PARASITOLOGY - Equine Gastrointestinal Parasites Flashcards
What are the most significant equine nematodes?
Parascaris equorum
Large strongyles
Small strongyles
Strongyloides westeri
Oxyuris equi
Dictyocaulus arnfieldi
Describe the lifecycle for parascaris equorum
- Host ingests infectious L2 larvated eggs
- L2 moult into L3 and hatch within the small intestine
- L3 penetrate the small intestinal veins and travel to the liver via the hepatic portal vein
- L3 travel from the liver through the caudal vena cave to the right side of the heart and to the lungs
- L3 penetrate into the alveoli and migrate to the trachea where they are coughed up and swallowed
- L3 travel to the small intestine where they moult into L4 and then into adults
- Female adult worms produce eggs which are excreted into the faeces
What is the pre-patent period for parascaris equorum?
10 weeks
(T/F) Parascaris equorum eggs can persist in the environment
TRUE.
Which signalement is affected by parascaris equorum?
Parascaris equorum affects young horses such as foals, weanlings and yearlings. Adult horses develop resistance against parascaris equorum
How does parascaris equorum cause colic?
Adults parascaris equorum reside in the small intestine where they can cause small intestinal obstruction and colic
How do you diagnose parascaris equorum?
You can diagnose parascaris equorum using faecal egg flotation and egg counts. If one young horse is diagnosed, you should treat all surrounding young horses
How do you treat parascaris equorum?
Treat the adult parascaris equorum with fenbendazole or pyrantel and treat the larval stages with ivermectin
Which anthelmintic drugs should you avoid using in young horses with a high parascaris equorum worm burden?
Pyrantel
Ivermectin
Why should you avoid using high dose anthelmintics in young horses with high parascaris equorum worm burdens?
Pyrantel and ivermectin both cause rapid paralysis and death of the worms which can cause colic due to the increased risk of small intestinal obstruction
How should you treat young horses with a high parascaris equorum worm burden?
Treat with repeated doses of fenbendazole on days 1, 4 and 7 in combination with a low bulk diet and nasogastric liquid paraffin to help lubricate the intestines to improve worm excretion and reduce the risk of obstructions. Repeat the faecal flotation and egg count three weeks after the final dose of fenbendazole to ensure the worms have been excreted
How do you control parascaris equorum?
- Regular faecal monitoring
- Stable and pasture hygiene
- Avoid using the same paddocks for nursing mares and foals in successive years as the eggs persist and infect the foals
- Do faecal egg count reduction tests (FECRT) to determine if there is any anthelmintic resistance
- Regular deworming
Which anthelmintics are parascaris equorum resistant to?
Ivermectin
What is the deworming protocol for parascaris equorum?
To control parascaris equorum, administer anthelmintics to foals from 1 month old for every 4 weeks until they are 6 months old
What is the most significant species of large strongyles that affects horses?
Stongylus vulgaris
Describe the lifecycle for strongylus vulgaris
- Host ingests infective L3 larvae
- L3 penetrate the large intestinal mucosa and moult into L4
- L4 migrate via the large intestinal arteries to the cranial mesenteric artery where they moult into pre-adults
- Pre-adults migrate to the large intestine where they penetrate the large intestinal mucosa and enter the lumen where they moult into adults
- Female adults produce eggs which are excreted into the faeces
- L1 develop and moult into L2 and L3 in the environment
Where specifically in the large intestine do adult strongylus vulgaris reside?
Lumen of the caecum and ventral colon
What is the pre-patent period for strongylus vulgaris?
6 to 7 months
How does strongylus vulgaris cause colic?
When strongylus vulgaris L4 larvae migrate through the cranial mesenteric artery, this leads to thrombosis, non-strangulation infarction and large intestinal necrosis which results in colic which requires surgical correction
How do you diagnose strongylus vulgaris?
You can diagnose strongylus vulgaris using faecal egg flotation and egg counts
How do you treat strongylus vulgaris?
Treat the adult strongylus vulgaris with oxibendazole, fenbendazole or pyrantel. Treat the larval stages with ivermectin or moxidectin
(T/F) Strongylus vulgaris infection is very common in horses in the UK
FALSE. Strongylus vulgaris is no longer very common in the UK as it is very sensitive to anthelmintics so has become less prevelant due to routine deworming protocols. However there is a risk of re-emergence due to strategic deworming strategies
What is the most significant species of small strongyles that affects horses?
Cyathostomins (red worm)
Cyathostomins are the most prevalant and pathogenic nematodes in horses!!!
