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Parasites of Horses

Exam II
STUDY
PLAY
Drachia megastoma:
Taxonomy
Class: Nematoda
Order: Spirurida
Superfamily: Habronematoidea
Genus species: Drachia megstoma
Common Name: Stomach Nematode
Drachia megastoma:
Hosts
All equid species
Drachia megastoma:
Intermediate Hosts
Musca domestica, Musca spp (Fly)
Drachia megastoma:
Adult Identification
-13mm long
-Funnel shaped bucccal cavity
-Form nodules close to margo plicatus
Drachia megastoma:
Egg Identification
-Thin shelled
-Elongated
-Larvated
-40-55x8-16um
Drachia megastoma:
Life Cycle
-Indirect
-Flourishes in the summer
-Eggs leave in feces and hatch into L1 larvae
-Fly larvae eat L1 larvae and becomes L2
-Fly larvae form pupae in soil and L2 becomes L3
-Fly hatches from pupa and carries L3 larvae
-Fly deposits L3 larvae on lips, eyes, wounds or be ingested themselves
-L3 larvae is released as fly is digested
-Adult worms in stomach
Drachia megastoma:
Sites of Infection
-Adults and larvae in stomach
-Larval stages in skin ("wrong place at wrong time")
Drachia megastoma:
Pathogenesis and Lesions of Larvae
-Cutaneous habronemiasis and cutaneous draschiasis
-Ulceration
-Granular conjunctivitis
-Nodules in the lungs
Drachia megastoma:
Pathogenesis and Lesions of Adults
-Gastritis
-Nodules or tumors
Drachia megastoma:
Clinical Signs of Larvae
"Summer sores" (cutaneous habronemiasis)
Drachia megastoma:
Clinical Signs of Adults
Gastritis
Drachia megastoma:
Diagnosis of Larvae
-Cutaneous lesions ("summer sores")
-Presence of larvae can be verified by biospy or scraping of lesions
-Microscopic identification of larvae
Drachia megastoma:
Diagnosis of Adults
-Thin walled
-Collapse with a loss of buoyancy in routine fecal exams
Drachia megastoma:
Treatment and Prevention
-MCL or macrolide
-Local treatment of summer sores
-Anthelmintics and fly control
Habronema muscae and majus:
Taxonomy
Class: Nematoda
Order: Spirurida
Superfamily: Habronematoidea
Genus species: Habronema muscae; Habronema majus
Common Name: Stomach Nematode
Habronema muscae and majus:
Hosts
All equid species
Habronema muscae and majus:
Intermediate Hosts
H muscae: Musca domestica, Musca spp (Fly)
H. majus: Musca spp, Stomoxys calcitrans (Fly)
Habronema muscae and majus:
Adult Identification
-22-25mm
-Cylindrical buccal cavities
Habronema muscae and majus:
Egg Identification
-Thin shelled
-Larvated
-40-55x8-16um
Habronema muscae and majus:
Life Cycle
-Indirect
-Flourishes in the summer
-Eggs leave in feces and hatch into L1 larvae
-Fly larvae eat L1 larvae and becomes L2
-Fly larvae form pupae in soil and L2 becomes L3
-Fly hatches from pupa and carries L3 larvae
-Fly deposits L3 larvae on lips, eyes, wounds or be ingested themselves
-L3 larvae is released as fly is digested
-Adult worms in stomach
Habronema muscae and majus:
Sites of Infection
-Adults and larvae in stomach
-Larval stages in skin ("wrong place at wrong time")
Habronema muscae and majus:
Pathogenesis and Lesions of Larvae
-Cutaneous habronemiasis and cutaneous draschiasis
-Ulceration
-Granular conjunctivitis
-Nodules in the lungs
Habronema muscae and majus:
Pathogenesis and Lesions of Adults
-Gastritis
-Nodules or tumors
Habronema muscae and majus:
Clinical Signs of Larvae
"Summer sores" (cutaneous habronemiasis)
Habronema muscae and majus:
Clinical Signs of Adults
Gastritis
Habronema muscae and majus:
Diagnosis of Larvae
-Cutaneous lesions ("summer sores")
-Presence of larvae can be verified by biospy or scraping of lesions
-Microscopic identification of larvae
Habronema muscae and majus:
Diagnosis of Adults
-Thin walled
-Collapse with a loss of buoyancy in routine fecal exams
Habronema muscae and majus:
Treatment and Prevention
-MCL or macrolide
-Local treatment of summer sores
-Anthelmintics and fly control
Parascaris equorum:
Taxonomy
-Order: Ascaridida
-Superfamily: Ascaridoidea
-Genus species: Parascaris equorum
Parascaris equorum:
Hosts
-All equid species
-Ascarids are host specific
Parascaris equorum:
Adult Identification
-Long, measuring 30cm
-White to cream colored
-3 large lips
Parascaris equorum:
Egg Identification
-Thick walled
-90um in size
-Resistant to the environment
-Females produce a large number of eggs
-Infect young animals
Parascaris equorum:
Life Cycle
-Direct
-NO Transmammary or Transplacental Transmission
-Eggs survive in environment 23 months or longer
-Infective stage (L2 in egg) is swallowed and hatches in small intestine
-L2 burrows through wall of small intestine, liver and lungs (hepatic tracheal migration)
-Migrate from trachea, are swallowed and develop to L3
-Migrate to small intestine 14-17 days after infection
-Develop to adults which copulate and fertilize female lay eggs which pass in feces
Parascaris equorum:
PPP
2 1/2 months
Parascaris equorum:
Sites of Infection
Adults in small intestine
Parascaris equorum:
Pathogenesis and Lesions
-Perforation
-Intestinal obstruction (Obstruction can occur with immature populations)
-Unthriftiness or production losses
Parascaris equorum:
Clinical Signs
-Frequent coughing during migratory phase
-Moderate to heavy infections cause unthriftiness in young animals
Parascaris equorum:
Diagnosis
