Roundworms, Tissue

Basics

Tissue or lymphohematogenous system infection by adult or larval roundworms (nematodes)
Infections can be subclinical (asymptomatic) or present with acute/chronic manifestations.
Filarial infections (Filarioidea superfamily)
- Wuchereria bancrofti (bancroftian filariasis)
- Brugia malayi (Malayan filariasis)
- Brugia timori (Timorian filariasis)
- Loa loa (eye worm)
- Onchocerca volvulus (river blindness, onchocerciasis)
- Mansonella perstans, Mansonella ozzardi, Mansonella streptocerca (mansonellosis)
Other tissue nematode infections
- Dracunculus medinensis (Guinea worm, dracunculiasis)
- Ancylostoma braziliense, Ancylostoma caninum (cutaneous larva migrans, creeping eruption)
- Toxocara canis, Toxocara cati (visceral larva migrans [VLM] or ocular larva migrans [OLM], toxocariasis)
- Gnathostoma hispidum, Gnathostoma spinigerum (gnathostomiasis)
- Dirofilaria immitis (dog heartworm), Dirofilaria repens, Dirofilaria tenuis (dirofilariasis)
Systems affected: cardiovascular, gastrointestinal, hematologic/lymphatic/immunologic, musculoskeletal, nervous, renal/urologic, skin/exocrine

Distribution

W. bancrofti: tropics worldwide; mosquito vector (Culex, Mansonia, Anopheles, Aedes)
B. malayi: Southeast Asia and Pacific islands; mosquito vector
B. timori: Indonesia; mosquito vector
L. loa: Africa and India; deer fly vector (Chrysops spp.)
O. volvulus: Africa, Middle East, and South America; blackfly vector (Simulium)
Mansonella spp.: Central Africa and South America; midge vector (Culicoides)
D. medinensis: Ethiopia, Ghana, Mali, Sudan; contaminated water
A. braziliense, A. caninum: tropics and subtropics worldwide; contaminated soil
T. canis, T. cati: worldwide; contaminated food or soil
G. hispidum, G. spinigerum: Asia, emerging in Central/South America; undercooked intermediate host (fish, eel, frog, reptiles, or birds) or contaminated water (copepods)
D. immitis: worldwide; mosquito vector
D. repens: Europe, Southeast Asia, and Africa; mosquito vector
D. tenuis: North America; mosquito vector

Prevalence

Prevalence in endemic areas increases with age. Worm burden increases with exposure over time.
Lymphatic filariasis affects ~120 million and is the second leading cause of permanent disability worldwide. Infection is likely first acquired in childhood; up to 1/3 asymptomatically infected by age 5 years
Onchocerciasis affects 37 million and is the second leading cause of blindness in the world.
Estimated 3,000 to 10,000 were infected with dracunculiasis due to focused eradication program.
Toxocariasis (VLM/OLM) is more prevalent in children.

Filarial infections—adult nematodes live in subcutaneous tissues and lymphatic vessels for years. They produce microfilariae offspring which circulate in blood or tissues until ingested by arthropod vectors. In this intermediate host, they develop into infective larval stages which are then transmitted to the definitive human host.
Carnivores are natural hosts for certain nematodes that are unable to complete their life cycles in humans, who are accidental hosts.
In human tissue, worms mature over 6 to 12 months and survive up to 15 years.

Travel precautions in endemic areas, arthropod bite precautions, avoid infected rivers and streams, avoid infected food/water sources and contaminated soils, filter water appropriately
Vector control: bed nets, larvicides, insecticides, repellent, clothing
WHO recommended mass drug administration for lymphatic filariasis: albendazole 400 mg with either ivermectin 150 to 200 μg/kg or diethylcarbamazine (DEC) 6 mg/kg annually OR albendazole 400 mg twice yearly in areas endemic for L. loa (1)[A].
DEC 300 mg once weekly for L. loa (2)[A]

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