Echinococcus multilocularis
| Echinococcus multilocularis | |
|---|---|
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| Cotton rat infected with Echinococcus multilocularis | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Platyhelminthes |
| Class: | Cestoda |
| Order: | Cyclophyllidea |
| Family: | Taeniidae |
| Genus: | Echinococcus |
| Species: | E. multilocularis |
| Binomial name | |
| Echinococcus multilocularis Leuckart, 1863 |
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Echinococcus multilocularis is a cyclophyllid cestode that, like Echinococcus granulosus, produces hydatid disease in many mammals, including rodents and humans. Unlike E. granulosus, E multilocularis produces many small cysts ("multilocular infection") that spread throughout the infected animal. When these cysts are ingested by a canid, usually by eating an infected rodent, it produces heavy infection with tapeworm adults.
The parasite Echinococcus multilocularis has become an increasing problem in urban areas. Since wild foxes are migrating to urban and periurban areas they maintain a closed contacts with human population (Vuitton, 2009[1]), consequently, the spreading of E.multilocularis seems to be increasing. Children, health workers, and domestic pets are affected by touching or handling wild foxes feces infected with the parasite. Even with the improvement of health in developed/industrialized countries, the prevalence of AE did not decrease (Vuitton, 2009[2]). On the contrary, incidents of AE have now also been registered in eastern European countries and sporadic incidences in other European countries (Vuitton, 2009[3]).
A study by Purdue veterinary parasitologists indicated that the disease is spreading throughout the American Midwest, where it was previously rare or nonexistent. Additionally, the disease has extended its range in Europe in the last few decades[1]. Still the infection is fairly rare. Between 1982 and 2000 559 cases were reported in entire Europe [2].
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Life Cycle
The Echinococcus multilocularis life cycle involves a definitive host and an intermediate host, each harboring different life stages of the parasite. Foxes or domestic canine are the definitive hosts for the adult stage of the parasite. The parasite attaches and resides in the mucosa of the intestines by hooks and suckers. It then produces hundreds of microscopic eggs, which are dispersed through the feces of foxes or carnivores (Vuitton, 2009[4]). 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[5]).
The following is a summary of this parasites life cycle:
(1) adult worms in bowels of definitive host. (2) eggs passed in feces, ingested by humans or intermediate host. (3) onchosphere penetrates intestinal wall, carried via blood vessels to lodge in organs. (4) hydatid cysts develop in liver, lungs, brain, heart. (5) protoscolices (hydatid sand) ingested by definitive host. (6) attach to small intestine and grow to 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.[6]
Symptoms
Patients infected with Alveolar Echinococcosis can be asymptomatic for many years. Following the asymptomatic period of this disease, commons symptoms are: headache, nausea, vomiting, abdominal pain, and hepatomegaly. Jaundice is rare but has also been seen.[7]
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.[8]
Disease Staging
Alveolar Echinococosis (AE) is a severe helminth disease that is highly lethal in humans caused by the larval form of the parasitic tapeworm Echinococcus 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 ([9]). Alveolar Echinococosis primarily affects the liver by inducing a hepatic disorder similar to liver cancer ([10]), 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([11])..
Guided by the Tumor-Node-Metastasis (TNM) system of liver cancer, the European Network for Concerted Surveillance of Alveolar Echinococcosis and the WHO 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.[12]
Treatment
If no specific therapy is initiated, in 94% of patients the disease is fatal within 10-20 years following diagnosis.[13]
- Currently, benzimidazoles (albendazole) is used to treat AE: only halt their proliferation and do not actually kill the parasites, bad side effects such as liver damage
- 2-ME2, a natural metabolite of estradoil, is tested with some results in vitro: decreased transcription of 14-3-3-pro-tumorogenic zeta-isoform, causes damage to germinal layer , but does not kill parasite in vivo
- Treatment with a combination of albendazole/2-ME2 showed best results in reducing parasiting weight[14]
- Despite the improvements in the chemotherapy of Echinococcus multilocularis 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 mebendazole may cause the death of the parasite.
See also
References
- ^ http://emedicine.medscape.com/article/214349-overview
- ^ http://emedicine.medscape.com/article/214349-overview
- ^ http://emedicine.medscape.com/article/214349-overview
- ^ http://emedicine.medscape.com/article/214349-overview
- ^ http://emedicine.medscape.com/article/214349-overview
- ^ John, David T., Petri Jr., William A. “Markell and Voge’s Medical Parasitology, 9th Edition”. St. Louis: Elsevier, 2006.
- ^ Kayacan SM, Vatansever S, Temis S, Uslu B, Kayacan D, Akkaya V, Erk O, Saka B, Karadug A, Turkmen K, Yakar F, Guler K. Alveolar echinococcosis localized in the liver, lung and brain. Chin Med J 2008: 121 (I) 90-92.
- ^ Kayacan SM, Vatansever S, Temis S, Uslu B, Kayacan D, Akkaya V, Erk O, Saka B, Karadug A, Turkmen K, Yakar F, Guler K. Alveolar echinococcosis localized in the liver, lung and brain. Chin Med J 2008: 121 (I) 90-92.
- ^ http://www.cdc.gov/ncidod/dpd/parasites/alveolarechinococcosis/factsht_alveolarechinococcosis.htm#what
- ^ http://www.cdc.gov/ncidod/dpd/parasites/alveolarechinococcosis/factsht_alveolarechinococcosis.htm#what
- ^ http://emedicine.medscape.com/article/214349-overview
- ^ Kern P, Sato N, Vuitton DA. WHO classification of alveolar echinococcosis: principles and application. Parasitol Int 2006: 55 (Suppl.): S283. Epub 2005 Dec 15.
- ^ Heike Jura, Augustinus Bader, and Matthias Frosch1. In Vitro Activities of Benzimidazoles against Echinococcus multilocularis Metacestodes:Antimicrob Agents Chemother. 1998 May; 42(5): 1052–1056.
- ^ Spicher M, Naguleswaran A, Ortega-Mora LM, Müller J, Gottstein B, Hemphill A (March 2008). "In vitro and in vivo effects of 2-methoxyestradiol, either alone or combined with albendazole, against Echinococcus metacestodes". Exp. Parasitol. 119: 475. doi:10.1016/j.exppara.2008.02.012. PMID 18442817. http://linkinghub.elsevier.com/retrieve/pii/S0014-4894(08)00061-1.
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