Echinococcus multilocularis
Encyclopedia
Echinococcus multilocularis is a cyclophyllid
tapeworm
that, along with some other members of the Echinococcus
genus
(especially E. granulosus
), produces the disease
known as echinococcosis
in certain terrestrial
mammals, including wolves, foxes, jackals, coyotes, domestic dogs
and humans. Unlike E. granulosus, E. multilocularis produces many small cyst
s (also referred to as locule
s) that spread throughout the internal organs of the infected
animal. Ingestion
of these cysts, usually by a canid
eating an infected rodent
, results in a heavy infestation
of tapeworms.
for many years. Following the asymptomatic period of this disease, commons symptom
s are headache
, nausea
, vomiting
, abdominal pain
. Jaundice
is rare, but hepatomegaly
is a common physical finding
.
and a secondary or intermediate host, each harboring different life stages of the parasite.
Foxes, domestic dogs and other canids are the definitive hosts for the adult stage of the parasite. The head of the tapeworm attaches to the intestinal
mucosa
by hooks and suckers. It then produces hundreds of microscopic eggs, which are dispersed through the feces (Vuitton, 2009).
Wild rodents such as mice serve as the intermediate host. Eggs ingested by rodents develop in the liver, lungs and other organs to form multilocular cysts. Humans could also become an intermediate host by handling infected animals or ingesting contaminated food, vegetable, and water. The life cycle is completed after a fox or canine consumes a rodent infected with cysts. Larvae within the cyst develop into adult tapeworms in the intestinal tract of the definitive host (Vuitton, 2009).
Except in rare cases where infected humans are eaten by canines, humans are a dead-end or incidental host (an intermediate host that does not allow transmission to the definitive host) for E. multilocularis.
Summary of the life cycle:
(AE) is a highly lethal helminthic disease in humans, caused by the larval form of the parasitic tapeworm E. multilocularis. The disease represents a serious public threat in China, Siberia, and central Europe. However since the 1990s, the prevalence of the disease seems to be increasing in Europe, not only in the historically endemic areas but its neighboring regions .
AE primarily affects the liver by inducing a hepatic disorder similar to liver cancer , therefore becoming extremely dangerous and difficult to diagnose. If the infection metastases, it may spread to any other organ and could be lethal if not treated. The most common treatment for AE is to surgically remove the parasite. Since it is difficult and not always possible to remove the entire parasite, medicine such as Albendazole is utilized to keep the cyst from growing back..
Guided by the Tumor-Node-Metastasis (TNM) system of liver cancer, the European Network for Concerted Surveillance of Alveolar Echinococcosis and the World Health Organization
Informal Working Group on Echinococcosis, a clinical classification system has been proposed. This classification system has been designated as the "PNM" system (P = parasitic mass, N = involvement of neighboring organs, M = metastasis). The system was developed by a retrospective analysis of records from 97 patients treated in France and Germany (2 treatment centers). Amongst other characteristics, the system takes into consideration the localization of the parasite in the liver, the extent of lesion involvement, regional involvement, and metastasis.
A study by veterinary
parasitologists
from Purdue University
indicated that the disease is spreading throughout the Midwestern United States
, where it was previously rare or nonexistent. Additionally, the disease has extended its range in Europe
in the last few decades http://www.cdc.gov/ncidod/EID/vol10no7/03-1027-G.htm. Still the infection is fairly rare. Between 1982 and 2000 559 cases were reported in entire Europe http://www.cdc.gov/NCIDOD/eid/vol9no3/02-0341.htm.
Cyclophyllidea
Tapeworms of the order Cyclophyllidea are the most important cestode parasites of humans and domesticated animals. All have multiple proglottid "segments," and all have four suckers on their scolex , though some may have other structures as well...
tapeworm
Cestoda
This article describes the flatworm. For the medical condition, see Tapeworm infection.Cestoda is the name given to a class of parasitic flatworms, commonly called tapeworms, of the phylum Platyhelminthes. Its members live in the digestive tract of vertebrates as adults, and often in the bodies...
that, along with some other members of the Echinococcus
Echinococcus
The genus Echinococcus includes six species of cyclophyllid tapeworms to date, of the family Taeniidae. Infection with Echinococcus results in hydatid disease, also known as echinococcosis....
genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
(especially E. granulosus
Echinococcus granulosus
Echinococcus granulosus, also called the Hydatid worm or Hyper Tape-worm, is a cyclophyllid cestode that parasitizes the small intestine of canids as an adult, but which has important intermediate hosts such as livestock and humans, where it causes hydatid disease...
