ECHINOCOCCOSIS By Dr. Ameer kadhim Hussein. M.B.Ch.B. FICMS (Community Medicine).
INTRODUCTION Species under genus Echinococcus are small tapeworms of carnivores with larval stages known as hydatids proliferating asexually in various mammals including humans. There were five morphologically distinct species in this genus including: E. granulosus, E. multilocularis, E. oligarthus, E. vogeli and Echinococcus shiquicus.
Ehinococcosis due to Echinococcus granulosis (Cystic echinococcosis or cystic hydatid disease)
ECHINOCOCCUS GRANULOSUS
IDENTIFICATION It is larval stage of the tape worm Echinococcus granulosus. It is the most common Echinococcus cause hydatid disease. Hydatid cysts enlarge slowly and required several years for development. The cyst range from (1-15 cm) in diameter but may be larger. Infections may be asymptomatic until cysts cause noticeable mass effect. Signs and symptoms vary according to cyst location, size, type and numbers.
Infectious agent: Echinococcus granulosus, a small tapeworm of dogs and other canids. Occurrence: All continents except Antarctica depend on close association of humans and infected dogs especially common in grazing countries where dogs eat viscera containing cysts. In endemic regions, human incidence rates for cystic echinococcosis can reach greater than 50 per 100 000 person-years, and prevalence levels as high as 5% 10% may occur in parts of Argentina, Peru, East Africa, Central Asia and China.
Reservoir: The domestic dog and other canids which are definitive hosts for echinococcus granulosus which may harbor thousands of adult tapeworms in their intestines without sign of infection. Intermediate hosts include sheep, goats, pigs, horses and other animals. Humans also regard as intermediate host. Incubation period: 12 months to years depending on number and location of cysts and how rapidly they grow.
Period of communicability: Not directly transmitted from person or from one intermediate host to another. Infected dogs begin to pass eggs (5-7) weeks after infection. Most canine infections resolve spontaneously by 6 months however some adult worms may survive up to 2-3 years. Dogs may become infected repeatedly. Susceptibility: Children who are more likely to have close contact with infected dogs and less likely to have adequate hygienic habits so have more risk of infection. Mode of transmission: Human infection often take place directly with hand to mouth transfer of eggs after association with infected dogs or indirectly through contaminated food, water, soil or fomites. In some instances flies have dispersed eggs after feeding on infected feces.
LIFE CYCLE OF ECHIONCOCCUS GRANULOSUS
CYST LAYERS AND CONTENTS
Methods of control a. Preventive measures: 1. Avoid ingestion of raw vegetables and water that may have been contaminated with feces of infected dogs. Application of hygiene practices such as hand washing and washing of fruits and vegetables. Educate those at high risk to avoid exposure to dog feces and possibly infected dogs. 2.Interrupt transmission from intermediate to definitive hosts by preventing access of dogs to potentially contaminated and uncooked viscera. Disposal of viscera should be by incineration or by deep burial. 3. Periodically treat high risk dogs and all dogs in high risk area. 4. Field and laboratory personnel must observe strict safety precautions to avoid ingestion of tapeworm eggs.
CONTROL PATIENT, CONTACTS AND IMMEDIATE ENVIRONMENT 1. Report to local health authority. 2. Isolation, concurrent disinfection, Quarantine and immunization of contacts : Not applicable. 3. Investigation of contacts and source of infection: Examine families for suspected cysts by using ultrasound, chest x-ray and other imaging techniques. Check dogs in and around houses for infection. Determine beliefs, practices and behaviors increase risk of infection.
Specific treatment: must be based on WHO classification of liver cysts usually surgical intervention is a common treatment. Other cysts types treated by percutaneous techniques such as PAIR ( Puncture, Aspiration, Injection, re-aspiration). Treatment with mebendazole and albendazole has proved successful and may be preferred treatment in many cases. If primary cyst ruptures praziquentel and Protoscolicidal agent reduce risk of secondary cysts. Other cyst types may not need sugical, percutaneous or medical intervention and can follow for long time by (wait and watch).
Echinococcosis due to Echinococcus multilocularis (Alveolar echinococcosis)
ECHINOCOCCUS MULTILOCULARIS
Identification: A highly invasive destructive disease caused by the larval stage of echinococcus multilocularis. Lesions usually found in the liver but because their growth is not restricted by a thick laminated cyst wall they may expand to periphery to produce solid tumor like masses. Metastases can result in secondary cysts and larval growth in other organs. Clinical manifestations depend on the size and location of cysts but are often confused with hepatic carcinoma and cirrhosis. The disease is often fatal although spontaneous cure and calcification has been observed. Diagnosis is often based on histopathology. Sero-diagnosis using purified E. multilocularis antigen is highly sensitive and specific.
Staging and classification system recently proposed by WHO named PNM is based on: a. Hepatic location of the parasite (P). b. Extra hepatic involvement of neighboring organs (N). c. Metastases (M). Infectious agent: Ehinococcus multilocularis. Occurrence: Distribution is limited to areas of the Northern Hemisphere (China, Turkey, Canada, Central Europe, Russia etc). The disease is usually diagnosed in adults.
LIFE CYCLE OF E. MULTILOCULARIS The life cycle is basically the same of E. granulosus except there are different definitive and intermediate hosts.
Reservoir: adult tape worms are largely restricted to wild animals such as foxes and E. multilocularis is commonly maintained in nature of fox-rodent cycles. Dogs and cats can be sources of human infection if hunting wild intermediate hosts such as rodents. Mode of transmission: Ingestion of eggs passed in the feces of canidae and felidae that have fed on infected rodents. Fecally soiled dog hair, and environmental fomites also serve as vehicles of infection. Incubation period, period of communicability, Susceptibility and methods of control: as for E. granulosus.
Radical surgical excision is less often successful and must be followed by chemotherapy. Mebendazole or albendazole use for a limited period after surgery or long term for inoperable patients which may prevent progression of the disease. Pre-surgical chemotherapy is indicated in rare cases.
Echinococcosis due to E. Vogeli and E. Oligarthrus (polycystic and unicystic echinococcosis)
This disease occurs in the liver, lungs and other viscera. Symptom vary depending on cyst size and location. This species is distinguished by its rostellar hooks. This species is unique in that the germinal membrane proliferate externally to form new cysts and internally to form septae that divide the cavity into numerous microcysts. Brood capsules containing many protocolices develop in the microcysts. The causal agents are E. vogeli and E.oligarthrus occur in Central and South America. Immuno-diagnosis using purified antigen of E. Vogeli does not always allow differentiation from alveolar echinococcosis. Albendazole has been used for chemotherapy.
SUMMARY Human echinococcosis is a parasitic disease caused by tapeworms of the genus Echinococcus. The 2 most important forms of the disease in humans are cystic echinococcosis (hydatidosis) and alveolar echinococcosis. Humans are infected through ingestion of parasite eggs in contaminated food, water or soil, or through direct contact with animal hosts. Echinococcosis is often expensive and complicated to treat, and may require extensive surgery and/or prolonged drug therapy.
SUMMARY Prevention programmes involve deworming of dogs, improved food inspection and slaughterhouse hygiene, and public education campaigns; vaccination of lambs is currently being evaluated as an additional intervention. More than 1 million people are affected with echinococcosis at any one time. WHO is working towards the validation of effective cystic echinococcosis control strategies by 2020.
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