Medical Care
Praziquantel 10-20 mg/kg as a single dose or 25 mg/kg 3 times a day is the recommended treatment for intestinal flukes (including F buski infection). It should be taken with liquids during a meal. [4] Praziquantel is the drug of choice for most intestinal fluke infections, although niclosamide has been reported to have some in vitro efficacy. [55]
Praziquantel is a pyrazinoisoquinoline anthelmintic that was discovered in 1972 by Bayer Germany. Although widely used, praziquantel exhibits low and erratic bioavailability because of its poor water solubility. Nanostructured lipid carriers (NLC), second-generation solid lipid nanoparticles, were developed in the 1990s to improve the bioavailability of poorly water-soluble drugs. [56]
After 4 weeks, if the repeat stool examination result is again positive, retreatment with praziquantel is indicated. [41]
Artesunate has been used in vitro and in vivo for Echinostoma and Heterophyes infections, with promising results as alternative therapy. Although the exact mechanism of action for artesunate is still unknown, studies have demonstrated that parasites exposed to artesunate had slowed movement, tegument damage, and death at higher drug concentration and longer exposure time (72 hours). [57, 58]
The CDC recommends a 2-dose regimen of triclabendazole as the drug of choice for fascioliasis (liver fluke infection with F hepatica or F gigantica). Triclabendazole was approved by the FDA in 2019 after being available from the CDC for many years. [59]
Based on limited data from the CDC, nitazoxanide might be effective in some patients. Bithionol, a halogenated phenol previously used as a first-line agent for the treatment of fascioliasis in the United States, is no longer available. Praziquantel, which is active against most trematodes (flukes), is typically not active against Fasciola parasites. Therefore, the CDC does not recommend praziquantel therapy for fascioliasis. [60]
For Opisthorchis infections, praziquantel 25 mg/kg 3 times a day for 2 days taken with liquids during a meal is the recommended treatment. [4] An open-label phase II trial found that tribendimidine had similar tolerability and efficacy to praziquantel against O viverrini. [61] In contrast, mefloquine, artesunate, and mefloquine-artesunate were not effective in the same trial and were associated with vertigo, nausea, vomiting, and anxiety. Further large-scale clinical trials are needed to identify the best role of tribendimidine; future data may support this drug as yet another potential treatment option.
For Clonorchis infections, praziquantel 25 mg/kg 3 times a day for 2 days taken with liquids during a meal is also the recommended treatment, although albendazole 10 mg/kg as a single dose for 7 days may also be used. [4]
The WHO states that all confirmed cases of fascioliasis, opisthorchiasis and clonorchiasis should be treated, as well as all suspected cases in endemic areas. [62]
Diet
Proper cleaning and processing of raw vegetables by immersing in boiling water for a few seconds, followed by peeling and washing in clean water is important in preventing infection with intestinal flukes, especially in endemic areas.
The importance of thoroughly cooking contaminated vegetables cannot be overemphasized.
Do not eat raw or undercooked fish.
The diet in infected individuals should contain adequate protein.
Activity
The patient should be on bed rest.
Prevention
Eliminating the intermediate host snail is the key to controlling infection with intestinal flukes.
Proper cleaning and processing of raw vegetables by immersing in boiling water for a few seconds, followed by peeling and washing in clean water, is important in preventing infection with intestinal flukes, especially in endemic areas.
Night soil (human excreta) and pig excreta should not be used as fertilizers.
Metacercariae are not necessarily inhibited or destroyed by interventions such as smoking or freezing; and the practice of fish pickling is ineffective. Irradiation practices may be of benefit in managing the burden of metacercariae in the process of food preparation.
