29 Questions
Which groups asexually replicate in the primary host?
Bacteria, Viruses, Fungi, and Protozoa.
What is the defining characteristic of Parasitism?
The parasite is metabolically dependent on the host.
What does subclinical infection refer to?
Infection with no clear signs; subtle performance losses.
What is a characteristic of Trematoda (Flatworms: Flukes)?
Blind pouch digestive tract and hermaphroditic reproductive system.
Why is accurate communication regarding parasites important?
To identify the Genus and sometimes species names of parasites.
Which of the following groups do not asexually replicate in the primary host?
Helminths and Arthropods.
What is the free-living infectious stage of nematodes?
Infective larva develops in the egg and hatches in the environment
What is the first step in the indirect life cycle of nematodes?
Egg or embryo or larva ingested by or penetrates intermediate host
What is the role of the snail in the life cycle of trematodes?
The snail is the intermediate host where the larval stages develop and replicate
What is the infective stage of trematodes that is ingested by the definitive host?
Metacercaria
What is the relationship between the definitive host and the intermediate host in the life cycle of advanced tapeworms?
The definitive host is a predator of the intermediate host
What is the sexually mature form of a parasite known as?
Adult stage
Which of the following is an example of a cestode that requires an intermediate host?
Taenia
Which type of host is accidentally infected by a parasite but does not allow the parasite to continue development?
Paratenic host
What is the term for the movement of immature parasite stages within the tissues of a host?
Larval migration
Which type of vector is necessary for pathogen development?
Biological vector
In which life cycle does the parasite require an intermediate host?
Indirect life cycle
What is the first step in the general helminth life cycle?
Contamination of the host's environment
Which of the following is NOT a characteristic of tapeworms (Cestoda)?
Dioecious (having separate sexes)
Which of the following arthropod groups has adults with 8 legs?
Arachnida
What is the term used to describe an infection where sexually mature parasites are generating offspring?
Patency
Which of the following is NOT a reason for understanding parasite life cycles?
Determination of parasite taxonomy
What is the term used to describe the developmental/maturation time needed between infection and the production of offspring?
Prepatent period
Which of the following arthropod groups includes lice and fleas?
Insecta
What is the role of the 2nd intermediate host (fish or frog) in the life cycle of primitive tapeworms (Spirometra)?
Develops into a 3rd larval stage (pleurocerecoid)
What is the first step in the life cycle of primitive tapeworms (Spirometra)?
Eggs are passed in the feces of the definitive host
Which host ingests the free-living larval stage (coracidium) in the life cycle of primitive tapeworms?
1st intermediate host (crustacean)
When does the infective larval stage develop in the intermediate host in the life cycle described?
After ingestion by the 2nd intermediate host
What triggers the ingestion of infective larva by the definitive host?
Consuming the 1st intermediate host
Study Notes
Parasitology
- Parasitism: intimate relationship between two hetero-specific organisms, where the parasite is metabolically dependent on the host.
Groups of Organisms
- Protozoa: unicellular
- Helminths: worms
- Arthropods: "bugs"
- Microbes: Bacteria, Viruses, Fungi
Parasite Effects on Host
- Continuum of effects: no effect, subclinical infection, clinical infection
- Clinical judgement: assessing whether the effect on the patient is significant enough to justify treatment
Classification of Parasites
- Based on morphology
- Protozoa:
- Apicomplexa: coccidians and hemosporidians
- Mastigophora: mucoflagellates and hemoflagellates
- Helminths:
- Nematoda (Roundworms): body cavity, pass-through alimentary canal, surface cuticle, dioecious
- Trematoda (Flatworms: Flukes): no body cavity, blind pouch digestive tract, surface tegument, hermaphroditic
- Arthropods:
- Arachnida: adult stage has 8 legs, larval stage has 6 legs (e.g., mites, ticks)
- Insecta: adult stage has 6 legs, some with wings (e.g., lice, fleas, flies)
Life Cycles of Helminths
- General cycle: contamination, development of preinfective stages, infection, maturation of adult stage
- Nematodes:
- Direct life cycle: no external stages, infective larva develops in egg
- Indirect life cycle: egg or embryo/ larva ingested by or penetrates intermediate host
- Trematodes:
- Require snail intermediate hosts
- Life cycle: egg passed in feces, larval stage develops in snail, infective larva (metacercariae) develops
- Cestodes (Tapeworms):
- Require intermediate hosts
- Direct life cycle: infectious stage develops in environment
- Indirect life cycle: larval stage develops in intermediate host
Importance of Life Cycles
- Control of disease
- Diagnosis of disease and parasite identification
- Prediction of disease
- Prevention of cross-host infection and zoonosis
- Environmental management to minimize host infection
- Timing of treatment and repeat treatment
Test your knowledge on general concepts in parasitology and microbiology, including parasitism, infectious groups of organisms, and asexual replication in the primary host.
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