What are the symptoms of parasites?

Symptoms of Parasitic Infections

Parasitic infections present with a wide spectrum of symptoms depending on the parasite type, location, and host immune status, but gastrointestinal manifestations—particularly persistent watery diarrhea lasting more than 7 days—are the most common presentation across multiple parasitic infections. 1, 2, 3

Gastrointestinal Manifestations

The digestive system is the primary target for most parasitic infections:

• Persistent watery diarrhea (lasting >7 days) is the hallmark symptom that should trigger suspicion for parasitic infection, particularly with Cryptosporidium, microsporidia, Giardia, and Cyclospora 1, 2, 3
• Abdominal cramping and pain occur frequently across multiple parasitic infections including amebiasis, giardiasis, strongyloidiasis, and hookworm 1, 2
• Nausea, vomiting, and bloating are common accompanying symptoms, especially in acute presentations 1, 2
• Weight loss, anorexia, and failure to thrive develop in chronic infections, particularly severe in children and immunocompromised patients 1, 2
• Intestinal obstruction can occur with heavy Ascaris infections or advanced strongyloidiasis 1, 2
• Biliary obstruction may develop when parasites like Ascaris or liver flukes migrate into bile ducts, presenting with right upper quadrant pain and jaundice 1, 2

Dermatological Manifestations

Skin symptoms are particularly prominent with tissue-invasive helminths:

• Urticarial rash is common during acute phases of helminth infections including schistosomiasis (Katayama syndrome), strongyloidiasis, hookworm, and Ascaris 1, 2
• "Larva currens"—a rapidly moving (5-15 cm/hour) linear urticarial rash—is pathognomonic for Strongyloides infection 1, 2
• Cutaneous larva migrans presents as an intensely itchy, serpiginous rash migrating 1-2 cm per day, caused by dog/cat hookworm larvae penetrating skin 1
• "Ground itch"—a blister-like eruption at hookworm entry sites—occurs with human hookworm penetration 1, 2
• Pruritus ani is characteristic of pinworm (Enterobius) infection 1
• Calabar swellings—migratory subcutaneous nodules with edema—indicate Loa loa infection 1

Respiratory Manifestations

Pulmonary symptoms occur during larval migration phases or with specific parasitic infections:

• Löffler's syndrome—dry cough, wheeze, and transient pulmonary infiltrates with eosinophilia—occurs during the migratory phase of Ascaris, hookworm, and Strongyloides 1, 2
• Cough with dyspnea and pleuritic chest pain may indicate paragonimiasis (lung fluke) or disseminated parasitic infection 1, 2
• Tropical pulmonary eosinophilia presents with dry cough, wheeze, and breathlessness in lymphatic filariasis 1

Neurological Manifestations

Central nervous system involvement carries significant morbidity:

• Seizures are the most common presentation of neurocysticercosis (Taenia solium), often appearing years after initial infection 1, 2
• Severe headache with meningism suggests eosinophilic meningitis from Angiostrongylus cantonensis 1
• Focal neurological deficits, altered mental status, and myelopathy can occur with cerebral schistosomiasis, neurocysticercosis, or gnathostomiasis 1, 2
• Hydrocephalus develops when cysts mechanically obstruct ventricles or cause inflammatory arachnoiditis 1, 2

Ocular Manifestations

Eye involvement occurs with specific parasites:

• Retinochoroiditis is the hallmark of toxoplasmosis, a leading parasitic cause of ocular inflammation 1
• Keratitis and anterior uveitis occur in onchocerciasis (river blindness) 1
• Visual changes with retinal granulomas suggest ocular toxocariasis 1
• Conjunctival worm migration is pathognomonic for Loa loa infection 1

Systemic Manifestations

Non-specific systemic symptoms accompany many parasitic infections:

• Eosinophilia (elevated blood eosinophil count) is a key laboratory finding in tissue-invasive helminth infections, though notably absent in purely luminal parasites like Giardia 1, 2
• Fever occurs in acute infections, particularly Katayama syndrome (acute schistosomiasis), malaria, and during Löffler's syndrome 1, 2
• Fatigue and malaise are common non-specific symptoms across multiple parasitic infections 1, 2
• Hepatosplenomegaly develops in chronic schistosomiasis and other liver-affecting parasites 1, 2
• Anemia results from chronic blood loss in hookworm infections, particularly affecting children 1, 2

Genitourinary Manifestations

Specific parasites target the urogenital system:

• Hematuria, dysuria, and proteinuria are characteristic of Schistosoma haematobium infection 1
• Hematospermia and intermenstrual bleeding may occur with urogenital schistosomiasis 1
• Vaginal discharge can result from Trichomonas vaginalis infection 4

Critical Clinical Pearls

Important caveats to recognize:

• Symptoms are typically more severe in children, elderly patients, and immunocompromised individuals, who may develop life-threatening complications including severe dehydration, malnutrition, and disseminated disease 1, 2
• Clinical presentation alone cannot differentiate between specific parasitic pathogens—laboratory confirmation is essential 1, 2
• Many parasitic infections remain asymptomatic in immunocompetent hosts but cause severe disease in immunocompromised patients 2, 4
• Symptoms may not appear until years after initial infection, particularly with neurocysticercosis 1, 2
• Parasite excretion is often intermittent, requiring multiple stool samples (at least 3) for diagnosis 1, 2