Paragonomiasis Brijesh Singh Yadav brijeshbioinfo@gmail.com Disease Type: Parasitic DiseaseCommon Name: ParagonomiasisCausative Agent: P. westermani

Disease Discription:

Paragonomiasis is the result of an infection with one or other lung flukes of the genus paragonimus, usually P. westermani. (There are 15 other species of paragonimus, which can infect man.) The infection is found throughout the tropics but particularly in Asia, and is usually mistaken for tuberculosis. Paragonimiasis is acquired by eating raw or inadequately cooked crabs, crayfish, and occasionally from eating animals which also enjoy fresh water crabs. The life cycle is similar to that of schistosomiasis, and includes warm water snails, but there is no direct infection of man. Clinically, the majority of patients, even with heavy infections, are not ill. The minority will complain about chest pain, chronic cough and chocolate-coloured sputum, while remaining remarkably well in general health. At this stage the sputum often contains multiple recognizable eggs of P. westermani.[2]

Figure. Paragonomiasis.a) Bilateral interstitial and basal consolidation in a patient with paragonomiasis. b) Tomography of the right upper chest showing the nodular and fibrotic pattern of paragonomiasis. This is indistinguishable from tuberculosis.

Causative Agent: Pathogen Name: Paragonimus westermaniPathogen Description:

Paragonimus westermani is a lung fluke and is most prominent in Asia and South America. It was discovered from two Bengal tigers that died in zoos in Europe in 1878. Several years’ later, infections in humans were found in Formosa.

Taxonoimic Classification:

Adult Paragonimus westermani

Other Pathogenic speices: Paragonimus africanus, P. bangkokensis, P. heterotremus, P. hueitungensis, P. kellicotti, P. mexicanus, P. miyazakii, P. ohirae, P. philippinensis, P. sadoensis, P. skrjabini, P. uterobilateralis

Morphology and toxin production:

Many different species of Paragonimus all with some different levels of human host adaptability. Eggs expectorated in sputum into fresh water hatch as ciliated miracidia which penetrate specific snails and multiply within. Free-swimming cercaria leave the snail and penetrate fresh water crabs and crayfish, infecting any that consume them. The consumed  metacercaria penetrate the human small intestine wall and migrate to the lungs where they mate and live for a number of years laying eggs which are expectorated or swallowed. [1]

Size, shape, and color resembles a coffee bean when alive. Adult worms are 7.5 mm to 12 mm long and 4 mm to 6mm wide. The thickness ranges from 3.5 mm to 5 mm. The skin of the worm (tegument) is heavily covered with scalelike spines. The oral and ventral suckers are similar in size, with the later placed slightly pre-equatorially. The excretory bladder extends from the posterior end to the pharynx. The lobed testes are adjacent from

Domain: Eukaryota

Kingdom: Animalia

Phylum: Platyhelminthes

Class: Trematoda

Subclass: Digenea

Family: Paragonimidae

Genus: Paragonimus

Species: P. westermani

each other located at the posterior end, and the lobed ovaries are off-centered near the center of the worm (slightly postacetabular). The uterus is located in a tight coil to the right of the acetabulum, which is connected, to the vas deferens. The vitelline glands, which produce the yolk for the eggs, are widespread in the lateral field from the pharynx to the posterior end. By viewing the tegumental spines and shape of the metacercariae, one could distinguish between the ~30 species of Paragonumus spp.[3]

adult Paragonimus  7-12 mm long        Paragonimus egg   80-120 µm  long

                                                                      

History: It was discovered from two Bengal tigers that died in zoos in Europe in 1878. Several years’ later, infections in humans were found in Formosa.Epidemiology:

Prevalent in the Far East; also areas in Central America and Africa.  Transmission is related to the consumption of raw fresh water crabs and crayfish which contain the larvae (metacercaria) of Paragonimus.

Disease Host: Human and other animal

Disease Transmission:Transmission via eating infected crabs and crayfish.Adult worms live in the lungs. Eggs pass to the outside with the sputum. If sputum is swallowed, eggs may also be found in faeces. Once in the outside world and in water, miracidia (first-stage larvae) emerge from the eggs. They penetrate snails, where they undergo a transformation. After 3 to 5 months cercariae (second-stage larvae) leave the snail and penetrate crabs. Here the cercariae develop into metacercariae (third-stage larvae). It is this form which is infectious for the definitive host. Paragonomiasis is a zoonosis of carnivorous animals. Humans are only an exceptional host. They become infected by eating raw fresh-water crabs and river crayfish which contain infectious metacercariae. Excystation occurs in the duodenum. The larvae bore through the intestinal wall and migrate via the abdominal cavity to the lungs. There they develop into adult worms. The worms form a cavity 1 to 4 cm in

diameter. Egg-laying begins 8 to 10 weeks after infection. The worms rarely migrate to ectopic sites.[6]

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. [5]

Signs and symptoms of disease:

Mild infections are asymptomatic. In the acute stage (invasion and migration of the larvae) there may be diarrhoea, abdominal pain, urticaria and eosinophilia. This is followed by fever, thoracic pain, cough, dyspnoea and malaise. The chronic illness resembles chronic bronchitis and TB. There is spasmodic cough (especially after exertion) with expectoration of blood stained sputum, as well as dyspnoea sometimes with wheezing and pleural pain. When the parasite is located in an ectopic site (brain, subcutis, etc.) the symptoms depend on the place where the worms are. www.itg.be

Diagnosis:

To properly diagnosis this parasite infection is by looking at the sputum and finding the eggs. Sometimes eggs are shed in the feces. Radiological methods

can be used to X-ray the chest cavity and look for worms. This method is easily misdiagnosed, because pulmonary infections look like tuberculosis,

pneumonia, or spirochaetosis. A lung biopsy can also be used to diagnose this parasite. An assay that detects worm antigens using monoclonal antibody

can also be used to diagnosis. The drug of choice is praziquantel. [4]

P. westermani in tissue. P. westermani head.

Diagnosis is by detecting the eggs. The eggs often need to be concentrated (e.g. mix sputum + water + potassium hydroxide, then centrifuge and examine the sediment). Differential diagnosis includes tuberculosis of the lungs, pulmonary abscess, chronic bronchitis, melioidosis, and lung carcinoma and lung metastases. If sputum is swallowed, eggs may also be found in the faeces.

Treatment:

Praziquantel 75 mg/day for 3 days is very effective. In cases of cerebral localisation higher doses must be given but only under the protection of steroids due to the risk of epileptic fits secondary to perilesional oedema.

Prevention of disease:

Not eating raw fresh water crabs can dramatically reduce the chance of infection.

Geographical Distribution: The parasite occurs in Southeast Asia and the Far East, in Central and West Africa. In America its distribution is limited to Central America and the north of South America. Usually P. westermani is reported, but there are a number of other species which can cause infection in humans. www.itg.be

Refrence:

1. www.medicine.mcgill.ca

2. www.medcyclopaedia.com

3. Foundations of Parasitology” Larry S. Roberts and John Janovy, Jr., seventh edition McGraw Hill 2005, pages 279-283.

4. Emerging and Reemerging Helminthiases and the Public Health of China” Peter J. Hotez, Feng Zheng, Xu Long-qi, Chen Ming-gang, Xiao Shu-hua, Liu Shu-xian, David Blair, Donald P. McManus, and George M. Davis

5. http://www.cdc.gov/ncidod/eid/vol3no3/hotez.htm6. www.itg.be7.