What is the most likely diagnosis for a patient presenting with vomiting, diarrhea, and swelling of the feet, with laboratory findings of small, reddish-grey leaf-like worms and large operculated spineless eggs in stool, and a history of consuming undercooked fish and snails?

Diagnosis: Echinostomiasis

Based on the morphological features described—dorsoventrally flat worm measuring 6mm × 2mm × 1.5mm with an oral sucker surrounded by a circumoral disc crowned with 49-51 spines, ventral sucker in the anterior fifth, and body covered with spines in the anterior third—this is definitively echinostomiasis. The large operculated spineless eggs measuring 96 µm × 70 µm and the history of consuming roasted fish and snails in an endemic area (vicinity of pond with dog/cat contact) further confirm this diagnosis 1, 2.

Morphological Differentiation from Your Differentials

Echinostomiasis is distinguished by the characteristic collar of spines (circumoral disc with 49-51 spines) surrounding the oral sucker, which is pathognomonic for Echinostoma species 1, 2. This feature definitively excludes your other differentials:

• Heterophyiasis: Worms are much smaller (1-2mm length), lack the circumoral collar of spines, and eggs are smaller (26-30 µm × 15-17 µm) 1, 2
• Fasciolopsiasis: While large flukes (20-75mm), they lack the collar of spines and have much larger eggs (130-140 µm × 80-85 µm) 1, 2
• Clonorchis/Opisthorchis: These are lancet-shaped flukes (10-25mm), lack collar spines, and have smaller eggs (26-30 µm × 12-19 µm) 1, 2

Additional Differential Considerations

Other intestinal trematodes that should be considered in the differential diagnosis of foodborne intestinal flukes include 1, 2:

Family Echinostomatidae (Most Relevant)

• Echinostoma revolutum: 37-43 collar spines, eggs 83-116 µm × 58-69 µm 1
• Echinostoma cinetorchis: 37 collar spines, eggs 90-100 µm × 60-70 µm 1
• Echinostoma ilocanum: 49-51 collar spines (matches this case), eggs 83-116 µm × 58-69 µm 1
• Artyfechinostomum malayanum: 27-29 collar spines, eggs 90-100 µm × 60-70 µm 1

Family Heterophyidae

• Metagonimus yokogawai: 1-2.5mm, no collar spines, eggs 26-30 µm × 15-17 µm 1, 2
• Haplorchis taichui: 1-1.7mm, no collar spines, eggs 26-30 µm × 14-16 µm 1, 2

Family Fasciolidae

• Fasciolopsis buski: 20-75mm (much larger), no collar spines, eggs 130-140 µm × 80-85 µm 1, 2

Family Brachylaimidae

• Brachylaima cribbi: Small flukes acquired from eating raw snails, but lack collar spines 3, 1

Clinical Significance and Management

The clinical presentation of vomiting, diarrhea, pedal edema, hepatomegaly, and pallor is consistent with moderate-to-heavy echinostome infection 1, 2. The vomiting of adult worms indicates significant worm burden 1.

Treatment Protocol

Praziquantel is highly effective against echinostome infections and should be administered immediately 1, 2. The standard dosing is not explicitly stated in the evidence for echinostomes, but based on general trematode treatment protocols, praziquantel 40-60 mg/kg in divided doses is recommended 4.

Diagnostic Confirmation

Three consecutive stool examinations for ova and parasite (O&P) with permanent stained smears should be performed to confirm diagnosis and assess treatment response 4, 5. The large operculated eggs (96 µm × 70 µm) are diagnostic 1.

Public Health Considerations

This case should be reported to local public health authorities, as foodborne trematode infections indicate environmental contamination and potential for outbreak 4. Investigation of the pond environment and screening of household contacts who consumed similar foods is warranted 4.

Critical Pitfalls to Avoid

• Do not confuse echinostomes with heterophyids based solely on egg size—the collar of spines is the definitive morphological feature 1, 2
• Do not assume single stool examination is sufficient—parasite shedding can be intermittent, requiring multiple specimens 4, 5
• Do not overlook the significance of hepatomegaly and edema—these indicate significant worm burden requiring prompt treatment 1
• Do not forget to assess for anemia—pallor suggests chronic blood loss from intestinal mucosal damage 1, 2