Equine Parasites

Equine Clinic at OakenCroft Client Education Originally Presented 2013, updated January 2015 Overview of parasites • Internal parasites, or worms, can cause extensive damage to the host (horse) without the owner even realizing the horse is heavily infected. • Effects of parasites range from dull hair coat and weight loss to colic and death • These parasites lower the horse’s resistance to infection, steal valuable nutrients, and can cause permanent damage to internal organs Definition: . A parasite uses another living organism to live at the expense of that organism Types of Internal Parasites

There are more than 150 species of parasites that can affect the horse. The most common are as follows: Strongyles Roundworms Strongyloides Tapeworms Pinworms Bots Life Cycle of the Parasite

• Eggs or larvae are deposited on the ground in the manure of an infected horse. • They then develop in the environment and are swallowed by the horse while it is grazing • Larvae then mature in the horse’s digestive tract. Some parasites migrate to other tissues or organs before returning to the intestines to mature into egg‐laying adults. Small Strongyles

Cyanthostomes

Most common intestinal parasite in horses today

Infect cecum and colon Small Strongyles

• Encysted stage – burrow into lining of intestines – dormant for months before completing life cycle – many dewormers ineffective when in this stage • Damage to intestines can be severe when larvae emerge • Signs (not very specific): – slow growth in young horses, – poor hair coat, lethargy – colic, diarrhea, weight loss Small Strongyles ivermectin or moxidectin may be used against adult worms in lumen.

Evidence of strong resistance to current dewormers

To kill encysted larvae in mucosa of intestine need to do a “Panacur Powerpac®” (twice the dose of Panacur® (fenbendazole) once a day for five days) or Quest® Large Strongyles

• Name: Strongylus vulgaris • Affects cecum & colon • Tx: Ivermectin – Current deworming programs have eliminated most problems with large strongyles although some parasitologists are concerned about resistance Roundworms (ascarids) Roundworms

• Name: Parascaris equorum

• Most common in horses <2 years old • Infection of adult ascarids in large numbers can cause blockage (impaction) of the intestines • Eggs can survive in environment for several years • Tx: Fenbendazole (double dose) Foals start at 60 days and treat every 60 days until 2 years old Roundworms

• Potential clinical signs in young horses – Coughing – Rough hair coat – Poor body condition & growth – Pot belly – Colic—most often seen when deworming older foals for the first time Roundworm Impaction in Weanling Tapeworms

• Anoplocephala spp.

• Intermediate host = orbatid mite

• Horse ingests mite during grazing

• Usually do not see eggs on fecal Tapeworms

• Tx: – PRAZIQUANTEL – Pyrantel (at two times the dose) • Recommendations vary

Equimax: Abamectin and Praziquantel

Strongid: Pyrantel Zimecterin: Ivermectin & Praziquantel What is a ‘fecal’ test?

• Fecal Egg Count – Manure sample examined to estimate number of eggs being shed by individual horse – Best to take samples from each horse 1‐4 x/year depending on individual horses – Can also do before and after deworming to evaluate effectiveness of medication • Effectiveness can vary from horse to horse depending on type of parasites and resistance levels • Some horses inherently more susceptible to heavy parasite loads Foal Specifics

• Young horses are more susceptible, in general, to everything, including parasites • Protocol: – Birth: Ivermectin to Dam for Strongyloides – Birth to two years: Double dose fenbendazole every 60 days starting at day 60, skip dose at one year – One year of age: Ivermectin – Fecal Egg Counts every six months for first few years Interpreting a Fecal Exam

• A Negave Fecal ≠ Parasite Free! – May be before pre‐patent period (i.e., worm not producing eggs) – Eggs might be missed (i.e., tapeworms) – Eggs are not passed in every fecal ball – Lab error – Poor quality sample Parasite Management

• Pasture Rest—prevent overgrazing if possible • Pasture Rotation with cattle or sheep • Manure removal—AT LEAST 2x weekly • Compost before spreading manure – Do not spread on your grazing fields • Remember to only harrow fields when HOT & HUMID other wise you are just redistributing eggs • Parasites concentrated on grass, not dirt – Edges of paddocks are the worst • Deworm as needed Dewormers (Anthelmintics)

I AM SO CONFUSED! Dewormers 1890–1940 Turpentine Boiled linseed oil Mixtures of asafetida Areca nut powder Savin fern extracts Iron sulfate Gentian Bran mash Tobacco – nicotine Anthelmintics 1940–1997

In 1940  phenothiazine In 1970  pyrantel now useless strongid and strongic C In 1950  piperazine In 1980  macrocyclic now useless lactone (ivermectin) In 1960  benzimidazoles In 1997  macrocyclic panacur (fenbendizole), lactone, (moxidectin, oxibendizole Quest)

Praziquantel (tapes) Drug Name Trade Names Effective Against Not Effective Against Ivermectin Eqvalan, Large strongyles; adult Encysted small small strongyles; bots; strongyles Zimecterin roundworms; pinworms; strongyloides Moxidectin Quest Large strongyles; adult & Some encysted small some encysted small strongyles strongyles; bots; roundworms; pinworms

Fenbendazole Panacur Large & small strongyles; Higher dose kills more pinworms; roundworms encysted small strongyles

Praziquantel Equimax, Tapeworms QuestPlus; Zimectrin Gold Pyrantel Strongid Large & small strongyles; pinworms; roundworms Strategic deworming

• What is it? – Deworm only when needed by doing FECs (Fecal Egg Counts) on all horses – The less dewormer we use, the less resistance we develop – It takes 7 years for new products to get approved and nothing new is on the horizon—what we have now we are stuck with! – In upstate NY we only need to deworm between April/May to October/November. Parasites are dormant in the winter. Strategic deworming

• Check fecals first thing in the spring before deworming • If negative, recheck again later in year. Time frame will depend on risk level • If you have dewormed, you need to wait a specific time period before checking fecals again unless you are looking for effectiveness of dewormer • Many horses need deworming only 1‐2x yearly Things to think about

• Read the chemical name—generics work just as well • Strongid (pyrantel) and Panacur (fenbendazol) have significant resistance, esp. in the South • Quest is a good dewormer but must be dosed accurately based on horse’s weight • Don’t use Strongid C through the winter months—breeds resistance Questions?