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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Trematodes

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Paragonimiasis ( Lung Fluke Infection ) : Clinical Aspects

The presence of the adult worms in the lung elicits an eosinophilic inflammatory reaction and, eventually, the formation of a 1- to 2-cm fibrous capsule that surrounds and encloses one or more parasites.

PARAGONIMIASIS( LUNG FLUKE INFECTION )

EPIDEMIOLOGY

Although most of the 5 million human infections are concentrated in the Far East (eg, Korea, Japan, China, Taiwan, the Philippines, and Indonesia), paragonimiasis has recently been described in India, Africa (P. africanus), and Latin America (P. mexicanus). P. kellicotti, a parasite of mink, is widely distributed in eastern Canada and the United States but rarely produces human infection. Approximately 1% of recent Indochinese immigrants to the United States are found to be infected with P. westermani.Infection of the snail host, which is typically found in small mountain streams located away from human habitation, is probably maintained by animal hosts other than humans. Human disease occurs when food shortages or local customs expose individuals to infected crabs. When these crustaceans are prepared for cooking, juice containing metacercariae may be left behind on the working surface and contaminate other foods subsequently prepared in the same area. Fresh crab juice, which is used for the treatment of infertility in Cameroon and of measles in Korea, may also transmit the disease. In the Far East, crabs are frequently eaten after they have been lightly salted, pickled, or immersed briefly in wine (drunken crab), practices that are seldom lethal to the metacercariae. Children living in endemic areas may be infected while handling or ingesting crabs during the course of play.

 

PARAGONIMIASIS ( LUNG FLUKE  INFECTION ) : CLINICAL ASPECTS

MANIFESTATIONS

The presence of the adult worms in the lung elicits an eosinophilic inflammatory reaction and, eventually, the formation of a 1- to 2-cm fibrous capsule that surrounds and encloses one or more parasites. The infected patient may harbor as many as 25 such lesions. With the onset of oviposition, the capsule swells and erodes into a bronchiole, resulting in ex-pectoration of the brownish eggs, blood, and an inflammatory exudate. Secondary bacter-ial infection of the evacuated cysts is common, producing a clinical picture of chronic bronchitis or bronchiectasis. When cysts rupture into the pleural cavity, chest pain and ef-fusion can result. Early in infection, chest x-rays demonstrate small segmental infiltrates; these are gradually replaced by round nodules that may cavitate. Eventually, cystic rings, fibrosis, and calcification occur, producing a picture closely resembling that of pulmonary tuberculosis. The confusion is compounded by the frequent coexistence of the two diseases.

 Adult flukes in the intestine and mesentery produce pain, bloody diarrhea, and on oc-casion, palpable abdominal or cutaneous masses; the latter is characteristic of a second Chinese fluke, P. skrjiabini. In approximately 1% of cases in the Far East, more com-monly in children, parasites lodge in the brain and produce a variety of neurologic mani- festations, including epilepsy, paralysis, homonymous hemianopsia, optic atrophy, and papilledema.

DIAGNOSIS

Eggs are usually absent from the sputum during the first 3 months of overt infection; however, repeated examinations eventually demonstrate them in more than 75% of in-fected patients. When a pleural effusion is present, it should be checked for eggs. Stool examination is frequently helpful, particularly in children who swallow their expectorated sputum. Approximately 50% of patients with brain lesions demonstrate calcification on x-ray films of the skull. The cerebrospinal fluid in such cases shows elevated protein levels and eosinophilic leukocytosis. A diagnosis in these cases, however, often depends on the detection of circulating antibodies. Their presence usually correlates well with acute dis-ease and disappears with successful therapy. Recently developed antigen detection tech-niques have been proven to be both highly sensitive and specific and may soon displace antibody detection procedures.

TREATMENT AND PREVENTION

The disease responds well to praziquantel or bithionol therapy. Control requires adequate cooking of shellfish before ingestion.

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