1. Antiparasitics Chapter 12-1
Dr. Dipa Brahmbhatt VMD MpH

2. Objectives Terminology – antiparasitics MOA antiparasitics
Precautions of antiparisitics

3. Parasites and Animal Disease
Parasitism is a relationship between two different organisms in which one of the organisms (parasite) benefits while the other (the host) is harmed
The harm inflicted depends on the health of the host and can range from minor illness to generalized impairment
Some parasitic infections can be zoonotic.

4. Parasites and Animal Disease
Parasites can be contracted by:
Animal to animal contact
Ingestion of contaminated food or water
Insect transmission
Direct contact with the parasite
Walking, lying, or rolling on infected soil
Some parasites might not cause any clinical signs in the animal
Most intestinal parasites are diagnosed by microscopic fecal examinations
Some clinical signs may manifest before eggs are detected

5. Basic Terminology
Endoparasites live within the body of the host and cause internal parasite infections.
Helminths
Protozoa
Ectoparasites live on the body surface of the host and cause external parasite infestations.
Arthropods
Insects: flies, mosquitoes, bots, cuterebra, lice & fleas
Arachnids: spiders, scorpions, ticks & mites

6. Endoparasites Helminths are divided into two major groups:
Nematodes: cylindrical, nonsegmented worms commonly called roundworms
Platyhelminthes: flattened worms that are subdivided into two groups:
Cestodes (tapeworms)
Trematodes (flukes)

7. Endoparasites Nematodes (roundworms)
Inhabit stomach and intestine: domestic animals, wild animals and birds
Mostly by fecal-oral route (Except mff)
Platyhelminths (flatworms)
Cestode: can be in body tissue/ intestinal
Trematode: can be in bile ducts of ruminants

8. Helminths of Veterinary Significance

9. Endoparasites Protozoa Single-celled parasites
Categorized by type of movement
Cilia, flagella,
pseudpodia , no movement
Eimeria
Giardia

10. Ectoparasites Fleas Mosquitoes Bots Cuterebra Lice Flies Arachnids
Ticks
Mites

11. Antiparasitic Drugs Endoparisticides treat endoparasites
Anthelmintics treat helminth internal parasites (worm) infections (disrupt metabolic pathway): vermicide (kills worms) and vermifuge (paralyzes worm +/- live worm in stools)
Antinematodals: hookworms, ascarids, whipworms, strongyles
Avermectins and Milbemycins
Benzimadazoles
Pyrantel pamoate
Piperazines
Organophosphates
Anticestodals (cestocides, taeniacides): Praziquantel, Epsiprantel

12. Antiparasitic Drugs Ectoparisiticides treat ectoparasites
Antitrematodals: Paragonimus, Fasciola and Dicrocoelium
Antiprotozoals treat protozoan parasite infections: Coccidia, Giardia, Toxoplasmosis
Coccidiostats: against coccidia
Amprolium, Metronidazole, Fenbendazole (Panacur), Ponazuril (Marquis)
Ectoparisiticides treat ectoparasites
OP and carbamates, Antidotes, pyrethrins, Amitraz, Macrolides, Imidaclopromid, Fipronil, Nitenpyram, Lufenuron,
Endectocides treat internal parasitic (endoparasites) infections and external parasitic (ectoparasites) infestations.
Caution in old, young, pregnant, breed & debilitated animals

13. Ideal Antiparasitic Selective toxicity to parasite
Does not induce resistance in target parasite
Economical: esp. in food animal
Effective against all parasite stages in 1 application
Other: lack of offensive odor, environment safety

14. Antihelmintics Water-insoluble Orally: suspension, paste, granules
Water soluble
Injection
Orally: solution
Topically: pour-on
Particle size
Small: Easily absorbed GI
Large: May be less toxic

15. Macrolides: Avermectins and Milbemycin Tetrahydropyrimidines
Antinematodals
Macrolides: Avermectins and Milbemycin
Benzimidazole drugs
Imidazothiazoles
Tetrahydropyrimidines
Organophosphates
Piperazine compounds

16. Macrolides: Avermectin and Milbemycin
Avermectins (macrocyclic lactones): Thank Streptomyces bacterium
MOA: Bind to Glutamate receptors > increases flow of chloride ion > parasite nerve and muscle cells > causing paralysis (unable to depolarize muscle – unable to contract) and death of the parasite
Adv: Safest for mammals, broad spectrum activity (internal/ external parasites)
Ivermectin: Heartguard (+ pyrantel pamoate), Ivomec: parenteral, Eqvalan
Extralabel use: demodex, ear mites, mff
Oral or injectable
Not effective against cestodes or trematodes (NO GLUTAMATE RECEPTORS)

18. Macrolides: Avermectin and Milbemycin
Ivermectin
Collies (collie like breeds: Shetland sheepdogs, Australian shepherds)
Have ivermectin sensitive – GABA receptor effect inhibits host function. DO NOT HAVE much P – glycoprotein in BBB hence allows in CNS where there are GABA receptors.
Toxicosis: 0.1 – 0.2 mg/kg (using LA products)
CNS: sedation, ataxia, mydriasis, loss of menace reflex, vomiting, salivation, stupor, coma. Bradycardia
TX: No antidote. IV fluids, O2, counteract hypothermia, atropine

19. Macrolides: Avermectin and Milbemycin
Selamectin: Revolution
Broad spectrum endectocide
Topical: fleas, ear mites, hwd: cats and dogs, sarcoptic mange and tick: dog, intestinal hookworms and roundworms: cats
Don’t use in sick, debilitated, underweight animals, cats: minimum age: 8 weeks
SE: pruritus, fever, rarely seizures

20. Livestock Macrolides Both: internal parasites, grubs, lice, mange
Doramectin: Dectomax (livestock)
Injectable, topical, pour – on
Safe in cattle (same dose in dogs can cause death)
Don’t use in veal calves and lactating cattle
Eprinomectin: Eprinex – cattle
Topical application - cattle

21. Macrolides: Avermectin and Milbemycin
Macrocyclic ring: avermectin, milbemycin, moxidectin – same MOA
Milbemycin oxime
Interceptor (hw prevention: dogs/cats)and Sentinel and trifexis
Heartworm preventative, mites, antinematodal: hookworms and roundworms, demodex, sarcoptes
Use with caution in heartworm positive animals and collies

22. Macrolides: Avermectin and Milbemycin
Moxidectin
Proheart (dogs), Cydectin – cattle (pour on), Quest – horses (oral gel OTC)
Uses: intestinal parasites, mites, cattle grubs, horse stomach bots, lice, flies, nematodes
Overdose: like ivermectin
Don’t use in horses < 4 months
Dogs: HW prevention and hookworms, > 7 months < 7 years of age. 6 months injectable

23. References
Romich, J.A. Pharmacology for Veterinary Technicians, 2nd edition
Bill, R.L. Clinical Pharmacology and Therapeutics for the Veterinary Technician, 3rd edition