9.2. PARASITES

• What are the general methods used for detection and identification of parasites?

• Macroscopic Examination

• Microscopic Examination

• Serologic Examination

• Nucleic Acid Hybridization

• Culture

• Animal Inoculation

• Xenodiagnosis

Macroscopic Examination

Involves the visual inspection of specimens for parasites or their segments. Effective for larger parasites like tapeworm proglottids, often found in stool samples. Quick but limited due to the need for visible size of parasites.

Microscopic Examination - Wet Mount

A simple technique where a sample is placed on a slide with saline or iodine solution, covered with a cover slip. Ideal for detecting live motile parasites, such as Giardia lamblia. Offers real-time observation of parasite movement and structure.

Microscopic Examination - Permanent Stains

Enhance visibility of parasites through staining. Types include Trichrome Stain (for protozoa in stool), Iron Hematoxylin (useful for stool samples), and Phosphotungstic Acid-Hematoxylin (for visualizing amoebic cysts). These stains provide detailed visualization of parasite structure.

Microscopic Examination - Stool Concentration

Techniques like Formalin-Ethyl Acetate Sedimentation and Zinc Sulfate Flotation concentrate parasites from large stool volumes, enhancing detection chances. Formalin-Ethyl Acetate is broadly useful, while Zinc Sulfate is particularly effective for protozoan cysts and helminth eggs.

Serologic Examination

Involves two main approaches: Antibody Response (measuring immune response to parasites, can indicate past infections) and Antigen Detection (directly detects parasite components, indicates active infection and can estimate parasite load).

Nucleic Acid Hybridization

Utilizes DNA or RNA probes and Polymerase Chain Reaction (PCR) to detect parasite genetic material. PCR amplifies specific DNA/RNA sequences, making this method highly sensitive and specific for identifying parasitic infections.

Culture Method

Involves growing parasites in specific media. For instance, Entamoeba histolytica can be cultured from feces using Robinson's medium, and some Leishmania species in Novy-MacNeal-Nicolle (NNN) medium. Not standard for all parasites but crucial for some.

Animal Inoculation

Involves detecting parasites by inoculating animals and monitoring for infection. This method is specific to certain organisms and is not a routine diagnostic tool but provides valuable insights for particular parasites.

Xenodiagnosis

A specialized method where uninfected vectors (like bugs for Trypanosoma cruzi) feed on a potentially infected host. The vector is later examined for the presence of the parasite. Primarily used for certain diseases like Chagas disease.