-Fecal exam reveals eggs
-Eggs can occasionally be absent when when clinical signs are evident
Parascaris equorum:
Treatment and Prevention
-Many anthelmintics are approved
-Treatment not recommended prior to 60 days of age of foal when ascarids are small and immature
-After maturation, there is more of a chance of blockage and perforation of the small intestine if treatment kills adults and they accumulate
Strongyloides westeri:
Taxonomy
-Order: Rhabditida
-Superfamily: Rhabditoidea
-Family: Rhabditidae
-Genus species: Strongyloides westeri
-Common Name: Threadworm
Strongyloides westeri:
Hosts
All equids species
Strongyloides westeri:
Adult Identification
-Slender, hair-like nematodes
-Less than 1 cm long
-Long esophagus may occupy 1/4 of body length
Strongyloides westeri:
Egg Identification
-Thin shelled larvated eggs
-30-40um in size
Strongyloides westeri:
Life Cycle
-Direct
-Parasitic (homogonic) and free-living (heterogonic) phase
-Transmammary transmission (larvae present in milk of mare by 4th day)
Strongyloides westeri:
Life Cycle- Homogonic
-When environmental conditions are unfavorable
-Eggs containing a fully developed, sheathed L1 or liberated L1 are passed in feces
-In the soil L1 develop to L3
-Infective L3 penetrate the host's skin or oral mucosa to undergo migration to the heart, through the lungs and up to trachea, are swallowed and then migrate to intestine
-Develop to adult females only and parthenogenesis takes place
-Some larvae arrest in somatic tissues
Strongyloides westeri:
PPP
10-14 days
Strongyloides westeri:
Life Cycle- Heterogonic
-In favorable environmental conditions
-Eggs containing a fully developed, sheathed L1 or liberated L1 are passed in feces
-In the soil L1 develop to L3, then adult male and females
-Female lay eggs, which develop to free-living L3
-Infect percutaneously and per os (from grass or through milk)
Strongyloides westeri:
Sites of Infection
-Adults in small intestine
-Larvae in somatic tissues
Strongyloides westeri:
Pathogenesis and Lesions
-Skin penetration by migration migration causes an erythematous (redness of the skin) reaction
Strongyloides westeri:
Clinical Signs of Larvae
-Infection in skin causes urticaria (wheals)
-"Frenzy" described with sawdust bedding
Strongyloides westeri:
Clinical Signs of Adults
-Diarrhea
-Observed in young horses
-Does occur in both young and older equids
Strongyloides westeri:
Diagnosis
-Fecal exam with flotation
-Only expect to see eggs in horses under 5 months of age
-Any suspect egg in older animals is likely a strongyle egg
Strongyloides westeri:
Treatment and Prevention
-
2 Subfamilies of Strongyles
-Strongylinae
-Cyathostominae
Strongylinae:
Common Name
Large stongyles
Strongylinae:
Size of Adults
Large (1.5-5cm)
Strongylinae:
Size of Eggs
60-120x35-60um
Strongylinae:
PPP
Direct, 6-11 months
Strongylinae:
Development
Through organs
Strongylinae:
Anthelmintic Resistance
No
Cyathostominae:
Common Name
Small strongyles (cyathostomins)
Cyathostominae:
Size of Adults
Small (usually less than 15mm)
Cyathostominae:
Size of Eggs
60-120x35-60um
Cyathostominae:
PPP
-Direct, 1.5-2 or 4 months
-May be as long as 2-2.5 years after arrested development
Cyathostominae:
Development
Encyst in large intestinal walls (small intestinal walls of wild equids)
Cyathostominae:
Anthelmintic Resistance
Yes
Strongylus vulgaris:
Hosts
All equid species
Strongylus vulgaris:
Adult Identification
-1-2cm in length
-Mouth capsule globular
-Two dorsal ear-shaped teeth in mouth
Strongylus vulgaris:
Egg Identification
-Typical strongyle
-60-120x35-60um
Strongylus vulgaris:
Life Cycle
-Direct
-Infective L3 are ingested during grazing and penetrate the mucosa and begin to migrate beneath the arterial intima
-Molt to L4 during migration to cranial mesenteric and ileocolic arteries
-After 3-4 months they molt and develop further and migrate in arteries back to large intestine
-Develop to adults which mature sexually and copulate after fertile females lay eggs which are passed in feces
Strongylus vulgaris:
PPP
6 months
Strongylus vulgaris:
Sites of Infection
-Migrating larvae in arterial vessels of the intestine
-Adult stages in large intestine
Strongylus vulgaris:
Pathogenesis and Lesions of Larvae
-Arteritis in cranial mesenteric and ileocolic arteries
-Marked thickening of arterial wall
-Thrombus formation
-Infarction (an area of necrosis in a tissue as a result of obstruction of circulation to an area, usually thrombus)
-Death
-Aberrant migration can occur in such arteries as coronary, carotid, external iliac and spermatic
Strongylus vulgaris:
Pathogenesis and Lesions of Adults
Bloodsuckers and remove plugs of mucosa
Strongylus vulgaris:
Clinical Signs of Larvae
-Abdominal colic, thrombo-embolus (obstruction of a blood vessel with thrombus which has broken loose)
Strongylus vulgaris:
Clinical Signs of Adults
Attach to intestinal wall and if in heavy infections can cause anemia
Strongylus vulgaris:
Dignosis of Eggs
-Observed in fecal exam
-Cannot differentiate the eggs of small strongyles from large strongyles
Strongylus vulgaris:
3rd Stage Larvae
Culture and identification of L3 differentiates these 2 strongyle groups
