Echinococcosis is a parasitic zoonotic disease caused by a specific cestode, the dog tapeworm. Zoonosis, or zoonotic disease, refers to diseases that are transmitted from animals to humans. Cestodes are a class of parasitic flatworms. Echinococcosis is transmitted to humans from animal hosts by a fecal-oral route.
There are two forms of echinococcosis: the cystic form, caused primarily by Echinococcus granulosus, and the alveolar form, caused by Echinococcus multilocularis. In the cystic form of echinococcosis, pouch-like structures are formed, while in the alveolar form, the lesions formed resemble little sacs or alveoli similar to the sacs in the lungs. E. granulosus is found in the feces of infected dogs and E. multilocularis in that of foxes, coyotes, wolves, and dogs.
E. granulosus is present worldwide, especially in areas where livestock is raised in close proximity to dogs. There are areas in southern South America, northern Africa, Uganda, Kenya, Australia, New Zealand, the Mediterranean coast, the southern part of the former Soviet Union, the Middle East, and southwestern Asia in which echinococcosis is endemic. A disease is said to be endemic in a region if it occurs with predictable regularity, with only relatively minor fluctuations in its frequency over time. It is estimated that 6.6% of the population on the Tibetan Plateau is infected with E. granulosus cysts. E. multilocularis is more common in the Northern Hemisphere.
Echinococcosis causes productivity losses in human and domestic animal populations. Infection with E. granulosus is rarely fatal but may cause blindness from an infection of the eye socket or paralysis from brain infection. E. multilocularis infection is fatal if left untreated.
The number of human cases diagnosed varies greatly across countries, ranging from one to a few hundred out of 100,000 people. For example, the number of human cases in Greece is 13 out of 100,000.
Treatment of echinococcosis is difficult, and a complete cure is not always achieved. Patients may require lifelong medication therapy to keep the infection under control.
In view of the inadequacy of treatment options, prevention plays a very important role in reducing the rate of infection. Fencing around vegetable fields, thoroughly washing fallen wild berries before eating, washing hands after handling pets, preventing dogs from consuming infected meat, and treatment of infected dogs may be effective preventive measures.
Albendazole, cestode, definitive host, echinococcal cyst, echinococcosis, Echinococcus granulosus, Echinococcus multilocularis, EG95, ELISA, EM2, EM18, eosinophilia, hydatid cyst disease, hydatid disease, hydatidosis, immunoelectrophoresis, immunofluorescence, indirect hemagglutination, intermediate host, PAIR, pericystectomy, praziquantel, protoscolice, Western blot, zoonosis, zoonotic disease.
types of the disease
There are two forms of echinococcosis: the cystic form, caused primarily by Echinococcus granulosus, and the alveolar form, caused by Echinococcus multilocularis. The cystic form refers to the formation of pouch-like structures, and the alveolar form to the lesions that resemble little sacs or alveoli similar to the sacs in the lungs.
Polymerase chain reaction (PCR) in combination with specific deoxyribonucleic acid (DNA) probes is expected to simplify diagnosis in the future. PCR is an enzymatic method to make many copies of the two strands of DNA in a particular gene sequence. It is widely used to amplify minute quantities of biologic material to provide adequate specimens for laboratory research. DNA probes are specific DNA sequences that have complementary base pairs to the target DNA sequence. The detection and diagnosis of echinococcal infection utilizing PCR may become rapid, efficient, and accurate, thereby aiding in early detection and treatment of the infection.
A specific diagnostic Western blot technique using the Em18 antigen or the Em18 recombinant protein has been developed, but it is not commercially available. A recombinant protein is a protein developed by genetic engineering.
A vaccine that prevents the Echinococcus infection in intermediate hosts has been developed. A cloned recombinant antigen (EG95) developed from the echinococcal egg was used to prepare the vaccine. It offered 96-98% protection in sheep exposed to infection with E. granulosus eggs. The same vaccine has been suggested for humans in endemic areas, but its usefulness is questionable. Moreover, trials to test its use in humans are difficult to conduct.
Numerous immunomodulatory molecules are secreted by Echinococcus, which helps the parasite evade destruction by the host's immune system. An immunomodulatory molecule is capable of regulating immune function. These molecules are being characterized to understand the method by which the parasite persists in the host and causes chronic disease.
An oral recombinant vaccine in dogs has shown promising results.
Recombinant vaccines are those in which genes for specific antigens are inserted into a vector, which is a vehicle used to transfer foreign genetic material to a target cell. The vector expresses the antigen, which is purified and used in the vaccine. The vector used in one study was a live, attenuated (weakened) strain of the bacterium Salmonella enterica serovar Typhimurium, which does not cause disease in its attenuated state. Further research in being carried out on this vaccine.