Parasitology reading

Introduction to Parasitology

Parasites are defined as organisms that live on or within other organisms (hosts) and derive benefits such as nutrition, habitation, or mobility from place to place. Parasitism is most severe in animals under 1 year of age but may affect animals of any age. Damage may be exacerbated by the number of parasites present, location within the host, production of toxins, and interference with the host’s normal physiological processes. Clinical signs associated with parasitism may include anemia, hypoproteinemia, diarrhea, vomiting, weight loss, intestinal obstruction, and possibly death. Damage from parasites can interfere with normal physiological processes such as breeding and milk production.

Classification of Parasites

Parasites are divided into two large groups:

  1. Endoparasites (internal parasites)
    • Include:
      • Nematodes (roundworms)
      • Cestodes (tapeworms)
      • Trematodes (flukes)
      • Protozoa
      • Acanthocephalans
  2. Ectoparasites (external parasites)
    • Include:
      • Fleas
      • Lice
      • Ticks
      • Mites
      • Chiggers
      • Biting flies
      • Myiasis-inducing flies

Some parasites are host-specific, while others can infect a broad range of species. Modes of transmission vary considerably, from direct contact with hosts to complex life cycles involving multiple hosts.

Diagnosis of Parasitic Infections

General Principles

  • Microscopic Examination: Parasites that infect the oral cavity, esophagus, stomach, intestines, and other organs are detected by fecal examination, identifying specific life-cycle stages (eggs, oocysts, larvae, segments, and adults).
  • Fecal Sample Collection: Should be fresh, ideally examined within 24 hours, and may be preserved if delayed.
    • Older samples may alter the appearance of stages due to development.
  • Fecal samples for diagnostic purposes should include fresh specimens collected immediately after defecation, stored in clean containers, and labeled properly.

Small Animal Techniques

  1. Fecal Sample Collection:
    • Owners can collect samples using any container (zippered bag or jar).
    • Only 1g is needed, ideally collected from various areas.
    • Samples can also be collected in veterinary hospitals using a gloved finger or fecal loop.
    • The fecal loop must be lubricated before insertion for collection.
  2. Skin Scraping:
    • Used to evaluate animals suspected to have external parasites with necessary equipment such as clippers, a scalpel or spatula, and mineral oil.
    • Scrape typical lesions (e.g., ear margins for Sarcoptes mites) at a 3cm² to 4cm² area to collect enough parasitic samples.

Large Animal Techniques

  1. Fecal Specimens from Livestock:

    • Collected directly or pooled from several animals in a clean, tightly sealed container.
    • Labeling includes species name and pen/group number.

  2. Necropsy Sampling:

    • Methodical examination of the digestive tract to recover parasites can be performed using decanting or sieving methods.
    • Must handle specimens and maintain proper labeling for sample submissions.
    • Bladder worms require special attention due to their allergenic and zoonotic potential.

Sample Collection Procedures

Fecal Samples

  • Fecal samples from small animals are collected fresh; refrigeration or 10% formalin is needed if not examined within a few hours. Only a small amount (1g) is necessary for examination. All specimens must be correctly labeled with the owner’s name, animal’s name, species, and date of collection.

Skin Scraping Procedures

  • Equipment includes:
    • Electric clipper with no. 40 blade
    • Scalpel or spatula
    • Mineral oil
  • Scraping depth varies by parasite location; e.g., Sarcoptes mites require scraping until a drop of blood appears for accurate diagnosis.

Skin Samples via Cellophane Tape Preparation

  • Clear tape applied to the skin (especially for lice and surface mites) picks up epidermal debris for microscopic examination.

Vacuum Collection for Ectoparasites

  • A vacuum may collect surface parasites; this method may require additional precautions for patient distress.

Direct Examination of Samples

  • Microscopic examination should involve a binocular microscope, requiring clean methodology to avoid contamination.

Evaluation and Interpretation of Fecal Specimens

Gross Examination

  • Consistency, color, and presence of foreign bodies (blood, mucus, adult parasites) are noted.
  • Diarrhea may indicate parasitism; normal to loose stool characteristics vary with canine or felines.

Direct Smear Technique

  • Direct smear requires minimal equipment, used to observe eggs or larvae. It involves placing a small amount on a slide and is a rapid initial test but may not be conclusive due to small sample size.

Fecal Examination Methods

Fecal Flotation Method

  • Differentiates life-cycle stages based on specific gravity differences of eggs and fecal debris.
  • Common solutions used: sugar, sodium chloride, sodium nitrate, magnesium sulfate, zinc sulfate, etc.
  • Specific gravity typically should be higher than the eggs to facilitate floating.

Centrifugal Flotation

  • More sensitive than simple flotation with enhanced recovery of eggs/cysts from samples.

Fecal Sedimentation

  • Useful for heavy eggs that may not float; allows collection of sediment from 5 to 20 minutes and examination of upper, middle, and lower sediment sections.

Modified McMaster Technique

  • Estimates the number of eggs/oocysts per gram in livestock and horses.
  • Important for monitoring worm populations and tackling multiple infections among species.

Blood Sample Collection and Examination

Blood Sample Collection

  • Important in diagnosing parasitic infections.
  • Use sterile equipment; label samples appropriately.

Microfilariae Examination

  • Performed through diffusion techniques: either direct, concentration techniques like the modified Knott's test or commercial kits, aid in identifying Dirofilaria and D. reconditum species.

Immunologic and Molecular Diagnostic Tests

  • Antigen tests such as ELISA are crucial for diagnosing certain parasitic infections due to their accuracy.

Hematological Analysis and Interpretation

Complete Blood Count (CBC)

  • Identifies abnormalities such as counts of erythrocytes, leukocytes, platelets, and differentials.
  • Analysis often reveals fatal pathologies of various organ systems.

Biochemical Assessments

  • May indicate organ function; common issues can include the balance of fluid, electrolytes, and enzymes, with patterns indicating specific organ dysfunction.

Diagnostic Techniques for Protozoans

Identification of Giardia and Other Protozoans

  • Giardia cysts diagnosed via fecal floatation; specific diagnostic tests may occur if the infections are suspected to be silent.

Cryptosporidium Examination

  • Requires special staining due to the small size of oocysts; can be life-threatening in immunocompromised individuals.

Parasitic Diseases of Large and Small Animal Species

Common Parasitic Conditions

  • Specific zoonotic diseases pose threats, emphasizes the education of owners regarding preventive measures to bolster both animal and public health.

Treatment Protocols

  • Treatments vary greatly per species but aim to eradicate parasites and control infections using anthelmintics specific to species and age.

Prevention Strategies

  • Ensures veterinary technicians educate clients on sanitation, proper deworming procedures, and environmental management to minimize reinfections and transmission.