Strongylus vulgaris:
Migrating Larvae
-Ultrasound
-Rectal exam
-Palpation
-Arteriography
Strongylus vulgaris:
Adults
Recovery and identification of adults stages at necropsy
Strongylus edentatus:
Identification of Adults
-3-4cm in length
-Mouth capsule globular
-No teeth in mouth
Strongylus edentatus:
Identification of Eggs
Typical strongyle egg
Strongylus edentatus:
Life Cycle
-Direct
-Migration is through liver from 9th week to tissues of abdominal flanks
Strongylus edentatus:
PPP
11 months
Strongylus edentatus:
Sites of Infection
-Migrating larvae in liver and abdominal tissues
-Adults stages in large intestine
Strongylus edentatus:
Pathogenesis and Lesions of Larvae
-Acute resulting from massive infection (30,000-75,000 L3) with fever, anorexia, constipation, reddish urine, can lead to death
-Chronic involves intermittent colic (no rise in temperature)
Strongylus edentatus:
Pathogenesis and Lesions of Adults
Bloodsuckers and remove plugs of mucosa
Strongylus equinus:
Identification of Adults
-3-4cm in length
-Mouth capsule globular
-One large tooth with a bifid tip at base of mouth capsule
-Two smaller subventral teeth
Strongylus equinus:
Identification of Eggs
Typical strongyle egg
Strongylus equinus:
Life Cycle
-Direct
-Migration to liver and return to cecum by unknown route
Strongylus equinus:
PPP
9 months
Strongylus equinus:
Sites of Infection
-Larvae in liver
-Adults in large intestine
Strongylus equinus:
Pathogenesis and Lesions of Larvae
-Hemorrhagic tracts
-Damage to pancreas during larval migration
Strongylus equinus:
Pathogenesis and Lesion of Adults
Bloodsuckers
Cyathostomins:
Hosts
All equid species
Cyathostomins:
Identification of Adults
-Generally less than 15mm in length
-Mouth capsule not globular but rectangular or square
Cyathostomins:
Identification of Egg
Typical strongyle egg
Cyathostomins:
Life Cycle
-Direct
-L3 ingested during grazing
-L3 exsheath and penetrate the large intestinal wall
-After 1-2 month they emerge in intestinal lumen as L4 and develop to adults
Cyathostomins:
PPP
1.5-4 months depending on the species
Cyathostomins:
Sites of Infection
-Larvae in cecum, ventral colon and dorsal colon intestinal mucosa
-Adults in intestinal lumen
Cyathostomins:
Epidemiology
-mare is origin of infection for the foal (ie. persistent larvae on pasture)
-Each animal has its own supply of mucosal larvae which can mature to become next season's adult (ie. annual population turnover in early spring)
Cyathostomins:
Epidemiology in Northern Temperate Climates
Egg counts increase in spring as a consequence of recently emerged adults, which were arrested during winter as encysted mucosal stages
Cyathostomins:
Epidemiology in Southern Temperate Climates
-The pattern differs
-Larvae encyst through the summer and active transmission occurs during the winter months
Cyathostomins:
Pathogenesis and Lesions
-Larval cyathostominosis/nodular cyathostominosis/larval cyathostominosis
-Lymphocytic and eosinophilic infiltration
-Catarrhal (inflammation of mucous membrane) colitis
-Protein losing enteropathy (chracterized by the severe loss of serum proteins into the intestine which lead to hypoalbuminemia, weight loss and ventral edema)
Cyathostomins:
Hematology
-Increase Beta-globulins
-Decrease albumin
-Increase WCC
-All useful pointer but not pathognomonic (specially distinctive or characteristic of a disease)
Cyathostomins:
Clinical Signs
-Affect young horses and up to 6-15 years of age
-Chronic diarrhea occurs with or without weight loss and can be recurrent. Prominent appearance of L4 stages in diarrheal fluids
-Seasonality in northern and southern temperate climates
-Associated with presence of or emergence of large number of L4 from the intestinal wall
-Chronic or sudden severe weight loss
-Generally debility, weakness, cachexia, edema
-Intussesception and colic
Cyathostomins:
Cachexia
General ill health and malnutrition
Cyathostomins:
Intussesception
Prolapse of one part of the intestine into the lumen of an immediately joining part
Cyathostomins:
Additional Comments
-Accurate diagnosis is required
-Larvae can live in the intestinal wall for up to 2.5 years
-Have become more important as a cause of colic compared to the 1990's
Cyathostomins:
Diagnosis
-Eggs in fecal exam
-Eggs found inf eces of foals under 6 weeks age are due to coprophagia
-L3 are distinct for small strongyles
Cyathostomins:
Treatment and Prevention
2 parasiticides are approved for the removal of mucosal larval stages of cyathostomins; Fenbendazole and moxidectin
Oxyuris equi:
Taxonomy
-Order: Oxyurida
-Superfamily: Oxyuroidea
-Genus species: Oxyuris equi
-Common Name: Large pinworm
Oxyuris equi:
Hosts
All equid species
Oxyuris equi:
Identification of Egg
-85x40um in size
-Has a single operculum
-Flatter on 1 side
Oxyuris equi:
Identification of Adults
-Long and white
-Pointed tails
-reaching 10cm
-Males seldom seen
Oxyuris equi:
Life Cycle
-Direct
-Adults live in dorsal colon
-Gravid female migrates through anus to lay eggs around the perineum, leaving deposit of eggs and associated gelatinous substance which are irritating to skin
-Eggs develop to contain L3 which is infective stage and are ingested with food and water
