Pruritus Flashcards
(54 cards)
1
Q
Pruritus definition
A
- unpleasant sensation that provokes the desire to scratch
- C-poymodal receptor units with C axons localised around hair follicle
- triggered by the release of inflammatory mediators
2
Q
In pruritus, the local release of vasoactive substances stimulates…
A
- histamine
- eicosanoids
- serotonin
- kallikrein
- bradykinin
3
Q
Broad causes of pruritus
A
- ectoparasites
- bacterial
- fungal
- hypersensitivity
- drug reactions
4
Q
Types of mites in horses
A
- Chorioptes equi
- Trombicula autunnalis
- Psoroptes equi
- Dermanyssus gallinae
5
Q
Chorioptes equi (lesion location)
A
- distal limb +++
- groin/abdomen
6
Q
Chorioptes equi (season)
A
- winter
(- asymptomatic horses as carriers)
6
Q
Chorioptes equi (clinical signs)
A
- rubbing distal limbs
- biting
- stamping
- exudation
- matting of the hair
- alopecia
- scabs
- secondary bacterial infections
6
Q
Chorioptes equi (type of horse affected)
A
- draft breeds with dense feathering
7
Q
Trombicula autunnalis (lesion location)
A
- head and legs (+++)
8
Q
Trombicula autunnalis (season)
A
- autumn/winter
(- contaminated hay/straw/bedding)
9
Q
Trombicula autunnalis (clinical signs)
A
- biting
- stamping
- small papule on the pastern and/or nose
9
Q
Trombicula autunnalis (type of horse affected)
A
- all
- dense feathering most likely
10
Q
Psoroptes equi (lesion location)
A
- head
- tail
- ears
10
Q
Psoroptes equi (season)
A
- all year round
11
Q
Psoroptes equi (type of horse affected)
A
- all horses
12
Q
Dermanyssus gallinae (lesion location)
A
- legs
- face
- abdomen
12
Q
Dermanyssus gallinae (season)
A
- contact with poultry
12
Q
Psoroptes equi (clinical signs)
A
- tail rubbing
- broken tail hairs
- scaling of ears
- ear discharge
13
Q
Dermanyssus gallinae (type of horse affected)
A
- all horses
13
Q
Dermanyssus gallinae (clinical signs)
A
- small orange/red mite
- biting/stamping legs
- small papule/crusts
14
Q
‘Causes’ of constant reinfection of mites
A
- wood partitions
- lots of manure closeby
- lack of ventilation
- usually live in straw
15
Q
How to differentiate between the mites on microscopy (+ other facts)
A
- Trombicula = chubby, round oval mite, legs not well differentiated
- Chorioptes = articulated legs
- Psoroptes = often in Europe, not as common in the UK
16
Q
Clinical signs of lice infestation
A
- ‘moth eaten’ ‘snowflake’ coat appearance
- severe pruritus
- self-mutilating
- biting
- rubbing
- alopecia
- excoriation
- serum exudation
17
Q
Areas of the horse commonly affected by lice
A
- mane
- base of tail
- dorsum
18
Seasonality of lice (and potential cause)
- more common in winter months
- crowded barns
19
Characteristics of biting lice
- small
- yellowish
- broad flatted heads
- feeds on scales
20
Characteristics of sucking lice
- dark colour
- blood sucking
- narrow head
- slightly bigger cf biting lice
21
Control measures for Chorioptes equi
- clip feather/hair (& burn the hair)
- highly infectious so tx of all horses on the property may be necessary
- disinfect stables and allow them to rest (~70d ideally)
- extensive disinfection of tack
- regular tx in affected horses?
