Nematodes-Tissue Nematodes

• Nematodes can be classified according to their habitat

  • Intestinal human nematodes
  • Somatic human nematode
  • Animal nematodes infecting man (rare)

  
• Intestinal human nematodes


  • Ascaris lumbricoides
  • Ancylostoma duodenale
  • Necator americanus
  • Wuchereria bancrofti
  • Brugia malayi
  • Brugia timori

  
• Somatic human nematodes


  • Visceral Larva migrans
  • Cutaneous Larva migrans
  • Capillaria hepatica
  • Trichinella spiralis
  • Dracunculus medinensis

  
• Animal nematodes infecting man (rare)

  • Toxocara
  • Angiostrongylus cantonensis
  • Angiostrongylus costaricensis
  • Anisakis
  • Gnathostoma
  • Baylisascaris
  • Dirofilaria

  
• Intestinal nematodes


  • Capillaria philippinensis
  • Trichostrongylus
  • Strongyloides fuelleborni
  • Oesophagostomum
  • Ternidens spp

  
• Nematodes infecting other body parts

  • Conjunctiva: Thelazia spp
  • Skin: Cutaneous Larva migrans
  • Liver: Capillaria hepatica
  • Kidney: Dioctophyma spp
  • Respiratory tract/lungs: Mammomonogammus, Capillaria aerophila, Ascaris suum

  
• Nematodes can be classified according to their habitat
• Intestinal human nematodes include Ascaris lumbricoides, Ancylostoma duodenale, Necator americanus, Wuchereria bancrofti, Brugia malayi, and Brugia timori

  
• Somatic human nematodes include Visceral Larva migrans, Cutaneous Larva migrans, Capillaria hepatica, Trichinella spiralis, and Dracunculus medinensis

  
• Animal nematodes that can infect man (rarely) include Toxocara, Angiostrongylus cantonensis, Angiostrongylus costaricensis, Anisakis, Gnathostoma, Baylisascaris, and Dirofilaria

  
• Intestinal nematodes include Capillaria philippinensis, Trichostrongylus, Strongyloides fuelleborni, Oesophagostomum, and Ternidens spp

  
• Nematodes can infect other body parts such as the conjunctiva (Thelazia spp), skin (Cutaneous Larva migrans), liver (Capillaria hepatica), kidney (Dioctophyma spp), and respiratory tract/lungs (Mammomonogammus, Capillaria aerophila, Ascaris suum)

  
• Filarial nematodes


  • Wuchereria bancrofti
  • Brugia malayi
  • Brugia timori
  • Loa loa
  • Onchocerca volvulus
  • Mansonella species
• Other somatic nematodes


  • Dracunculus medinensis
  • Gnathostoma spinegerum
• Filaria nematodes


  Class: Secernentea; Superfamily: Filarioidea; Family: Onchocercidae
• Habitat of filaria nematodes

  Reside in the lymphatic system, skin, subcutaneous tissue, and rarely body cavity

  
• Adult filaria nematodes


  • Slender, round, measuring 2–10 cm in length (except the female Onchocerca 35–50 cm)
  • Some can survive for many years in humans causing chronic obstructive and inflammatory conditions including elephantiasis and hydrocele

  
• Microfilariae


  • L1 larvae which are highly motile thread like larvae
  • Hypersensitivity reactions can occur against the microfilarial antigen resulting in tropical pulmonary eosinophilia (TPE)

  
• Habitat of filaria nematodes

  • Lymphatic: Wuchereria bancrofti, Brugia malayi, Brugia timori
  • Subcutaneous tissues: Loa loa, Onchocerca volvulus, M. streptocerca
  • Body cavity: Mansonella species

  
• Vectors of filaria nematodes

  • Mosquitoes: Wuchereria, Brugia spp
  • Midges: Mansonella species
  • Black fly: Onchocerca
  • Chrysops fly: Loa loa

  
• Microfilarial periodicity


  • Nocturinal: Night time (between 9 pm and 2 am)
  • Diurnal: Day time
  • Subperiodic: Present throughout, with slight increase in the afternoon
  • Non periodic: Any time
• Wuchereria bancrofti


  Also known as Bancroft's filaria
• Wuchereria bancrofti microfilaria


  • Measures 240-300 um x 7.5-10 um
  • Covered by a long hyaline sheath within which it moves
  • Head is blunt, tail is pointed
  • Unstained: transparent and colorless; stained with Giemsa or other romanowsky stains: pink with a column of violet nuclei
  • Nuclei are present throughout the body except near the head and tail end
• Wuchereria bancrofti adult worm