), produces the disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
known as echinococcosis
Echinococcosis
Echinococcosis, which is often referred to as hydatid disease or echinococcal disease, is a parasitic disease that affects both humans and other mammals, such as sheep, dogs, rodents and horses. There are three different forms of echinococcosis found in humans, each of which is caused by the larval...
in certain terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
mammals, including wolves, foxes, jackals, coyotes, domestic dogs
Canidae
Canidae is the biological family of carnivorous and omnivorous mammals that includes wolves, foxes, jackals, coyotes, and domestic dogs. A member of this family is called a canid . The Canidae family is divided into two tribes: Canini and Vulpini...
and humans. Unlike E. granulosus, E. multilocularis produces many small cyst
Cyst
A cyst is a closed sac, having a distinct membrane and division on the nearby tissue. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, a cyst could go away on its own or may have to be removed through surgery.- Locations :* Acne...
s (also referred to as locule
Locule
A locule is a small cavity or compartment within an organ or part of an organism ....
s) that spread throughout the internal organs of the infected
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
animal. Ingestion
Ingestion
Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in the substance through the mouth into the gastrointestinal tract, such as through eating or drinking...
of these cysts, usually by a canid
Canidae
Canidae is the biological family of carnivorous and omnivorous mammals that includes wolves, foxes, jackals, coyotes, and domestic dogs. A member of this family is called a canid . The Canidae family is divided into two tribes: Canini and Vulpini...
eating an infected rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
, results in a heavy infestation
Infestation
Infestation refers to the state of being invaded or overrun by pests or parasites. It can also refer to the actual organisms living on or within a host.-Terminology:...
of tapeworms.
Signs and symptoms
People infected with E. multilocularis may be asymptomaticAsymptomatic
In medicine, a disease is considered asymptomatic if a patient is a carrier for a disease or infection but experiences no symptoms. A condition might be asymptomatic if it fails to show the noticeable symptoms with which it is usually associated. Asymptomatic infections are also called subclinical...
for many years. Following the asymptomatic period of this disease, commons symptom
Symptom
A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality...
s are headache
Headache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
, nausea
Nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...
, vomiting
Vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...
, abdominal pain
Abdominal pain
Abdominal pain can be one of the symptoms associated with transient disorders or serious disease. Making a definitive diagnosis of the cause of abdominal pain can be difficult, because many diseases can result in this symptom. Abdominal pain is a common problem...
. Jaundice
Jaundice
Jaundice is a yellowish pigmentation of the skin, the conjunctival membranes over the sclerae , and other mucous membranes caused by hyperbilirubinemia . This hyperbilirubinemia subsequently causes increased levels of bilirubin in the extracellular fluid...
is rare, but hepatomegaly
Hepatomegaly
Hepatomegaly is the condition of having an enlarged liver. It is a nonspecific medical sign having many causes, which can broadly be broken down into infection, direct toxicity, hepatic tumours, or metabolic disorder. Often, hepatomegaly will present as an abdominal mass...
is a common physical finding
Medical sign
A medical sign is an objective indication of some medical fact or characteristic that may be detected by a physician during a physical examination of a patient....
.
Life cycle
The life cycle of E. multilocularis involves a primary or definitive hostHost (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
and a secondary or intermediate host, each harboring different life stages of the parasite.
Foxes, domestic dogs and other canids are the definitive hosts for the adult stage of the parasite. The head of the tapeworm attaches to the intestinal
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
mucosa
Mucous membrane
The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs...
by hooks and suckers. It then produces hundreds of microscopic eggs, which are dispersed through the feces (Vuitton, 2009).
Wild rodents such as mice serve as the intermediate host. Eggs ingested by rodents develop in the liver, lungs and other organs to form multilocular cysts. Humans could also become an intermediate host by handling infected animals or ingesting contaminated food, vegetable, and water. The life cycle is completed after a fox or canine consumes a rodent infected with cysts. Larvae within the cyst develop into adult tapeworms in the intestinal tract of the definitive host (Vuitton, 2009).
Except in rare cases where infected humans are eaten by canines, humans are a dead-end or incidental host (an intermediate host that does not allow transmission to the definitive host) for E. multilocularis.
Summary of the life cycle:
- adult worm present in intestine of definitive host
- eggs passed in feces, ingested by humans or intermediate host
- onchosphere penetrates intestinal wall, carried via blood vessels to lodge in organs
- hydatid cysts develop in liver, lungs, brain, heart
- protoscolices (hydatid sand) ingested by definitive host
- ingested protoscolices attach to small intestine and develops into adult worm
Morphology
The adult parasite is a small tapeworm that is 3- 6mm long, and lives in the small intestine of canines. The segmented worm contains a scolex with suckers and hooks that enable attachment to the mucosal wall, since tapeworms do not have a digestive tract. A short neck connects the head to three proglottids, the body segment of the worm which contains the eggs to be excreted in the feces.Diagnosis
Serological and imaging tests are commonly used to diagnose this disease. Frequently used serological tests include antibody tests, ELISA and indirect hemaglutination (IHA). Also, an intradermal allergic reaction test (Casoni test) has also been used to diagnose patients. Imaging tests include: X-rays, cat scans, MRI, and ultrasound.Disease staging
Alveolar echinococcosisAlveolar hydatid disease
Alveolar hydatid disease , also known as alveolar echinococcosis, alveolar colloid of the liver, alveolococcosis, multilocular echinococcosis, and “small fox tapeworm,” is a disease that originates from the parasite...
