# Clinical Cases: Parasites - Helminths

## Case 1: Neurocysticercosis

### Presentation
A 28-year-old man who immigrated from Mexico 5 years ago presents after having a witnessed generalized tonic-clonic seizure. He has no prior seizure history. He reports occasional headaches over the past few months. He has no fever. Neurological examination is non-focal. MRI of the brain reveals multiple cystic lesions of varying sizes scattered throughout the cerebral hemispheres; some lesions show ring enhancement, and several demonstrate calcifications. He has no history of eating raw pork, but he grew up in a rural area.

### Clinical Image
![MRI showing neurocysticercosis](image_01.png)
*Brain MRI demonstrating multiple cystic lesions characteristic of neurocysticercosis. Different lesion stages are visible: viable cysts (non-enhancing), degenerating cysts (ring-enhancing), and calcified lesions representing dead parasites.*

**Image Source**: Lecture image - neurocysticercosis imaging

### Questions

1. **What is the diagnosis, and what organism is responsible?**

2. **How did this patient acquire the infection, and how does this differ from intestinal tapeworm infection?**

3. **What do the different MRI lesion appearances represent?**

4. **What is the approach to treatment?**

### Answers

1. **Diagnosis and organism**: This is **neurocysticercosis (NCC)**, caused by the larval stage (cysticercus) of the pork tapeworm **Taenia solium**. NCC is the most common parasitic CNS infection worldwide and the leading cause of acquired epilepsy in endemic regions. The diagnosis is supported by characteristic imaging, serologic testing (EITB - enzyme-linked immunoelectrotransfer blot), epidemiologic risk factors, and clinical presentation.

2. **Transmission mechanism**: Critically, neurocysticercosis is acquired by ingesting **T. solium eggs** (from feces of a human tapeworm carrier), NOT by eating undercooked pork. The transmission occurs through:
   - Fecal-oral transmission from a tapeworm carrier (often a household contact)
   - Contaminated food or water containing eggs

   **Eating undercooked pork** containing cysticerci causes **intestinal taeniasis** (adult tapeworm in the gut), not cysticercosis. The patient became an intermediate host (like a pig) when he ingested eggs; the eggs hatched, larvae penetrated the intestine, and disseminated to tissues (especially CNS, muscles, eyes).

3. **MRI lesion stages**: The different lesion appearances represent stages of cysticercus evolution:
   - **Viable cysts**: Fluid-filled, non-enhancing, with visible scolex ("hole-with-dot" sign)
   - **Colloidal/degenerating cysts**: Ring enhancement around edematous, inflamed lesion as immune system attacks dying parasite
   - **Granular nodular stage**: Retracting lesion with surrounding gliosis
   - **Calcified lesions**: End-stage; represents dead, calcified parasites (may still cause seizures)

   Multiple stages coexisting suggests infection over time or repeated exposures.

4. **Treatment approach**:
   - **Antiepileptic drugs (AEDs)**: First priority for seizure control (levetiracetam, carbamazepine); may need long-term therapy
   - **Antiparasitic therapy**: **Albendazole** (preferred) or praziquantel
     - Indicated for viable parenchymal cysts
     - **Corticosteroids (dexamethasone)** started before or with antiparasitic therapy to control inflammation from dying parasites
     - Controversial/contraindicated for calcified-only disease, massive infection, or intraventricular cysts
   - **Calcified lesions only**: AEDs alone; antiparasitics not indicated (parasites already dead)
   - **Intraventricular cysts**: May require surgical removal to prevent hydrocephalus
   - **Ophthalmologic examination**: Rule out ocular involvement before treatment (ocular cysts require surgery, not medical therapy)

---

## Case 2: Ascariasis with Intestinal Obstruction

### Presentation
A 6-year-old boy from rural Guatemala presents with severe colicky abdominal pain, bilious vomiting, and abdominal distension for 24 hours. He has had no bowel movement or passage of flatus. His mother reports that he had a cough 2-3 weeks ago that resolved spontaneously. On examination, temperature is 37.8°C, the abdomen is distended and tympanitic with high-pitched bowel sounds and diffuse tenderness. Abdominal radiograph shows dilated loops of small bowel with air-fluid levels and an unusual "whirlpool" pattern of soft tissue density in the right lower quadrant.

### Clinical Image
![Ascaris worm bolus causing obstruction](image_02.png)
*Surgical specimen showing a bolus of Ascaris lumbricoides worms causing intestinal obstruction - a serious complication of heavy worm burden in children.*

**Image Source**: Lecture image - Ascaris complications

### Questions

1. **What is the diagnosis, and what caused the earlier respiratory symptoms?**

2. **Explain the life cycle of this parasite and how it relates to the clinical presentation.**

3. **What is the mechanism of intestinal obstruction?**

4. **What is the management of this condition?**

### Answers

1. **Diagnosis and respiratory symptoms**: This is **intestinal obstruction caused by Ascaris lumbricoides** (roundworm) infection. The earlier cough represents **Loeffler syndrome** - transient pulmonary infiltrates and eosinophilia occurring when migrating larvae pass through the lungs. This phase occurs 1-2 weeks after egg ingestion, before adult worms mature in the intestine.