22
Medical tx of Chorioptes equi
- doramectin injection (SC/IM single or 2 injections 2w apart)
- 0.25% Fipronil spray (daily application for 1w, then weekly for 4w)
- 5% lime sulphur solution (applied weekly for 1m)
23
Control measures for Trombicula autunnalis
- remove straw bedding
- avoid infected tall or grass or woods
24
Medical tx of Trombicula autunnalis
- normally self-limiting but might need some local tx
- lime sulphur solution
- pyrethrin spray (daily application for 1w, then weekly for 4w)
- 0.25% Fipronil spray (daily application for 1w, then weekly for 4w)
- if severe pruritus: short term steroid therapy might be required to avoid self-trauma
25
Control measures for Psoroptes equi
- remove organic debris from stables
- make sure the stable is dry and well ventilated
- disinfection of stable is required and resting period ~70d
- disinfect tack
26
Medical tx of Psoroptes equi
- otitis is responsive to oral macrocytic lactones (ivermectin or moxidectin)
- lime sulphur solution (every week for 1m)
- pyrethrin spray (every week for 1m)
27
Control measures for lice
- clean stable and disinfect with diluted bleach (10%), rinse and let it dry
- tx of in-contact horses may be required
- wash tack (esp rugs, saddle pads, etc): 60C and/or permethrin application
28
Medical tx of lice
- permethrin pour-on
- 0.25% Fipronil spray
- 1% Se sulphide shampoo q10d (3x)
29
Oxyuris equi characteristics
- pinworm
- nematode
- females large, grey (>10cm) with long pointed tail
- males smaller (<1cm)
30
Clinical signs of pinworms
- rubbing tail
- broken hair on tail head
- abrasions on perineum
30
Why do pinworms cause pruritus?
- live attached to caecum and colon mucosa
- once the female is fertilised, migrates to anus to lay eggs -> intense pruritus
31
What horses are pinworms more common in?
- young horses never treated with ivermectin
32
Tx of pinworm
- oral pyrantel (or ivermectin)
32
Diagnosis of pinworm
- acetate tape on anus, leave for a min, can see round eggs on microscopy
33
Sweet itch
= culicoides hypersensitivty
34
Seasonal presentation of sweet itch
- spring-early autumn
34
What type of HS reaction does culicoides saliva cause?
- type I: immediate and late phase response
- type IV: delayed response
34
What breeds potentially have an increased risk of sweet itch? (+ why)
- Icelandic
- German shire horses
- Welsh ponies
- Shetlands
- Connemara
(- lack of evolution between breeds affected and the saliva of the insects - never been exposed but due to climate change and rise in temperature it means culicoides are more common)
35
When does sweet itch develop?
- early in life (3-4y), but worsens with age (each time/year it'll worsen)
36
Areas where sweet itch is worse
- wet areas
- riverside
- marshes
37
What areas of the horse are affected by sweet itch?
- dorsal +/- ventral distribution
38
Clinical signs of sweet itch
- rubbing against object
- chewing dorsum
- crusted papules (main, rump, base of tail that extend tp face, pinna, neck)
- chronic cases: excoriation, alopecia, lignification, secondary bacterial infections (superficial folliculitis)
39
Sweet itch management
- mosquitos feed from dusk to dawn: stable overnight with fly-screen
- clean water troughs regularly
- keep fly-rug cover while on pasture from early spring into autumn (some horses may be allergic to other insect species)
- keep away from water sources
- reduce decaying vegetation and manure accumulation
- insecticide spray system in barn
- stall window fans (20") (midges are poor fliers)
- permethrin pour-on / other fly spray
40
Medical tx for sweet itch
- steroids during flares
- insol vaccine (off-licence, given before midge season (feb) 2w apart
- immunotherapy with IL-5 blockers (3 SC injections at monthly intervals, followed by annual booster) (blocks degranulation of mast cells)
41
Theoretical explanation for insol use for sweet itch
- dampens down the immune system so its ready for exposure to the saliva
- works due to immunological mimicking
- might be similar antigens in the ringworm vaccine and in the ringworm DNA code that are able to trigger a dampening down reaction in the immune system so there's a lesser reaction to culicoides saliva
42
Food allergy characteristics
- face, neck, trunk lesions, angioedema and urticaria common
- no age, sex or breed predisposition
- alfalfa, barley, beet pulp, bran, clover
- feed additives and supplements
- type I HS
- more likely to see in those fed commercial diets or high protein feeds
43
Contact dermatitis characteristics
- localised in areas in contact with tack predominantly
- erythema, oedema, oozing leading to alopecia and lichenification
- pasture or bedding: mouth, ventral abdomen
- type IV HS