-L3 live in the crypts of dorsal colon
-Develop to L4 and adults in dorsal colon
Oxyuris equi:
PPP
4-5 months
Oxyuris equi:
Sites of Infection
Adults live in large intestine
Oxyuris equi:
Pathogenesis and Lesions
Irritation lead to pruritus (itching)
Oxyuris equi:
Clinical Signs
Peri-anal irritation
Oxyuris equi:
Diagnosis
Broken hair at tailhead from rubbing (ex: against feces)
-Perianal scraping method
-Scotch tape test
Oxyuris equi:
Treatment and Prevention
-No parasiticide is 100% effective against adults
-MCL resistance is suspected, but not yet demonstrated
Dictyocaulus arnfieldi:
Taxonomy
-Order: Strongylida
-Superfamily: Trichostrongyloidea
-Family: Trichostrongylidae
-Genus species: Dictyocaulus arnfieldi
-Common Name: Lungworm
Dictyocaulus arnfieldi:
Hosts
-Donkeys
-In horses, adults do not usually reach sexually maturity and patency
Dictyocaulus arnfieldi:
Adult Identification
-White nematode
-8cm long
Dictyocaulus arnfieldi:
Egg Identification
Delicate as cmpared to the ascarids L1 (400um) and eggs (75um) recovered in feces and bronchial washings
Dictyocaulus arnfieldi:
Life Cycle
-Direct
-Adult stages in bronchi lay eggs containing L1, which hatch in lungs then pass in the feces
-Eggs develop further to L3, migrate on pasture and are ingested during grazing
-L3 penetrate mucosa of small intestine where they enter lymphatics and blood and migrate to lungs
Dictyocaulus arnfieldi:
PPP
2-4 months
Dictyocaulus arnfieldi:
Sites of Infection
Bronchi of lungs
Dictyocaulus arnfieldi:
Pathogenesis and Lesions
In caudal lung lobes there are raised circumscribed areas of over-inflated pulmonary tissue
Dictyocaulus arnfieldi:
Clinical Signs
Do not cause observable clinical signs in donkeys
Dictyocaulus arnfieldi:
Diagnosis
-L1 and eggs are recovered in feces and lung washings using Baermann test
-Eosinophils are noted in tracheal mucus
-Adults in lungs at necropsy
-Bronchi alveolar lavage (BAL) is used to recover eggs and larvae
Dictyocaulus arnfieldi:
Treatment and Prevention
-
Setaria equina:
Taxonomy
-Order: Spirurida
-Superfamily: Filarioidea
-Family: Onchocercidae
-Genus species: Setaria equina
Setaria equina:
Hosts
-All equid species
-IH: mosquitoes
Setaria equina:
Adult Identification
-Long and slender
-Up to 12cm in length
-Site and gross appearance sufficient for generic identification
Setaria equina:
Life Cycle
-Indirect
-Mff in the bloodstream are ingested by mosquitoes
Setaria equina:
PPP
8-10 months
Setaria equina:
Sites of Infection
-Adults often in peritoneal cavity
-Mff in blood
-Larvae can be found in the eye
Setaria equina:
Pathogenesis and Lesions
Nematodes are not pathogenic and detected at necropsy
Setaria equina:
Clinical Signs
No clinical signs, unless nervous tissue is involved
Setaria equina:
Diagnosis
-Mff in blood smears
-Adults in peritoneal cavity
Setaria equina:
Treatment and Prevention
-
Onchocerca cervicalis:
Taxonomy
-Order: Spirurida
-Superfamily: Filarioidea
-Family: Onchocercidae
-Genus species: Onchocerca cervicalis
Onchocerca cervicalis:
Hosts
-All equid species
-IH: Culicoides spp
Onchocerca cervicalis:
Adult Identification
-Slender
-2-6cm in length
-Lie tightly coiled in tissue nodules
Onchocerca cervicalis:
Life Cycle
Following inoculation of L3 by the IH, Culicoides, the arrival of the parasites intheir final site results in a host reaction
Onchocerca cervicalis:
Sites of Infection
-Ligamentum nuchae in the region of the withers
-Mff occur in tissue spaces of the skin rather than the peripheral bloodstream and are also found in the skin of the umbilicus area
Onchocerca cervicalis:
Pathogenesis and Lesions
Fibrous tissue, usually of ligaments and intermuscular connective tissue
Onchocerca cervicalis:
Clinical Signs
-Pruritic dermatitis
-Common names for this condition are microfilarial pityriasis (disease characterized by fine scales), summer mange, equine dhobie itch and plica polonica
Onchocerca cervicalis:
Diagnosis
-Mff occur in tissue spaces of the skin rather than the peripheral bloodstream
-Microfilariae recovered in a saline incubation of skin biopsies
-Open purulent lesions, called "fistulous withers" may occur. May be related to the presence of nematodes or the presence of a bacterium (Brucella abortus)
Onchocerca cervicalis:
Treatment and Prevention
-
Anoplocephala perfoliata:
Taxonomy
-Phylum: Plathelminthes
-Class: Cestodes
-Order: Cyclophyllidea
-Family: Anoplocephalidae
-Genus species: Anoplocephala perfoliata
Anoplocephala perfoliata:
Hosts
All equid species
Anoplocephala perfoliata:
Adult Identification
-Large, up to 4cm
-White
-Rounded scolex with a lappet behind each of the 4 suckers
Anoplocephala perfoliata:
Egg Identification
-Typical anoplocephalid
-Contains small embryo and often irregularly shaped
-50-80um
Anoplocephala perfoliata:
Life Cycle
-Mature segments pass in feces and disintegrate, releasing eggs which develop to oncospheres
-These are ingested by oribatid or forage mites and develop to cysticercoid stage
-The mite with the cysticercoids is ingested by the equid
-One-two months later, adult tapeworms are found in the intestine of equids
-Mites are also found in bedding and hay, and equids continue to be infected through winter months
