ECHINOCOCCOSIS (HYDATID DISEASE)

Ehinococcosis is a tissue tapeworm infection of humans caused by the larval stage (a hydatid cyst) ofEchinococcus granulosus.

The adult worm measuring 5 mm in length and consisting of a scolex and three proglottids is found in the small intestines of dogs, wolves and other canines, sheep, and cattle that are infected from contaminated pastures or water. The terminal or gravid proglottid splits, releasing eggs into the stool. These eggs pass to the external environment and are ingested by an intermediate host (e.g. sheep or human). Humans may ingest the eggs by handling a dog or drinking contaminated water. The embryo is liberated from the ovum in the small intestine (60-70% of these remain at this site) and gains access to the blood stream and thus to the liver, or beyond (in about 10-15% of cases) to the lung, brain, kidney, bones, and other tissues. The resultant cyst grows very slowly (1 mm a month), sometimes intermittently (and may outlive the patient) to produce pressure symptoms and aseptic productive inflammation around the cyst. It is fluid-filled and contains scolices, brood capsules, and 2^nd generation (daughter) cysts containing infectious scolices. When the intermediate host is eaten by a carnivore, the scolices are released into the GI tract, where they develop into adult worms.

The dog is the principal definitive host and the sheep the most common intermediate. Human infection, often acquired in childhood during play with infected dogs, is most common in the sheep-raising areas of the world, including Caucasus, West Siberia, Central Asia.

The majority of cysts are found in the liver, where, after remaining asymptomatic for decades (stage 1), they finally produce clinical signs and symptoms such as abdominal pain or a palpable mass (stage 2). The pressure symptoms vary, depending on the organ or tissue involved. In nearly 75% of patients with hydatid disease the right lobe of the liver is invaded and contains a single cyst. In others, a cyst may be found in the lung, bone, brain or elsewhere. At stage 3, complications may occur e. g. jaundice, if the bile duct is obstructed. Rupture into the bile duct, abdominal cavity, peritoneal cavity, or lung may produce fever, urticaria, or a serious anaphylactoid reaction. The released scolices may produce metastatic infection. Pulmonary cysts are usually discovered on routine chest X-ray. Some rupture, and cough, chest pain, and haemoptysis result.

The diagnosis depends on the clinical, radiological (a round, often irregular, pulmonary mass of uniform density on chest X-ray or CT scan, or an avascular area on angiography) and ultrasound findings (fluid-filled cysts) in a patient who has lived in close contact with dogs in an endemic area. Serologic tests (complement fixation and enzymelinked immunosorbent assay) are positive in approximately 60% of pulmonary and 90% of hepatic lesions.

Complete blood count may reveal eosinophilia, sometimes being as severe as 10-13%, often following palpation of cyst or Cazoni's skin test, which involves intradermal injection of 0, 2 ml of echinococcal cyst fluid. Marked hyperaemia and oedema help confirm the diagnosis. In 10-20% of cases the reaction may be false-negative.

Surgery, or echinococcectomy, is the only definitive treatment of the hydatid cysts which involves their removal. The cyst may be removed together with the fibrous capsule or with part of the organ affected, e.g. pulmonary resection. Incision of the cyst, orechinococcotomy, is indicated if the removal of the cyst cannot be performed. Prevention of dissemination of the neighbouring tissues with the scolices should be borne in mind during the procedure. The cyst fluid and daughter cysts are removed by incision of the superficial and, in part, fibrous capsule. The resultant cavity should be cleansed with antiseptic solutions of specific activity (formaldehyde or hypertonic saline with hydrogen peroxide) and drained. The cavity may also be shrunk by means of suturing the fibrous capsule.

Alveococcosis is a parasitic disease with primary damage to the liver caused by larvae of Alveococ-cus multilocularis.

Alveococcosis is an endemic disease with prevalence lower than that of echinococcosis. It is found in Canada, Alaska, Austria, Japan and Germany, in some regions of Siberia and the Far East.

Foxes, dogs, wild cats, and other small carnivores are the definitive hosts of the helminth.

The intermediate hosts include voles and other microtine rodents, and humans. It is noteworthy that humans are a «dead-end» intermediate host only and cannot serve as final host for intestinal adult A. multilocularis.

