Parasitology and Sample Collection Guide

Parasitology

• A parasite is a living organism that lives in or on another living organism (host) and benefits by obtaining food and shelter.
• The host is the organism that provides the parasite with food and shelter.
• The infective stage of the parasite is the stage that is capable of causing disease. This stage can be in the form of an ovum, larva, cyst, or adult.

Sample Collection

• Stool samples should be collected in a clean, watertight container with a tight-fitting lid.
• Urine should not be allowed to contaminate the stool specimen.
• Stool should not be retrieved from toilet bowl water.
• The specimen container should be labeled with the patient's name, identification number, physician's name, and the date and time of sample collection.
• Stool samples from patients taking barium, bismuth, or mineral oil should be collected prior to or after therapy.
• Stool samples from patients taking antibiotics or antimalarial medications should be delayed for 2 weeks.
• The typical stool collection protocol consists of three specimens collected every other day or totaling three collected in 10 days.
• Up to six specimens in 14 days are acceptable for diagnosing amebiasis.
• Liquid specimens should be examined within 30 minutes of passage.

Laboratory Diagnosis

• Direct examination is the most important laboratory diagnosis method because it is the primary method of identifying the parasite.
• Direct stool examination involves macroscopic and microscopic examination.
• Macroscopic examination involves assessing the stool's consistency, color, odor, and the presence of worms, mucus, pus, or blood.
• Microscopic examination involves using normal saline, iodine solution, or hematoxylin stain to examine the parasite under a microscope.
• Direct wet mounts and concentration methods are used for microscopic examination.

Direct Wet Mount

• Materials used: Microscope slide, cover slide, stool sample, plastic pipette, stick.

Concentration Methods

• Concentration methods are used when parasites are not readily visible in a direct wet mount but symptoms are continuous.
• Concentration methods include flotation and sedimentation.

Flotation

• Materials: Test tube, zinc sulfate solution, formalin, stool sample, plastic pipette, stick

Sedimentation

• Materials: Test tube, formalin, saturated solution of NaOH, stool sample, absorbent, stick, slides, cover slips.

Direct Blood Examination

• A drop of blood is placed on a clean slide and smeared with a spreader, creating a thin film.
• The slide is washed with methyl alcohol and dried at room temperature.
• Stains such as Leishman, Giemsa, or field stain are used to visualize parasites.

Preserving Stool Specimens

• Preservatives are used to prevent the deterioration of parasites in stool specimens that are delayed in delivery or testing.

Formalin

• Advantages: Suitable for helminth eggs, larvae, and protozoa cysts, used for sedimentation techniques, long shelf life, commercially available.
• Disadvantages: Permanent stained smears not possible, trophozoites do not preserve well.

Sodium Acetate Acetic Acid Formalin (SAF)

• Advantages: Good fixative for protozoa cysts and trophozoites, helminth eggs and larvae, easy to prepare, long shelf life, no mercury compounds, less toxic.
• Disadvantages: Poor adhesive properties, permanent stains not optimal.

Polyvinyl Alcohol (PVA)

• Advantages: Recommended for preserving trophozoite and cyst stages, serves as adhesive, long shelf life.
• Disadvantages: Difficult to prepare in the lab, toxic (contains mercury compound).

Merthiolate Iodine Formalin (MIF)

• Advantages: Easy preparation, good preservation and staining for most stages found in stool.
• Disadvantages: Short shelf life, permanent stained smears not possible, iodine can distort protozoa.