Internal Parasites in Horses

Parasite

• Organism that lives off another organism at the expense of the host

What are symptoms of worms?

• Dull hair coat

• Weightloss

• Recurring colic

• Diarrhea

• Slow growth

• Stomach ulcers

• Pot Belly

Major Equine Parasites

• Strongyles (Large and Small)

• Roundworms

• Bots

• Pinworms

• Tapeworms

Strongyles

• Includes both large and small strongyles

• Most common

• Commonly referred to as bloodworms– Because of color after it ingests blood from

host animal

Life Cycle

• Larvae develop to infective stage within one week

• Larvae crawl up blades of grass and are ingested by the horse

• Once ingested, larvae travel through the digestive system to the large intestine– S. vulgaris migrate to the anterior mesenteric

artery

Life Cycle

– S. endentatus to the liver and flank area– S. equinus migrate to the liver and pancreas

• Adult large strongyles live in the cecum and large intestine

• Eggs are laid in the cecum and large intestine and passed through the feces

• Superior mesenteric artery

Adult Strongyle Damage

• These worms are aggressive feeders

• After feeding, move to a fresh site leaving a bleeding crater

• Craters ulcerate and heals, leaving scar

Large Strongyles in Mesenteric Artery

• Large strongyles can live in mesenteric artery, which supplies blood to the intestine

• Inflame artery wall

• Create blood clots that interfere with oxygen and nutrients to/from the intestine

• Leads to severe and often fatal colic

Small Strongyles

• Also called cyathostomes• Cause under-performance

– Loss of condition– Feed inefficiency– Predisposition to secondary diseases

• Are extremely prolific• Emerge from lining of intestines and leave

an ulcerated gut wall

Roundworms

• Adult roundworms are visible to the eye

• Roundworm larvae migration through the lungs and liver is most dangerous

• Often causes foal pneumonia – potentially fatal

Large Roundworms

• Most common in young horses

• Intestinal infections may show no clinical signs

• Can decrease gut motility

• Intestinal impactions from clustered roundworms may cause rupture to the intestine and produce peritonitis

Roundworm Life Cycle

• Host foal ingests infected eggs from contaminated environment and/or feed. Eggs pass through oral cavity to the stomach and into the small intestine. (Solid Arrows)

• Eggs hatch in intestine and migrate through the liver to the lungs via the circulatory system. Larvae then travel to the pharynx and are swallowed (tracheal migration shown by the interrupted arrows). Larvae mature to adult state in the small intestine

Roundworm Life Cycle

• Adult roundworms in small intestine• Eggs are laid in the small intestine• Eggs are excreted in feces• Larvae develop to infective 2nd state eggs

within two weeks• Emaciated infected foal• Adult roundworms clustered in ruptured

small intestine

Bots

• Eggs are yellow in color• Eggs are difficult to remove• Each female bot fly may lay as many as 1,000

eggs• Removal of eggs on hair coat when present is

essential• Use lvermectin or Moxidectin 1 month after first

frost and in spring to eliminate larvae in stomach

Bot life Cycle

• Pupae form in loose soil• Adult bot fly emerges from pupa in 3-10 weeks.

Female posterior is long and pointed to deposit eggs.

• Common bot fly (G. intestinalis) lays eggs on leg hairs. Eggs must be licked to hatch larvae. After ingestion, larvae tunnel in epithelium of tongue and form pockets between upper molars. One month later, larvae migrate to stomach or duodenum

Bot life Cycle

• Throat bot fly (G. nasalis) lays eggs on hairs around side and back of mouth. Eggs are ingested with food and water.

• Nose bot fly (G. hemorroidalis) lays eggs around nose and mouth. Eggs ingested with food and water.

• Larvae of bot fly cluster on linings of stomach and proximal duodenum

Bot life Cycle

• Larvae passed in feces

• Common bot fly larva

• Throat bot fly larva

Pinworms

• Major sign is horse rubbing his tail or rear quarters on any available surface

• Caused by females depositing eggs• Eggs are pale yellow to cream colored• Contain fluid• Need a microscope or hand lens to view

them• Cleanliness is essential prevention

Pinworm Life Cycle

• Sticky eggs will adhere to walls, fences, bedding, and will be found in water or feed

• Larvae develop into infective stage within the eggs

• Infective larvae are ingested by the host. Larvae travel through digestive system to the cecum and large intestine where they mature in four or five months.

Pinworm Life Cycle

• Adult pinworms reside in the lumen of the cecum and large intestine

• Adult female crawls to the skin around the anal area to deposit eggs in clusters

Tapeworms

• Tapeworms have a head (known as the scolex) and a segmented body. There are three known species of pathogenic tapeworm, with Anoplocephala perfoliata being the most common. Other species reported are rare and rarely cause disease.

• Tapeworms do not have separate sexes, the segments (proglotids) contain eggs which develop and mature. These mature segments detach and are passed out in the horse's faeces where they disintegrate, releasing the eggs.

Tapeworms

• Tapeworms can be up to 20cm in length, although normally average around 4-5cm; rarer species can be up to 80cm long. They are white in colour.

• Looks like rice• Found at the narrow junction between the small

and large intestine, tapeworm use the four suckers on their head to attach to the lining of the digestive tract to avoid being swept away from the intestine by peristalsis.

Tapeworm Life Cycle

• The tapeworm life cycle is about 6 months long and has an intermediate host called the oribatid (forage) mite found on the pasture, as well as in food and bedding. The mite consumes the egg passed in the feces, and the immature tapeworm (cysticercoid) then develops inside the mite before it itself is ingested by the horse.

Treatment

Depends on

Time of

Year!

Fenbendazole

• treatment of large strongyles, small strongyles, pinworms, and ascarids

Moxidectin

• kills bots, small strongyle larvae encysted in the intestinal wall. These larvae are responsible for many of the late winter/early spring colics when they emerge from the intestinal wall

Pyrantel Pomoate

• Kills large strongyles, pinworms, large roundworms, and small strongyles

• Can kill tapeworms if a “double dose” is given.(Off label)

Praziquantel

• Excellent at killing tapeworms

• Only comes combined with either Ivermectin or Moxidectin.

Ivermectin

• small strongyles, large strongyles, pinworms, ascarids, hairworms, large-mouth stomach worms, bots, lungworms, summer sores, and intestinal threadworms

Oxibendazole

• roundworms, strongyles, threadworms, pinworms and lungworm

January: Broad Spectrum de-wormer such as fenbendazole (Panacur, Safe-Guard); oxibendazole (Anthelcide EQ)

 

March: Ivermectin 1.87% (Equell, Equimectrin, Eqvalen, Ivercare, Zimectrin), for general de-worming.

 

April: Moxidectin plus praziquantel (Quest Plus or Combo Care), to treat encysted strongyles and tapeworms.

 

June: Either double dose pyrantel pamoate (Strongid, Strongyle Care) OR single dose praziquantel combination product with either ivermectin or moxidectin (Equimax, ComboCare, Quest Plus, Zimectrin Gold), to treat tapeworms.

 

August: Ivermectin 1.87% (Equell, Equimectrin, Eqvalen, Ivercare, Zimectrin) for bots; first dose.

 

October: Ivermectin 1.87% (Equell, Equimectrin, Eqvalen, Ivercare, Zimectrin) for bots; second dose.

 

November: Broad Spectrum de-wormer such as fenbendazole (Panacur, Safe-Guard); oxibendazole (Anthelcide EQ)