parasitology endoparasites
Endoparasites Lecture Notes
Definitions and Terminology
Endoparasite: A parasite that lives inside its host.
Most endoparasites are helminths (worms) or protozoa.
Parasite Terminology:
Anthelmintic: A drug used to treat parasitic worms.
Ectoparasite: A parasite that lives on the outside of an animal.
Helminths: Worms found mostly in the gastrointestinal tract, lungs, liver, and circulatory system. They are categorized into two major groups:
Nematodes (roundworms)
Platyhelminths (flatworms), which further divide into:
Cestodes (tapeworms)
Trematodes (flukes)
Host: An organism from which a parasite obtains nutrition or completes its lifecycle.
Definitive Host: The host of the sexual, adult stages of the parasite.
Intermediate Host: The host of the asexual or larval stages of the parasite.
Paratenic (Transport) Host: A host where the parasite lives but does not develop or reproduce.
Operculum: A cap or lid on some parasite eggs from which larvae emerge.
Parasitology: The study of organisms that live in or on another organism (host) to obtain nutrients.
Patent Period: The time during which the parasite is detectable via identification of ova or larval forms.
Prepatent Period: The time between initial infection and when the parasite becomes detectable.
Protozoa: Single-celled organisms characterized by one or more membrane-bound nuclei.
Trophozoite: The vegetative form of the protozoa life cycle that can feed, move, and reproduce.
Vector: An organism or vehicle that carries disease from one animal to another.
Biological Vector: Functions as an intermediate host for a parasite.
Mechanical Vector: Transports the parasite without it developing further.
Zoonosis: Diseases that can be transferred between animals and humans.
Overview of Parasitism and Symbiosis
Symbiosis: Refers to the interaction between two organisms living together.
Types of symbiotic relationships include:
Commensalism: One species benefits while the other is unharmed.
Mutualism: Both species benefit from the relationship.
Parasitism: One species benefits at the expense of the other.
The life cycle of a parasite describes the maturation through various hosts and developmental stages. Life cycles may be:
Direct: Does not require a vector.
Indirect: Requires one or more vectors.
Cestodes (Platyhelminthes/Flatworms)
Tapeworms
Subclasses:
Eucestoda: True Tapeworms
Cotyloda: Pseudotapeworms
All tapeworms require an intermediate host to develop larval stages.
Eggs are contained in segments called proglottids.
Each proglottid contains both male and female reproductive organs.
The scolex serves as the mouth part, while proglottids are the reproductive parts.
Clinical Signs of Tapeworms:
Generally mild, may include vague signs of intestinal upset.
Heavy infections may lead to:
Abdominal discomfort
Intermittent diarrhea or constipation
Vomiting
Flatulence
Enteritis leading to poor absorption of food
Enteric distress may encourage animals to drag their rear or bite at their tail due to irritation from migrating proglottids.
Dipylidium caninum (Flea Tapeworm) - Zoonotic
General Information: Most common tapeworm, known as the "cucumber seed tapeworm", found in the intestines of dogs, cats, and occasionally humans.
Size: 10-70 cm
Color: White to yellowish
Proglottids may be found in feces or moving outside the anus, resembling grains of rice or sesame seeds.
Life Cycle:
A flea (or occasionally a dog louse) serves as the intermediate host; larvae ingest the Dipylidium egg, maturing to the infective stage in the flea/louse.
Infection occurs when animals ingest the mature flea during grooming.
Prepatent Period: 14 to 21 days.
Diagnostic Test: Identification of proglottids or fecal flotation.
Taenia pisiformis (Rabbit Tapeworm)
General Information:
Intermediate Host: Rabbits and hares
Size: Up to 200 cm long
Color: White to yellow
Proglottids visible on anus and feces.
Life Cycle:
Eggs develop in the abdominal cavity; rabbits eat grass contaminated with feces containing eggs. Infection occurs by consuming viscera or whole rabbits.
Diagnostic Test: Identification of proglottids.
Echinococcus granulosa (Hydatid Tapeworm) - Zoonotic
General Information:
Associated with hydatid cysts; important due to zoonotic potential.
Size: Very small (2-5 cm).
Life Cycle:
Man, domestic animals, and wild animals serve as intermediate hosts.
Larvae create hydatid cysts in sheep, cattle, and humans.
Cysts are fluid-filled, surrounded by connective tissue, and contain numerous larvae (brood capsules).
