25: Lice Flashcards
What is the only louse that isn’t host-specific?
Bovicola in sheep and goats
What is the only louse that isn’t permanent?
The human body louse
What are the two methods by which lice can be transmitted?
Mother to young, or direct contact
Why does louse population increase in winter?
Like warm and dark
Why does lice population decrease with age?
Protective immunity
What do adult lice look like?
Have head, thorax, abdomen, 3 pairs of legs, DV flattened, wingless
How long is the lice life cycle?
3-4 weeks
How long does the louse egg take to hatch?
One week
Where are louse eggs found?
Single and cemented to the hair
Which part of the egg does the nymph hatch from?
From the operculum (this differentiates them from other parasites)
What do nymphs look like?
Like the adult, but are sexually immature
What are the two groups of lice?
Chewing/biting (mallophaga, with broad blunt head) and sucking (siphunculata, with narrow pointed head)
Why do you need to know if the louse is chewing or sucking?
Because some drugs act systemically and are ingested by the sucking lice but won’t affect the chewing louse
What type of reaction do sucking lice cause?
Antigenic saliva with enzymes and anti-coagulants so more excoriation and more type I/IV hypersensitivity
What type of reaction do chewing lice cause?
Chronic, exfoliatory, dandruff
What colour do sucking lice go when fed?
Blue (usually brown)
What are some clinical signs of lice?
Immediate and delayed hypersensitivity, pruritis, licking, sucking, biting, alopecia, wool damage, tags of wool, secondary infections, exfoliative dermatitis, anaemia
Which type of cattle mainly get mixed lice infections?
Housed cattle in winter
What degree of production loss can lice infections in housed cattle cause?
10%
Why did lice infection in sheep used to be rare?
Because of sheep scab dipping
After introducing infected sheep, how long until clinical signs occur?
Tags and rash by 6 weeks
After introducing infected sheep, how long until all are infected?
6 months
How do you tell the difference between sheep scab and lice in sheep?
Scab is rapid whereas lice is slow, lice has poor BCS and sheep scab is good, in scab they are pruritic with scabs and wool pulled out whereas with lice the skin is irritated, damaged and scaly.
What are the only type of lice pigs get?
Sucking
What can happen in debilitated animals?
Large numbers can build up and there may be marked hypersensitivity
What kind of lice do birds get?
Chewing