Anoplocephala perfoliata:
Sites of Infection
-Adults in cecum around ileocecal valcve
-Cystercercoids in forage or oribatid mites
Anoplocephala perfoliata:
Pathogenesis and Lesions/Clinical Signs
-Light infections in horses produce no clinical signs, -Large numbers may cause ill health, unthirftiness and even death
-Heavy infections causes ulcerations
-Frequently localizes near ileocecal valve, which may show ulcerations and a diphtheritic membrane
-Can lead to partial occulsion of ileocecal valve and intussuscception of the terminal ileum and cecum
Anoplocephala perfoliata:
Diagnosis
-Fecal exam in horses can give some indication of infection
-Experts contend that postmortem findings are considered more definitive
-Centrifugation/flotation, sedimentation and ELISA which detects antibodies in the serum of a horse that has been infected historically
Anoplocephala perfoliata:
Treatment and Prevention
-Praziquantel is the treatment of choice
Anoplocephala magna:
Hosts
All equid species
Anoplocephala magna:
Adult Identification
-Larger than A. perfoliata
-80cm
-Rounded scolex with no lappets
Anoplocephala magna:
Egg Identification
-Typical anoplocephalid
-Contains small embryo and often irregularly shaped
-50-80um
Anoplocephala magna:
Life Cycle
-Mature segments pass in feces and disintegrate, releasing eggs which develop to oncospheres
-These are ingested by oribatid or forage mites and develop to cysticercoid stage
-The mite with the cysticercoids is ingested by the equid
-One-two months later, adult tapeworms are found in the intestine of equids
-Mites are also found in bedding and hay, and equids continue to be infected through winter months
Anoplocephala magna:
Sites of Infection
-Adults in small intestine
-Cysticercoids in forage or oribatid mites
Anoplocephala magna:
Pathogenesis and Lesions/Clinical Signs
-Large numbers may cause ill health, unthirftiness and even death
Anoplocephala magna:
Diagnosis
-Fecal exam in horses can give some indication of infection
-Experts contend that postmortem findings are considered more definitive
-Centrifugation/flotation, sedimentation and ELISA which detects antibodies in the serum of a horse that has been infected historically
Anoplocephala magna:
Treatment and Lesions
-Praziquantel is the treatment of choice
Gasterophilus intestinalis:
Taxonomy
-Phylum: Arthropoda
-Order: Diptera
-Suborder: Cyclorrhapha
-Family: Gasterophillidae
-Genus species: Gasterophilus intestinalis
-Common Name: Bot fly larvae or instars, armed bot fly, common bot fly
Gasterophilus intestinalis:
Hosts
All equid species
Gasterophilus intestinalis:
Life Cycle
-Eggs are deposited on hair of forelegs and shoulder (site is species specific)
-First instar hatches from the egg when licked by the horse and attaches to the tongue/lips
-In the oral cavity they develop to second instars and are then swallowed
-Develop to third instars (or "bots") and theses live for up to 12 months in the stomach (site is species specific)
-From late spring these will pass out with the feces to pupate in the soil
-Adult bot flies emerge 3-9 weeks later
Gasterophilus intestinalis:
PPP
Up to 14 months
Gasterophilus intestinalis:
Sites of Infection
-Eggs deposited on hair of forelegs and shoulders
-Third instars attach in clusters in the nongladular part of the stomach near the margo plicatus and cardiac region
-They are red with 2 rows of coarse spines blunted on ends
-Eggs deposited on hair of forelegs and shoulders of horse
Gasterophilus intestinalis:
Pathogenesis and Lesions
-Adult flies are an annoyance
-Attachment of instars provokes an inflammatory reaction in the stomach lining
-Although dramatic, their true pathogenic significance remains obscure
Gasterophilus intestinalis:
Clinical Signs
Fly worry, otherwise obscure
Gasterophilus intestinalis:
Diagnosis
-Differentiate species based on color, spines and location in host
-The bots are visualized during gastroscopy
Gasterophilus intestinalis:
Treatment and Prevention
-
Gasterophilus nasalis:
Taxonomy
-Phylum: Arthropoda
-Order: Diptera
-Suborder: Cyclorrhapha
-Family: Gasterophillidae
-Genus species: Gasterophilus nasalis
-Common Name: Throat bot fly larvae or instars, throat bot fly, bot fly larvae
Gasterophilus nasalis:
Hosts
All equid species
Gasterophilus nasalis:
Adult Identification
Flies are large and robust but rarely seen
Gasterophilus nasalis:
Third Instar Identification
-Often found in feces
-When fresh, they are yellow with 1 row of spines on each segment
Gasterophilus nasalis:
Life Cycle
-Eggs are deposited on hairs of the intermandibular area (site is species specific)
-First instar hatches spontaneously and crawls into the mouth
-In the oral cavity they develop to the second instars and are then swallowed
-Develop to third instars (or "bots") and these live for up to 12 months in the duodenal ampulla (site is species specific)
-From late spring these will pass out with the feces to pupate in the soil
-Adult bot flies emerge 3-9 weeks later
Gasterophilus nasalis:
PPP
14 months
Gasterophilus nasalis:
Sites of Infection
-Eggs deposited on hairs of intermandibular area
