Filariae

Taxonomy and morphology

The suborder Filariata includes several medically important families, among which are the causative agents of dangerous tropical infections. Key species include:

• Genus Wuchereria: Wuchereria bancrofti (Bancroft's filaria).
• Genus Brugia: Brugia malayi and Brugia timori.
• Genus Loa: Loa loa (African eyeworm).
• Genus Onchocerca: Onchocerca volvulus and Onchocerca coecutiens.

The structure of the reproductive system has specific features. Females have a single reproductive system (the vagina is located in the middle of the body and leads to two uteri). Depending on the species, they can be viviparous or lay from 1,000 to 3,500 eggs per day. Males possess a wavy, thread-like testis, and the ejaculatory duct opens at the posterior end of the body.

Main species and diseases

Brugia malayi localizes in lymphatic vessels, causing brugian filariasis. Vectors include mosquitoes of the genera Anopheles, Aedes, and Mansonia. Damage to the lymphatic system leads to the development of elephantiasis, most commonly affecting the lower extremities and scrotum.

Onchocerca species parasitize the subcutaneous tissue, forming specific nodules known as onchocercomas. Vectors are blackflies of the genus Simulium. The disease (onchocerciasis) is accompanied by severe dermatitis, skin atrophy, "hanging groin" formation, and severe eye damage up to blindness (hundreds of thousands of people lose their sight in endemic areas). Foci of the disease develop near rivers where blackflies breed.

Loa loa (African eyeworm) inhabits the skin, subcutaneous tissue, and subconjunctival space. Infection occurs through the bite of deer flies of the genus Chrysops. Geographically, loiasis is found exclusively in West and Central Africa. A characteristic sign of infection is Calabar swelling (migratory swelling without pitting on pressure) and pronounced blood eosinophilia.

Separately, dracunculus (the causative agent of dracunculiasis) is considered, whose cycle is associated with the aquatic environment. Humans become infected by drinking raw water containing infected cyclopoid copepods. The larvae migrate to the subcutaneous tissue of the legs, where the female grows for about a year. Upon contact with water, a blister forms on the skin, it bursts, and the larvae are released.

Pathogenesis of filariasis

The pathogenic action of filariae is based on two main factors:

1. Body sensitization. Metabolic and decay products of dying helminths are potent allergens. This causes fever, edema, muscle pain, and eosinophilia. Sometimes the helminth encysts—the capsule protects the parasite from the immune system while isolating the host from toxic metabolites, reducing the severity of the allergy.
2. Mechanical damage. Active migration of adults and larvae traumatizes tissues, causing inflammation (myositis, lymphadenitis) and secondary bacterial infection.

The intensity of symptoms is directly proportional to the number of larvae entering the body. In massive infections (e.g., 5 larvae per 1 kg of body weight), a fatal outcome is possible.

Diagnostics and prevention

Laboratory diagnosis depends on the species of the pathogen. In loiasis, a thick blood smear is examined for microfilariae (sampling can be done at any time of day). In onchocerciasis, the primary method is the examination of bloodless skin snips. Diagnosis also relies on the clinical presentation (presence of onchocercomas, guinea worm ulcers, Calabar swelling) and epidemiological history.

Prevention is comprehensive in nature:

• Individual: protection against insect bites (repellents, protective clothing), avoiding unboiled water from open water bodies.
• Public: treatment of insect breeding sites with insecticides, bank clearance, protection of water bodies from contamination by helminth larvae, detection and treatment of infected individuals.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• The developmental cycle of the guinea worm in the Cyclops and human body
• Mechanisms of elephantiasis development in lymphatic system damage
• Differential diagnosis of Calabar swelling
• Immunological responses of the host to helminth encystment
• Structural features and localization of onchocercomas

Other topics in the "Medical Helminthology" section

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