Nematodes: Trichostrongylus & Anisakis

• Focus is on parasitic worms, specifically nematodes.

Trichostrongylus spp.

• Parasites of herbivores
• Human infection occurs accidentally
• Infective species include Trichostrongylus orientalis, Trichostrongylus colubriformis, and Trichostrongylus axei
• Resides in the small intestine
• Transmission: Ingestion
• Infective Stage: L3-Filariform larvae
• Diagnostic Stage: Egg
• Pathogenesis: Blood loss
• Treatment: Mebendazole

Anisakis spp.

• Common names: Cod worm, Herring worm
• Intermediate hosts: Microcrustaceans
• Final hosts: Marine mammals
• Paratenic hosts: Fish and squids
• Accidental hosts: Humans
• Transmission: Ingestion
• Infective Stage: L3 Filariform Larvae
• Diagnostic Stage: L3 Larvae
• Habitat: GI Tract
• Diagnosis involves demonstrating worms via gastroscopy, surgery, or vomiting.

Anisakiasis or Anisakidosis:

• Results in clinical manifestations like abdominal pain
• "Tingling throat syndrome" when the oropharynx is involved
• Peritoneal irritation
• Eosinophilic granulomatous reaction

Filarial Nematodes

• Includes various species categorized by location in the host
  • Subcutaneous: Onchocerca volvulus, Mansonella streptocerca
  • Serous Cavity: Mansonella spp.
  • Lymphatic: Wuchereria bancrofti, Brugia malayi, Brugia timori

Microfilaria

• Modified eggs of filarial worms
• Serpentine shape
• Filled with nuclei of many cells that can be crowded or dispersed.
• May or may not be enveloped/sheathed
• Cephalic space can be long or short

Periodicity

• Describes the fluctuation in numbers of microfilariae in peripheral blood over 24 hours.
• Types include:
  • Nocturnal (10PM-4AM): Active at night.
  • Diurnal (10AM-3PM): Active during the day.
  • Subperiodic: Specific times when numbers increase.
  • Nonperiodic: No specific time preference.

Lymphatic Filariasis

• Neglected Tropical Disease (NTD)
• One of the most debilitating diseases.
• Second leading cause of permanent/long-term disability
• Causative agents include Wuchereria bancrofti and Brugia malayi

Parasitic NTDs

• Include Chagas Disease, Cysticercosis, Echinococcosis, Fascioliasis, Dracunculiasis, African Sleeping Sickness, Leishmaniasis, Lymphatic Filariasis, Onchocerciasis, Schistosomiasis, and STH.

Treatment for Nematodes

• Albendazole, Mebendazole, Thiabendazole, Pyrantel pamoate

Epidemiology of Nematodes

• Affects a large portion of the world's population
• Prevalent in areas with poor hygiene, sanitation, where human feces are used as fertilizer
• Survive for months in fecal matter, sewage, and 10% formalin.

1. Wuchereria bancrofti

• Common name: Bancroftian/Bancroft's filarial worm
• Final host: Man

3. Brugia Timori

• Resembles Bancroftian filariasis
• Final host: Man
• Intermediate host: Mosquito (Anopheles barbirostris)
• Habitat: Upper lymphatic system
• Transmission: Skin penetration
• Infective stage: L3-Filariform larva
• Diagnostic stage: Microfilaria
• Nuclei extend to the tip of the tail
• Sheath present
• Staining: (NO) Giemsa
• Has terminal nuclei (Two).
• Cephalic space LW is 3:1
• Kinky appearance
• Nocturnal periodicity

2. Brugia malayi

• Common Name: Malayan's Filarial worm
• Hosts:
  • Final: Man
  • Intermediate: Mosquito (Mansonia, Anopheles)
  • Reservoir: Macaques and leaf monkeys
  • Animals widen the distribution of diseases
• Habitat: Upper lymphatic system
• Transmission: Skin penetration
• Infective Stage: L3-Filariform larva
• Diagnostic Stage: Microfilaria
• Nuclei irregularly spaced
• Sheath present
• Staining affinity: (YES) Giemsa
• Terminal nuclei: Two
• Cephalic space LW: 2:1
• Appearance: Kinky
• Periodicity: Nocturnal/Subperiodic

Diagnosis

• Differentiation achieved through Thick and Thin Smear.
• Knott's Concentration Technique used for identifying Dirofilaria immitis microfilariae
• Nucleopore filtration used, as well as Diethylcarbamazine provocative test
• Serological tests detect circulating filarial antigens
• Skin test using D. immitis (W. bancrofti)

Pathogenesis

• W. bancrofti and B. malayi cause:
  • Lymphadenitis: Infection in one or more lymph nodes.
  • Lymphangitis: Infection of the lymphatic vessels.

Elephantiasis

• Infectious disease transmitted through mosquito bites.

