Introduction
Paragonimiasis is caused by the Trematodes of the Paragonimus genus. It leads to chronic inflammatory disease of the lungs. Paragonimus consists of ten or more species, out of eight can lead to significant infections in humans. In 1879, the first case of this infection was reported in Taiwan when adult flukes were detected in the lung during an autopsy.
The most commonly occurring fluke is the Paragonimus westermani (oriental lung fluke). Cases of this infection occur after an individual consumes raw or undercooked infected crayfish or crab. Paragonimiasis can lead to severe consequences if the fluke travels to the central nervous system.
What Is the Pathophysiology of Paragonimiasis?
The life cycle of paragonimus involves seven different phases that include egg, miracidium, sporocyst, redia, cercaria, metacercaria, and adult. Adult flukes reside in the human lungs and deposit their eggs in the bronchi. These eggs are transmitted through coughing or are passed through human feces. When raw infected crustaceans are consumed, larval flukes grow in the small intestine and enter the intestinal wall through the peritoneal cavity. Then they reach the abdominal wall or liver, where further development occurs. After around one week, these flukes penetrate the diaphragm and reach the lungs. The eggs may then be expectorated or swallowed. As these flukes mature, a fibrous cyst wall is formed around them, and after 5 to 6 weeks of the infection, eggs begin to deposit. These lung flukes may survive for more than 20 years.
What Is the Cause of Paragonimiasis?
In Asia, raw and undercooked crayfish or crabs are common delicacies. Moreover, in some places like Japan and Korea, raw crayfish are used to treat measles, skin diseases, and diarrhea. In certain African tribes, raw crustaceans are used to cure infertility. Exposure to these infected crustaceans causes paragonimiasis.
The following factors facilitate the life cycle of the flukes and promote the spread of the infection.
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A huge number of reservoirs and intermediate hosts.
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Behaviors such as spitting.
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High consumption of seafood, especially crustaceans.
How Is Paragonimus Transmitted?
The infection can be transmitted by:
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Consumption of infected crabs or crawfish that are partially cooked, raw, pickled, or salted.
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Use contaminated kitchen utensils, knives, cutting boards, or clothes used to strain crab juices during the soup preparation.
What Is the Epidemiology of Paragonimiasis?
In 1986, the first case of paragonimiasis was identified in the United States. However, a small number of cases have occurred in immigrants from endemic areas. The infection is seen commonly in Southeast Asians residing in different regions in the United States.
Paragonimus species are most prevalent in Southeast Asia, Latin America, and Africa. Paragonimiasis is less frequently found in West Africa and South America. Studies have revealed that around 22 million people are infected around the globe. This infection occurs more commonly in females. Prevalence usually increases with age, and the maximum cases occur in older adolescents and young adults. Then the prevalence progressively declines with age. By around sixty years of age, prevalence decreases to less than 25 percent of its peak in young adults.
What Is the Prognosis of Paragonimiasis?
The prognosis of this infection is generally good, with cure rates up to 90 to 100 percent. The symptoms usually resolve quickly, and eggs vanish from the sputum within a few weeks after treatment. Pulmonary paragonimiasis can be self-limiting.
What Are the Clinical Features of Paragonimiasis?
In around 20 percent of the cases with paragonimiasis, the patients are asymptomatic. The clinical features include:
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Abdominal pain.
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Urticaria (a skin rash caused by a reaction to food, medicine, or other irritants).
These initial symptoms are followed a few days later by:
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Fever.
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Dyspnea (difficulty in breathing).
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Cough.
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Chest pain.
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Sweating and restlessness.
Chronic pulmonary symptoms include:
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Dry cough and rusty sputum.
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Pulmonary symptoms start around six months after infection.
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Peripheral eosinophilia has been detected in 25 percent of the patients.
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Patients usually complain of chest pain, wheezing, or dyspnea (difficulty breathing).
How Is Paragonimiasis Diagnosed?
Paragonimiasis is diagnosed by the presence of Paragonimus eggs in sputum. Eggs can also be detected in the stool sample. To identify the eggs in the tissue samples, a tissue biopsy can be performed.
How Is Paragonimiasis Treated?
The Centres for Disease Control and Prevention (CDC) as well as the World Health Organization (WHO) recommended two drugs for paragonimiasis treatment.
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Praziquantel (Biltricide): Praziquantel is the most frequently used drug. It has a cure rate of 80 to 90 percent. It acts by increasing the cell membrane permeability in the worms and leads to massive contractions, loss of intracellular calcium, and paralysis of the muscle. It further causes the disintegration of schistosome tegument, attachment of phagocytes to the parasite, and death. It is available in tablet form, which has to be taken during meals. The tablet has a bitter taste that produces nausea or vomiting.
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Triclabendazole (Egaten): In 2019, the food and drug administration (FDA) approved another drug called Triclabendazole, which was available from the center for drug control and prevention (CDC). The center for drug control and prevention (CDC) recommends Triclabendazole for treating paragonimiasis. It is an anthelmintic agent and is approved for the treatment of fascioliasis, but off-label use of this drug for paragonimiasis is supported by recommendations from the CDC. Its mechanism of action is not fully understood. Studies suggest that Triclabendazole and sulfoxide or sulfone (its active metabolites) are absorbed by the tegument of the immature and mature worms, reducing the resting membrane potential and inhibiting tubulin function. It further stops the synthesis of proteins and enzymes.
Conclusion:
Certain complications may also be associated with paragonimiasis. Severe cases of this infection can cause secondary complications such as pneumonia, lung abscess, pleural effusion, bronchitis, bronchiectasis, and empyema. Cerebral complications like seizures and coma may also occur. Sometimes migratory allergies to the skin may be seen.
Untreated cases of cerebral paragonimiasis have a mortality rate of around five percent. In addition, persistent seizures may be present in cerebral infections. The complete resolution of abnormalities on chest radiographs takes a long time, depending on the severity of the infection.