-Third instars attach around small intestine around the pylorus and duodenum
-Eggs deposited in large numbers of hairs of intermandibular area in large numbers
Gasterophilus nasalis:
Pathogenesis and Lesions
-Adult flies are an annoyance when lay eggs
-Attachment of instars provokes an inflammatory reaction in the small intestinal lining
-Although dramatic, their true pathogenic significance remains obscure
Gasterophilus nasalis:
Clinical Signs
Fly worry, otherwise obscure
Gasterophilus nasalis:
Diagnosis
Differentiate species based on color, spines and location in host
Gasterophilus nasalis:
Treatment and Prevention
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Musca autumnalis:
Taxonomy
-Family: Muscidae
-Genus species: Musca autumnalis
-Common Name: Face fly
Musca autumnalis:
Hosts
-All equid species
-Cattle
-Other hosts
Musca autumnalis:
Adult Identification
-5.5-7.5mm in length
-Light to dark grey in color
-4 distinct dark longitudinal stripes on the thorax
-Greyish abdomen has various light and dark markings
-Mouthparts adapted for sponging are obvious when extending during feeding
-Fleshy retractable proboscis terminates in a pair of organs, the labella
Musca autumnalis:
NB Identification
-Presence of sticky hairs on pad-like structures at the end of the clawed legs
-These enable the fly to adhere to smooth surfaces (ex: when they feed on septic wounds and decaying organis matter)
Musca autumnalis:
Egg Identification
-1mm long
-Banana shaped
-Laid in batches of 100 in feces or rotting organic material or decaying vegetable matter
Musca autumnalis:
Life Cycle
-Typical muscid life cycle
-Eggs develop to larvae (maggots)
-Three larval instars, develop to pupae and then to adult flies
-Female flies lay batches of up to 100 creamy-white, 1mm long, banana-shaped eggs in feces or rotting organic material
Musca autumnalis:
Sites of Infection
Animal secretions and wounds
Musca autumnalis:
Pathogenesis and Lesions
-Source of annoyance to the equid and mechanically transmit viruses, bacteria, helminths and protozoa
-They are the intermediate host for horse eye nematodes (Thelazia lacrymalis)
-Feeds on face secretions
-Numerous on cattle
Musca autumnalis:
Clinical Signs
-Annoyance and can interfere with grazing and drop in performance
-Can result in eye disorders or conjunctivitis
Musca autumnalis:
Diagnosis
Confirm fly identification
Musca autumnalis:
Treatment and Prevention
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Stomoxys calcitrans:
Taxonomy
-Family: Muscidae
-Genus species: Stomoxys calcitrans
-Common Names: Stable fly, Biting housefly
Stomoxys calcitrans:
Hosts
-Most animals
-Humans
Stomoxys calcitrans:
Adult Identification
-5.5-7.5mm in length
-Shorter abdomen with 3 dark spots in second and third abdominal segments
-Proboscis is prominent, rigid, conspicuous and forward projecting
-This forms a piercing and sucking organ
-Characteristically sit with head end up and rear end down on buildings, walls, etc.
Stomoxys calcitrans:
Egg Identification
-1mm long
-Banana shped
-Creamy white
-Laid in batches of 25-50 in decaying vegetable matter, such as hay and straw contaminated with urine, lawn clippings, damp hay or grain
Stomoxys calcitrans:
Life Cycle
-Female flies lay batches of up to 25-50 creamy white, 1mm long, banana-shaped eggs in decaying vegetable matter
-Feed on blood 1-2 times a day and penetrates the skin
-Three minutes are required for each blood meal
-This time allows mechanical transmission of organisms
Stomoxys calcitrans:
Sites of Infection
General
Stomoxys calcitrans:
Pathogenesis and Lesions
-Attack cattle, horses and most other domestic animals and human on warm days throughout the summer
-Painful bites transmit diseases (ex: Habronema spp.) and mechanical transmission of trypanosomes
Stomoxys calcitrans:
Clinical Signs
Cause increased head and ear movement, skin twitches and tail swishes
Stomoxys calcitrans:
Diagnosis
Confirm fly identification
Stomoxys calcitrans:
Treatment and Prevention
-
Culicoides spp:
Taxonomy
-Phylum: Arthropoda
-Class: Insecta
-Suborder: Nematocera
-Family: Ceratopogonidae
-Genus species: Culicoides spp
-Common Name: Biting midges, "no-see-ums"
Culicoides spp:
Hosts
All domestic animals and humans
Culicoides spp:
Adult Identification
-1.5-5mm long
-Mottled wings held like a closed pair of scissors over the abdomen
-Short piercing proboscis
-800 species
Culicoides spp:
Life Cycle
-Eggs laid in damp marshy ground hatching in 2-9 days
-Four larval stages completed 14-25 days up to 7 months
-Pupae found at surface and edges of water
-Adult flies emerge 3-10 days
-Female suck blood
Culicoides spp:
Sites of Infection
General
Culicoides spp:
Pathogenesis and Lesion
-Annoyance
-Transmit viruses of bluetongue and African horse sickness, Onchocerca in horses and cattle and protozoan parasites
Culicoides spp:
Clinical Signs
-Inflict pain far out of proportion to the size of the fly
-"Queensland itch"
-Allergic dermatitis afflicts only certain horses
Culicoides spp:
Diagnosis
Confirm fly identification
Culicoides spp:
Treatment and Prevention
-
Tabanus spp:
Taxonomy
-Phylum: Arthropoda
-Class: Insecta
-Suborder: Brachycera
-Family: Tabanidae
-Genus species: Tabanus spp.
