MLSP 5113 W1: Parasitology

What defines a parasite?

An organism that lives on or in a host and derives benefit at the host’s expense.

What is a host?

An organism that harbors a parasite and provides nourishment or shelter.

What is a definitive host?

The host in which a parasite reaches sexual maturity.

What is an intermediate host?

The host that harbors immature or larval stages of a parasite

What is an accidental host?

A host not normally part of the parasite’s life cycle, often leading to dead-end infection

What is a reservoir?

A natural host or environment that maintains and spreads parasites to humans

What is a vector?

A living carrier (e.g., mosquito, tick) that transmits parasites between hosts

What is an ectoparasite?

A parasite that lives on the surface of the host (lice, mites)

How do parasites differ from bacteria?

Parasites are eukaryotic, larger, often multicellular, and require a host to complete their life cycle.

How do parasites differ from viruses?

Parasites are living organisms; viruses are acellular and require host cells to replicate.

How do parasites differ from fungi?

Parasites depend on hosts for survival; fungi can live independently in the environment.

Key immune responses to parasites?

IgE antibodies, eosinophils, mast cells, and inflammatory responses.

How do parasites evade the immune system?

Antigen masking, antigen variation, immune suppression, tissue encystment.

Why is prevention critical in parasitic disease control?

Treatment alone doesn’t stop reinfection; prevention interrupts transmission cycles.

Purpose of stool examination in parasitology?

Detect ova, cysts, larvae, trophozoites, or adult parasites.

Key steps in stool examination?

Collection → preservation → processing → staining → macroscopic & microscopic exam.

Purpose of a direct wet mount?

Rapid detection of motile trophozoites.

Purpose of concentration techniques?

Increase detection by concentrating parasites from stool.

Purpose of permanently stained slides?

Detailed morphologic identification of protozoa.

Purpose of pinworm paddle/tape test?

Detect Enterobius vermicularis eggs from perianal area.

Advantage of Schaudinn’s fixative with PVA?

Excellent preservation of protozoan morphology.

Major disadvantage of Schaudinn’s fixative?

Contains mercury (toxic, disposal issues).

Advantage of formalin and SAF preservatives?

Good for helminth eggs and larvae; SAF is mercury-free.

Purpose of thick vs thin blood smears?

Thick: detect presence

Thin: identify species

Best staining method for blood parasites?

Giemsa stain

Strength of molecular (PCR) parasite detection?

Very high sensitivity and specificity.

Why is microscope micrometer calibration important?

Ensures accurate parasite measurement for species identification.

What is the most common specimen submitted for parasitic examination?

stool

Which of the following is the best technique to identify protozoan trophs in stool?

trichrome stained permanent slide; the purpose is to detect and identify our smaller parasites.

In infections with Taenia solium, humans can serve as the:

either the definitive or intermediate host

Oocysts can be detected in stool specimens by using:

Modified Acid-Fast stain; Oocysts resist trichrome/iron hematoxylin stain

The concentration procedure for stool is used to observe/identify:

protozoan cysts and helminth eggs

Fecal immunoassays have become more commonly used to diagnose infections with:

Giardia duodenalis and Cryptosporidium spp.

In a pediatric patient, the recommended clinical specimens for recovery of pinworms (Enterobius vermicularis) are the:

series of cellophane tape preparations

There are few procedures considered STAT in parasitology. The most obvious would be:

blood films for malaria

Key characteristics of the thick smear include:

The necessity to lyse the RBCs to examine more blood volume