parasitology- intro

What is a parasite?

-An organism that lives on or in a host and causes harm.

-is physiologically dependent

What is parasitism?

One organism benefits while the other is harmed.

What is a definitive host (DH)?

Host that carries adult parasites and the parasite reproduces

What is an intermediate host (IH)?

Host that carries larval parasite stages.

What is a paratenic host (PH)?

Host that carries parasite stages without development.

What is a dead-end host (D-EH)?

parasite ends up killing the host

What is a direct life cycle?

Life cycle involving only a definitive host with no intermediate or paratenic host involved

What is an indirect life cycle?

Life cycle involving a definitive host and one or more intermediate or paratenic host(s)

What is the pre-patent period (PPP)?

Time from infection until parasites are detectable.

What is the patent period (PP)?

Period when parasites are detectable and cause disease.

-growing/developing/multiplies/reproduces, causing symptoms

What are infectious or diagnostic stages?

Detectable parasite forms such as eggs, oocysts, or larvae.

What are helminths?

-Multicellular eukaryotes.

-Kingdom Animalia

-nematodes, cestodes, trematodes

What are nematodes?

Roundworms with separate sexes and a complete digestive system.

What developmental stages do nematodes have?

Egg, L1-L5 larvae, and adult.

What superfamily do ascarids belong to?

Ascaroidea.

What are key characteristics of ascarids?

-large, thick bodied worms

-direct/indirect life cycle

-thick shelled single celled eggs passed in feces

-larvated eggs = infectious

How are ascarids typically diagnosed?

Fecal flotation.

What is the pre-patent period of ascarids?

Approximately 2-2.5 months.

What species does Ascaris suum infect?

Swine.

Is Ascaris suum zoonotic?

Yes.

What clinical signs does Ascaris suum cause?

Thumps, milk spots in liver, stunted growth, diarrhea, poor nutrient absorption, intestine perforation

What species does Parascaris equorum infect?

Horses.

Which horses are most susceptible to Parascaris equorum?

Foals 3-9 months old.

What clinical signs does Parascaris equorum cause?

Coughing, diarrhea, colic, poor appetite, failure to thrive

What species does Toxascaris leonina infect?

Dogs, cats, foxes, wolves, big cats in zoos

Is Toxascaris leonina zoonotic?

No.

Does Toxascaris leonina cause clinical disease?

no

What species does Toxocara cati infect?

Cats.

Is Toxocara cati zoonotic?

Yes.

How is Toxocara cati transmitted?

transplacental and transmammary routes.

What clinical signs occur in kittens with Toxocara cati?

Pot belly, dull coat, loose stool.

What species does Toxocara canis infect?

Dogs and wild canids.

Is Toxocara canis zoonotic?

Yes.

What percentage of puppies are born infected with Toxocara canis?

About 90%.

How are Toxocara species identified grossly?

Shape of cervical alae.

What is Baylisascaris procyonis?

Zoonotic raccoon and dog roundworm

What is visceral larva migrans (VLM)?

Larvae migrate through the liver, lungs, and heart

What is ocular larva migrans (OLM)?

Larval migration into the eye causing ocular disease

What is neural larva migrans (NLM)?

Larval migration and larval growth in the brain and spinal cord.

How is larval migrans diagnosed?

-Serologic assays (antibody testing)

-can differentiate between LM caused by Toxocara spp. and Baylisascaris spp.

Why are ascarid eggs difficult to eliminate?

They are highly resistant in the environment.

What is key to small-animal ascarid control?

• Deworming in females dogs and cats, or they can re-infect themselves and subsequent litters

• environmental management

  • remove top 6” of soil

  • entombing concrete

  • clean kennels of organic debris

  • clean kennels with bleach (won’t kill eggs)

  • flaming kennels with torch

What drug classes are used to treat ascarids?

• Macrocyclic lactones

  • milbemycin or ivermectin

• benzimidazoles

  • fenbendazole

• emodepside + praziquantel or another combo

what is the most common cause of disease in animals and humans?

parasites

why are parasites difficult to control?

complex life cycle

what is a major loss that occurs from parasites?

economic losses (globally)

here’s a little thing to help better understand direct vs indirect life cycles

direct

• only ONE host species is required

• the parasite develops to an infective stage in the environment or within the same host

• transmission is usually fecal-oral, skin penetration, or ingestion of larave/eggs

• no intermediate host = no biolgical development in another animal

• some paratenic hosts can be used by direct-cycle parasites but do not require them.

  • paratenic host = transport host

  • no development occurs

  • parasite just “waits” to be eaten

  • example: toxocara canis in rodents

• nematodes, protozoa

• fast transmission

• typical flow: adult parasite in host → eggs/larave shed into environment → eggs embryonate or larvae develop → same host species ingests or contacts infective stage → new adult develops

indirect

• requires two or more host species

• parasite must develop inside an intermediate host

• without the intermediate host, life cycle breaks

• typical flow

  • adult parasite in definitive host → eggs/larvae shed → intermediate host ingests or is penetrated → larval development to infective stage → definitive host eats intermediate host or is bitten → adult develops

• cestodes, trematodes

*ask yourself: can this parasite mature if the host never eats or is bitten by another species?

-yes: direct

-no: indirect

what are the 13 nematode superfamilies

1. ascaroidea

2. trichinelloidea

3. strongyloidea

4. spiruoidea

5. filariodea

6. dracunculoidea

7. physalopteroidea

8. oxyuroidea

9. rhabditoidea

10. ancylostomoidea

11. trichostrongyloidea

12. metastrongyloidea

13. dictophymoide

hopefully dont need to know these!!!!!!!!!!!!!!

which ascarid is also know as “arrow headed worm”

toxocara cati

what is the key to large animal parasite control?

• deworm pregnant mares prior to giving birth

• deworm gilts prior to breeding

• deworm sows prior to giving birth

  • keep stalls clean after delivery

• environment management

  • keep pens and stalls clean

  • remove top 6” of soil

why must you eliminate worms in female dogs and cats?

they can re-infect themselves and their litters