-Common Name: horse fly, Gadfly
Tabanus spp:
Hosts
Large domestic or wild animals, humans, small mammals or birds
Tabanus spp:
Adult Identification
-Large, stout bodied flies varying from size of house fly to hummingbird
-Clear to brownish wings
-Medium to large flies with wing span up to 6.5cm
-Mouthparts slashing/sponging, short, strong, adapted for bloodsucking
Tabanus spp:
Life Cycle
-After a blood meal the female lays several hundred eggs in muddy or marshly areas, on vegetation and stones
-Eggs hatch in 1-2 weeks to sluggish larvae
-Develop in 3 months-3 years
-Adult fly emerges from pupae in 1-3 week
Tabanus spp:
PPP
4-5 months or longer
Tabanus spp:
Sites of Infection
General
Tabanus spp:
Pathogenesis and Lesions
-Painful bites to their host
-Efficient mechanical vectors of organisms responsible for anthrax, pasteurellosis, trypanosomosis, anaplasmosis (=gallsickness, which is a disease of ruminants) and the human filarial disease, loasis
Tabanus spp:
Clinical Signs
Annoyance
Tabanus spp:
Diagnosis
-Confirm fly identification
-Clear or brownish wings
Tabanus spp:
Treatment and Prevention
-
Chrysops spp:
Taxonomy
-Phylum: Arthropoda
-Class: Insecta
-Suborder: Brachycera
-Family: Tabanidae
-Genus species: Chrysops spp.
-Common Name: Deer fly
Chrysops spp:
Hosts
Large domestic or wild animals, humans, small mammals or birds
Chrysops spp:
Adult Identification
-Large, stout bodied flies varying from size of house fly to hummingbird
-Clear to brownish wings
-Medium to large flies with wing span up to 6.5cm
-Mouthparts slashing/sponging, short, strong, adapted for bloodsucking
-Dark bands across wings
Chrysops spp:
Life Cycle
-After a blood meal the female lays several hundred eggs in muddy or marshly areas, on vegetation and stones
-Eggs hatch in 1-2 weeks to sluggish larvae
-Develop in 3 months-3 years
-Adult fly emerges from pupae in 1-3 week
Chrysops spp:
PPP
4-5 months or longer
Chrysops spp:
Sites of Infection
General
Chrysops spp:
Pathogenesis and Lesions
-Painful bites to their host
-Efficient mechanical vectors of organisms responsible for anthrax, pasteurellosis, trypanosomosis, anaplasmosis (=gallsickness, which is a disease of ruminants) and the human filarial disease, loasis
Chrysops spp:
Clinical Signs
Annoyance
Chrysops spp:
Diagnosis
-Confirm fly identification
-Clear or brownish wings
Chrysops spp:
Treatment and Prevention
-Perfer to bite horses when in shaded areas
-If pasture margins are wooded, horses may stand out in the sun just to avoid deer flies
Chorioptes bovis:
Taxonomy
-Class: Arachnida
-Order: Acari
-Family: Psoroptidae
-Genus species: Chorioptes bovis
-Common Name: Chorioptic mange mite, foot mange, leg mange, itchy heel
Chorioptes bovis:
Hosts
-Equids
-Cattle
-Sheep
-Goats
Chorioptes bovis:
Adult Identification
-Male has pretarsi on all 4 pairs of legs
-Females have suckers on short, unsegmented stalks on pairs of legs 1, 2, 3, and 4 (pair 4 is rudimentary)
Chorioptes bovis:
Life Cycle
-Similar to Psoroptes ovis in small ruminants
-Female lays 90 eggs during her lifetime of 4-6 weeks
-Egg, larval and nymphal stages to mature adult takes 10 days
-Exception is this mite feeds only on skin surface and does not pierce skin
Chorioptes bovis:
Sites of Infection
Distal parts of the limbs
Chorioptes bovis:
Pathogenesis and Lesions
Crusty lesions with thickened skin on distal parts of limbs
Chorioptes bovis:
Clinical Signs
Movement of mites on host causes irritation
Chorioptes bovis:
Diagnosis
-Close examination
-Skin scraping for mtie
Chorioptes bovis:
Treatment and Prevention
-
Eimeria leukarti:
Taxonomy
-Subkingdom: Protozoa
-Phylum: Apicomplexa
-Order: Eucoccidiorida
-Family: Eimeriidae
-Genus species: Eimeria leukarti
Eimeria leukarti:
Hosts
All equid species
Eimeria leukarti:
Egg Identification
-Oval oocyst very large, measuring 80x60um
-Thick dark shell
-Distinct micropyle
-Thick shell can come off and some oocysts in a fecal may not contain the thick dark outer oocyst wall
Eimeria leukarti:
Life Cycle
-3 phases:
-Sporulation
-Infection and schizogony
-Gametogony and oocyst formation
Eimeria leukarti:
Life Cycle-Sporulation
-Unsporulated oocyts pass in feces to exterior
-Under suitable conditions, these develop to sporoblasts
-Each sporoblast (at high humidity and optimal temp) develops to a sporocyst and divides into 2 banana-shaped sporozoites
-Under optimal conditions this takes 2-4 days
-The oocytst now consisting of an outer wall enclosing 4 sporocysts each containing 2 sporozoites is referred to as a sporulated oocyst and is the infective stage
Eimeria leukarti:
Life Cycle- Infection and Schizogony
-Asexual reproduction
-Hosts becomes infected by ingesting sporulated oocyst
-Sporocysts are liberated and aporozoites leave the sporocyst
-In most species, each sporozoite penetrates an epithelial cell, rounds up and is known as a trophozoite
-After a few days trophozoite divides by multiple fusions to form a schizont
-A schizont is a structure consisting of a large number of elongated nucleated organisms known as merozoites
-When division is complete and schizont mature, the host cell and schizont rupture and the merozoites escape to invade neighboring cells
