What are the other Names for this Condition? (Also known as/Synonyms)

• Japanese Lung Fluke Infection
• Oriental Lung Fluke Infection due to Paragonimus Spp
• Paragonimus Infection

What is Paragonimiasis? (Definition/Background Information)

• Paragonimiasis is a parasitic worm infection caused by several species of a flatworm belonging to the genus Paragonimus
• The infection occurs as a result of consuming undercooked or raw shellfish. Paragonimus is also known as a lung fluke (a type of flatworm)
• The parasite infects the lungs of the human host causing respiratory infection. A severe, but rare case, involves a migration of the parasite to the central nervous system (CNS) leading to associated symptoms
• The signs and symptoms of Paragonimiasis are milder during the early stages, but may progress rapidly, when the infection reaches the lungs. The symptoms may include abdominal pain, fever and productive cough (mimicking bronchitis and tuberculosis) that may contain blood
• A diagnosis of Paragonimiasis may be undertaken using blood and sputum tests, including imaging studies, if necessary. Following a diagnosis, antiparasitic worm medication may be administered towards treating the infection
• The prognosis of Paragonimiasis is usually good with adequate early treatment. In case of a delay in or absence of treatment, the infection may progress to involve several organs apart from the lungs. In such cases, the prognosis may be guarded and ascertained only on a case-by-case basis

Who gets Paragonimiasis? (Age and Sex Distribution)

• Approximately, 20 million individuals are annually infected by Paragonimiasis worldwide (that includes countries in Asia, Africa, and both South and North Americas)

• Due to certain cultural habits, the frequency of infection is higher among East Asians, Hispanics, and Africans
• There are more number of Paragonimiasis cases reported in middle age men (particularly in Japan), which may be associated with their food choices. Babies and children often eat much less raw shellfish/crustaceans and thus, the incidence is low

What are the Risk Factors for Paragonimiasis? (Predisposing Factors)

The risk factors for Paragonimiasis may include:

• Consumption of raw or undercooked shellfish, including pickled shellfish (with brine salt or vinegar)
• Not being aware of local traditions and customs while traveling, and consuming raw or undercooked shellfish

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your health care provider.

What are the Causes of Paragonimiasis? (Etiology)

• Flatworms belonging to the genus Paragonimus cause Paragonimiasis infection
• The flatworm is introduced into human hosts (or non-human hosts) by the consumption of raw or undercooked shellfish such as freshwater crabs and crayfish (or crawfish)

The following are some known species of Paragonimus that cause infection in humans: 

• P. westermani: Most commonly found in human infections, the parasite is found in Asian countries including China, the Philippines, Vietnam, South Korea, Taiwan, Thailand and Japan. This species is also known as “the oriental lung fluke”
• P. africanus; causing infection in Africa
• P. mexicanus, which is endemic to South and Central America
• P. kellicotti: It has been known to cause rare human infections in the Midwestern United States)

What are the Signs and Symptoms of Paragonimiasis?

In general, the signs and symptoms of Paragonimiasis may include the following: 

• Abdominal pain and discomfort
• Low grade fever
• Diarrhea 

Signs and symptoms due to migration of Paragonimus spp. to lungs may cause:

• Acute cough that is similar to symptoms found in bronchitis or tuberculosis
• Productive cough that may contain blood or bloody streaks

Signs and symptoms related to migration of worms to the central nervous system that include:

• Headache
• Confusion
• Numbness
• Seizures

Signs and symptoms associated with migration of Paragonimus worms to internal organs:

• Formation of masses
• Organ dysfunction

Other organs may be infected, but this can disturb the maturation process and development of the parasite.

How Is Paragonimiasis Diagnosed?

Paragonimiasis is diagnosed on the basis of the following information:

• Thorough physical examination by a healthcare provider/professional
• Evaluation of medical history, including recent travel and consumption of raw shellfish/crustaceans
• Assessment of symptoms of the affected individual

• Blood test to check for levels of eosinophil (a type of white blood cell), which may be elevated
• Blood tests to check for the presence of parasitic worm antigens or antibodies in serum
• Microscopic detection of Paragonimus eggs in the sputum; the number of eggs may indicate the extent of infection
• Imaging tests (such as X-ray, ultrasound, CT and MRI scans, etc.) to check if the lungs and other internal organs are affected
• Differential diagnosis to rule out tuberculosis 

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Paragonimiasis?

Health complications of Paragonimiasis are dependent on the severity and/or location of infection and may include:

• Abscess in the lung
• Bronchitis
• Inflammation in the respiratory tract
• Secondary bacterial infections in the respiratory tract
• Pneumonia
• Risk of falls and injury due to seizures
• Abscess formation in the affected organs
• Severe organ dysfunction

How is Paragonimiasis Treated?

The treatment for Paragonimiasis may include the following:

• Prescription antiparasitic medication
• Follow-up with healthcare provider/professional post-treatment, to ensure clearance of infection
• Adequate rest

How can Paragonimiasis be Prevented?

The following are some tips to prevent contracting Paragonimiasis:

• Avoiding consumption of raw or undercooked shellfish/crustaceans 
• Ensuring that all meals consisting of crab, crayfish, or other crustaceans are cooked thoroughly to an internal temperature of 165°F
• Being aware of local customs and traditions (especially with respect to food) while traveling
• Seeking medical attention for unusual symptoms, particularly after returning from traveling to a place known for cases of Paragonimiasis
• Following up with a healthcare professional after treatment, to ensure that the parasite has been completely cleared from the body

What is the Prognosis of Paragonimiasis? (Outcomes/Resolutions)

• The prognosis of Paragonimiasis is good, if diagnosed and treated in a timely manner. Although, if left untreated, it may be a fatal infection
• Permanent damage to tissues and organs may occur, if the parasitic infection is severe and resulted in significant symptoms and complications. In some individuals, the condition may persist from several years to up to 20 years

Additional and Relevant Useful Information for Paragonimiasis:

• The metacercarial stage of Paragonimus spp is considered to be infectious to humans
• The development of metacercariae from cercariae occurs in the secondary intermediate host alone
• Development of miracidia into cercariae occurs in the primary intermediate host (mainly a marine snail) and is not an infective state    

The life cycle of Paragonimus spp. is described below:

• Unfertilized eggs leave the body of the infected host (such as humans) in sputum excretions from coughing, sneezing, spitting, etc. The eggs may be also found in the stool of infected individuals
• The eggs become embryonated (contain an embryo) and then hatch. The hatchling is called a “miracidia”, which has cilia, enabling it to move freely 
• The miracidia searches for its first “intermediate host”. A snail is usually a good target and the hatchling infiltrates the soft tissue of the snail
• Once inside the first intermediate host, the miracidia develop and produce many cercariae larvae
• The cercariae larvae search for a “second intermediate host”. The second intermediate host is usually a crustacean (crabs, shellfish). Once infected, a cyst forms in the second intermediate host where the “metacercariae” forms. This form of the Paragonimus is infectious to mammals
• If the shellfish (secondary host) is consumed by humans (or other mammals) without thorough cooking, then they become infected too
• Inside the mammalian host, the parasite forms a cyst in the duodenum, where it then migrates through the body into the diaphragm and finally reaches the lungs
• Once in the lungs, the parasites develop into adults and become encapsulated; and the cycle repeats