Antiparasitics Chapter 12-1 Dr. Dipa Brahmbhatt VMD MpH dbrahmbhatt@vettechinstitute.edu

Objectives Terminology – antiparasitics MOA antiparasitics Precautions of antiparisitics

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.

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

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

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)

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

Helminths of Veterinary Significance

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

Ectoparasites Fleas Mosquitoes Bots Cuterebra Lice Flies Arachnids Ticks Mites

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

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

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

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

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

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)

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

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

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

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

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

References Romich, J.A. Pharmacology for Veterinary Technicians, 2nd edition. 2010. Bill, R.L. Clinical Pharmacology and Therapeutics for the Veterinary Technician, 3rd edition. 2006.