Diagnostic Test: Fecal flotation.
Echinococcosis is a reportable zoonotic disease and must be reported to state authorities, often transmitted through infected dogs in areas with sheep.
Control and Treatment of Tapeworms
Primary Aims: Prevent the completion of the tapeworm life cycle:
Keep the environment clean and free of feces.
Remove intermediate hosts such as fleas.
Avoid letting pets consume undercooked meat.
Treatment: Praziquantel (Droncit®).
Nematodes (Ascarids/Roundworms)
Toxacara canis (Dog Roundworm) - Zoonotic
General Information:
Found in the small intestine of dogs, particularly in puppies and kittens.
Size: Males 3.5-5 cm, females 10-15 cm.
Shape: Cylindrical and tapered at both ends, white to cream in color.
Eggs: Large, oval, dark with a thick, rough shell; very resistant and can persist for years.
Life Cycle:
Egg develops into larvae within the egg.
Infective stage: Eggs hatch; larvae penetrate the mucosa, migrate through the liver, then to the heart/lungs.
Larvae further develop in the lungs, coughed up, and swallowed.
Mature into adult worms in the small intestine.
Zoonosis: People (especially children) may ingest ova from soil, leading to "Visceral Larval Migrans" causing problems in various organs, including CNS issues and pneumonia.
Clinical Signs:
Pneumonia, coughing, dyspnea during the first 2 weeks.
Irritation in the stomach/intestines leading to vomiting and diarrhea.
Less severe infections may cause symptoms like pot belly, poor coat condition, emaciation, anemia, and restlessness.
Diagnostic Test: Fecal flotation.
Control: Maintain a clean environment; puppy owners need to clean up after worming to avoid reinfection. Regular fecal analyses are recommended.
Toxocara cati (Feline Roundworm) - Zoonotic
General Information:
Prenatal infection (transplacental) does not occur, but neonatal infection occurs via trans-mammary.
Tracheal migration is likely throughout the cat's life.
Diagnostic Test: Fecal flotation.
Toxascaris leonina (Roundworm)
General Information:
Found in the intestines of dogs and cats.
Similar size, shape, and color to Toxocara spp., but eggs are lighter, more egg-shaped, with a thick, smooth shell.
Life Cycle:
The developmental period to the infective stage ranges from 3 days to normally one week.
After egg hatching, larvae penetrate intestinal mucosa to develop and return to the lumen as adult worms in about 2.5 months.
Adults may be present by 6 weeks; eggs in feces by 8 weeks.
Clinical Signs: Same as for less severe infections of Toxocara spp.
Death is rare, with some discrepancies regarding parturition relationships.
Diagnostic Test: Fecal flotation.
Control: Clean environment; rodents and poultry can harbor infective larval stages.
Prevention and Treatment of Toxocara and Toxascaris spp.
Anthelmintics include:
Pyrantel (Nemex® or Strongid®)
Milbemycin oxime (Interceptor®)
Fenbendazole (Panacur®)
Febantel (Rintal®)
Strongyloides stercoralis (Threadworm) - Zoonotic
Free-living or parasitic, with a patent period of 5-7 days.
Route: Skin → blood → lungs → intestine.
Severe cases may cause diarrhea; most cases can be asymptomatic.
Diagnostic Tests: Baermann or fecal culture.
Hookworms
Ancylostoma caninum (Hookworm) - Zoonotic
General Information:
Located in the stomach and small intestine of dogs.
Size: Males 6-12mm; females 6-20mm.
Color: Gray to reddish brown.
Uncinaria stenocephala (Northern Hookworm) - Zoonotic
Similar to Ancylostoma, but smaller in size.
Life Cycle:
Developmental period: 2-8 days.
Eggs pass into the environment, hatch into first-stage larvae, advancing through three stages.
Routes of Infection:
Skin penetration: “Cutaneous Larval Migrans” where larvae travel through blood to lungs, then swallowed to develop in the intestine.
Oral ingestion: Larvae migrate through the intestinal wall, complete life cycle as described above.
Transplacental or trans-mammary infection may occur in prenatal pups.
Clinical Signs: Vary by the route of infection, can lead to:
Anemia
Lethargy
Emaciation
Altered stool consistency.
Diagnostic Test: Fecal flotation.
Control: Ensure cleanliness in kennel areas and regular check-ups.
Whipworms
Trichuris vulpis
General Information:
Found in the cecum and colon of dogs.
