Introduction to Ectoparasites
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What type of skin disease do ectoparasites often cause?
What is pruritus?
What type of ectoparasite causes 'worry'?
What is the name of the condition where ectoparasite larvae invade the body of an animal and cause tissue destruction?
What disease can some obligate blood feeder ectoparasites cause in animals?
What is the difference between mechanical and biological vector disease transmission?
Mechanical transmission takes place when a vector simply carries pathogenic microorganisms on (or in) their body and transfers them to the host. There is no development of the parasite life cycle within the vector. Whereas biological transmission involves the multiplication and growth of a disease-causing agent inside the vectors body.
What are the two classes of ectoparasites? And what features define each class?
Insecta and arachnida. Insects have a head, thorax and abdomen, and 6 legs. Arachnids have a fused head and thorax and abdomen.
What type of ectoparasites fall into each class?
- Insecta - flies, lice, fleas
- Arachnida - mites and ticks
What type of mite causes sheep scab?
What is the proper term for 'sheep scab'?
Ovine Psoroptic mange
True or false: sheep scab is highly contagious?
True or false: sheep scab is a notifiable disease in Scotland?
The pathogenesis of sheep scab is cause by a ... reaction to mite antigens (present in mite faeces)?
allergic, type I hypersensitivity
What does the reaction to the mite antigens generate? What does this form on the sheep?
Inflammation and serous exudate. The exudate dries to form a scab surrounded by a moist border and inflamed skin.
Where on the sheep are the mites active?
The mites are active in the scab border so as the population expands the scabs spread
What are the clinical signs of sheep scab?
Lighter wool is first visible sign, usually over shoulders. Sheep are restless, rub and scratch. Wool becomes ragged/stained. Large areas of wool loss along with open bleeding wounds and thickened skin.
Where would you take skin scrapings from to confirm it was sheep scab?
From the edge of the lesion
Describe the difference between P. ovis and lice
- P. ovis - 8 legs, rounded body, pointed head
- Lice - 6 legs, elongated abdomen, definite rounded head
What family of flies cause fly worry?
Why type of flies are part of the muscidae family?
Musca (house fly), Hydrotea (head fly) and Stomoxys (stable fly)
What type of ectoparasite causes worry/irritation in sheep?
What do musca (house) flies feed on?
Secretions from the eyes, nose and mouth, as well as blood left in wounds caused by other flies
How does 'worry' affect production animals?
Animals become so distressed by the presence of flies swarming around them that they will eat less and therefore have a reduced weight gain, leading to production losses. Animals may also move suddenly to try and escape the flies, causing self trauma.
What is the difference between obligate and facultative myiasis?
Obligate myiasis is when the parasitic development of the larvae on a living host is a necessary stage within the life cycle. Whereas facultative is opportunistic - they have the ability to exploit living tissue but this is not a required stage in the life cycle.
What can myiasis result in?
- Serious tissue damage often accompanied by putrid discharge
- Loss of tissue function
- Secondary infections
All ostridae flies cause obligate/facultative myiasis?
What are the three types of flies whose larvae are parasitic and host specific?
- Hypoderma (warble flies) Oestrus (nasal bots)
- Gastrophilus (bot flies)
What type of fly causes facultative myiasis?
What species are affected by blow flies?
Sheep mainly, but also rabbits
What condition is associated with blowflies?
Describe the difference between the role of primary and secondary flies during blowfly strike
Primary flies can initiate a strike on living sheep whereas secondary flies cannot initiate a strike but can only attack areas of existing strike or damage
Describe the life cycle of a blowfly
- Eggs are laid on fleece. Flies are attracted to areas that are wet, contaminated with faeces or necrotic. Eggs hatch within 10-12 hours.
- New larvae quickly grow, develop oral hooks and produce enzymes.
- The larvae drop to the ground, burrow into the soil and pupate.
- Adult flies emerge from pupa and have a lifespan of ~30 days.
- The whole life cycle last for 3-4 weeks.
What can secondary bacterial infection of a blowfly strike lesion lead to?
What areas of the body do you get blowfly strike on?
Body, breech, penile sheath, tail, poll
What effect do blowflies have on sheep productivity?
- Downgrading wool
- Reducing reproductive potential and lamb crops
- Increasing time to market for lambs
- Reducing leather quality
Give examples of ectoparasites that are obligate blood feeders
Ticks, Dermanyssus gallinae (poultry mite), Gad flies, keds, sucking lice
What type of disease do the following ectoparasites transmit? a) Midges b) Sandflies c) Tetse flies d) Fleas
- a) Blue tongue, Schmallenberg
- b) Leishmania
- c) Trypanosomad) Myxomatosis virus, Yersinia pestis (plague), Dipylidium canium
What genus is the major european species of tick?
What is the latin name for the a) european sheep tick b) british dog tick c) hedgehog tick
- a) Ixodes ricinusb) Ixodes canisuga
- c) Ixodes hexagonus
Why is Ixodes ricinus a great vector?
It is a great vector because all stages are obligate blood feeders and feed on multiple hosts in the life cycle
Describe the life cycle of Ixodes ricinus
Adults mate on the host and the female completes a large blood meal over 14 days. She then drops to the ground and converts the blood meal into eggs. Eggs hatch into larvae in the autumn. The following spring the larvae actively quest for a host. They attach and feed for 6 days. After, they drop to the ground and moult to a nymph. Nymphs overwinter and feed the next spring.
What are the main symptoms of secondary infection of Ixodes ricinus lesions caused by a) Blow fly strike b) Tick pyaemia c) Red water d) Tick-borne fever e) Louping ill f) Lyme disease
- a) Tissue destruction/anorexia
- b) Septicaemia/abscesses/arthritis
- c) Fever/anaemia/haemoglobinuria
- d) Fever/abortion
- e) Encephalitis/abnormal gait/death
- f) Persistant fever/arthritis/lameness
List reasons why ectoparasites can be difficult to control
- Resistance to drugs has emerged
- Proliferation of ectoparasite populations is prodigious
- Large reservoir of host spa
- Infestations can be highly contagious
- Huge populations in the environment - some can be localised and targeted (e.g. fleas) but others are more difficult (ticks, flies)
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