VT 120 Parasite lesson

Parasite Terminology

  • Antihelmintic: A drug used to treat parasitic worms.
  • Ectoparasite: A parasite that lives on the outside of an animal.
  • Endoparasite: A parasite that lives on the inside of an animal.
  • Helminths: Worms that predominantly inhabit the gastrointestinal tract, lungs, liver, and circulatory system. It comprises two major groups:
    • Nematodes (roundworms)
    • Platyhelminths (flatworms, including cestodes and trematodes).
  • 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 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 through which the larvae emerge.
  • Parasitology: The study of organisms that live in or on another organism (host) where they acquire their nutrients.
  • Patent Period: The time during which a parasite is detectable via identification of ova or larval forms.
  • Prepatent Period: The time between initial infection and the detection of the parasite.
  • Protozoa: Single-celled organisms with 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: Acts as an intermediate host for a parasite.
    • Mechanical Vector: Transports the parasite without allowing it to develop.
  • Zoonosis: Diseases that can be transferred between animals and humans.

Overview

  • Symbiosis: Involves two organisms living together. There are three types:
    • Commensalism: One organism benefits, and the other is unharmed.
    • Mutualism: Both organisms benefit.
    • Parasitism: One organism benefits, and the other is harmed.
  • Life Cycle of Parasites: Describes the process of parasite maturation through various hosts and developmental stages. These life cycles can be:
    • Direct: Does not require a vector.
    • Indirect: Requires one or more vectors.

Cestodes - Tapeworms

General Information on Tapeworms

  • Characteristics: Flatworms that lack a body cavity. Two subclasses include:
    • Eucestoda: True tapeworms.
    • Cotyloda: Pseudotapeworms.
  • Development Mechanism: All tapeworms require an intermediate host to develop the larval stage of the life cycle.
  • Proglottids: Segments containing eggs.
  • Control Measures: Dependent on the species of the worm.
  • Anatomy: Contains a Scolex (mouth part) and Proglottids (reproductive part).

Dipylidium caninum

  • Common Name: Cucumber seed tapeworm.
  • Habitat: Found in the small intestine of dogs, cats, and occasionally humans.
  • Size: 10-70 cm.
  • Color: White to yellowish.
  • Detection: Proglottids may be found in feces or moving outside the anus, resembling grains of rice or dried sesame seeds.
  • Life Cycle:
    • Intermediate Host: Flea (or occasionally the dog louse).
    • Process: Flea ingests the dipylidium egg, matures to the infective larval stage in the flea, infection occurs when the dog or cat eats the mature flea.
    • Prepatent Period: 14 to 21 days.
  • Diagnostic Tests: Identification of proglottids or fecal flotation.

Taenia pisiformis

  • Intermediate Host: Rabbits and hares.
  • Size: Up to 200 cm long.
  • Color: White to yellow.
  • Detection: Proglottids seen on the anus and feces.

Echinococcus granulosus (ZOONOTIC)

  • General Information: Associated with hydatid cysts; significant zoonotic potential.
  • Size: Very small (2-5 cm).
  • Life Cycle: Man, domestic animals, and numerous wild animals act as intermediate hosts, larvae create hydatid cysts.
  • Diagnostic Tests: Fecal flotation.

Clinical Signs of Tapeworms

  • Generally not harmful, but can exhibit 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 and an unthrifty animal.
  • Behavior indicating irritation from proglottids includes:
    • Dragging of the rear end.
    • Biting or chasing the tail.
  • Check for fullness of anal sacs.

Control and Treatment of Tapeworms

  • Aim: Prevent the completion of the life cycle of tapeworms by:
    • Keeping the environment clean and free of feces.
    • Removing intermediate hosts, such as fleas.
    • Preventing pets from eating undercooked meat.
    • Regular veterinarian check-ups.
  • Antihelmintic Medication: Praziquantel (Droncit).
  • Zoonotic Risks: Common contact with infected dogs in areas where sheep are kept. Must be reported to the State Veterinarian and other authorities.

