Arthropods Identification

Arthropods

• Insects: have three pairs of legs, head, thorax, abdomen, and antennae
• Arachnids: have four pairs of legs (nymphs and adults), larvae have three pairs of legs, body is divided into cephalo-thorax and abdomen, no antennae, and have palps

Identification

• Flies (Diptera): identification characteristics unknown
• Fleas (Siphonaptera): identification characteristics unknown
• Lice (Phthiraptera): identification characteristics unknown
• Ticks (Acari): identification characteristics unknown
• Mites (Acari): identification characteristics unknown

Symbiosis

• Definition: an association of two organisms that cannot exist independently
• Types of symbiosis:
  • Phoresis: an association in which two organisms merely travel together
  • Mutualism: an association in which both organisms benefit
  • Commensalism: an association in which one partner benefits and the other is unaffected
  • Parasitism: an association in which one partner benefits and the other is harmed

Parasitism

• Definition: an association in which one partner benefits and the other is harmed
• Host: the partner who is harmed
• Parasite: the partner who is benefited

Hosts

• Types of hosts:
  • Definitive host: harbors the adult (sexual) stage of a parasite
  • Intermediate host: harbors the larval (asexual) stage of a parasite
  • Paratenic host: harbors a parasite that does not undergo required development; a transfer host
  • Reservoir: an animal (definitive) host that serves to maintain the parasite's life cycle in nature
  • Incidental host: an unusual host, unnecessary for the maintenance of the parasite in nature

Vector

• Definition: an organism responsible for transmitting a parasite from one host to another
• Types of vectors:
  • Biological vector: a vector in which the parasite multiplies or develops
  • Mechanical vector: one which transmits the parasite unchanged from host to host

Parasites

• Types of parasites:
  • Obligate parasite: totally physiologically dependent upon its host
  • Temporary parasite: parasitic for limited periods for either feeding or reproduction
  • Facultative parasite: organisms that are not normally parasitic but can survive for a limited period when they accidentally find themselves within another organism

Ectoparasites and Endoparasites

• Ectoparasite: lives on the host, causes infestations
• Endoparasite: lives in the host, causes infections

Zoonosis

• Definition: any disease of animals that is transmissible to humans
• Examples: Trichinellosis, Chagas' disease, Schistosomiasis, Giardiasis, Toxoplasmosis, Amebiosis, Echinococcosis

Principles of Parasitology

• Protozoa: multiply in the definitive host
• Helminths: adult worms do not multiply in the definitive host, worms die over time unless the host is re-exposed, severity of disease is proportional to worm load introduced into the host

Host Specificity

• Parasites (particularly helminths) have specificity for particular definitive and intermediate hosts
• Often, parasite life cycles can only be completed in a particular host
• Disease manifestations of a host can differ depending on whether they serve as a definitive, intermediate, or an incidental host

Survival Facts and Functions

• Parasites adapt to every niche in the host
• Best adapted are least pathogenic
• Parasite-host relationship is typically long-term/chronic/"intimate"

Conditions Required for Endemic Parasitism

• Reservoir of infection
• Means of transmission to susceptible hosts
• Ability to invade and establish in new hosts
• Ability to reproduce

Veterinary Parasitology

• Three groups of eukaryotic organisms that affect the health and wellbeing of animals:
  • Protozoa (Protozoology): single-celled, nucleated
  • Helminths (Helminthology): worm-like animals showing differentiation, metazoans
  • Arthropods (Entomology): arachnids and insects; ectoparasites

Parasites of Veterinary Importance

• Phylum Nemathelminthes (Roundworms):
  • Class Nematoda (Roundworms)
• Phylum Platyhelminthes (Flatworms):
  • Class Cestoda (Tapeworms)
  • Class Trematoda (Flukes)
• Phylum Arthropoda:
  • Class Insecta
  • Class Arachnida
• Kingdom Protozoa: nine phyla contain at least one genus of veterinary importance

Nematodes (Roundworms)

• Characteristics:
  • Round/cylindrical
  • Complete alimentary canal
  • Celom, body cavity
  • Sexes usually separate
• Examples: Ascaris suum

Cestodes (Tapeworms)

• Characteristics:
  • Flat body with no colem (body cavity)
  • No alimentary canal
  • Hermaphroditic
  • Scolex (head) with 4 suckers or bothria
  • Strobila (body) with head, neck, and proglottids (segments)
  • All are parasitic with an indirect life cycle

Trematodes (Flukes)

• Characteristics:
  • Dorso-ventrally flattened, leaf-like
  • Incomplete alimentary canal
  • No celom
  • Hermaphroditic
  • Oral and ventral suckers for attachment
• Examples: Fasciola spp.

Protozoa Study Notes

Disease Transmission

• Contaminated water and food, vectors like insects, and direct contact can transmit diseases caused by protozoa
• Malaria is transmitted by Plasmodium, which is spread through the bite of an infected mosquito
• Giardiasis is transmitted by Giardia, which is commonly found in contaminated water and food
• Amoebiasis is transmitted by Entamoeba, which can be spread through contaminated food and water, as well as direct contact
• Cryptosporidiosis is transmitted by Cryptosporidium, which is commonly found in contaminated water

Host-Parasite Interactions

• Trichomonas forms a mutualistic relationship with its host, providing a benefit to both the host and the parasite
• Giardia forms a commensalistic relationship with its host, providing a benefit to the parasite but not the host
• Plasmodium forms a parasitic relationship with its host, providing a benefit to the parasite but harming the host
• Protozoa can evade host immune responses by varying their antigens, manipulating cytokines, and suppressing the immune system

Reproduction Strategies

• Binary fission involves the division of a parent cell into two daughter cells
• Multiple fission involves the division of a parent cell into multiple daughter cells
• Budding involves the formation of a new individual from a parent cell
• Sexual reproduction involves the fusion of gametes to form a zygote
• Plasmodium exhibits an alternation of generations, involving a life cycle that alternates between different hosts
• Trypanosoma exhibits metamorphosis, involving a significant change in form during its life cycle

Modes of Nutrition

• Phagocytosis involves the engulfing and digesting of solid particles
• Pinocytosis involves the engulfing and digesting of fluids and dissolved substances
• Amoeba proteus feeds on bacteria
• Ophrydium versatile feeds on algae
• Some protozoa absorb nutrients through their cell membrane

Protozoan Structure

• Protozoa are eukaryotic cells with a true nucleus and membrane-bound organelles
• Cilia, flagella, or pseudopodia are used for movement
• The pellicle is a rigid layer of proteins and lipids that provides structure and support
• The cyst wall is a protective layer that surrounds the cell
• The axostyle is a rod-like structure involved in movement and feeding