-Schizogony may be repeated, the number of schizont generations depending on the species
-It is not known how many stages of schizogony occur with E. leukarti
Eimeria leukarti:
Life Cycle- gametogony and Oocyst Formation
-Schizogony terminates when the merozoites give rise to male and female gametocytes
-The macrogametocytes are female, remain unicellular, but increase in size to fill the parasitized cell
-They are distinguishable from trophozoites or developing schizonts by the single large nucleus
-The male microgametocytes undergo repeated division to form a large number of flagellated uninucleate organisms, the microgametes
-This is the only time coccidia have organs of locomotion
-The microgametes are freed by rupture of host cell, one penetrates a macrogamete and fusion of micro- and macrogamete nuclei take place
-A cyst wall forms resulting in a zygote, now an oocyst
-The next stage is the liberation of this unsporulated oocyst passing in the feces of the host
Eimeria leukarti:
PPP
15 days
Eimeria leukarti:
Sites of Infection
Small intestine
Eimeria leukarti:
Pathogenesis and Lesion
Inflammatory changes in mucosa and a disruption of villous architecture
Eimeria leukarti:
Clinical Signs
-Largely benign
-Foals may be susceptible with intermittent diarrhea
Eimeria leukarti:
Diagnosis
-Microscopic exam of feces for presence of oocytes or exam of affected tissues
-Difficult to diagnose because of heavy nature of oocytes
-Flotation method with sugar is the flotation medium of choice
-Specific sedimentation techniques can be employed
Eimeria leukarti:
Treatment and prevention
-Little known, but by analogy with other hosts
-Antiprotozoal remedies should be tried
Sarcocystis neurona:
Taxonomy
-Subkingdom: Protozoa
-Phylum: Apicomplexa
-Order: Eucoccidiorida
-Family: Sarcocystidae
-Genus species: Sarcocystis neurona
-Common Name of Disease: Equine Protozoal Myeloencephalitis (EPM)
Sarcocystis neurona:
Hosts
-Definitive Host: Opossum
-Accidental Host: Horse
-IH: Cats, striped skunks, nine banded armadillos, fishers, sea otters and raccoons
Sarcocystis neurona:
Egg Identification
-Sporulated oocysts with 2 sporocysts each with 4 sporozoites
-18um size
-These develop inside the final host and are then excreted in the feces
-It is impossible to make a diagnosis as to species based on finding sporocysts in opossum feces
-Several Sacrocystis spp are found in opossum feces and oocyst structure in not diagnostic
Sarcocystis neurona:
Life Cycle
-Gametogony (sexual) in the definitive final host
-Schizogony (asexual) in the intermediate host
Sarcocystis neurona:
Life Cycle- Gametogony
-Infection is by ingestion of bradyzoite cysts in the muscles of the IH
-The bradyzoites are liverated in the intestine and the freed zoites pass to the sub-epithelial lamina propria and differentiate into micro and macrogametocytes
-Fusion of gametes takes place and thin-walled oocysts are produced which unlike most enteric coccidia sporulate within the body
-Two sporocysts are formed, each containing 4 sporozoites
-Usually the fragile oocyst wall ruptures and free sporocysts are found in feces
Sarcocystis neurona:
Life Cycle- Schizogony
-Infection is by ingestion of the sporocysts and this is followed by at least 3 asexual generations
-In the first, sporozoites released from sporocysts, invade the intestinal wall and enter the capillaries where they locate in endothelial cells and undergo 2 schizogonous cycles
-A third asexual cycle occurs in the circulating lymphocytes, the resulting merozoites penetrating muscle cells
-There they encyst and divide by a process of budding which gives rise to broad banana-shpaed bradyzoites contained within a cyst
-this is the mature sarcocyst and is the infective stage for the carnivorous final host
Sarcocystis neurona:
PPP of Carnivores
-1-2 weeks
-During which sporocysts are passed in feces by carnivores is 1 week to several months
-Can total 2.5-16 months
Sarcocystis neurona:
PPP of IH
From ingestion of sporocysts to presence of infective bradyzoites in muscles of IH hosts is usually 2-3 months but may extend to 12 months
Sarcocystis neurona:
Sites of Infection
-In muscles are bradyzoites
-In horses that have accidentally ingested sporocysts, there are schizonts that develop within neurons and other cells and which cause disease
-In these horses, one does not see the development of the muscle cysts that occur in the true IH
Sarcocystis neurona:
Pathogenesis and lesions
-Infection in final host is normally non-pathogenic
-In the IH the pathogenic effect is attributable to the second stage of schizogony in the vascular endothelium
-In the accidental host, the pathogenic effect occurs when nervous tissue rather than muscle tissue is infected
Sarcocystis neurona:
Clinical Signs
-In bothe sexes and all ages
-Neurological disease
-Stumbling, paresis (slight paralysis), lameness, ataxia (failure of muscle coordination), recumbency, constipation, urinary incontinence, muscle atrophy
Sarcocystis neurona:
Diagnosis
-Positive diagnosis based on histopathological demonstration of EPM organisms in association with lesions in the CNS
-The Western blot test on cerebral spinal fluid is the most commonly used
Sarcocystis neurona:
Treatment and Prevention
-