When talking about parasites of the skin, we refer mainly to fleas, lice, mites, nuisance & biting flies, myiasis-producing flies such as warble flies and blowflies. What type of animals are these? Ie., what is their phylum?
These are all arthropods, from the phylum of Arthropoda.
They include insects, arachnids & crustaceans, and are characterised by having an exoskeleton, segmented bodies and jointed legs. Both the number of body segments and appendages differ between insects and arachnids. Many also have wings to fly, such as flies.
Fleas are INSECTS from the Siphonaptera order.
The main animal species with which we are concerned begin with Ctenocephalides or Ceratophyllus.
What are the most important flea species?
Ctenocephalides felis - cat flea
Ctenocephalides canis - dog flea
Ceratophyllus gallinae - poulty flea
Pulex irritans - human flea
In general, how would you characterise the appearance of a flea?
Laterally compressed to fit in-between hairs
Long hind legs for jumping - three pairs of legs (see photo)
Chitinous combs on chin (genal) & behind head (pronotal)
They are very small, only 2-3 mm long
Mouthparts for piercing skin & sucking blood
Given that there are at least three types of animal fleas you will see in practice (cat flea, dog flea, poultry flea), how can you distinguish between them morphologically?
Under a microscope you look at the rows of chitinous spines on their heads. These spines are called combs or ctenidia.
The combs or ctenidia are either ventral (genal) or posterior (pronotal).
NB The human flea, Pulex irritans, does not have combs or ctenidia. It is characterised by a naked rounded head anteriorly and it might have some hairs, not to be mistaken for combs/ctenidia.
Ctenocephalides felis (see picture) - has both genal (ventral on head, but have mouthparts) & pronotal (anterior to head) combs. The first genal comb is equal in the size to the next spine. Also, the head length is 2x the height, giving it an elongated appearance.
C. canis - has both the genal & pronotal combs but doesn't have an elongated head like C. felis.
Ceratophyllus gallinae - only pronotal comb.
How does the flea cause damage & irritation?
The flea is a blood-sucker only as an adult and can lead to anaemia in serious cases.
It can cause irritation and hypersensitivity in dogs & cats through its saliva: Flea Allergy Dermatitis (FAD)
It is an intermediate host for tapeworm Dipylidium.
It is a vector for several diseases: bubonic plague (humans), Parvovirus (cats) & myxomatosis (rabbits)
What is the most common flea found on dogs & cats?
What is a wildlife flea that can be found on rabbits & is also known as the rabbit flea?
Most parasites of the skin are in the phylum Anthropoda. Some speces are Insecta class (six legs) & some are Arachnida (eight legs).
Which speces are Insecta? Which are Arachnida?
What is special about the life-cycle of a flea?
Once an adult, the flea spends most of its life ON ONE HOST.
That is about 7-10 days, depending on grooming by the host.
Where are most adult fleas found in a household?
95% of fleas in a household are eggs, larvae, pupae & newly formed "unfed fleas" in the environment.
Only 5% are found on the host animal.
This is important in treatment.
What is the basic life cycle of the flea, using the adult Ctenocephalides felis as a starting point?
Life cycle is about 3-4 weeks in summer from egg to adult.
Adult flea uses light intensity, warmth & CO2 to locate host.
Once there, it takes frequent blood meals.
It produces lots of faeces, aka "flea dirt".
After 1-2 days, it starts laying eggs - about 15 per day. Flea eggs drop to ground within hours.
After 1-6 days, eggs hatch into yellowish-white larvae, 2-5 mm long & covered with bristles with anal struts, mouthparts and bristles. These feed on flea dirt, skin flakes & organic debris in the environment.
Two moults in 1-7 weeks - controlled by hormones
Pupates - silken cocoon (5mm) usually seen covered in debris. Pupal window can delay hatching of adult by 140 days. Otherwise:
After 6-7 days, adult emerges.
