1. INTRO TO PARASITOLOGY

Introduction to Veterinary Parasitology

Veterinary parasitology is a specialized field focused on the study of parasites that affect domesticated, wild, exotic, and laboratory animals. It encompasses the understanding of parasites that may be transmitted from animals to humans, an aspect which is critical for public health and the management of zoonotic diseases.

Parasites

• Definition: Organisms that live in or on another organism (the host) and draw sustenance from it, often causing harm or disease to the host.

• Types of Parasites: These include a wide variety of life forms such as animals (e.g., protozoa, helminths), plants (e.g., parasitic plants like dodder), fungi (e.g., molds affecting animals), bacteria (e.g., Rickettsia), and viruses (e.g., those causing diseases in hosts).

• Host Dependency: Parasites rely on hosts for survival and reproduction and exhibit a range of adaptations to suit their parasitic lifestyle.

Parasitology

• Definition: The scientific study of parasitic organisms, encompassing their biology, life cycles, ecology, and interactions with their hosts.

Parasitic Relationships

Parasitism

• Definition: Involves an association between two organisms of different species where one organism (the parasite) lives on or within the other (the host), potentially causing harm. The parasite often becomes metabolically dependent on the host for its sustenance.

Species Interactions

Symbiotic Relationships

• Definition: The coexistence of different species that involves interactions with various benefits and costs.

• Types:

  • Mutualism: Both partners benefit from the relationship (e.g., bees and flowering plants).

  • Antagonism: Only one organism benefits while the other is disadvantaged.

  • Commensalism: One organism benefits while the other remains unaffected.

  • Parasitism: One member benefits at the expense of the host, often leading to injury or disease.

Parasitic Relationships Defined

• Parasitiasis: The presence of parasites on or within a host without outward clinical signs of disease, often leading to chronic conditions.

• Parasitosis: The presence of parasites that unequivocally results in obvious injury or harm, often detectable through clinical signs and symptoms.

Types of Parasites

Ectoparasites vs. Endoparasites

• Ectoparasites: Organisms that live on the surface of the host, leading to infestations. Common ectoparasites include fleas, ticks, and lice.

• Endoparasites: Parasites that live within the host, often causing infections. Examples include worms such as roundworms and tapeworms.

• Classification based on interaction:

  • Erratic and Incidental Parasites:

    • Erratic/Aberrant Parasites: Parasites that deviate from their usual site of infection, potentially causing unusual disease presentations.

    • Incidental Parasites: Found in hosts they do not usually inhabit; often unable to complete their life cycle in these non-typical hosts, and frequently perish.

Free Living vs. Non-Free Living Parasites

• Facultative Parasites: Capable of leading a free-living existence but can become parasitic in the presence of a suitable host (e.g., certain free-living nematodes).

• Obligatory Parasites: Must lead a parasitic existence and cannot survive freely without a host (e.g., tapeworms).

Periodic Parasites

• Definition: Parasites that make frequent and short visits to the host for nourishment; a classic example is the female mosquito, which requires blood meals for the development of her eggs.

Pseudoparasites

• Definition: Non-parasitic organisms that may be mistakenly identified as parasites during diagnostic tests, such as pollen grains or air bubbles in fecal flotation examinations, erroneously affecting the diagnosis.

Life Cycle of Parasites

• Development: Parasites undergo various life stages, each adapted to specific hosts or environments.

• Hosts:

  • Definitive Host: The primary host where the parasite reaches adulthood and reproduces.

  • Intermediate Hosts: Hosts through which the parasite develops, occasionally undergoing one or more life stage changes.

  • Transport Hosts: Intermediate hosts that do not undergo any changes in life stage but assist in the transmission of the parasite.

  • Reservoir Hosts: Maintain the parasite in nature and serve as a source of infection for other hosts (e.g., wildlife reservoirs for zoonotic parasites).

Taxonomy and Parasites

• Scientific Taxonomy: The classification of organisms based on evolutionary relationships and characteristics, facilitating a deeper understanding of ecological interactions.

• Common vs. Scientific Names: Scientific names provide a universal system for identifying species, while common names may vary based on regional dialects and languages.

Linnaean Classification Scheme

• Organisms are classified hierarchically with a standardized naming convention (Genus species).

• Hierarchical Classification Example for the Domestic Dog (Canis familiaris):

  • Domain: Eukaryota

  • Kingdom: Animalia

  • Phylum: Chordata

  • Class: Mammalia

  • Order: Carnivora

  • Family: Canidae

  • Genus: Canis

  • Species: familiaris

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Taxonomic Hierarchy Overview

• Largest Categories:

  • Domain: Bacteria, Archaea, Eukaryota

  • Kingdom: Fungi, Plantae, Protista, Animalia

  • Phylum: E.g., Arthropoda, Nematoda, Chordata

  • Class: Mammalia, Insecta, etc.

  • Order: For example, Carnivora

  • Family: Related organisms like Felidae or Canidae

  • Genus: Class based on shared characteristics (first part of the scientific name, capitalized)

  • Species: Similar individuals (second part of the scientific name, lowercase)

References

• Sirois M. (2020). Laboratory Procedures for the Veterinary Technician, (7th ed.). St Louis: Elsevier.

• Bassert, J.M., & McCurnin, D.M. (2022). McCurnin’s Clinical Textbook for Veterinary Technicians, (10th Edition). St. Louis: MO. Elsevier Saunders.

• Robinson, E., Hendrix, C. (2022). Diagnostic Parasitology for Veterinary Technicians, 6th Edition. St. Louis: MO. Elsevier.