Exam2 Flashcards
Gastrointestinal Nematodes of Horses
**Strongyles Large -3 species Small -Several different genera -Many different species **Ascarids -Parascaris equorum **Pinworms -Oxyuris equi **Spiruid worms of incidental interest
Large stongyles and small strongyles
a. k.a: Cyathostomes Small strongyles
- Adults in large intestine or colon
- Direct life cycle
- Infective stage: L3 larvae in pasture environment
- Primary target for control by equine owners
- ~40 species
Large strongyles Morphology
-Medium size worms
-Males (14-35 mm) with capulatory bursa
-Femalres (20-47 mm)
-Dimorphic
*Prominent buccal capsule
-Adults in large intestine
Life Cycle
-Eggs passed in feces ~14 days and develop into L3 larvae
-Larvae migrate externally
-Arrive In the large intestine and reproduce (6, 8, or 12 mts)
-Long PPP or ERP following treatment
Large Strongyles
Strongylus Vulgaris 6 mts
Strongylus equinis 8 mts
Strongylus edentatus 12 mts
Strongylus vulgaris **most important disease causing
- Larvae migrate in walls of small arteries and anterior mesenteric artery
- arrive in cecum/colon mature and reproduce
- PPP = 6 mts
Strongylus equinis
- Larvae migrate in peritoneal cavity and liver
- Arrive cecum/colon
- PPP 8 mts
Strongylus edentatus
- Larvae migrate in peritoneal cavity and liver
- arrive in cecum/colon
- PPP 12 mts
Disease in older foals occurs in the PPP
-pathology associated with larvae migration through arteries **cranial mesenteric artery
-Host inflammatory response
-Aneruysm and infraction
-Colic by interruption of blood supply
-Diarrhea when adult worms reach large intestine
-Adult worms suck blood
**Fecal exams can be negative
Dx: clinical signs, age, and risk factors
-Associated with older animals w high FEC
-No consistent worming program
Small Strongyles
Large Strongyles
- Cylicocyclus (10-25 mm)
- Cyathostomum (5-12 mm)
Sexually dimorphic
- Males capulatory bursa
- **Anterior end w/ prominent “corona radiata”
Life cycle
- eggs passed in feces 2 wks = L3 infective satage
- Larvae penetrates and encyst in intestinal wall
- Late L3 becomes reproducing adult
- Eggs in feces 9 wks post infection without hypobiosis
- 9 wks PPP
Clinical Disease
-Foals diarrhea, disease occurs before worms sexually mature
-Mass encysted parasites wall of LI
-Damage from emergence out of colonic wall
Dx: clinical signs, age, and risk factors
-Associated with older animals w high FEC
-No consistent worming program
**Red worms (L4) passed in feces
-Possible detection of eggs by fecal flotation
-ERP 28 days for some species, 6-12 wks for others
Large Strongyles
- ERP 6,8,12 mts
- Hatch and later identify larvae
- FEC useful to monitor drug effectiveness, pasture contamination, identification of wormy animals can’t not be used to predict worm burden
Deworming products
3 families
- Bensimidazoles (B-tubulin synthesis)
- Imidazothiazole (nicotinic agonists)/ Tetrahydropyrimidines
- Macrocyclic Lactones (gated glutamate chloride channels.
- Large strongyles: no resistance
- Small strongyles: responsive to macrolcylic lactones with shorter ERPs.
Pharmacologic Control
-Interval dosing: most common, deworm all horses at fixed intervals. suppressive deworming to minimize contamination. Shorter than ERPs (2 mts or 8 wks)
-Strategic dosing: Active grazing period deworming, at greater risk. Lifecycle while hypobiosis. Fewer treatments, less intensity
-Continuous daily treatment: Pyrantel tartrate (Strongid C). Kills L3 before it can invade mucosal tissue. Believed to have fostered resistance
-Selective treatment: only horses above FEC threshold.
Allows REFUGIA: the portion of the parasite population not subject to drug selection pressure.
Practice Control
- Not target adults: small strongyles still mass emerge, large strongyles still larvae invasion
- Interval treatment: Pyrantel, Benzimidazoles (FBZ, TBZ, etc). Low levels of persistent in tissues allow for rapid reinfection.
