VET 350 Sections 5.5-5.7.2 PowerPoint-1

Cestocidal Drugs, Trematodes, and Flukicidal Drugs

Cestocidal Drugs

  • Tapeworm treatments: Limited to praziquantel and epsiprantel.

  • Treatment targets: Adults are the easiest to treat.

  • Efficacy of praziquantel: Effective against Echinococcus.

  • Other options: Benzimidazoles work against some tapeworm species; Pyrantel is useful for Anoplocephala in horses.

Praziquantel Mechanism

  • Action: Causes Ca2+ influx across the tegument, resulting in muscular spasms that dislodge the parasite.

  • Aftermath: Dead worms are targeted by immune cells and digested.

Trematodes Overview

  • Adult flukes: Flat, leaf-shaped with suckers.

  • Two groups:

    • Monogenean Trematodes: Ectoparasites of fish; single oral sucker and multiple posterior suckers, direct life cycles.

    • Digenean Trematodes: Endoparasites in vertebrates; possess oral and ventral suckers; lack anuses.

Digenean Trematodes Immunity Evasion Strategies

  • Rapid surface turnover: Sloughing off of antibodies and host cells.

  • Molecular disguise: Mimicking host molecules on parasite surfaces.

  • Immunomodulation: Factors released reduce host immune response.

  • Antibody cleavage: Enzymes deactivate host antibodies.

Life Cycle of Digenean Trematodes (Example)

  • Infection to maturation: Eggs in feces -> Miracidium hatches -> Encysts as metacercaria -> Development in lymnaeid snails for weeks.

Important Digenean Trematodes

  • Fasciola: Causes production losses in ruminants.

  • Dicrocoelium: Prefers drier environments, less damaging.

  • Fascioloides: Harmless in wild animals, but lethal to sheep.

  • Schistosomes: Serious pathogens in humans and animals, especially in tropics.

Fasciola Specifics

  • Fasciola hepatica: 2-5 cm adults, live in the bile ducts of various animals; zoonotic.

  • Life-cycle: Eggs require 50°F+ to develop; several weeks in snails.

Snail Biology

  • Habitat: Prefer wet, muddy conditions; feed on green slime.

  • Survival: Freezes kill most adults; new generations hatch in spring.

Parasitic Migration of Fasciola

  • Process: Metacercaria swallowed, penetrates small intestine, reaches liver to mature.

  • Prepatent period: 10-12 weeks.

Disease Manifestations of Fasciola

  • Acute Disease Pathogenesis: Large numbers of metacercaria lead to severe tissue damage; may cause Black Disease toxin from Clostridium novyi type B.

  • Chronic Disease Pathogenesis: Smaller ingestions cause poor weight gain, production losses, liver fibrosis, and edema due to protein loss.

Other Digenean Trematodes

  • Paramphistomum: Cylindrical, attaches to rumen, causes enteritis and diarrhea.

  • Dicrocoelium: Asymptomatic, requires two intermediate hosts: land snail and ant.

Additional Digenean Trematodes

  • Fascioloides magna: Can be large, with moose and deer as final hosts; aberrant hosts include sheep and goats.

  • Schistosoma: Blood flukes living in blood vessels, causing swimmer’s itch and serious zoonoses in Asia.

Trematodes Affecting Dogs and Cats

  • Alaria: Snails and frogs/toads as intermediate hosts; rodents as paratenic hosts.

  • Nanophyetus: Fish hosts; can transmit Neorickettsia salminicola, leading to salmon poisoning.

Flukicidal Drugs

  • Praziquantel: Treats human schistosomosis; not effective for Fasciola.

  • Benzimidazoles: Albendazole targets adult Fasciola hepatica; netobimin effective against Dicrocoelium.

  • Triclabendazole: Effective against all stages of F. hepatica.

  • Salicylanilides: Closantel, nitroxynil, and oxyclozanide; limited use in dairy due to plasma protein binding; ineffective against young migrating flukes.