Parasite Transmission and Hosts Quiz

Parasite Transmission and Exposure

• Migratory birds serve as reservoir hosts for the parasite Capillaria philippinensis, which is typically acquired through contaminated freshwater.
• Paratenic hosts act as transport vehicles for parasites, allowing them to reach their final hosts.

Sources of Exposure

• Contaminated soil and water can harbor parasitic worms or helminths, such as Ascaris lumbricoides, Trichuris trichiura, and Strongyloides stercoralis.
• Blood-sucking insects, like female Anopheles mosquitoes, can transmit parasites like Plasmodium.
• Domestic or wild animals can harbor parasites, such as the dog tapeworm Echinococcus granulosus.
• Another person's clothing, bedding, or environment can also serve as a source of exposure to parasites.

Modes of Transmission

• Fecal-oral transmission: the most common mode of transmission for most intestinal parasites, typically through contaminated food and water.
• Contaminated water: can transmit intestinal protozoa and the embryonated egg stage of intestinal roundworms.
• Penetration of the skin: can occur through contact with contaminated soil or water, allowing parasites like hookworms and Strongyloides to enter the body.
• Bite of blood-sucking insects: can transmit parasites like malaria, leishmaniasis, and trypanosomiasis.
• Inhalation: can transmit parasites like pinworms or Enterobius vermicularis.
• Transplacental or congenital infection: can occur through transmission from mother to child, such as with Toxoplasma gondii.
• Transmammary infection: can occur through mother's milk, such as with Strongyloides.
• Sexual intercourse: can transmit parasites like Trichomonas vaginalis.

Portals of Exit

• Anus: the most common portal of exit for parasite eggs, such as those of medically important roundworms.
• Urine: can transmit parasites like Trichomonas vaginalis, Strongyloides stercoralis, and Schistosoma haematobium.
• Sputum: can transmit parasites like lung fluke Paragonimus westermani and the intestinal roundworm Ascaris lumbricoides.
• Vaginal discharge: can transmit parasites like Trichomonas vaginalis.

Mechanisms of Disease Production

• Trauma or physical damage: can occur through direct physical damage caused by the parasite.
• Lytic necrosis: can occur through enzymes and other substances released by parasites, such as Entamoeba histolytica.
• Stimulation of host tissue reaction: can occur through cellular proliferation and infiltration at the site of parasite entry.
• Toxic and allergic phenomena: can occur through immunopathologic reactions, such as anaphylactic shock, bronchospasm, and local inflammation.

Specimen Collection and Handling

• Stool specimens: should be collected in a clean, water-tight container, and covered tightly, with approximately 2-5g of stool recommended.
• Blood specimens: should be collected using universal precautions and asepsis, with blood from the fingertip or earlobe (without anticoagulant) or from standard venipuncture (with anticoagulant).
• Cerebrospinal fluid (CSF) specimens: should be immediately examined if detection of parasite motility is desired.
• Tissue and biopsy specimens: can be used to detect parasites like Leishmania, Toxoplasma gondii, Trypanosoma, and Trichinella spiralis.
• Genitourinary secretions: can be used to detect parasites like Schistosoma haematobium.

Microscopic Examination

• Three stages: including preparation, concentration, and staining.
• Zinc sulfate flotation technique: uses differences in specific gravity to separate parasites from debris, with advantages including removal of fecal debris and yielding a cleaner preparation.
• Permanent stains: used in the final step of microscopic examination, involving staining of a fixed sample on a slide glass.