Tropical Pulmonary Eosinophilia (TPE)

• Persistent hypereosinophilia (>3000/uL of blood
• Concentration Technique yields a negative result
• Lung biopsy yields a positive microfilaria

Occult Filariasis

• Occurs when blood is negative

Chyluria

• Rare condition where lymphatic fluid leaks into kidneys, turning urine milky white

Hydrocele

• Swelling of the scrotum

4. Loa loa

• Common Name: African eye worm
• Host:
  • Final: Man
• Intermediate hosts: Chrysops (Mango fly, Tabanid fly, deer fly, horsefly, mangrove fly)
• Habitat: Subcutaneous tissue
• Transmission: Skin penetration
• Infective stage: L3 Filariform larva
• Diagnostic stage: Microfilaria, Adult

Clinical Manifestations

• Migration of adult worms in subcutaneous tissues
• Calabar swelling (temporary swelling)
• Hydrocele (swelling of the scrotum)
• Orchitis
• Urticaria/Skin infection
• Lymphadenitis:
  • Requires surgery
• Distribution is in West and Central Africa
• Typically bite during the day, and more common during the rainy season

5. Onchocerca volvulus

• Common name: Blinding worm, Craw craw
• Habitat: Subcutaneous Tissue
• Pathology: River blindness
• Vector: Black fly (Simulium)
• Microfilaria migrate continuously throughout the skin
  • Non periodic
  • Unsheathed
  • Lacks nuclei in the tail tip

Pathogenesis

• Results in Onchodermatitis, Mal morado/erisipela de la costa, Leopard skin, Sowda, Hanging groin, Blindness, Wolbachia endosymbiosis

Diagnosis

• Utilizes Skin snips, Mazzotti test
• Treatment with DEC, Ivermectin, Suramin, Nodulectomy

Epidemiology

• Widely distributed throughout Central Africa
• Contributory factor: Breeding of vector
• Those who live/work near streams/rivers most at risk

6. Mansonella spp.

• Intermediate host: Culicoides gnats (Biting midges)
• Transmission: Skin penetration
• Infective stage: L3 Filariform
• Diagnostic stage: Microfilaria
• Periodicity: Nonperiodic
• Microfilariae are unsheathed.Body nuclei extend to the tip
• Habitats vary
  • Mansonella ozzardi:
    • Adults: Mesentery, visceral fat, body cavities
  • Mansonella streptocerca:
    • Microfilariae: Skin, blood
    • Adults: Subcutaneous tissue
  • Mansonella perstans:
    • Adults: Deep connective tissues, body cavities, mesentery

Zoonotic filariae

7. Dirofilaria immitis

• Common Name: Dog heartworm
• Vector: Mosquito
• Habitat: Heart (right ventricle and pulmonary arteries)
• Diagnosis: Histologic examination of “coin lesion” on chest radiograph
• Infective stage: L3 Larva
• Diagnostic Stage: Microfilariae
• Cosmopolitan in dogs in North and South America, Australia, Japan and Europe

Treatment

• M. ozzardi:
  • Asymptomatic, does not require treatment, but Ivermectin can be used
• M. streptocerca:
  • Treated with DEC, Ivermectin
• M. perstans:
  • Requires Albendazole

Tissue Dwelling Nematodes

1. Dracunculus medinensis:

• Common name: Guinea Worm, Fiery serpent of the Israelites, Medina worm, Dragon worm
• Final host: Man
• Intermediate host: Copepod
• Habitat: Subcutaneous Tissues
• Transmission: Ingestion of infected copepods
• Infective stage: L3 larva from infected copepods
• Diagnostic stage: L1 larva from ulcer

2. Trichinella spp.:

• *T. spiralis
• T. pseudospiralis (mammals and birds worldwide)
• T. nativa (Arctic bears)
• T. nelsoni (African predators and scavengers)
• T. britovi (carnivores of Europe and western Asia)
• T. papuae (wild and domestic pigs of Papua New Guinea and Thailand)
• Trichinella zimbabwensis
  • Found in crocodiles in Africa
  • Currently with no known associations with human disease

Trichinella spiralis

• Common Name: Muscle Worm, Trichina Worm Host: Carnivores and Omnivores MOT: Ingestion of undercooked pork meat Habitat:
• Adult: Small intestine
• Larvae: Striated muscle
• IS: Encysted larva from undercooked meat
• DS: Encysted larva from striated muscle
• Angiostrongylus costaricensis
  • Transmitted through ingestion

Pathogenesis

• Urticaria, erythema, tenderness

Diagnosis

• Observation of larva through flooding of area in water.

Treatment

• Surgical removal
• Metronidazole, thiabendazole, mebendazole

Epidemiology

• Almost completely wiped out in Asia.
• Great progress of elimination in Africa.
• Affects poor communities that do not have safe water to drink.

Pathogenesis

• Intestinal symptoms
• Muscle invasion
• CNS involvement

Diagnosis

• Stool examination
• Muscle biopsy
• Bachman intradermal test
• Beck's xenodiagnosis
• Bentonite flocculation test
• Knott's concentration, membrane filtration technique:

Treatment

• Mebendazole, corticosteroids

Epidemiology

• Once prevalent in Europe, now in China.
• Common in areas where pork scraps are fed to hogs/pigs.

3. Toxocara canis/cati

• Common name: dog/cat roundworm
• Causative agent of visceral larva migrans.
• Natural hosts: Dogs (young puppies) and Cats
• Accidental/Dead-end hosts: Man and non-dog/cat animals
• MOT: Ingestion
• IS: Embryonated egg, Larva in tissues (foodborne)
• DS: Larva in tissues

Pathognesis

• Hypereosinophilia
• Visceral larva migrans

Diagnosis

• Clinical Symptoms
• Serologic Testing

Treatment

• Corticosteroids
• Albendazole, Mebendazole

4. Angiostrongylus cantonensis

• Common Name: Rat Lungworm
• Intermediate host: Mollusk/snail
• Final host: Rats
• Accidental host: Humans
• Paratenic host: Prawn, crab, vegetation MOT: Ingestion IS: L3 Larva DS: Larva in tissues