2. **Life cycle and clinical correlation**:
   - **Egg ingestion**: Fertilized eggs in contaminated soil/food hatch in small intestine
   - **Larval migration**: Larvae penetrate intestinal wall, enter bloodstream, travel to liver, then lungs (causing Loeffler syndrome at 1-2 weeks)
   - **Pulmonary phase**: Larvae ascend airways, are swallowed, return to intestine
   - **Adult worms**: Mature in small intestine over 2-3 months; can live 1-2 years, reaching 15-35 cm length
   - **Egg production**: Female worms produce 200,000 eggs/day, passed in stool

   The timeline fits: ingestion → pulmonary symptoms at 2-3 weeks → intestinal symptoms as worm burden increases.

3. **Mechanism of obstruction**: Ascaris causes mechanical intestinal obstruction through:
   - **Worm bolus**: Mass of entangled adult worms (can be dozens to hundreds) physically blocks intestinal lumen
   - **Most common in children**: Narrower intestinal diameter relative to worm size, and often heavier worm burdens
   - Can also cause **biliary obstruction** (worms migrate into biliary tree), **appendicitis** (worms in appendix), and **intestinal perforation**
   - The "whirlpool" sign on imaging represents the tangled worm mass

4. **Management**:
   - **Partial obstruction** (most cases): Conservative management
     - NPO, IV fluids, nasogastric decompression
     - **Anthelmintic therapy** once obstruction resolving: Albendazole or mebendazole
     - Avoid anthelmintics during complete obstruction (paralyzed worms may worsen blockage)
   - **Complete obstruction** or complications (perforation, volvulus):
     - **Surgical intervention**: Manual extraction of worm bolus, bowel resection if necrotic
   - **Supportive care**: Monitor for worm passage in stool after treatment
   - **Prevention**: Improved sanitation, periodic mass deworming programs in endemic areas

---

## Case 3: Schistosomiasis with Portal Hypertension

### Presentation
A 45-year-old man from Egypt presents with progressive abdominal distension and fatigue over 6 months. He immigrated 15 years ago and recalls swimming in the Nile River as a child. Examination reveals splenomegaly, ascites, and dilated veins visible on the abdominal wall (caput medusae). There is no jaundice or hepatic encephalopathy. Liver function tests show mildly elevated alkaline phosphatase but normal bilirubin and transaminases. Ultrasound shows periportal fibrosis with a characteristic "clay pipe stem" pattern and moderate ascites. Stool examination reveals eggs with a prominent lateral spine.

### Clinical Image
![Schistosoma eggs with lateral spine](image_03.png)
*Stool microscopy showing Schistosoma mansoni egg with characteristic lateral spine, diagnostic of intestinal schistosomiasis.*

**Image Source**: Lecture image - Schistosoma egg morphology

### Questions

1. **What is the diagnosis, and which species is responsible?**

2. **How did this patient acquire the infection, and what is the life cycle?**

3. **Explain the pathophysiology of portal hypertension in this disease.**

4. **What is the treatment approach?**

### Answers

1. **Diagnosis and species**: This is **hepatosplenic schistosomiasis** with portal hypertension caused by **Schistosoma mansoni** (identified by the lateral-spined egg). S. mansoni is the species found in Africa, the Middle East, and South America. The clinical picture of portal hypertension with preserved hepatic synthetic function (normal bilirubin, no encephalopathy) is characteristic of "pipestem fibrosis."

2. **Life cycle and transmission**:
   - **Cercariae** (free-swimming larvae) released from freshwater snails penetrate human skin during water contact (swimming, bathing, farming)
   - Larvae migrate through lungs to liver, maturing into adult worms
   - **Adult worms** live in mesenteric venules (S. mansoni, S. japonicum) or bladder venous plexus (S. haematobium)
   - Female worms release eggs; eggs must penetrate vessel wall and intestinal/bladder mucosa for excretion
   - **Eggs trapped in tissues** cause the inflammatory response and pathology
   - Eggs in stool/urine reach freshwater, hatch, infect snails, and the cycle continues

3. **Pathophysiology of portal hypertension**: Unlike cirrhosis, schistosomal liver disease is caused by:
   - **Egg embolization**: Eggs carried by portal blood lodge in portal venules within the liver
   - **Granulomatous inflammation**: Immune response to eggs causes granuloma formation around each egg
   - **Periportal fibrosis** ("Symmers' pipestem fibrosis"): Progressive fibrosis around portal tracts, NOT diffuse parenchymal cirrhosis
   - **Portal vein obstruction**: Fibrosis obstructs portal blood flow
   - This is **presinusoidal** portal hypertension, so hepatocyte function is preserved (normal synthetic function, no encephalopathy)
   - Splenomegaly results from portal congestion

4. **Treatment**:
   - **Antiparasitic therapy**: **Praziquantel** 40 mg/kg in divided doses (single day treatment); kills adult worms; should be given even in chronic disease to prevent ongoing egg production
   - **Portal hypertension management**:
     - Beta-blockers for variceal prophylaxis
     - Endoscopic band ligation for varices
     - Diuretics for ascites
     - TIPS or surgical shunts in refractory cases
   - **Prognosis**: Unlike cirrhosis, hepatic function may be preserved for years; treatment can halt progression
   - **Screening**: Travelers and immigrants from endemic areas with eosinophilia or liver disease should be tested