  • Male: 4 cm x 0.1 mm, small size, cork-screw like tail and presence of two spicules (helps in copulation) at posterior end
  • Female: 6-10 cm x 0.2-0.3 mm, directly discharge larvae without any eggs, indistinguishable from female Brugia malayi

  
• Wuchereria bancrofti life cycle

  1. Definitive host: Man

  2. Intermediate host: Mosquito - Culex quinquefasciatus (principal vector worldwide); rarely Anopheles or Aedes

  3. Infective form: Third stage/ Filariform larvae found in the proboscis of the mosquito

  4. Infective larvae get deposited in skin by the insect bite

  
• Vectors of Wuchereria bancrofti

  • Aedes spp., Anopheles spp., Culex spp., Mansonia spp., and Coquillettida juxtamansonia
• Clinical features of Wuchereria bancrofti infection

  • Asymptomatic filariasis
  • Acute dermatolymphangioadenitis (ADLA)
  • Acute filarial lymphangitis (AFL)
  • Lymphedema and elephantiasis
  • Genitourinary lesions (Hydrocele, Chylocele)
  • Tropical Pulmonary eosinophilia (Occult filariasis/ Weingarten's syndrome)

  
• Classical filariasis vs Occult filariasis

  Classical: Inflammatory changes to adult worm, microfilaria in blood and fluid, lymph nodes and lymphatic vessels affected

  Occult: Hypersensitivity reaction to microfilaria antigen, microfilaria absent in blood, lungs, liver, and spleen affected

  
• Laboratory diagnosis of Wuchereria bancrofti

  1. Sample: Blood, occasionally in hydrocele fluid, urine, or other body fluids

  2. Specimen collection: Between 8 p.m. and 4 a.m.

  3. Microscopic examination: Direct wet mount, stained thick smear

  4. Concentration techniques: Nucleopore filter, Knott's method

  5. DEC provocation test

  6. QBC (Quantitative Buffy coat examination)

  7. Detection of circulating filarial antigens

  8. Antibody detection: IHA, IFA, ELISA

  9. Xenodiagnosis

  
• Treatment for Wuchereria bancrofti

  Drug of choice: Diethylcarbamazine (DEC)

  Combination of DEC, ivermectin and albendazole

  Doxycycline and related antibiotics to kill the endosymbiont Wolbachia

  Use of special boots, elastic bandages and simple elevation to reduce limb size
• About 120 million people worldwide are affected by lymphatic filariasis, and more than 1 billion people are at risk
• In the Philippines, 45 provinces are endemic for lymphatic filariasis, with Aedes poecilus as the mosquito vector in most provinces

  
• Majority of lymphatic filariasis cases have been reported from India, Pakistan, Sri Lanka, Brazil, Guyana and Southeast Asia, with males affected more than females
• Prevention and control measures for lymphatic filariasis

  • Mass Chemoprophylaxis
  • Vector control
  • Hygiene education programs
• Brugia malayi


  Also known as Malayan filaria
• Brugia malayi microfilaria


  • Measures 200-280 um x 7.5-10 um

  Presence of two distinct nuclei in the tip of the tail, with the organism tissue tending to bulge around each of the two nuclei

  
• Brugia malayi adult worm


  • Essentially similar to Wuchereria bancrofti, but smaller in size: Typical adult female 53 mm, adult male 24 mm

  
• Brugia malayi life cycle

  Definitive host: Man

  Intermediate host: Mosquito - Mansonia, Anopheles and Aedes

  Reservoir: Humans are the main reservoir, except for subperiodic strains where monkeys, cats and dogs are animal reservoirs

  Infective form: Third stage/ Filariform larvae found in the proboscis of the mosquito

  Infective larvae get deposited in skin by the insect bite

  Main vector: Mansonia spp (M. annulifera and M. uniformis)

  
• Clinical features of Brugia malayi infection

  Often asymptomatic even with presence of microfilariae

  Similar to Wuchereria bancrofti infection, but more frequent episodes of acute adenolymphangitis and filarial abscesses, and more chronic manifestations like lymphedema and elephantiasis

  
• Intermediate host


  Mosquito - Mansonia, Anopheles and Aedes