Size: Males and females: 45-70mm, very thin anteriorly and thickened posteriorly, resembling a whip.
Eggs: Thick, brown-yellow shell with polar plugs; very resistant to environmental stressors.
Life Cycle:
Developmental period: ~3-4 weeks, optimally as short as 9-10 days.
Larvae develop within the egg once ingested, maturing in the cecum.
Clinical Signs: Mostly asymptomatic, especially in light infections; however, heavy infections may cause lethargy, anemia, and either diarrhea or normal stool with blood/mucous.
Diagnostic Test: Fecal flotation.
Control: Difficult due to resilient eggs; keep areas clean; sunlight helps; and multiple fecal exams may be necessary due to erratic egg-laying.
Organ-Specific Nematodes
Dioctophyme renale (Kidney Worm) - Zoonotic
Largest nematode species, can reach 1 meter in length.
Produces brownish, thick-shelled eggs passed in the urine.
Diagnostic Test: Urine sedimentation.
Capillaria plica (Dog Bladder Worm)
Found embedded in the mucosa of the bladder, ureters, and renal pelvis. Eggs have bipolar plugs and are acquired from earthworms.
Diagnostic Test: Urine sedimentation.
Capillaria aerophila (Lungworm) - Zoonotic
Found in cats and dogs; adults live in the respiratory mucosa; smaller eggs than Trichuris.
Diagnostic Test: Fecal flotation.
Aelurostrongylus abstrusus (Feline Lungworm)
Small, delicate adults form nodules in the lungs.
Larvae appear in feces after being ingested post-hatching. Can cause chronic cough.
Diagnostic Test: Baermann technique.
Thelazia californiensis (Eyeworm) - Zoonotic
Found in the conjunctival space and lacrimal glands. Infestation occurs from flies.
Diagnostic Test: Identification of the adult.
Acanthocheilonema reconditum (Connective Tissue Nematode)
Occurs in subcutaneous tissue and travels through blood. Generally harmless, often confused with heartworm.
Diagnostic Test: Modified Knott's test or Millipore filtration.
Dirofilaria immitis (Heartworm) - Zoonotic
Found in dogs, cats, marine mammals, and humans.
General Information:
Adults inhabit right ventricle and pulmonary artery.
Size: Males 12-20cm; females 25-31cm; very thin and cylindrical.
Human Health Concerns: Can cause "coin lesions" in the lungs.
Life Cycle:
Mosquitoes serve as intermediate hosts, where larvae undergo maturation before migrating to new hosts with blood meals.
Migration in the bloodstream to heart takes 85-120 days.
Adults live approximately 5 years; microfilaria about 2-3 years.
Clinical Signs:
Mild signs: weight loss, poor coat.
Severe signs: chronic cough, lack of stamina, scarring of heart lining.
Diagnostic Tests:
Animals over 6 months should be tested before starting heartworm prevention. Tests include ELISA antigen testing, direct smear, Knott's test, and other hematological methods.
Control: Mosquito control is crucial, monthly preventatives aimed at juvenile worms.
Treatment:
Requires assessments of health status using CBC, chemistry panels, and radiographs.
Preventatives: Ivermectin, Interceptor®, Revolution®.
Adult Treatment: Immiticide for adult worms, monitoring for potential complications during adjustment periods.
Assess the health of animals before prescribing any treatment to minimize risks of organ damage during therapy.
Trematodes (Unsegmented Flatworms)
General Information:
Trematode life cycles are complex, involve various larval stages, and typically require more than one intermediate host, often mollusks.
Paragonimus kellicotti (Lung Fluke) - Zoonotic
Eggs are coughed up or shed in feces, hatch in water, infecting snails, which then infect crayfish consumed by final hosts.
Prepatent Period: 30-36 days.
Diagnostic Tests: Urine sedimentation.
Nanophyetus salmincola (Salmon Fluke)
Vector for the disease known as salmon poisoning in dogs in the Pacific Northwest.
Diagnostic Tests: Fecal sedimentation.
Blood Parasites
Mycoplasma spp. (Rickettsial Parasite)
General Information:
Mycoplasma is a rickettsial bacterial organism attacking erythrocytes.
Identified through blood smears or PCR testing.
Fresh blood smears are essential for diagnosis as organisms fall off in some anticoagulants (e.g., EDTA).