After ingestion of eggs from handling fur of infected carnivores oncospheres which form multi-chambered solid cysts without an enveloping membrane are released in the intestine and penetrate it with subsequent entering bloodstream of the intermediate host. The cysts continue to grow in the liver, usually with fatal outcome.

As a result of definitive hosts' feeding on infected rodents the worms attach to their small intestines, mature and produce eggs which leave their bodies with faeces.

The metastases take place in the liver, lungs and brain. Compression of the bile ducts results in obstructive jaundice.

The cysts of the tapeworm resemble porous cheese with small cavities that are filled with puslike contents.

Secondary suppuration evolves into hepatic abscess of the liver or purulent cholangitis.

The disease develops slowly with a long asymptomatic period. It is usually recognised accidentally (e. g. clinical screening accompanied by ultrasound investigation).

The complications of the disease (cholangitis, obstructive jaundice or pulmonary or cerebral metastases) may be its early signs. Peripheral localization of the worm in the liver may produce tumourlike appearance of the organ. On palpation, non-tender hepatomegaly with hard consistency of the liver is a common presentation. The patient's general condition is usually satisfactory.

Parahilar localization of the cyst brings about early jaundice which occurs due to compression of the bile ducts.

The historical data (i.e. residing 5-15 years ago in endemic regions, episodes of contact with wild animals via hunting, processing animal carcasses and skins, intake of wild berries) should raise suspicion of the condition.

To confirm the diagnosis, laboratory (eosinophilia) and skin tests (Cazoni's reaction or haemagglutinin with latex, which are positive in 70-75% of cases) are used.

For the differential diagnosis X-ray, angiography, CT, radioisotope or US scanning may be helpful. Chest X-ray is mandatory, persistent headache requires meticulous neurological examination.

Treatment. Surgery, i.e. hepatic resection coupled with the solid cyst enucleation, should be combined with specific drug therapy. Small residual part of the parasite should be infiltrated with antiparasitic drugs (20 ml Tripaflavine 0, 1%).

For systemic therapy levamisole and mebendazole are used.

Prevention of both echinococcosis and alveococcosis includes strict epidemiological control at slaughterhouses and destruction of infected organs of killed animals. Moreover, contacts with dogs should be minimised, especially those of children who are unaware of the danger of infection and safety measures. The veterinary control of guard dogs is also of importance.

OPISTHORCHIASIS

Opisthorchiasis is an important hepatic and pancreatic fluke of humans. It is caused by Opisthorhis felineus orDistomum sibiricum. The other principal mammalian hosts of the disease are dogs, cats, foxes, pigs, while the first and secondintermediate hosts are snails and fresh-water fish (e. g. the carp and salmon), respectively.

The egg, on reaching fresh water, hatches into a free-swimming miracidium. After multiplication and further development within the snail, thousands of free-living cercariae are released and must enter the second intermediate host, where they encyst to form metacercariae. Infections follow ingestion of raw, dried, salted, or pickled fish containing the metacercariae. The larvae are released in the duodenum, enter the common bile duct, and migrate to the 2^nd order bile ducts (or, occasionally, the gallbladder and pancreatic ducts), where they mature in about 1 month into adult, flat flukes varying from a few mm to several cm in length. Endemic in West Siberia, Kazakhstan, in the regions of the Volga, Dnieper, and Neman Rivers, the infection is found elsewhere most frequently among immigrants from those areas and in fish imported from there.

The mode of spread of the fluke is via ova in faeces or water.

The parasite may cause hepatic dystrophy and necrobiosis. The common surgical complications of opisthorchiasis are suppurative cholangitis with hepatic abscess. The perforation of the bile ducts results in peritonitis and hepatic abscess penetration into abdominal or thoracic cavities. Often, chronic opisthorchiasis may even cause hepatic carcinoma. Opisthorchiasis of the pancreas may be complicated by acute pancreatitis or pancreatic carcinoma.

The complications of opisthorchiasis lack characteristic signs. However, clinical and epidemiological findings often suggest the diagnosis, which can be confirmed only by identification of the eggs in faeces or duodenal contents.

The treatment of the complicated opistorchiasis involves conventional methods applied in parasitic diseases coupled with preand postoperative medical therapy with hexachlorparaxicol. The surgery on the organs other than the liver or bile ducts or pancreas requires that specific therapeutic agents should be given postoperatively.

ASCARIASIS

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