Nematode Infections Clinical Presentation

Updated: Oct 23, 2019
  • Author: Murat Hökelek, MD, PhD; Chief Editor: Michael Stuart Bronze, MD  more...
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Several clinical signs and symptoms can occur in patients with nematode infections.

  • Lung invasion - Löeffler or Löefflerlike syndrome (ascariasis, hookworm infections, strongyloidiasis)

    • Fever

    • Cough

    • Blood-tinged sputum

    • Wheezing

    • Rales

    • Dyspnea

    • Substernal pain

    • Pulmonary consolidations

    • Eosinophilia

    • Urticaria

    • Asthma

    • Angioneurotic edema

  • Intestinal invasion

    • May be asymptomatic (small number)

    • Abdominal pain (usually vague)

    • Abdominal cramps/colic

    • Diarrhea

    • Vomiting (rarely)

    • Constipation (occasionally)

  • Muscle and other tissue invasion - Trichinosis

    • Myalgias

    • Fever

    • Edema and spasm

    • Periorbital and facial edema

    • Photophobia

    • Sweating

    • Conjunctivitis

    • Weakness or prostration

    • Pain upon swallowing

    • Subconjunctival, retinal, and ungual hemorrhages

    • Rashes and formication

    • Encephalitis, myocarditis, nephritis

    • Pneumonia, meningitis, neuropathy

  • Lymphatic filariasis - W bancrofti, B malayi, B timori

    • Inflammatory signs (pain, tenderness, swelling, erythema)

    • Lymphadenitis/lymphangitis

    • Orchitis

    • Fever

    • Abscesses

    • Obstructive signs (lymphatic varices, hydrocele)

    • Lymphedema and elephantiasis

    • Chyluria

    • Hypereosinophilia

  • Loiasis - Loa loa

    • Calabar swellings (recurrent subcutaneous inflammation/swelling)

    • Eye worm (adults or larvae migrating under conjunctiva)

    • Eosinophilia (may exceed 70%)

    • Fever, irritability, urticaria, and pruritus

  • Onchocerciasis - O volvulus

    • Dermatitis

    • Nodules

    • Lymphadenitis

    • Ocular changes

      • Intraocular microfilariae

      • Punctate keratitis

      • Sclerosing keratitis

      • Anterior uveitis chorioretinitis

      • Optic neuritis

      • Optic atrophy

      • Glaucoma

      • Blindness (river blindness)

  • Dracunculiasis - D medinensis, Guinea worm disease

    • Allergic manifestations

      • Erythema

      • Urticaria

      • Pruritus

      • Nausea

      • Vomiting

      • Giddiness

      • Syncope

      • Fever (occasionally)

    • Local lesions

      • Papule

      • Sterile blister

      • Ulceration

      • Abscesses

    • Worm protrusion from skin

  • Toxocariasis - Toxocara canis/Toxocara cati, visceral or ocular larva migrans

  • Cutaneous larva migrans - Ancylostoma braziliense,Ancylostoma caninum, creeping eruption

    • Itching and red papules

    • Serpiginous track

    • Edema and acute inflammation

    • Scars

    • Secondary infection

  • Anisakiasis -Anisakis simplex,Pseudoterranova decipiens

    • Violent epigastric pain

    • Mild fever

    • Nausea

    • Vomiting

    • Diarrhea

    • Allergic reactions

  • Dirofilariasis

    • Chest pain, cough, hemoptysis, fever, and malaise in the pulmonary type

    • Creeping eruption and elevated sinuous track under the skin in the subcutaneous type

    • Ocular pain, grittiness, and eye redness in the ocular type

  • Angiostrongyliasis (rat lungworm disease) [3]

    • Nausea/vomiting

    • Neck stiffness

    • Headaches (may be global and severe)

    • Abnormal sensations in the legs and arms (some cases)

    • May report consumption of raw or undercooked slugs or snails



T trichiurainfections

In heavily infected people, trichuriasis appears to manifest as mild anemia, eosinophilia, bloody diarrhea (classic trichuris dysentery syndrome), growth retardation (chronic trichuris colitis with growth retardation), abdominal pain, finger clubbing, and rectal prolapse (especially in children). See the image below.

A typical Trichuris trichiura egg in feces. A typical Trichuris trichiura egg in feces.

E vermicularisinfection (pinworm)

The most common symptom of pinworm infection is nocturnal perianal pruritus. Occasionally, the migration of the parasite produces ectopic disease (eg, appendicitis, vulvovaginitis, chronic salpingitis, ulcerative lesions in the small or large bowel). [11] Enuresis has been blamed on the pinworm.

A lumbricoidesinfection

A more serious complication of ascariasis is encountered when a mass of worms obstructs the lumen of the small bowel. This acute abdominal condition is commonly observed in children with heavy infections. The presentation is similar to that of acute intestinal obstruction, with vomiting, abdominal distention, and cramps.

Another obstructive syndrome is encountered when Ascaris worms invade the biliary duct and cause pancreatic-biliary ascariasis. The most common presenting feature is abdominal pain, observed in 98% of patients. Less common features include ascending cholangitis, acute pancreatitis, and, rarely, obstructive jaundice.

Ascariasis in pregnant women results in intrauterine growth retardation. See the image below.

