Background
Trematodes of the Paragonimus genus cause paragonimiasis, a parasitic disease that strikes carnivores, causing a subacute to chronic inflammatory disease of the lung. Of the 10 or more Paragonimus species that are human pathogens, only 8 cause significant infections in humans.
The first case described in humans was at autopsy in Taiwan in 1879, when adult flukes were found in the lung.[1] The most common is the Oriental lung fluke, Paragonimus westermani. The adult trematode is reddish-brown and ovoid. Adults have 2 muscular suckers, an oral sucker situated anteriorly and a ventral sucker at mid body on the ventral surface. The eggs, golden brown and asymmetrically ovoid, have a thick shell with an operculum.
This micrograph depicts an egg from the trematode parasite Paragonimus westermani. Eggs range in size from 68-118 µm x 39-67 µm. They are yellow-brown and ovoidal or elongated, with a thick shell. They are often asymmetrical, with one end slightly flattened. At the large end, the operculum (ie, lid or covering) is visible. Photo courtesy of The Centers for Disease Control and Prevention. Pathophysiology
The life cycle of these flukes involves 2 intermediate hosts plus humans. Its complex life cycle involves 7 distinct phases: egg, miracidium, sporocyst, redia, cercaria, metacercaria, and adult. Adult flukes live in human lungs and deposit eggs into the bronchi. Eggs are expelled either by coughing or by being swallowed and passed in human feces. Eggs then develop in water for 2-3 weeks and ultimately release miracidia, which invade the first intermediate host (ie, a specific species of fresh water snail). These miracidia develop through sporocyst and rediae stages into cercariae. The cercariae emerge and invade the second intermediate host (ie, a crustacean such as crabs or crayfish), in which they become metacercariae.
This is an illustration of the life cycle of Paragonimus westermani, one of the causal agents of paragonimiasis. Photo courtesy of The Centers for Disease Control and Prevention. When humans ingest raw infected crustaceans, larval flukes develop in the small intestine and penetrate the intestinal wall into the peritoneal cavity 30 minutes to 48 hours after excysting. They then migrate into the abdominal wall or liver, where they undergo further development. Approximately 1 week later, adult flukes reenter from the abdominal cavity and penetrate the diaphragm to reach the pleural space and lungs. The eggs may then be expectorated or swallowed. If these eggs reach a water source, the life cycle will start over again.[2] Flukes mature, a fibrous cyst wall develops around them, and then egg deposition starts 5-6 weeks after infection. Lung flukes may live 20 years or more. In Japan, transmission has also occurred following human ingestion of raw pork from wild pigs that contained the juvenile stages of Paragonimus species.
Epidemiology
Frequency
United States
Generally, small numbers of cases have occurred in immigrants from endemic areas; however, the first case of paragonimiasis was reported in the United States in 1986 in a nonimmigrant adult. It is an important infection to consider in Southeast Asians who have settled in various areas of the United States.[3]
International
Paragonimus species are endemic to Southeast Asia, Latin America (most commonly in Peru), and Africa (most commonly in Nigeria). Paragonimiasis is less commonly found in West Africa and Central and South America.[2] An estimated 22 million people are infected worldwide. Prevalence of infection in endemic areas ranges from 0.1-23.75%.
Mortality/Morbidity
Death may occur during the acute phase of infection. For those who survive the acute phase, spontaneous recovery usually occurs within 1-2 months, but symptoms may recur intermittently over several years. Complications of untreated heavy infection include interstitial pneumonia, bronchitis, and bronchiectasis. Secondary complications may include bronchopneumonia, lung abscess, pleural effusion, or empyema. Untreated cerebral paragonimiasis has a mortality rate of approximately 5%.
Race
Paragonimiasis is most common in Asians, Africans, and Hispanics.
Sex
Prevalence of infection is higher among females. An increase in infection in men, most notably those who are middle aged, because of their traditional culinary habits, has been observed in Japan.
Age
Prevalence reportedly increases with age and peaks in older adolescents and young adults; prevalence then declines progressively with age. By the sixth decade of life, prevalence is less than 25% of its peak in young adulthood.
Liu Q, Wei F, Liu W, Yang S, Zhang X. Paragonimiasis: an important food-borne zoonosis in China. Trends Parasitol. Jul 2008;24(7):318-23. [Medline].
Boe DM, Schwarz MI. A 31-year-old man with chronic cough and hemoptysis. Chest. Aug 2007;132(2):721-6. [Medline].
Vidamaly S, Choumlivong K, Keolouangkhot V, Vannavong N, Kanpittaya J, Strobel M. Paragonimiasis: a common cause of persistent pleural effusion in Lao PDR. Trans R Soc Trop Med Hyg. Jan 29 2009;[Medline].
Rosen MJ. Chronic cough due to tuberculosis and other infections: ACCP evidence-based clinical practice guidelines. Chest. Jan 2006;129(1 Suppl):197S-201S. [Medline].
Robertson KB, Janssen WJ, Saint S, Weinberger SE. Clinical problem-solving. The missing piece. N Engl J Med. Nov 2 2006;355(18):1913-8. [Medline].
Tsang KW, File TM Jr. Respiratory infections unique to Asia. Respirology. Nov 2008;13(7):937-49. [Medline].
Calvopina M, Guderian RH, Paredes W, Chico M, Cooper PJ. Treatment of human pulmonary paragonimiasis with triclabendazole: clinical tolerance and drug efficacy. Trans R Soc Trop Med Hyg. Sep-Oct 1998;92(5):566-9. [Medline].
Anonymous. Drugs for parasitic infections. Med Lett Drugs Ther. Aug 2004;46(1189):1-12.
Blair D, Xu ZB, Agatsuma T. Paragonimiasis and the genus Paragonimus. Adv Parasitol. 1999;42:113-222. [Medline].
Christie JD, Garcia LS. Emerging parasitic infections. Clin Lab Med. Sep 2004;24(3):737-72. [Medline].
Dainichi T, Nakahara T, Moroi Y, et al. A case of cutaneous paragonimiasis with pleural effusion. Int J Dermatol. Sep 2003;42(9):699-702. [Medline].
Hawn TR, Jong EC. Update on Hepatobiliary and Pulmonary Flukes. Curr Infect Dis Rep. Dec 1999;1(5):427-433. [Medline].
Kagawa FT. Pulmonary paragonimiasis. Semin Respir Infect. Jun 1997;12(2):149-58. [Medline].
Maguire JH. Trematodes (Schistosomes and other Flukes). In: Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. Vol 2. 6th ed. Philadelphia, PA: Churchill Livingstone; 2004:3283-4.
Nakamura-Uchiyama F, Mukae H, Nawa Y. Paragonimiasis: a Japanese perspective. Clin Chest Med. Jun 2002;23(2):409-20. [Medline].
Print