Three common types:
Mycoplasma hemofelis: Causes severe hemolytic anemia in cats, transmitted via blood-sucking arthropods. Symptoms include lethargy and anorexia. Treatment: doxycycline or enrofloxacin.
Mycoplasma haemocanis: Found in dogs, is non-pathogenic unless splenectomized.
Mycoplasma bovis: Found in cattle, causing various diseases including abortion.
Anaplasma marginale (Rickettsial Parasite)
General Information:
A red blood cell parasite transmitted by ticks, upper respiratory infections can result in severe anemia.
Diagnostic Tests: blood smear.
Ehrlichia canis (Rickettsial Parasite)
General Information:
A tick-borne infectious disease typically affects dogs, can lead to anemia and other systemic issues due to its effect on white blood cells.
Diagnosis: Blood smear and laboratory testing.
Babesia canis (Protozoal Parasite)
General Information:
Tick-borne infection leading to intracellular parasites in red blood cells; identification often via blood smear diagnostics.
Trypanosoma spp. (Protozoal Parasite)
General Information:
Unicellular, parasitic protozoa spread by biting flies, causing diseases like African Sleeping Sickness in humans.
Intestinal Protozoal Parasites
Coccidia spp. (Coccidiosis)
Species:
Isospora spp.: Infecting puppies and kittens.
Eimeria spp.: Infecting ruminants and small mammals.
Symptoms: Diarrhea and gastrointestinal upset more common in young animals; some cases asymptomatic.
Transmission: Ingested sporulated oocysts from contaminated sources, excyst in the intestines.
Diagnosis and Treatment: Direct smear, fecal flotation, treated with sulfadimethoxine (Albon®) or ponazuril (Marquis® paste).
Toxoplasma gondii (Toxoplasmosis) - ZOONOTIC
Definitive host: cats. Infection in humans via ingested oocysts.
Precautions are critical, especially for pregnant women due to risks of severe fetal complications.
Cryptosporidium spp. (Cryptosporidiosis) - ZOONOTIC
Very small protozoans causing diarrhea in various hosts, can contaminate water supplies near dairy farms.
Diagnosis: Fresh fecal smear or float; serological tests may not indicate active infections.
Giardia spp. (Giardiasis) - ZOONOTIC
Flagellated protozoan identifiable via cysts or trophozoites. Causes watery diarrhea and weight loss; zoonotic potential.
Diagnosis and Treatment: Various methods including ELISA and fecal floats; treated with metronidazole (Flagyl®), fenbendazole (Panacur®), or albendazole (Valbazen®).
Large Animal Parasites
Equine Parasites
Strongylus vulgaris: Causes severe arterial blockage, prevention through regular deworming and pasture management.
Parascaris equorum: Roundworm species causing gastrointestinal issues, diagnosed via fecal flotation.
Oxyuris equi: Pinworm causing irritation in foals, identifiable through tape mounts.
Ruminant Parasites
Haemoncus and Osteragia: nematodes affecting cattle.
Moniezia expansa: cestode in ruminants.
Fasciola hepatica: liver fluke (trematode affecting liver functionality).
Pig Parasites
Trichinella spiralis: Affects pigs and can be transmitted to humans; strict cooking practices are essential for prevention.
Antiparasitic Drugs
General Information: Anthelmintics work on various metabolic pathways of worms to kill or expel them.
Drug Types:
Antinematodal: Treat nematode (roundworm) infections, examples include:
Benzimidazoles: Broad spectrum (e.g., fenbendazole, thiabendazole, mebendazole, albendazole).
Organophosphates: Narrow action, high toxicity potential (e.g., trichlorfon, coumaphos).
Imidazothiazoles: Effective on various nematode species (e.g., levamisole).
Avermectins: Broad effectiveness, often used for heartworm prevention (e.g., ivermectin, moxidectin).
Miscellaneous: Safe against ascarids, effective in young animals (e.g., pyrantel, morantel, piperazine).
Anticestodal Drugs: Targeting tapeworm infections, examples are praziquantel (Droncit®) and epsiprantel (Cestex®).
Antitrematodal Drugs: Target flatworm infections (e.g., clorsulon, albendazole).
Antiprotozoal Drugs: Target protozoal infections, e.g., for coccidia (sulfadimethoxine, monensin) and Giardia (metronidazole, fenbendazole, albendazole). Some antiprotozoal medications act as coccidiostats, inhibiting reproduction without killing the parasites.