6.4.1: introduction to veterinary parasitology

- Explain the concept of parasitism and appreciate the diversity of parasites that infect domestic animals and humans. - Explain in general terms why parasites are important pathogens for veterinary and human health. - Describe some of the challenges that parasites face on a day-to-day basis.

Explain the meaning of these terms: commensalism, symbiosis, parasitism.

• Commensalism: two species living together, with no metabolic dependence

• Symbiosis: two species living together, each dependent on the other

• Parasitism: two species living together, one (parasite) at the expense of the other (host).

Explain the meaning of these terms: endoparasites and ectoparasites.

• Endoparasites: live within the body of the host

• Ectoparasites: live on the surface of the host, or embedded into the skin.

Explain the meaning of these terms: obligatory parasites, facultative parasites and temporary parasites.

• Obligatory parasite: has to be parasitic for at least part of its life-cycle.

• Facultative parasite: can be parasitic, but not essential for completion of its life cycle.

• Temporary parasite: only visits the animal to feed.

Explain the meaning of these terms: adult, larva, nymph and embryonated egg.

• Adult: life cycle stage involving sexual multiplication

• Larva: immature life cycle stage - not like an adult

• Nymph: immature life cycle stage - similar to the adult

• Embryonated egg: an egg containing a fully formed larva

Explain the meaning of the term parthenogenesis.

• Parthogenesis: the production of fertile eggs by a female that hasn’t mated.

Explain the meaning of these terms: definitive host, intermediate host, paratenic host, transport host, vector and reservoir host.

• Definitive host: the host where sexual reproduction takes place inside

• Intermediate host: a host where development of the parasite takes place

• Paratenic host: a host where the parasite enters its tissues but no development or growth takes place (the parasite is usually waiting for this host to be eaten by its next intermediate/final host)

• Transport host: a host of loose association, the parasite is merely carried on it.

• Vector: invertebrates that spread pathogenic organisms

• Reservoir host: an infected definitive host, acting as a source of infection for other animals

Explain the meaning of host specificity.

• Host specificity: some parasites have a wide host range, others have a narrow host range, others are highly specific.

Explain the meaning of these terms: direct life-cycle and indirect life-cycle.

• Direct life-cycle: no intermediate host in the life-cycle

• Indirect life-cycle: there is an intermediate host in the life-cycle

Explain the meaning of these terms: predilection site and prepatent period.

• Predilection site: where most parasites establish at a particular site or in a particular tissue

• Prepatent period: the time from infection of the host to the appearance of eggs or larvae in faeces/urine/blood

Explain the meaning of these terms: parasitaemia, autoinfection, biotic potential and generation time.

• Parasitaemia: the presence of parasites in the circulating blood

• Autoinfection: the establishment of the products of sexual reproduction in the animal they were formed inside.

• Biotic potential: an organism’s ability to increase in numbers (for parasites - largely determined by the numbers of offspring by sexual and asexual phases of reproduction and their generation time)

• Generation time: time taken for one generation to complete its life cycle. This can take a few days or several years, and depends on climate.

Explain the meaning of these terms: horizontal transmission, vertical transmission and faceal-oral transmission.

• Horizontal transmission: transmission of the parasite through the host population.

• Vertical transmission: direct transmission of the parasite from one host generation to the next. This can be done prenatally, via milk, or neonatal transfer.

• Faecal-oral transmission: transmission of an organism by ingesting the life-cycle stage (usually eggs/oocyst) that has passed into faeces.

Explain the meaning of these terms: dispersal mechanisms, bionomics, epidemiology, hypobiosis and pathogenesis.

• Dispersal mechanisms: may be geographical or temporal (synchronising parasite reproduction with onset of favourable climate)

• Bionomics: the influence of environment on the development of the free-living life-cycle stages.

• Epidemiology: factors governing the spread of infection and disease through host populations

• Hypobiosis: when the parasite development within the host is stopped. This can occur when the outside conditions are unfavourable.

• Pathogenesis: the sequential development of pathological changes that take place during disease.

Explain the meaning of these terms: mucosal larvae and pathogenicity.

• Mucosal larvae: developing/hypobiotic larvae in the wall of the alimentary tract.

• Pathogenicity: the damage that can be inflicted by an infectious agent.

Explain the meaning of these terms: resilience, resistance and tolerance.

• Resilience: the innate ability of an animal to withstand the effects of infection.

• Resistance: the ability of an animal to prevent the establishment or development of infection.

  • It can also refer to a parasite’s ability to resist a parasiticide that would normally wipe out a normal population of that species.

• Tolerance: the innate insusceptibility of a parasite population to a potentially lethal chemical.

Explain the meaning of these terms: refugia and formulation.

• Refugia: sites where parasites escape antiparasitic drugs when animals are being treated (e.g. nematode larvae on the grass when sheep are wormed).

• Formulation: where the physical/biological characteristics of a pharmaceutical are modified by combining it with other substances.

What are the major parasite groups?

• Arthropods: insects and acarina

• Protozoa: single celled organisms

• Helminths: cestodes, trematodes and nematodes

What is the difference between a micro-parasite and a macro-parasite?

• Micro-parasites multiply inside the host

• Macro-parasites do not multiply inside the host