Describe the lifecycle of cyathostomins
- Host ingests infective L3 larvae
- L3 penetrate the large intestinal mucosa and moult into L4
- L4 migrate back into the large intestinal lumen and moult into adults
- Female adults produce eggs which are excreted into the faeces
- L1 develop and moult into L2 and L3 in the environment
Or the L3 larvae can encyst in the large intestinal mucosa and undergo arrested development for a period of 1 -2 years and eventually there will be synchronous emergence of L4 larvae into the lumen, damaging the intestinal mucosa. There is a risk that when you treat the adults with anthelmintics, this can trigger larval emergence
Where specifically in the large intestine do adult cyathostomins reside?
Lumen of the caecum and the large colon
What is the minimum pre-patent period of cyathostomins?
6 weeks
Describe the pathogenesis of cyathostomins disease
When L3 encyst in the large intestinal mucosa and eventually there will be synchronous emergence of the L4 larvae into the lumen, damaging the intestinal lining which causes swelling, hindering digestion and nutrient uptake resulting in diarrhoea, life-threatening colitis, protein losing enteropathy and colic
What can trigger cyathostomins L4 emergence?
Synchronous emergence of L4 cyathostomins can be triggered when the adult worms are killed by anthelmintic treatment, which can cause a change in the intestinal environment which prompts the larvae to emerge
When is cyathostomins disease most prevalent?
Cyathostomins disease is most prevelant in late winter/spring
How do you treat cyathostomins disease?
Fluid therapy
Plasma transfusion or synthetic colloids
Corticosteroids
Deworming using moxidectin
Why should you administer plasma/synthetic colloids to patients with cyathosyomins disease?
Plasma transfusions and synthetic colloids can be used to replenish protein loses as a result of severe diarrhoea
Why is moxidectin the anthelmintic of choice when treating cyathostomins disease?
Moxidectin targets all stages of the cyathostomins lifecyle, including the larval stages within the large intestinal mucosa
(T/F) You can use ivermectin to kill cyathostomin larvae
FALSE.
How do you control cyathostomins?
- Control of cyathostomins is challenging due to the encysted larval stage of the lifecycle which will not be detected by faecal eggs counts so it is challenging to monitor for this parasite. However, you can use a serum ELISA which will detect antibodies against the larvae - which is especially useful if the faecal egg count is low but you still suspect cyathostomins based on the clinical history
- Deworming protocols with moxidectin
Which anthelmintic are cyathostomins resistant to?
Fenbendazole
(T/F) Strongyloides westeri is very clinically significant
FALSE. Strongyloides westeri is not very clinically significant
Where do adult strongyloides westeri reside?
Adult strongyloides westeri reside in the small intestine of nursing foals
How do strongyloides westeri enter the small intestine of nursing foals?
Strongyloides westeri larvae encyst in the abdominal wall of the dam and will be mobilised and excreted in the milk resulting in transmammary transmission to the nursing foals
What is the main clinical sign of strongyloides westeri in nursing foals?
Diarrhoea
|Very uncommon cause of dirrhoea in foals
How do you prevent strongyloides westeri?
Treat the dam with moxidectin 4 weeks prior to parturition
What is the other name used for oxyuris equi?
Pinworms
(T/F) Oxyuris westeri is very common
FALSE. Oxyuris is not very common however it is beginning to become more prevelant due to anthelmintic resistance
Where do adult oxyuris equi reside?
Adult oxyuris equi reside in the lumen of the colon
What are the three main clinical signs of oxyuris equi?
Rubbing of the tail
Perianal alopecia
Eggs present in the perianal area
Describe the pathogenesis of oxyuris equi
Adult oxyuris equi reside in the lumen of the colon. Gravid female oxyuris equi will migrate to the anus and deposit eggs in the perianal area, resulting in itching and perianal alopecia
How do you diagnose oxyuris equi?
You diagnose oxyuris equi using an acetate tape sample of the perianal area and assessing for eggs under the microscope
How do you treat oxyuris equi?
Treat oxyuris equi with fenbendazole or pyrantel
How do you control oxyuris equi?
- Oxyuris equi is challenging to control as the eggs become well dispersed within the environment
- Clean the environment
- Deworming protocol (fenbendazole or pyrantel)
Describe the lifecycle of dictyocaulus arnfieldi
- L3 larvae are ingested by host
- L3 larvae penetrate the intestinal mucosa and travel to the mesenteric lymph nodes where they moult into L4 larvae
- L4 larvae travel via the blood and lymphatics to the bronchioles where they moult into young adults
- Young adults migrate to the bronchi where they moult into mature adults and produce eggs
- Eggs are shed in the faeces
- L1, L2 and L3 develop in the faeces
What is an important history question to ask if you suspect a horse has dictyocaulus arnfieldi?
