Download Paragonimus spp

Paragonimus spp.
A. Classification
Phylum Platyhelminthes
Class Trematoda
Order Plagiorchiformes
Suborder Troglotrematata
Family Troglotrematidae
Common Name “Lung Fluke”
B. Morphology
Egg




Adult





Size-Range, 68-118 µm x 39-67 µm.
Ovoidal, slightly elongated, may be slightly flattened on one side, posterior end
may be thicker
Yellow brown to dark brown color
Has a flattened operculum and wider posterior end
Size: 8-16mm x 4-8mm
Tegument (skin) is covered in many small spines
Bifurcated gut is not multi-branched
Testes and ovary lobed (ovary above testes and next to tightly coiled uterus)
Adult has “coffee bean” appearance
1
C. Lifecycle & Epidemiology
1.
Adult Paragonimus typically reside in the bronchiolar lumen and peribronchial
tissues of carnivorous mammals, where they produce eggs.
2.
These unembryonated eggs exit the definitive host in either the sputum (they are
“coughed up” and spit out) or swallowed and passed through the stool.
3.
The eggs become embryonated in the freshwater environment and develop into
miracidia after 17 to 21 days at 30C (86F).
2
4.
When the miracidia hatch, they infect the first intermediate host, a snail, by
penetrating its soft tissue. The principle snail hosts are species of the genus
Semisulcuspira.
5.
The miracidia then asexually develop into sporocysts, then two different
generations of redia, and then into cercariae.
6.
The free-swimming cercariae exit the snail and within 48 hours either crawl in a
leech-like manner or are carried by water currents until they find their second
intermediate host, fresh-water crustaceans such as crabs or crayfish.
7.
The cercariae migrate to the muscles or heart of this host where they encyst as
metacercariae, where they are infective after approximately 6 weeks.
8.
Infection of the definitive host occurs when they ingest inadequately cooked or
pickled crab or crayfish that harbor these metacercariae.
9.
The metacercariae excyst in the duodenum of the host, then penetrate the
intestinal wall, and stay in the peritoneal cavity for a while. They then travel through the
abdominal wall and diaphragm into the lungs, where they become encapsulated and
develop into adults approximately 8-10 weeks after metacercarial infection. The
migration through the body takes about 15 to 20 days
-These parasites can live as long as 20 years, although 6 is more normal.
-Infection of the brain and other organs and tissues can also occur but the completion
of the lifecycle is not achieved since the eggs cannot exit from these other places.
D. Geographic Distribution.
The Genus Paragonimus composed of over 40 species. Human infections occur in
restricted areas where local people consume improperly cooked freshwater crustaceans.
Paragonimus westermani, the Oriental Lung Fluke, is found in several Asian countries
of Korea, Japan, China, Far-east of Russia, Taiwan, the Philippines, Malaysia, Indonesia,
and India, P. africanus in Africa, P. mexicanus in Latin America, and P. kellicotti in
North America also invoke human infection. There are an estimated 21 million cases
worldwide.
3
E. Pathology/Symptoms
The acute phase of infection is classified as the period in which the immature
flukes are invading the host and migrating to the site of infection and further
development. The acute phase of paragonimiasis can be characterized by diarrhea,
abdominal pain, fever, cough, urticaria (hives), enlargement of the spleen and liver,
pulmonary abnormalities, eosinophilia, and elevated total IgE levels in the serum The
acute phase usually persists for several weeks unless treated.
The chronic phase of infection is classified as the period in which the flukes are
fully mature and have “settled in” to a site of infection. The pulmonary chronic phase is
the most commonly seen and usually begins about six months after infection. It is
characterized by cough, expectoration of discolored sputum (a secretion that is produced
in the lungs and the bronchi), hemoptysis (coughing up blood), and chest radiographic
abnormalities. Over time, thick fibrous granulomas form. Generalized or localized
fibrosis of the lung and cystic dilation of bronchi are the main histopathological changes
in the lung. Pulmonary paragonimiasis is often confused with tuberculosis and therefore
inappropriate treatment is administered.