- Maturing sexually active worms result in bad things for pasture
Survival of parasite populations
- Adult worms are short lived 35-55 days
- Seasonally hostile conditions reduce population
- Summer in TN Cyathostome hypobiosis, in Fall/Spring favorable for pasture
**Minimum treatment of “selective deworming” high FEC animals to reduce pasture contamination and preserves genetic diversity
Nematodes of Horses
Ascarids
Pinworms
Draschia/Habronema
Parascaris equorum
- Large stout worm Males 15-28 cm, Females up to 50 cm
- Dimorphic
- Anterior opening w/ 3 lips
- Adults parasites in small intestine
- Direct life cycle
- Infective larvated eggs
- Tracheal migration
- *primarily parasites of Foals
- PPP ~ 12 wks
- Round eggs ~90um (look like ascarids canis eggs)
Clinical signs:
- Diarrhea, enteritis, respiratory issues and nasal discharge
- dull hair coat and poor growth
- Extreme infections can be fatal
- Large worm burden, worm grows faster than Foals’ intestinal tract
- Impaction colic, intestinal perforation and rupture (4 worms trying to get out through the same hole)
Tx and control:
- Clean mare’s udders, provide clean nursing environment
- Graze low FECs animals
- **Effective therapy @ 2,4,6,7 months
- Pyratel pamoate (early)
- Fenbendazole (early)
- Macrocyclic lactone (widespread)
- Potential of colic if all and too many killed at once
OXyuris equi
Equine Pinworm
Medium size worms
- dimorphic males (9-12 mm) Females (40-150 mm)
- Adult worms: long tail with acute distal end, Muscular bulb (esophagus)
- Adults parasitic in colon, small, and large intestines.
Direct life cycle
- Embryonated eggs infective
- Larvae hatches and penetrates the colon wall develop and return to lumen to reproduce
- Females deposit cement eggs in perianal folds
- PPP ~5 mts
- Eggs flake off and adhere to everything
- Infective eggs after 4-5 days in the environment developing
Clinical significance
- Intense anal prutitis and itching
- Behavioral issues
Tx and control
- Adult worms susceptible to treatment
- Pyrantel
- Ivermectin paste
- L4 larva stages were >99% susceptible to drugs
- No evidence of drug resistance
- **Attention to hygiene
Strongyloides westeri
Equine Threadworm
-Small worms
-Adults in small intestine
**only females are parasitic
-morphology and life cycle similar to canine species
**Homogonic life cycle
**Hetrogonic
-Infection in foals
Lactogenic
-PPP= ~7 days
-L3 infective
-Percutaneous
-Eggs: 50x35 um
Clinical significance
-Primarily infection of foals
Eggs disappear from feces by 24 wks of age
Arrested in tissue for life
-Diarrhea, dehydration, poor growth
-Treatment to remove adults from small intestine
-Supportive care
Draschia and Habronema
Equine Stomach Worms
- Adults live in the stomach of horses
- Small worms usually dimorphic
- *Obligate indirect life cycle
- Transmission of infective worm larvae via FLY
- FLY intermediate host
- Larvae in cutaneous wounds
- Eggs passed in feces, ingested by maggots
- *Trans-stadial transmission
- Horses accidentally ingest fly
- PPP ~5mts
- Eggs 45x12 occasionally seen
Clinical significance
Disease process associated with deposited larvae by fly
- Cutaneous Harbronemiasis a.k.a ‘summer sore’, ‘swamp cancer’
- Granulomatous lesion persistent through the fly season
- Worldwide distribution
- Tx single dose macrocyclic lactone is usually effective
- Fly control important
Ecology, epidemiology and disease risk horses
-Horse feral, nomadic, little contact with the same infective pasture before domestication
Principles of parasite control
- Pasture contamination: best 1-2 horse/Acre
- Pasture infectivity: Low FEC horses allow to graze
- Differential risk of infection/disease: young animals associated with high FEC
- Parascarids equorum - Pasture hygiene and management
- No pharmacologic solutions for poor pasture management : “smart deworming”
Resistance
- Drug treatment increases the frequency of naturally occurring ‘resistance’ genes in the parasite population
- Parasites that are treatment resistant reproduce differently without competition from other worms
- management factors: exclusive use of a single drug, resistant worms reproduce continually through ERP
- Frequent use of drug: denies susceptible worms an opportunity to reproduce
- *Benzimidazoles, Panacur, Safeguard: widespread resistance in small strongyles, none in large and early indication in Parascaris
- *Mycrocyclic lactones, Ivermectin, Moxidectin: widespread resistance Parascarids, none large, some in small strongyles
Differential selection by drug used:
- Pyrantel, adults only, no effect on encysted eggs (best refugia)
- Ivermectin, Late L3 and Adults
- Moxidectin, Early and Late L3 and adults (poor refugia)
Selective treatment
- Maximizes refugia
- Mitigate negative selection pressure of treatments
- Facilitates heterogenous mix of susceptible and resistant parasite types
Parasite targets:
- Age based susceptibility
- Adults >3 yrs old acquired immunity
Parasite control for 1st year, @nd year, 3rd year
Deworm @ 8 weeks: FBZ targets Parascaris, Pyrantel when worm burden is low
Deworm @ 16 weeks: Pyrantel to target Prascaris, IVM for Cyathostomes
Deworm @ 24 weeks: Macrocyclic lactone to target small strongyles
Deworm @ 32-24 weeks: Macrocyclic lactone to target small strongyles
Deworm @ 52 weeks
2nd year
Consider animals with high FEC Tx: @ 10-12 weeks intervals, -Fall, winter, spring -Season with highest pasture transmission -Largest possible REFUGIA
3rd year
- Tx at least once annually for large strongyles and Tapeworms. Macrocyclic lactones and Prazinquantel
- Identify and treat high FEC shedders by selective deworming. **No more than x3 @ 12 wks intervals.