Nematodes - Ascarids (Roundworms)

Toxocara canis

  • General Information: Found in the small intestine of dogs, more frequently in puppies and kittens due to their life cycle.
  • Size: Males 3.5-5 cm; Females 10-15 cm.
  • Shape: Cylindrical, tapered at both ends.
  • Color: White to cream.
  • Egg Characteristics: Resistant, large, oval, dark in color with a thick rough shell.
  • Life Cycle:
    • Developmental period to infective stage averages about 4 weeks with 5 stages of development:
    1. Egg.
    2. Larvae develops within the egg.
    3. Infective stage larva.
    4. Egg hatches in small intestine.
    5. Infective larvae penetrate mucosa, migrate through the liver, heart, and then to lungs.
    • Further developments occur in the lungs where larvae are coughed up and swallowed. They then become mature worms in the small intestine.
  • In older pups and adults: Migration of infective stage ceases in body tissues. In pregnant bitches, larvae migrate again during pregnancy, passed to the fetus (transmammary or transplacentally).
  • Adult Stage is reached: 23-40 days in pups.
  • Clinical Signs:
    • Pneumonia, coughing, and dyspnea during the early larval migration period.
    • Irritation to the stomach and intestines leads to:
    • Vomiting and diarrhea.
    • Less severe infections can result in:
    • General unthriftiness.
    • Pot belly.
    • Poor hair coats.
    • Emaciation, anemia, diarrhea, or constipation.
    • Restlessness.
  • Diagnostic Tests: Fecal flotation.
  • Control Measures:
    • Maintain a clean environment and concrete kennel for effective control.
    • Turn the soil during hot weather and use a flame thrower for disinfection.
    • Puppies must be cleaned post-worming to prevent reinfection by the mother.
  • Zoonotic: Significant health hazard - visceral larval migrans in humans.
  • Symptoms in humans: Cann cause central nervous system problems, pneumonia, muscle aches, and vision problems.

Toxocara cati

  • General Information: Transplacental infection does not occur; neonatal infection via transmammary is significant.
  • Migration Pattern: High chance of tracheal migration continues throughout the cat's life.
  • Human Health Hazard: Significant.
  • Diagnostic Tests: Fecal flotation.

Toxascaris leonina

  • General Information: Found in the intestines of dogs and cats.
  • Size, shape, color: Same as Toxocara spp. but eggs are lighter and more egg-shaped with a thick, smooth shell.
  • Life Cycle:
    • Developmental period to the infective stage ranges from 3 days to about a week.
    • Five developmental stages:
    1. Third stage infective larvae hatch from the egg and penetrate the intestinal mucosa to develop for about 2.5 months before returning to the intestinal lumen as adults.
    • Adult worms may be detected by six weeks and eggs in feces by eight weeks.
  • Clinical Signs: Same as less severe infections of Toxocara spp., rarely causing deaths.
  • Diagnostic Tests: Fecal flotation.
  • Control Measures: Clean environment; rodents can harbor infective larvae, but the life cycle must be completed in a dog or cat.
  • Prevention and Treatment:
    • Pyrantel (Nemex or Strongid).
    • Milbemycin oxime (Interceptor).
    • Fenbendazole (Panacur).
    • Febantel (Rintal).

Strongyloides stercoralis

  • Common Name: Threadworm.
  • Life Cycle: Free-living or parasitic.
  • Patent Period: 5-7 days.
  • Symptoms: Severe cases may cause diarrhea; most cases are asymptomatic.
  • Diagnostic Tests: Baermann or fecal culture.

Hookworms

Ancylostoma caninum (ZOONOTIC)

