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| | Myiasis is the parasitism of living animals by dipteran larvae. Myiasis can be obligatory or facultative (optional) and is described as cutaneous, nasal or somatic. | | Myiasis is the parasitism of living animals by dipteran larvae. Myiasis can be obligatory or facultative (optional) and is described as cutaneous, nasal or somatic. |
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| | + | <big> |
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| − | ==Oestridae==
| + | '''[[Oestridae|''Oestridae'']] |
| − | [[Image:Warble flies.jpg|thumb|right|150px|Warble Fly - Geo. H. Carpenter, Cambridge University Press 1913 - Wikimedia Commons]] | |
| − | *The larvae of ''Oestridae spp.'' are '''obligatory''' parasites
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| − | *The three important species of veterinary interest
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| − | **''Hypoderma''
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| − | **''Oestrus''
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| − | **''Gasterophilus''
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| − | ===''Hypoderma spp.''===
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| − | *Also known as warble flies
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| − | *Important cattle parasites
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| − | **Also parasitise horses, small ruminants and sometimes humans
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| − |
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| − | *The two main species in cattle are
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| − | **''H. bovis''
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| − | **''H. lineatum''
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| − | *''H. diana'' parasitises deer
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| − | *Infestation is largely confined to the Northern Hemisphere
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| − | '''Recognition'''
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| − | *Large 13-15mm long
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| − | *Similar to bumble bees in appearance
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| − | **Yellow abdomen
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| − | **Band of black hairs
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| − | *1 pair of wings
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| − | '''Life cycle'''
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| − | *Adult flies emerge on warm, sunny days between '''June and August'''
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| − |
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| − | *White eggs are laid around the belly and legs of the animal
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| − | **Eggs are attached to hairs by cement and a small terminal clasp
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| − | **''H. lineatum'' lays a whole row of eggs as it approaches the animal stealthily
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| − | **''H. bovis'' only deposits a single egg before the animal runs away ('''gadding''') as it makes a loud buzzing noise
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| − |
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| − | *The adult lives for 3 weeks
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| − | *Females can lay several hundred eggs in their life
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| − |
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| − | *A few days after eggs are laid, larvae emerge and crawl down the hairs into the hair follicles
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| − |
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| − | *Larvae penetrate the skin through wounds made by [[Biting Flies|biting flies]]
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| − |
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| − | *Larvae migrate through the subcutaneous tissue towards the diaphragm
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| − | **Enzymatic secretions and mouth hooks aid larval migration
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| − |
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| − | *After 3 months larvae reach '''winter resting sites''' where they remain from November to February/March whilst moulting to the L2 stage. These sites are different between the 2 species
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| − | **Epidural fat in the spinal canal for ''H. bovis''
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| − | **Wall of the [[Oesophagus - Anatomy & Physiology|oesophagus]] for ''H. lineatum''
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| − |
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| − | *Larvae then migrate back to the subcutis along the midline of the back where they bore a breathing hole through the skin and moult to the L3 stage
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| − | **Larvae are palpable as distinct swellings called '''warbles'''
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| − |
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| − | *L3 larvae emerge after 4-10 weeks where they fall to the ground and pupate under loose vegetation
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| − |
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| − | *Adult flies emerge from the pupa after 1 month where they copulate, lay eggs and die within 2 weeks
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| − | *''H. lineatum'' are on the wing 6-8 weeks before ''H. bovis''
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| − | *There is only '''1 generation''' of warble flies per year
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| − | '''Pathogenesis'''
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| − | *Causes [[Muscles Inflammatory - Pathology#Arthropods|myositis]]
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| − |
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| − | *Production losses
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| − | **Condemnation and down-grading of hides
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| − | **Reduced milk yield and reduced weight gain
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| − | **Injury from stock panic
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| − | **Trimmed meat losses from ''H. lineatum''
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| − | ***'Butcher's Jelly' around warbles which is green due to mass [[Eosinophils - WikiBlood|eosinophil]] attraction
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| − | *Paraplegia resulting from
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| − | **Toxin release
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| − | **Pressure on the spinal cord (''H. bovis'')
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| − | **Bloat from pressure on the [[Oesophagus - Anatomy & Physiology|oesophageal wall]] (''H. lineatum'')
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| − |
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| − |
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| − | '''Control'''
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| − | *Total eradication should be aimed for
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| − |
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| − | *Old methods include popping out warbles
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| − | **But this could lead to anaphylactic shock
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| − | *[[Ectoparasiticides]]
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| − | **Systemic organophosphorus [[Ectoparasiticides|insecticides]] in pour-on formula
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| − | **Avermectins and milbemycins in pour-on and injectible formulations
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| − | *Timing is crucial for treatment
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| − | **Larvae residing in winter resting sites, if killed, can lead to bloat and paraplegia
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| − | **It is safe to treat in the '''autumn''' before larvae reach their winter resting sites and in the '''spring''' when the warbles have migrated to the midline of the back
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| − | **Ivermectin can be given at any time without risking host infection as larval antigen is released much slower
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| − | '''Legislation in the UK'''
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| − | *'Warble Fly Order 1978' requires all clinically affected animals to be treated
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| − | *Notifiable disease
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| − | *'Warble Fly Infected Area Order 1983'
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| − | *For more information on the warble fly orders, see [http://www.defra.gov.uk/animalh/diseases/notifiable/brucellosis/surveillance.htm| here]
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| − | ===''Oestrus ovis''===
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| − | *Also known as the sheep nasal bot fly
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| − | *Larvae parasitise the nasal chambers of sheep and goats