Many strategies to control opisthorchiasis have been used in Thailand. The strategies include mass drug administration and education to decrease the consumption of raw fish. Over the last decade, these methods have changed the epidemiology of O viverrini infection in Thailand. In the past, O viverrini infections were characterized as heavy infections that were concentrated in particular villages. Now, because of these strategies, O viverrini infections have become "lighter" but more widespread in terms of geographic distribution. [63]
Parasitic helminths reside in immunologically exposed extracellular locations within their hosts, yet they are capable of surviving for extended periods. To enable this survival, these parasites have developed complex and multifaceted mechanisms to subvert or suppress host immunity. There are studies on the immunomodulation by helminth parasites of ruminants and the parasite-derived molecules involved in driving this modulation. Such immunomodulatory molecules have considerable promise as vaccine targets. [64]
Triclabendazole 10 mg/kg as a single dose is the preventive chemotherapy for fascioliasis and is recommended in subdistricts, villages, or communities with clustering of cases. The WHO recommends that all school-aged children (aged 5-14 years) or all residents should be given the preventive chemotherapy every 12 months. [62]
Praziquantel 40 mg/kg as a single dose is the preventive chemotherapy for clonorchiasis and opisthorchiasis and is recommended in all people residing in areas where the prevalence of infection is 20% and above. Among people who live in areas with less than 20% prevalence, the recommendation is to administer preventive chemotherapy (1) to everyone every 24 months or (2) every 12 months to those who eat raw fish. [62]
Further Inpatient Care
Antispasmodics may relieve abdominal pain.
Iron supplements may be used to treat anemia, which may require transfusions in severe cases.
Vitamin C (ascorbic acid) may be administered to facilitate iron absorption.
-
Life cycle of Fasciolopsis buski. Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
-
The life cycle of Fasciolopsis. Immature eggs are discharged into the intestine and stool and become embryonated in water. The eggs then release miracidia, which invade a suitable snail intermediate host, in which the parasites undergo several developmental stages (sporocysts, rediae, cercariae). The cercariae are released from the snail and encyst as metacercariae on aquatic plants, which are eaten by mammalian hosts (humans and pigs), who become infected. After ingestion, the metacercariae excyst in the duodenum and attach to the intestinal wall, where they develop into adult flukes (20-75 mm X 8-20 mm) in approximately 3 months and attach to the intestinal wall of the mammalian hosts. The adults have a life span of about one year. Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
-
Egg of Fasciolopsis buski. Images reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
-
Adult fluke of Fasciolopsis buski. Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
-
The life cycle of Heterophyes. The adult parasites release embryonated eggs (each with a fully developed miracidium), which are then passed in the host's feces. After ingestion by a suitable snail (first intermediate host), the eggs hatch and release miracidia, which penetrate the snail's intestine. Snails of the genera Cerithidea and Pirenella are important hosts in Asia and the Middle East, respectively. The miracidia undergo several developmental stages in the snail (sporocysts, rediae, cercariae). Many cercariae are produced from each redia. The cercariae are released from the snail and encyst as metacercariae in the tissues of a suitable freshwater or brackish-water fish (second intermediate host). The definitive host becomes infected by ingesting undercooked or salted fish that contains metacercariae. After ingestion, the metacercariae excyst, attach to the mucosa of the small intestine, and mature into adults (measuring 1-1.7 mm X 0.3-0.4 mm). Heterophyes heterophyes infects humans, various fish-eating mammals (eg, cats, dogs), and birds. Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
-
Life cycle of Metagonimus. The adult parasites release fully embryonated eggs (each with a fully developed miracidium), which are then passed in the host's feces. After ingestion by a suitable snail (first intermediate host), the eggs hatch and release miracidia, which penetrate the snail's intestine. Snails of the genus Semisulcospira are the most common intermediate host for Metagonimus yokogawai. The miracidia undergo several developmental stages in the snail (sporocysts, rediae, cercariae). Many cercariae are produced from each redia. The cercariae are released from the snail and encyst as metacercariae in the tissues of a suitable freshwater or brackish-water fish (second intermediate host). The definitive host becomes infected by ingesting undercooked or salted fish that contains metacercariae. After ingestion, the metacercariae excyst, attach to the mucosa of the small intestine, and mature into adults (measuring 1-2.5 mm X 0.4-0.75 mm). M yokogawai infects humans, fish-eating mammals (eg, cats, dogs), and birds. Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
-
Various animals may be definitive hosts for different Echinostoma species, such as aquatic birds, carnivores, rodents, and humans. Unembryonated eggs are passed in stool (1), and development occurs in the water (2). The miracidium takes an average of 10 days to mature and then hatches (3), penetrating the first intermediate host, a snail (4). Snails, in general, serve as the first intermediate host. The intramolluscan stages are as follows: sporocyst (4a); rediae (4b); and cercariae (4c). Cercariae may then encyst as metacercariae in the same first intermediate host or leave to penetrate a new second intermediate host (5). Several animals may become the second intermediate host, such as other snails, bivalves, fish, and tadpoles. The definitive host gets infected after eating infected second intermediate hosts (6). The metacercariae excyst in the duodenum (7). Adults then live in the small intestine (8). Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
-
Magnified image of Echinostoma spp. egg. Echinostoma eggs resemble F busk and Fasciola eggs, with the latter two only bigger in size. Specimen slides courtesy of the University of the Philippines - College of Public Health, Department of Parasitology.