  • General Information: Found in the stomach and small intestine of dogs.
  • Size: Males 6-12 mm; Females 6-20 mm.
  • Shape: Short, thick parasites.
  • Color: Gray to reddish-brown.
  • Ecosystem: Commonly found in warm, humid climates.
  • Life Cycle:
    • Developmental period is 2-8 days.
    • Undeveloped eggs pass into the environment, hatch, and release first stage larvae.
    • Larvae develop into second and third infective stages.
    • Routes of Infection:
    1. Cutaneous larval migrans (through skin penetration): Penetrates skin, migrates via blood to the lungs, coughed up, swallowed, and develops in the small intestine (takes 4-6 weeks).
    2. Oral ingestion: Larvae migrate through the intestinal wall to blood, completing the cycle as with skin penetration.
    3. Transplacental or transmammary infection: In prenatal pups, larvae remain dormant in tissues, completing migration through lungs post-birth, with eggs showing as early as 11-13 days in pups.
  • Clinical Signs:
    • Peracute disease: Seen in prenatal infections with deterioration post the first week.
    • Acute disease: Common in nursing and weaned pups, fecal diagnosis shows worms peaking in blood consumption before eggs are laid.
    • Chronic disease: Diagnosed through fecals; animals maintain poor health for extended periods.
  • Summary of Clinical Signs: Anemia, lethargy, emaciation, stunted growth, dry hair coat, fluid feces, skin lesions, and ulceration.
  • Diagnostic Tests: Fecal flotation.
  • Control Measures: Keep kennel area and bedding dry and clean, perform fecals on pups at 2-4 weeks, and treat sick animals that may need transfusion or other anthelmintics.

Uncinaria

  • General Info: Similar to Ancylostoma but much smaller.
  • Diagnostic Tests: Fecal flotation.

Whipworms

Trichuris vulpis

  • General Information: Found in the cecum and colon, with males and females about the same length (45-70 mm).
  • Shape: Very thin anteriorly and thickened posteriorly, resembling a whip and handle.
  • Ova Characteristics: Thick, brown-yellow shell with clear polar plugs at each end.
  • Resistance: Eggs are very resistant and may persist for several years.
  • Life Cycle:
    • Developmental period: about 3-4 weeks under optimum conditions, as short as 9-10 days.
    • Infection method: Ingested eggs release larvae in the intestine, developing for 8-10 days before attaching and maturing in the cecum over 60-80 days.
  • Clinical Signs:
    • Most animals are asymptomatic, but heavy infections can lead to lethargy, unthriftiness, and anemia. Bouts of diarrhea alternating with normal stool, possibly blood-streaked or with mucous.
  • Diagnostic Tests: Fecal flotation.
  • Control Measures: Control is challenging due to the eggs' resilience. Maintain a clean and dry environment; sunlight can help eliminate eggs. Rake and burn grassy or dirt areas if necessary. Multiple fecal tests may be required due to erratic egg laying.

Prevention and Treatment

  • Pharmaceuticals:
    • Drontal Plus (febantel, pyrantel pamoate, praziquantel).
    • Panacur (fenbendazole).
    • Interceptor (milbemycin oxime).
    • Sentinel (milbemycin oxime and lufenuron).

Specific Organ System Nematodes

Dioctophyma renale

  • General Info: Largest nematode species, reaching 1 meter in length and 1 cm in diameter. Uncommon.
  • Egg Characteristics: Brownish, thick, rough-shelled eggs with bipolar plugs, eliminated in urine.
  • Diagnostic Tests: Urine sedimentation.

Capillaria plica

  • General Information: Found in the bladder, ureters, and renal pelvis.
  • Egg Characteristics: Bipolar plugs; obtained from earthworms.
  • Diagnostic Tests: Urine sedimentation.

Capillaria aerophila

  • General Information: Present in cats and dogs, adult worms inhabit the respiratory mucosa.
  • Egg Characteristics: Smaller eggs with a granular shell, differentiating them from Trichuris.
  • Diagnostic Tests: Fecal flotation.

Aleurostrongylus abstrusus

  • Common Name: Feline lungworm.
  • Description: Adults are small, delicate, and form grayish-white nodules in the lungs.
  • Life Cycle: Eggs laid, hatch, ascend to the pharynx, swallowed, and appear in feces. Larvae can be seen using the Baermann technique. Cats can exhibit chronic cough.
  • Diagnostic Tests: Baermann.

Thelazia californiensis

  • Description: Found in conjunctival spaces and lacrimal glands. Adults deposit eggs containing larvae, developing into the infective stage in face flies.
  • Diagnostic Tests: Identification of adult worms.