Trichostrogylid Nematode Parasite of Cattle, sheep, goats, and camelids
- Small gut-dwelling nematodes
- No extensive tissue migration
- Arrested development (hypobiosis) as an important adaptation to survival and maintenance of parasite populations
- Primary target of producers initiated control programs
Arrested development
- remains juvenile for several months in gut tissue
- arrested larvae waits for favorable reproductive conditions, avoids adverse environmental conditions. Seed the pasture each season
Life Cycle
- Adults in gut and reproduce
- Infective larvae develops in environment
- PPP ~21 days
Dx:
- periodic assessment of herd health
- High FEC
- Eggs 70-90 x 40-45 um. Thin shell and morulated. Look like hookworm eggs
- fecal flotation
- McMasters Quantitative FEC
Ostertagia spp.
Brown stomach worm
- Adults in abomasum
- small dimorphic. males w/ copulatory bursa. SPICULES
- Direct life cycle
- Arrested development in gastric pits
- Type 1 and 2 disease
- *most economically important parasite in cattle
- Controlled with Smart deworming: as little as possible
Type 1 disease
- Usually young animals (1st season on pasture)
- Favorable environmental conditions, October/March
- Larvae begins hypobiosis April/Sep
- Larvae lives 30-52 days
- Damage when larvae matures, leaves the glands and reproduces
- Profuse water diarrhea
- Bottle jaw
- Loss of appetite, loss of BCS
- Positive response to timely treatment
Type 2 disease
- Occurs months after infection
- Older animals (2nd season on pasture)
- Larvae enters the gastric glands and remain dormant
- Leave the glands ‘en masse’ during summer-fall months
- Catastrophic or protracted
- Associated with stress (calving)
- Clinical signs similar to type 1 but more severe
- Fecal floatation likely negative
- Brown watery diarrhea
- Rumen pH approaches neutral
- *Poor response to treatment
Other trichostrongylid parasites of cattle
- Trichostrongylus sp.
- less pathogenic
- Young and stressed animals at greater risk
- Cooperia sp.
- Typically associated with calves
- Losses subclinical production
- Emerging drug resistance
- Macrocyclic lactones
- Pour on ML for fly control = resistance
- Nematodirus spp.
- Seasonal Spring hatching concentrates infective worms
- Disease typically associated with calves in late spring
- Large egg ~200 um x 90 um
Anthelmintic control of parasite in herd animals
Strategic deworming: removal of parasite from the host, targeting biological infective stages. Removal of adult parasites, less worm burden
Selective deworming: selected FEC high hosts. Allows refugia, heterogenicity. Host selection based on risk mapping. Ex: young vs. old, high FEC vs. low
**Treat young animals, high infective shedders, reduce adult worm burden, target inhibited larvae seasonally, reduce overall or selected portion of parasite population
Disease Mapping Ostertagia sp.
Type 1.
- Target young cattle
- Goal is to reduce pasture contamination and hazardous infection
- March/April
Type 2
- Older heifers
- Mass emergence of arrested larvae
- Fecal exams likely negative
- Sep/Oct
- Stockers and new addition must be treated
SMART Deworming
- Seasonal variation, life cycle, biology, disease risks
- Few as possible treatmens
- Time before ERPs
- Benzimidazole, Imidazothiazole, Tetrahydropyrimidine drugs: provide ~21 EPR protection. Use for Cooperia if drug resistance is an issue
- IVM, MOC remove adults, inhibited larvae, protection from reinfection 21 PPP + 21 ERP = 42 days