-
Low power magnification (arrow) of a Heterophyid egg. Specimen slides courtesy of the University of the Philippines - College of Public Health, Department of Parasitology.
-
Magnified view of a Heterophyid egg. Specimen slides courtesy of the University of the Philippines - College of Public Health, Department of Parasitology.
Tables
Infection |
Source* |
Geographic Distribution** |
|---|---|---|
Fasciolopsiasis |
Freshwater plants (water caltrop, water chestnut) |
Asia and Indian subcontinent, especially in areas where humans raise pigs and consume freshwater plants (as of December 8, 2017) |
Echinostomiasis |
Tadpoles, freshwater snails, fish, frogs |
Worldwide, but human cases seen most frequently in Southeast Asia and in areas where undercooked or raw freshwater snails, clams, and fish are eaten (as of December 27, 2017) |
Heterophyiasis |
Fish |
Egypt, Middle East, Far East (as of January 3, 2018) |
Metagonimiasis |
Fish (cyprinid) |
Far East, Siberia, Manchuria, the Balkan states, Israel, Spain (as of December 29, 2017) |
* Adapted with permission from Tribble D, Wagner KF. Trematode infections. Infectious Disease Practice. 1996; 20:69-73. ** Updated data from the Centers for Disease Control and Prevention (DPDx Laboratory Identification of Parasites of Public Health Concern. Available: http://www.cdc.gov/dpdx/) |
||
Infection |
Source |
Clinical Features |
Alaria americana |
Undercooked frog legs |
Disseminated fatal thoracic, gastrointestinal, retroperitoneal, and CNS manifestations; intraocular infections |
Echinostomiasis (16 species) |
Freshwater fish, aquatic plants, clams, snails, mollusks, contact with aquatic birds |
May be asymptomatic; mild abdominal pain, bloating, dyspepsia, diarrhea, eosinophilia |
Fibricola species |
Tadpoles |
Abdominal pain, diarrhea, fever, eosinophilia |
Fasciolopsis species |
Water chestnut, water calthrop, water bamboo, water morning glory lotus and water hyacinth |
May be symptomatic; may be subclinical; gastritis, nausea, diarrhea, eosinophilia; generalized edema in persons with heavy infection burden |
Gastrodiscoides species |
Vegetables, aquatic plants |
Often asymptomatic; may manifest as abdominal pain and diarrhea in severe cases |
Watsonius watsoni |
Water bamboo |
Severe diarrhea |
Fischoederius elongates |
Aquatic plants |
Epigastric pain and vomiting |
Heterophyes species |
Mullets, fish; brackish water |
May be asymptomatic; intestinal mucosal disease, ulcer-related abdominal pain, dyspepsia, nausea, vomiting, diarrhea, weight loss |
Gymnophalloides seoi |
Oysters |
Fever, abdominal pain, anorexia, weight loss, diarrhea, pancreatitis |
Carneophallus brevicaeca |
Shrimp |
Fatal when infection involves CNS and heart |
Brachylaima ruminae |
Poultry, rats |
Abdominal pain, diarrhea |
Metagonimiasis species |
Fish (ayu, golden carp) |
May be asymptomatic; intestinal mucosal disease, ulcer-related abdominal pain, dyspepsia, nausea, vomiting, diarrhea, weight loss |
Nanophyetus salmincola |
Undercooked fish (eg, salmon, trout, steelhead) |
May be symptomatic; mild diarrhea, abdominal pain |
*Adapted from Berger SA, Marr JS. Human Parasitic Diseases Sourcebook. 1st ed. Sudbury, MA: Jones and Bartlett; 2006. |
||
