Parasites of Horses

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Exam II

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

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