Acanthocheilonema reconditum

  • General Information: Resides in subcutaneous tissue; microfilariae travel through blood and settle in tissue, relatively harmless.
  • Intermediate Host: Flea; often confused with Dirofilaria immitis (heartworm).
  • Diagnostic Tests: Modified Knott's test or Milipore filtration.

Dirofilaria immitis (Heartworm)

  • General Information:
    • Location: Adults are in the right ventricle of the heart and pulmonary artery.
    • Size: Males 12-20 cm; Females 25-31 cm.
    • Shape: Very thin and cylindrical.
    • Color: White.
    • Hosts: Not limited to canines; also found in cats, marine mammals, and humans.
  • Life Cycle:
    • Intermediate host is the mosquito, which ingests microfilariae during a blood meal.
    • The larvae then mature within the mosquito to the infective stage, moving to the mouth parts and then into the next host.
    • It takes larvae 85-120 days to migrate into the bloodstream, leading to the heart and maturing for an additional 60-70 days to produce microfilariae in the bloodstream.
    • Longevity: Adults live around 5 years; microfilariae for about 2-3 years.
  • Clinical Signs: Signs depend on animal activity and infection severity:
    • Mild: Weight loss and poor hair coat.
    • Severe: Chronic cough, lack of stamina, rapid breathing, collapse after exercise, potential scarring in the heart lining.
  • Testing Methods: Direct smear/saline prep, microhematocrit method, Knott's test (Modified), Difil test, and occult/antigen testing.
  • Control Measures:
    • Mosquito control is crucial.
    • Use strategic drug treatments to kill microfilariae before they mature.
    • All animals should be tested for heartworm before starting preventative measures to avoid complications that can further harm the pet.
  • Treatment:
    • Begin with blood tests (CBC, Chemistry panel, UA, and Radiographs).
    • Administrate adult treatments:
    • Immiticide (melarsomine dihydrochloride) - safer with no renal or hepatic impairment.
    • Caparsolate (thiacetarsamide) - arsenic derivative with potential toxicity.
    • Both treatments are costly; pets must be cage-confined for 4-6 weeks due to thromboembolism risk from dead worms.
    • For microfilariae treatment in higher doses, use Ivermectin and Milbemycin Oxime preventatives (Interceptor, Revolution).

Human Health Concerns

  • Humans can experience "coin lesions" in the lungs as a dead-end host for heartworm.

Trematodes (Unsegmented Flatworms)

  • Life Cycle Complexity: Usually involves several larval stages and often more than one intermediate host, primarily mollusks (snails and slugs).
  • Examples:**
    • Paragonimus kellicotti: Adult lung fluke of pets; eggs coughed up and shed in feces, hatching in the water and infecting snails and crayfish.
    • Nanophyetus salmincola: Known as the salmon-poisoning fluke, impacting dogs in the Pacific Northwest; behaves as a vector for the rickettsial disease causing salmon poisoning.
  • Diagnostic Tests:
    • Fecal sedimentation.

Blood Parasites

Mycoplasma

  • General Information: A rickettsial organism that attacks erythrocytes, including species:
    • Mycoplasma hemofelis: Causes Feline Infectious Anemia, with spherical, ovoid, or rod-shaped bodies appearing on RBCs. Best stained with acridine orange but New Methylene is also effective. Associated with FeLV immunosuppressed cats.
    • Mycoplasma haemocanis: Found in dogs but nonpathogenic unless the dog is splenectomized.
    • Mycoplasma bovis: Present in cattle, causing arthritis, mastitis, pneumonia, and abortions. Treatment includes tetracyclines and transfusions.

Anaplasma marginale

  • General Information: Transmitted by ticks, impacting cattle and is a rickettsial organism disease.

Babesia

  • General Information: An intracellular red blood cell parasite, transmitted by the Boophilus tick. It appears as basophilic, pear-shaped trophozoites within canine red blood cells and can cause anemia.

Ehrlichia

  • General Information: A white blood cell parasite (Ehrlichia canis) that spreads through the body post-multiplication, affecting organs like the liver and spleen. It can cause anemia, leukopenia, and thrombocytopenia.

Trypanosoma

  • General Information: Spread by biting flies, causing African Sleeping Sickness via the tse tse fly and affecting ruminants, horses, and birds.