What stage of the flea life cycle is targeted by chemical anti-flea treatments?
Larval stage, which includes two moults over up to seven weeks before pupation. The goal is to arrest the larval stage & prevent pupation.
Insect Juvenile Hormone control embryonic development. If IJH is at a very high concentration above a "critical level", the larvae will NOT PUPATE.
Synthetic IJH called Methoprene can be sprayed on larvae to elevate the concentration, preventing it from pupating.
Insect Growth Regulators (IGRs) also disrupt insect development by targeting IJH.
What colour are flea eggs?
What environmental conditions can kill flea larvae?
Dessication/dryness (they need high humidity) & near-freezing temperatures.
How does the life cycle of Spilopsyllus differ from those of other major flea speces?
Spilopsyllus, the wildlife & rabbit flea, spends most of its adult life OFF THE HOST. It takes only occasional blood meals from the rabbits while living most of the time in their burrows.
When the rabbits are about to give birth, they attach to the rabbit's ears and take many blood meals, leaving lots of flea dirt. When the young are born, they move onto their fur, where they mate & produce eggs.
The eggs drop off the baby rabbits into the nest, where they hatch into larvae & pupate. They emerge as adults about the same time as the rabbits are ready to leave the nest.
What is the antibody of the immune system released to combat flea allergic dermatitis (FAD)?
In diagnosing FAD, what would you do if you can't find any adult fleas but the animal is showing clinical signs, such as pruirtic papules & excessive grooming?
Look for flea dirt by combing animal over white paper.
If you see something that resembles flea dirt, put it onto most blotting paper. A spreading reddish stain should become evident, indicating the flea dirt contains blood from the flea's blood meals.
What class of anthropoda are lice?
How does the morphology of lice differ most from fleas?
Lice are flattened dorso-ventrally to lie flat against the skin of the host, while fleas are flattened laterally (narrow) so they can jump around between hairs of the host.
How are lice classified?
Blood-sucking vs. Chewing
What are the morphological differences between blood-sucking and chewing lice?
Blood-sucking lice have large leg claws & narrow heads.
Chewing lice have tiny legs and broad heads.
What is the proper name of a lice infestation?
What is different about pediculosis in relation to the host compared with FAD caused by the flea, Ctenocephalides felis?
Pediculosis is a host-specific condition caused by permanent lice.
FAD isn't caused usually by host-specific flea, since C. felis infects both cats and dogs indiscriminately.
What is the damage to the host caused by pediculosis and lice?
Anaemia, hair loss, irritation, self-injury.
The dog-chewing lice, Trichodectes, are intermediate hosts for the tapeworm Dipylidium (as are fleas).
What are the target hosts for chewing (biting) lice and blood-sucking lice?
Chewing/biting lice target both mammals & birds, while blood-sucking lice only target mammals.
What do chewing/biting lice feed on? How does their morphology reflect their diet?
Epithelial scales, scabs & feathers. As such they have rasping mouth parts but no piercing proboscis.
How does the morphology of blood-sucking lice differ from chewing/biting lice?
Since they such blood, they have a piercing proboscis, while the chewing/biting lice has rasping mouth parts for chewing skin debris.
What are the KEY DIFFERENCES between the lice life cycle and the flea life cycle?
1. The louse spends its reproductive AND adult life cycle -- ie., its entire life -- on its host, while the flea spends only its adult life on the host; its eggs, larvae & pupae are in the environment.
The louse spends about 2-3 weeks on a host while a flea spends about 7-10 days on a host.
2. Louse eggs (nits) stick to host hairs or feathers; flea eggs drop to ground.
3. The louse does NOT undergo larval or pupal stages like the flea. Louse eggs hatch into nyphms, which moult three times into adults.
How do lice infect their hosts? How does this differ from fleas?
Lice infection is via close contact between animals. Fleas jump from the environment into host pelage.
During which season are you most likely to see pediculosis in farm animals?
Winter, when coats are thickest.