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| − | *Found in most sheep rearing areas of the world
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| − | '''Recognition'''
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| − | *13-15mm long
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| − | *Grey colouring
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| − | *Black spots on abdomen
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| − | *Clear wings
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| − | *Larvae have distinct black bands on each body segment
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| − |
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| − | '''Life cycle'''
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| − | *Larvae are squirted into the nostrils of sheep in a jet of liquid by the adult fly
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| − |
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| − | *The larvae crawl caudally into the nasal cavity and feed on the nasal mucosa and mature before returning to the nostrils
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| − |
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| − | *Larval development takes up to 2 months
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| − | **Larvae can overwinter in the nasal cavity if deposited late in the summer
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| − | *Once the larvae have developed they are sneezed out and pupate on the ground
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| − | *The adult fly emerges 1 months later
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| − | *Adult flies only live for 2-3 weeks
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| − | '''Pathogenesis'''
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| − | *Adult flies cause annoyance
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| − | **Interrupts feeding
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| − | **Leads to a decreased weight gain
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| − | *Larvae cause nasal irritation, nasal discharge and sneezing
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| − | **Irritate the nasal mucosa with oral hooks and spines causing a viscous exudate to be produced from which they feed
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| − | **Heavy infestations lead to erosion of the bones in the sinuses (turbinate bones)
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| − | **Penetration of the brain leads to '''false gid''' (high stepping gait and incoordination)
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| − | *[[Respiratory Parasitic Infections - Pathology#Oestrus ovis|Pathology in the nasal cavity]]
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| − | '''Control'''
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| − | *Systemic [[Ectoparasiticides|insecticides]] can be used in heavy infestations
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| − | *In warmer countries, strategic prophylactic treatment can be used
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| − | ===''Gasterophilus spp.''===
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| − | [[Image:Horse Bot Fly.jpg|thumb|right|150px|Horse Bot Fly - Dennis Ray - Wikimedia Commons]]
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| − | *Also known as the horse bot fly
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| − | *Obligate parasites of equids
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| − | *Spend most of life cycle in the equine stomach
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| − | **Of little pathogenic significance
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| − | *Three important species (in the UK)
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| − | **''G. intestinalis'' which is the most common
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| − | **''G. nasalis''
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| − | **''G. haemorrhoidalis'' which is rare
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| − | *Two other important veterinary species
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| − | **''G. nigricornis''
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| − | **''G. inermis''
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| − | '''Recognition'''
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| − | *Medium to large flies at 10-20mm long
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| − | *Look similar to drone bumble bees
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| − | **Body covered with dense yellow hair
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| − | **Dark coloured hairs produce a banding pattern
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| − |
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| − | *Clear wings with brown patches
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| − |
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| − |
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| − | '''Life cycle'''
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| − | *Adults are most active in '''late summer'''
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| − | *Eggs are laid on the body and hatch spontaneously or are stimulated to hatch through an increase in warmth and moisture from the animal self-grooming. They are laid in different areas according to species
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| − | **''G. intestinalis'' eggs are laid in the hair of the shoulders and fore legs
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| − | **''G. nasalis'' eggs are laid in the intermandibular area
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| − | **''G. haemorrhoidalis'' eggs are laid around the lips
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| − | *Creamy-white eggs
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| − | *1-2mm in length
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| − | *Larvae crawl into the mouth and penetrate the tissues of the tongue and buccal mucosa
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| − |
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| − | *Larvae then emerge after a couple of weeks and are swallowed
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| − |
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| − | *Larvae pass into the [[Forestomach - Anatomy & Physiology|stomach]] and attach to the gastric mucosa
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| − | **Larvae are now known as '''bots'''
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| − |
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| − | *Each species attaches to a specific part of the stomach
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| − | **''G. intestinalis'' attaches to the cardiac region
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| − | **''G. nasalis'' attaches to the pylorus
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| − |
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| − | *After 10-12 months in the stomach, the larvae detach and are passed out in the faeces
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| − | **''G. haemorrhoidalis'' attaches to the rectal mucosa before being passed out
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| − | *Larvae pupate on the ground
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| − | *Adults hatch after 1-2 months and survive from a few days to 2 weeks
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| − | **Adults have non-functional mouthparts so cannot feed
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| − | *There is only '''1 generation per year''' in temperate regions of the world
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| − | '''Pathogenesis'''
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| − | *Adults cause annoyance when egg laying
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| − | **Disturbance and panic can ensue
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| − | *Larvae cause a marked inflammatory reaction when attached to the gastric mucosa
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| − | **Ring like thickening around the base of each attached larvae
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| − | *Large numbers of larvae may interfere with the passage of food and action of gastric sphincters
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| − | *''G. haemorrhoidalis'' can cause mild irritation to the rectal wall
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| − | *Host reaction to larvae in the mouth is minimal
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| − | '''Control'''
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| − | *Treatment of horses with [[Ectoparasiticides|insecticides]] over winter
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| − | **Breaks the life cycle as all the population are present as bots in the [[Forestomach - Anatomy & Physiology|stomach]]
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| − | *If eggs are present in late summer, the horse's coat can be sponged with an [[Ectoparasiticides|insecticide]]
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| − | **Stimulates hatching
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| − | **Kills larvae
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| | + | </big> |
| | | | |
| | ===''Dermatobia hominis''=== | | ===''Dermatobia hominis''=== |