    • more common in summer
    • more common on back, ventral abdomen and inner thighs 
    • dog - discrete crusted papules which cause intense pruritis 
    • most intense damage by scratching and biting affected areas - alopecia or moist dermatitis 
    • cat - miliary dermatitis or eczema - skin is covered in small brown crusty papules wihich cause marked pruritis 
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C. felis - Diagnosis/Therapy and Control

  • cats kept in a flea infested environment groom at twice the rate of cats in a flea-free environment 
  • cat may ingest 50% of resident flea population - reduces chance of finding them
  • examination of mouth may be important - trapped fleas
  • environment should be investigated in negative result 
  • species identified by morphological characteristics - eg combs on head
  • can be controlled by insecticides or insect growth regulators (IGRs)
  • prevention of metamorphis to adult stage 
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C. felis - Vectorial Role

  • vectors of a range of virus and bacteria and pathogen transmission - esp as fleas are host-preferential rather than host-specific
  • fleas are intermediate hosts for common tapeworm of dogs and cats Dipylidium caninum 
    • tapeworm eggs are ingested by flea larvae
    • eggs hatch in midgut of flea larva 
    • worm penetrates gut wall and develop in flea body cavity throughout flea development 
    • eventually encapsulated as an infective cysticercoid 
  • C. felis is also an intermediate host of non-pathogenic subcutaneous filaroid nematode of dogs Dipetalonema reconditum 
    • adults ingest while blood feeding 
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Ctenocephalides canis (dog flea)

  • very similar to cat flea
  • female - more rounded on its upper and anterior surface than cat flea, less than twice as long as high
  • has both genal (7-8 spines) and pronotal (16 spines) combs 
  • first spine of genal comb is shorter than the rest 
  • life cycle is similar to C. felis - may take as little as 3 weeks to complete 
  • working dogs in kennels and rural areas or at higher altitudes likes to be infected by C. canis
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Pulex irritans (human flea)

  • neither genal nor pronotal combs 
  • outer margin of head is smoothly rounded and there is a pair of eyes
  • life cyle is typical - egg, three larval stages, pupa and adult 
  • P. irritans can infest cats, dogs and many other domestic animals - most common on pigs
  • may act as a vector for plague pathogen Yersinia pestis  
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Ceratophyllus gallinae (chicken flea)

  • eyes present, pronotal comb with >24 teeth, no genal comb
  • typical life cycle
  • chicken fleas spend most of their time in nest of host, only move on to birds to feed for short periods
  • large numbers may occur in nests of passerine birds - complete life cycle in nest - if nest reused will attach to new hosts 
  • not host-specific, will feed readily on humans and domestic pets 
  • in wild birds, reproduction and feeding -synchronised with breeding
  • in domestic chickens reproduction may occur all year round 
  • commonest flea of domestic poultry - not vector of disease 
  • symptoms - restlessness and scratching - bites may be visible on the skin, allergic dermatitis may be seen 
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