(AE) is a highly lethal helminthic disease in humans, caused by the larval form of the parasitic tapeworm E. multilocularis. The disease represents a serious public threat in China, Siberia, and central Europe. However since the 1990s, the prevalence of the disease seems to be increasing in Europe, not only in the historically endemic areas but its neighboring regions .
AE primarily affects the liver by inducing a hepatic disorder similar to liver cancer , therefore becoming extremely dangerous and difficult to diagnose. If the infection metastases, it may spread to any other organ and could be lethal if not treated. The most common treatment for AE is to surgically remove the parasite. Since it is difficult and not always possible to remove the entire parasite, medicine such as Albendazole is utilized to keep the cyst from growing back..
Guided by the Tumor-Node-Metastasis (TNM) system of liver cancer, the European Network for Concerted Surveillance of Alveolar Echinococcosis and the World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
Informal Working Group on Echinococcosis, a clinical classification system has been proposed. This classification system has been designated as the "PNM" system (P = parasitic mass, N = involvement of neighboring organs, M = metastasis). The system was developed by a retrospective analysis of records from 97 patients treated in France and Germany (2 treatment centers). Amongst other characteristics, the system takes into consideration the localization of the parasite in the liver, the extent of lesion involvement, regional involvement, and metastasis.
Treatment
If no specific therapy is initiated, in 94% of patients the disease is fatal within 10–20 years following diagnosis.- Currently, benzimidazoleBenzimidazoleBenzimidazole is a heterocyclic aromatic organic compound. This bicyclic compound consists of the fusion of benzene and imidazole. The most prominent benzimidazole compound in nature is N-ribosyl-dimethylbenzimidazole, which serves as an axial ligand for cobalt in vitamin B12. Benzimidazole, in...
s (such as albendazoleAlbendazoleAlbendazole, marketed as Albenza, Eskazole, Zentel and Andazol, is a member of the benzimidazole compounds used as a drug indicated for the treatment of a variety of worm infestations. Although this use is widespread in the United States, the U.S. Food and Drug Administration has not approved...
) are used to treat AE: only halt their proliferation and do not actually kill the parasites, side effects such as liver damage - 2-ME2, a natural metabolite of estradiolEstradiolEstradiol is a sex hormone. Estradiol is abbreviated E2 as it has 2 hydroxyl groups in its molecular structure. Estrone has 1 and estriol has 3 . Estradiol is about 10 times as potent as estrone and about 80 times as potent as estriol in its estrogenic effect...
, is tested with some results in vitroIn vitroIn vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
: decreased transcriptionTranscription (genetics)Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
of 14-3-3-pro-tumorogenic zeta-isoform, causes damage to germinal layer but does not kill parasite in vivoIn vivoIn vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research... - Treatment with a combination of albendazole/2-ME2 showed best results in reducing parasite burden
- Despite the improvements in the chemotherapy of echinococcosis with benzimidazole derivatives, complete elimination of the parasitic mass cannot be achieved in most of the infected patients, although there have been studies that indicate that long-term treatment with mebendazoleMebendazoleMebendazole or MBZ is a benzimidazole drug developed by Janssen Pharmaceutica and marketed as Vermox, Ovex, Antiox, and Pripsen...
may cause the death of the parasite.
Epidemiology
The incidence of human infestation with E. multilocularis and disease is increasing in urban areas, as wild foxes (an important reservoir species of the sylvatic cycle) are migrating to urban and suburban areas and gaining closer contact with human populations (Vuitton, 2009). Also, restocking fox enclosures for fox hunting with infected animals spreads the disease. Children, health care workers and domestic animals are at risk of ingesting the cysts after coming into contact with the feces of infected wild foxes. Even with the improvement of health in developed/industrialized countries, the prevalence of alveolar echinococcosis (AE) did not decrease (Vuitton, 2009). On the contrary, incidents of AE have now also been registered in eastern European countries and sporadic incidences in other European countries (Vuitton, 2009).A study by veterinary
Veterinary medicine
Veterinary Medicine is the branch of science that deals with the prevention, diagnosis and treatment of disease, disorder and injury in non-human animals...
parasitologists
Parasitology
Parasitology is the study of parasites, their hosts, and the relationship between them. As a biological discipline, the scope of parasitology is not determined by the organism or environment in question, but by their way of life...
from Purdue University
Purdue University
Purdue University, located in West Lafayette, Indiana, U.S., is the flagship university of the six-campus Purdue University system. Purdue was founded on May 6, 1869, as a land-grant university when the Indiana General Assembly, taking advantage of the Morrill Act, accepted a donation of land and...
indicated that the disease is spreading throughout the Midwestern United States
Midwestern United States
The Midwestern United States is one of the four U.S. geographic regions defined by the United States Census Bureau, providing an official definition of the American Midwest....
, where it was previously rare or nonexistent. Additionally, the disease has extended its range in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
in the last few decades http://www.cdc.gov/ncidod/EID/vol10no7/03-1027-G.htm. Still the infection is fairly rare. Between 1982 and 2000 559 cases were reported in entire Europe http://www.cdc.gov/NCIDOD/eid/vol9no3/02-0341.htm.