Extra-pulmonary paragonimiasis can occur either from the migration of young or mature
flukes to various organs or from eggs that enter the circulation and are carried to sites
such as the brain, peritoneal cavity, kidney, spleen, liver and under the skin. These
infections cause tissue damage cysts and abscesses at the site of infection. In the worst
case infection, cerebral paragonimiasis develops. Chronic infection involves calcifying
granuloma manifested by partial seizure, embolisms, visual disturbances, and headaches.
Dog lung infected with P. westermani showing
worm nodules and openings from which adults
escaped.
http://www.atlas.or.kr/atlas/include/viewImg.html?uid=474
4
F. Diagnosis
Microscopic examination of stool samples is the most common method of
detection. Eggs in the feces cannot be seen until 2-3 months after infection however.
Although paragonimiasis can be detected in the feces, it is often difficult; therefore
serological tests are often performed if they are available. The complement fixation (CF)
test is the standard test for infection but due to its technical difficulties enzyme
immunoassay, or Elisa, tests are also used for diagnosis. Both the CF and Elisa tests
work well to diagnose and to help assess treatment of an infected individual.
High resolution chest CT is definitive for paragonimiasis. Brain CT/MRI is definitive for
active and chronic calcified neuroparagonimiasis.
CT scan of multiple calcified density in the right frontal
and temporal areas of a chronic cerebral paragonimiasis
patient.
http://www.atlas.or.kr/atlas/include/viewImg.html?uid=473
G. Treatment of Individual
Praziquantel is 95% efficient in treating a Paragonimus infection
Bithionol and Triclabendazole have also been effective
Bithionol – alternative to praziquantel for those who are unable to use
praziquantel or individuals in whom praziquantel was previously unable to
eradicate infection
Triclabendazole – used mostly in for treatment of fascioliasis but also works for
paragonimiasis infection
Surgical removal for chronic calcified cerebral paragonimiasis is recommended
5
H. Public Health Strategies
Eradication is difficult because dogs and cats serve as reservoirs for the parasite.
The best prevention is to avoid eating meals that may contain raw or undercooked
crustaceans and to avoid using unboiled crab juice. If eating animals, which may contain
the parasite, they must be cooked thoroughly. This will help to prevent infection with
those species that will mature and migrate to the lungs as well as infection with species in
which the parasites remain immature and migrate through the body.
Education is the important mechanism for achieving the above recommendation. It has
been found that Snail control measures are not cost effective so are not recommended.
Works Cited:
Center for Disease Control, 5 May 2004, “Paragonimiasis”, Parasites and Health,
<http://www.dpd.cdc.gov/DPDx/HTML/Search_Choices.htm>, 30 January 2005.
University of Cambridge, Department of Pathology, Schistosomiasis Research Group, 5
October 1998, “Paragonimus westermani (The Lung Fluke)”, Helminthology and
General Parasitology Pages,
<http://www.path.cam.ac.uk/~schisto/OtherFlukes/Paragonimus.html>, 30 January 2005.
Web Atlas of Medical Parasitology, The Korean Society for Parasitology,
<http://www.atlas.or.kr/atlas/alphabet_view.php?my_codeName=Paragonimus%20weste
rmani>, 30 January 2005.
Cam.University Schistosome Research Group. October 5, 1998.
<http://www.path.cam.ac.uk/~schisto/OtherFlukes/Paragonimus.html>
Centers for Disease Control & Prevention, National Center for Infectious Diseases,
Division of Parasitic Diseases, Parasites and Health.
<http://www.dpd.cdc.gov/dpdx/HTML/Paragonimiasis.htm>, 30 January 2005.
Annette Reboli, MD, Head, Division of Infectious Diseases, Cooper Hospital; Associate
Professor, Department of Medicine, University of Medicine and Dentistry of New Jersey.
November 8, 2002.
<http://www.emedicine.com/ped/topic1729.htm>
Centers for Disease Control & Prevention, National Center for Infections Diseases,
Scientific Resources; Drug Service.
<http://www.cdc.gov/ncidod/srp/drugs/formulary.html#3a>, 30 January 2005.
MICROMEDEX Thomson Healthcare. 2004.
<http://health.yahoo.com/drug/203624/>, 30 January 2005.
Jenny Costanzo
Erin At Lee
Michele Alfred
February 2, 2005
6