Does you horse live with or has been in contact with any donkeys?
As donkeys are reservoirs for this parasite
What are the most significant equine cestode?
Anoplocephala perfoliata
What are the hosts for anoplocephala perfoliata?
Final host: Horse
Intermediate horse: Forage mites
Describe the lifecycle of anoplocephala perfoliata
- Eggs are ingested by forage mites (intermediate hosts) where they develop into cysticercoids
- Horses ingest infected mites and the cystircercoids are released when the mites are digested
- Cystircercoids attach to the ceacal wall, particularly at the ileo-caecocolic junction where they will develop into adults
- Gravid proglottids filled with eggs are expelled within the faeces
Where do adult anoplocephala perfoliata reside?
Lumen of the ceacum, particularly at the ileocaecocolic junction
Describe the pathogenesis of anoplocephala perfoliata
Anoplocephala reside at the ileo-caecocolic junction causing inflammation, colic, ileal impactions and even intussusception of the ceacum and colon
How do you diagnose anoplocephala perfoliata?
Anoplocephala perfoliata is not detected on routine faecal egg counts but a serum or saliva ELISA can be used
How do you control anoplocephala peroliata?
Deworm with praziquantel in Spring (routine) and Autumn (if high antibody titre)
Twice if there are high antibody titres
What is the most specific species of arthropod in horses?
Gasterophilus
Where in the gastrointestinal tract is gasterophilus intestinalis found?
Gasterophilus intestinalis is found in the lumen of the cardia of the stomach
Describe the lifecycle of gasterophilus intestinalis
- Horses ingest eggs from their fur as they’re grooming
- Larvae (bots) reside within the cardia of the stomach
- Pupae reside on pasture where they develop into adult flies
- Flies lay eggs on the hair of the host
(T/F) Gasterophilus intestinalis can cause colic
FALSE. Generally gasterophilus intestinalis don’t cause clinical disease, they eggs just cause irritation on the limbs
What is the clinical significance of gasterophilus haemorrhoidalis?
Gasterophilus haemorrhoidalis larvae (bots) attach to the rectal mucosa and can cause rectal prolapse
What are the goals of parasite control?
The aim of parasite control is not to eradicate all parasites, it is to limit parasite infections to prevent clinical illness, and to avoid further development of anthelmintic resistance as much as possible
What pasture management can be used to control parasites in horses?
Poo-picking
Rotational grazing
Mixed grazing with ruminants
Avoid high stocking density
What should you be aware of when carrying out mixed grazing between horses and ruminants?
Mixed grazing with ruminants increases the risk of liver fluke in horses
What is the general anthelmintic protocol for adult horses?
Depending on the climactic conditions, one to two annual anthelmintic treatments using moxidectin (one as routine, second based on faecal egg counts), and one annual treatment with praziquantel should be sufficient. It is important to use a treatment effective against cyathostomins at a time when the larval mucosal burden will be at it’s peak - typically towards the end of grazing season (autumn/winter)
How often should you evaluate the efficacy of anthelmintics in horses?
You should do faecal egg count reduction tests (FECRT) every three years using 5 - 10 horses to get a representative sample
What is the general anthelmintic protocol for foals, weanlings and yearlings?
During the first year of life, foals should dewormed a minimum of four times. First deworming should occur at 2 to 3 months old, including a benzimidazole to target parascaris equorum. Second deworming should occur just before weaning. At weaning, feacal egg counts are recommended to determine if the worm burderns are primarily strongyles or parascaris equorum, to facilitate the right choice of drug classification. Third and fourth treatments should be considered at around 9 to 12 months old and the treatment should primarily target strongyes and cestodes
When should you treat adult horses for parasites other than for regular deworming?
Treat adult horses for parasites if they have equal to or more than 200 eggs per gram (epg)
When should you treat young (less than 2 years) and geriatric horses for parasites other than for regular deworming?
Treat young and geriatric horses for parasites if they have equal to or more than 100 eggs per gram (epg)
What are the limitations of faecal egg counts?
Faecal egg counts do not reflect the total adult worm burden or detect the larval or encysted stages of the parasite. Furthermore, cestode and oxyuris equi infections are often missed or underestimated by faecal egg counts
