Nematodes - Part 3

Blood Nematodes (Filarial Worms)

Overview of Blood Nematodes

  • Alternative Names: Filarial worms, filariasis, African eyeworm, among others.

  • Transmission: Through blood-sucking arthropods; the larval stage resides in insects.

  • Pathogenicity: Adult worms inhabit the lymphatic system, muscles, or connective tissues of the host (typically humans).

Life Cycle and Identification

  • Microfilariae: The larvae produced by the female worm. This stage is critical for identification.

    • Habitat: Microfilariae may migrate in the bloodstream at specific times, particularly around the clock.

    • Identification Features: Key to recognizing the organism includes the arrangement of nuclei within the tail area and the presence or absence of a sheath.

Common Blood Nematodes

1. Wuchereria bancrofti

  • Transmission: Through small blood-sucking arthropods (specifically mosquitoes).

  • Specimen Collection: Best collected at night between 10 PM and 2 AM due to its nocturnal activity.

  • Symptoms:

    • Early Symptoms: Flu-like, including fever, chills, headache, lymph node inflammation.

    • Late Stages: Increased fibrotic changes in lymph nodes and vessels.

  • Tail Morphology: Nuclei arranged at the tail section.

2. Brugia malayi

  • Transmission: By mosquitoes, generally found in the Far East.

  • Symptoms: Similar to Wuchereria bancrofti with additional swelling in limbs.

  • Morphological Forms: Two distinct forms:

    • Nocturnal Form: Found in coastal rice fields; collect samples at night.

    • Non-periodic Form: Found in swampy forests.

  • Identification: Encased in a sheath, nuclei extending to the tail section.

3. Loa loa (African Eyeworm)

  • Transmission: By Tabanid (deer flies).

  • Location: Found in the rainforests of West and Central Africa.

  • Symptoms:

    • Calabar Swelling: Localized inflammation due to worm migration and pain.

    • Microfilariae migrate through the bloodstream and may reach the subconjunctival space in the eye.

  • Specimen Collection: Required during the day (10 AM - 12 PM) due to its diurnal periodicity.

  • Morphological Features: Microfilariae are encased in a sheath, with nuclei reaching the tip of the tail.

4. Onchocerca volvulus

  • Transmission: By black flies, widespread across Africa, Central America, and South America.

  • Infection Characteristics:

    • Microfilariae: Found in cornea and lacking a sheath; have tapering, non-nucleated tails.

  • Conditions Caused: Produces skin nodules that can lead to blindness and skin infections known as river blindness (onchocerciasis) and lymphadenopathy.

  • Adult Worms: Cause nodules in soft tissue, leading to serious complications like vision loss.

5. Mansonella species

  • Transmission: By midges, which are small flies.

  • Geographic Distribution: Various regions in Africa and South America; Mansonella ozardi specifically found in Central and South America and the Caribbean.

  • Clinical Manifestations: Generally asymptomatic; symptomatic cases may include rashes and swelling.

  • Morphological Characteristics:

    • Lack a sheath, characteristically absent in Mansonella species.

    • Types of Mansonella:

    • Mansonella streptocerica: Found in skin lesions causing rashes.

    • Mansonella perstans: May inhabit pericardial, pleural, and peritoneal cavities.

    • Mansonella ozardi: Found in the bloodstream and is comparatively low in pathogenicity but can still present with symptoms.