Ascaris lumbricoides egg in feces (formalin-ethyl Ascaris lumbricoides egg in feces (formalin-ethyl acetate sedimentation method).


The major manifestations of hookworm disease include iron deficiency anemia and chronic protein energy malnutrition. The development of these clinical features depends not only on the worm burden but also on the amount of absorbable dietary iron.

During the phase of worm attachment to small intestine mucosa, abdominal pain, diarrhea, and weight loss may be noted. In addition, malabsorption has been reported in children and, less commonly, in adults. [12]

S stercoralisinfection

Burning or colicky abdominal pain, often epigastric, occurs and is associated with diarrhea and the passage of mucus.

Some patients with strongyloidiasis report nausea, vomiting, and weight loss, with evidence of malabsorption or of protein-losing enteropathy.

Massive larval invasion of the lungs and other tissues may occur with hyperinfection, usually in immunocompromised hosts. In this syndrome, the worm is able to complete its entire life cycle in the human, and the symptoms are related to the large burden of larvae migrating in the host.

Severe generalized abdominal pain, diffuse pulmonary infiltrates, ileus, shock, and meningitis or sepsis due to gram-negative bacilli may occur. See the image below.

Strongyloides eggs in native examination from fece Strongyloides eggs in native examination from feces of a newborn.

T spiralisinfection

Myositis with pain, swelling, and weakness is common; it usually first develops in the extraocular muscles and then involves the masseters, neck muscles, limb flexors, and lumbar muscles. Some patients report headache, cough, shortness of breath, hoarseness, and dysphagia.


The ingestion of a parasitized fish with a nematode of the Anisakis genus may elicit symptoms within few hours.

Four principal clinical syndromes associated to anisakiasis have been described: gastric, intestinal, ectopic (or extragastrointestinal), and allergic. The onset of gastric anisakiasis begins within a few hours (generally 1 to 2 hours), when a live Anisakis larva reaches the human stomach.

Acute phase of the infection elicits severe epigastric pain, vomiting, diarrhea, and a mild fever. Generally, acute symptoms resolve within a few days, but untreated gastric disease can lead to chronic ulcerlike symptoms lasting for weeks to months.

Rare complications include small bowel obstruction, ileal stenosis, intussusception, intestinal perforation, and pneumoperitoneum.


Dirofilaria species are nematodes that infect domestic and wild canids, transmitted by several species of mosquitoes. Dirofilaria immitis causes severe disease (heartworm disease) in dogs and other carnivores and occasionally infects humans, while Dirofilaria repens usually causes a nonpathogenic subcutaneous infection in dogs and is the principal agent of human dirofilariasis in the Old World.

Dirofilariasis causes two main clinical syndromes: pulmonary dirofilariasis (caused by D immitis) and ocular or subcutaneous dirofilariasis (caused by several different dirofilarial species, particularly D repens). In addition to these syndromes, human dirofilariasis has been reported at other sites, such as the central nervous system, male genital system, peritoneal cavity, liver, or buccal mucosa. [8]

The diagnosis of Dirofilaria infection in humans is affected by the localization of the worm and the clinical symptoms. Serological investigations are not helpful in human cases.

The nematode can be removed via surgery, a practice that is also needed for etiological diagnosis and the exclusion of other severe diseases. [13]

 Dirofilaria repens: A. Front end (x400), B. Macro Dirofilaria repens: A. Front end (x400), B. Macroscopic size.
Dirofilaria from a scalp nodule. Dirofilaria from a scalp nodule.

Angiostrongyliasis (rat lungworm disease)

Angiostrongylus cantonensis infection has a presentation similar to that of bacterial meningitis (eg, nausea/vomiting, stiff neck, headaches). The infection can last from 2-8 weeks (or longer) but usually self-resolves without treatment. [3]



The following are potential causes of nematode infections:

  • Ingestion of mature eggs in fecally contaminated food or drink

  • Larval penetration of skin (hookworms and S stercoralis)

  • Larvae introduced into human host by arthropod vector (mosquitoes for filariasis and flies for O volvulus and Dirofilaria species)

  • Ingestion of raw or undercooked fish or cephalopods contaminated by third stage larvae (anisakiasis) or raw or undercooked snails or slugs (angiostrongyliasis [rat lungworm disease])



Potential complications of nematode infections are as follows:

  • Vomiting worms - Ascariasis, Anisakiasis

  • Worm migration

    • Cholangitis (migration to common bile duct)

    • Pancreatitis (migration to pancreatic duct)

    • Appendicitis (migration to appendix)

    • Diverticulitis (migration to diverticula)

  • Liver abscess

  • Intestinal obstruction, volvulus

  • Intussusception

  • Bowel penetration

  • Anemia, hypoproteinemia - Hookworm

  • CNS infection - Strongyloides infection

  • Onchocerciasis - Blindness

  • Filariasis - Lymphatic destruction leading to severe edema (elephantiasis)

  • Anisakiasis - Rare complications include small bowel obstructions, ileal stenosis, intussusception, intestinal perforation, and pneumoperitoneum

  • Neurohelminthiasis - CNS migrations and infection

  • Visceral worms

    • Hepatitis

    • Splenomegaly

    • Pleuritis

    • Peritonitis

    • Eosinophilic granuloma

    • Other organ damage because larvae migrate for as long as 6 months