Parasites 5: Food-borne trematodes

Question 1

What are the different trematodes we should be aware of for DTMH?

Answer 1

Question 2

Which organism is considered the lung fluke and where is most commonly found?

Answer 2

Paragonimus westermanii

• 20 million people world wide affected
• Subacute to chornic resp disease -> similar to TB
• Can cause extrapulmonary manifestations (cutaneous/cerebral)
• Most are asymptomatic

Question 3

What is the life cycle of the lung fluke?

Answer 3

Includes two intermediate hosts. The eggs are excreted unembryonated in the sputum, or alternately they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P. westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults . (7.5 to 12 mm by 4 to 6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycles is not achieved, because the eggs laid cannot exit these sites. Time from infection to oviposition is 65 to 90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P. westermani.

Question 4

What do the eggs/flukes of paragonimiasis look like?

Answer 4

Question 5

What is the pathophysiology of paragonimus infection and what are its clinical features?

Answer 5

• Paragonimus migrate the outside
• As they migrate they encounter other flukes
• They then form cysts, which cause the disease process of fibrotic cysts that form granulomatous lesions -> inflammatory response
• These cysts can rupture in the bronchi permitting the escape of cyst contents
• Three stages:
  
  • 1. Migratory Phase
       * 2 – 4 days after infection and lasts less than a month
       * Migration through GI wall, to pleural cavity, sometimes via liver
       * Signs and symptoms usually few and mild
• • 2. Pleural manifestations can appear before pulmonary ones due to migration -> pleura effusions, pneumothorax
       
       • Pulmonary manifestations
         
         • Six months after infection
         • Can be mistaken for symptoms of TB
         • Chornic productive cough, brownish sputum
         • Sometimes chest pain, fever, night sweats
         • Can be asymptomatic, reduced eosinophilia
           
           • 3. Extrapulmonary infection
       • Migration of young or mature flukes
       • Eggs that enter circulation
       • Circulation
         
         • Cerebral
           
           • 50% of extrapulmonary disease, particularly common in children
           • Early - can resemble meningoencephalitis
           • Chronic - headache, vomiting, seizures, weakness
           • Can be fatal, particularly when flukes wander
         • Cutaneous
           
           • Abdomen and anterior chest
           • Painless, mobile subcut swellings
         • Other extraabdominal locations: intestinal wall, liver, spleen, abdo wall, peritoneal cavity, mesenteric lymph nodes

Question 6

How do we diagnose paragonimus infection?

Answer 6

• On the basis of clinical picture and history
  
  • Parasitological techniques
    
    • Sputum, faeces, pleural fluid, CSF, pus
    • Egg detection difficult -> multiple samples taken, preferably through bronchoscopy
  • Serology
    
    • Useful in extrapulmonary presentations where eggs are not shed
    • Detection of antibodies or antigens in serum or stool samples
  • Imaging
    
    • CXR, CT, MRI, USS
    • Early: ptx, pleural effusion, consolidation, linear opacities
    • Established infection: cystic lesions and nodules, ring shadows, pleural thickening

Question 7

How do we treat paragonimus infection?

Answer 7

Question 8

Which organism is considered the liver fluke and where is it most prevalent?

Answer 8

• Endemic/sporadic in all farming areas inc UK but esp. Bolivia/South America.
• Eggs excreted from host faeces (human/sheep/cattle) near water.
• Invade fresh-water snail; cercariae then encyst on water plants (watercress).
• These are eaten by humans and travel to the liver and mature in the bile ducts, where the adults can live for years (and can cause obstructive symptoms).

Question 9

What are the clinical features of fascioliasis?

Answer 9

• Non-specific acutely e.g. fever, abdo pain, urticaria, can develop hepatomegaly.
• Ectopic flukes very rarely cause a cutaneous larva migrans or itchy skin nodules and spread to lung, brain, gut, etc.
• Chronic usually asymptomatic but can cause biliary obstruction-related. symptoms: intermittent biliary colic/cholangitis/pancreatitis/fatigue.

Question 10

How do we diagnose fascioliasis?

Answer 10

Question 11

How do we treat fascioliasis?

Answer 11

• Triclabendazole (praziquantel not reliable) -> cure rate > 90%

Question 12

Which organism is considered the chinese liver fluke?

Answer 12

Chinese Flukes: Opisthorchis/Clonorchis: C. Sinensis, O. Felineus, O. Viverrini

• Found in China, SE Asia, Russia & Eastern Europe
• Reservoir is fish rather then plants and cats and dogs instead of farm animals
• Animal hosts infected by eating raw or undercooked fish.
• Again travel to the bile duct to become adults

Question 13

What are the clinical features of chinese liver fluke?

Answer 13

• Asymptomatic usually. Text book symptom of biliary colic in the afternoon! But more generally in chronic infection recurrent RUQ, biliary colic, cholangitis, pancreatitis, etc. Can cause GI upset, hepatitis picture and hepatomegaly.
• O. viverrini chronic infection can lead to cholangiocarcinoma (very strong association) [most common form of liver cancer in in NE Thailand where 70% infected, also common in HK].

Question 14

How do we diagnose and treat chinese liver flukes?

Answer 14

Diagnosis:

• Stool examination
• Elisa
• PCR on stool

Treatment:

• Praziquantel 25mg/3x day

Question 15

MCQ tips

Answer 15

• Hint: eggs in sputum = paragonomiasis

MCQs

• These infections make good MCQ questions because of the way they mimic other hepatic/gastric/respiratory disease.

Public Health

• Choose a Trematode. Use the CDC Lifecycle diagram to understand the different stages at which “interventions” to break the cycle of infection are possible. This is a helpful approach for all Helminth infections you will encounter.

In humans, acute opisthorchiasis viverrini may be asymptomatic or scarcely symptomatic in light infections, but if the number of worms is significant (up to several thousands), fever and right upper-quadrant pain are not infrequent and may be associated with intermittent colic pain caused by obstruction of the gallbladder by the worms themselves.

Chronic chlonorchiasis is strongly associated with cholangiocarcinoma, a severe and often fatal form of bile duct cancer., Watercress and water-mint are good plants for transmitting fascioliasis, but encysted larvae may also be found on many other salad vegetables, Paragonimus spp. is a common parasite of crustacean-eating mammals such as tigers, leopards, domestic cats, dogs, mongooses, opossums and monkeys

Question 16

Microscopy of different eggs

Answer 16