Hydatid Cyst: Pathogenesis, Clinical Manifestations, and Management Strategies in Human Hosts

Hydatid cyst is a parasitic infection caused by the tapeworm Echinococcus, commonly found in livestock-rearing areas. The cysts typically develop in the liver and lungs, but can affect other organs, causing space-occupying lesions. It can lead to serious complications if ruptured and requires surgical or medical treatment.

1. WELCOME

2. Hydatid Cyst Dr. Sourav Debnath MD Resident (Phase B) Department of Microbiology & Immunology BSMMU

3. Definition The larval form of the tapeworm may lodge in various body sites where they form a  fluid-filled sac   known as a hydatid cyst The cysts contain immature forms of the tapeworm and can increase in size from 5–10 cm or more over a period of time. While some cysts may die, others can remain alive for many years Cystic echinococcosis (CE), also known as hydatid disease, is caused by  infection with the larval stage of Echinococcus granulosus , a ~2–7 mm long tapeworm

4. History Hydatid disease is one of the oldest diseases known to man It was first described in the Talmud as a “Bladder full of water” Hippocrates described the human hydatid disease more than two thousand years ago with a very interesting expression( liver filled with water) Al- Rahzes wrote detailed script on hydatid cyst of the liver about one thousand year ago

5. In 17th century, Francesco Redi illustrated that the hydatid cysts of echinococcosis were of “animal” origin During the early to mid-1900s, significant advancements were made in distinguishing Echinococcus granulosus and Echinococcus multilocularis , detailing their life cycles and mechanisms of disease

6. Causative agent Cystic echinococcosis (CE), known as hydatid disease: Echinococcus granulosus. Other: Alveolar echinococcosis: Echinococcus multilocularis. Polycystic hydatid disease: Echinococcus  vogeli . Echinococcus oligarthrus : polycystic disease rarely.

7. Epidemiology Caused by infection with the larval stage of  Echinococcus granulosus CE is found in Africa, Europe, Asia, the Middle East, Central and South America, and in rare cases, North America. Cystic echinococcosis (CE)   Alveolar echinococcosis (AE)   Caused by infection with the larval stage of  Echinococcus multilocularis Found across the globe and is especially prevalent in the northern latitudes of Europe, Asia, and North America.

8. Morphology Adult E.   granulosus worms are small (2-8 mm long) and have a scolex, a neck with three attached segments Tape-worms form three different developmental stages: eggs; larvae; and adults Scolex have four suckers & 2 circular rows of hooks

9. Egg

10. Larval form The larval form is found within the hydatid cyst inside various organs of the intermediate host It represents the structure of the scolex of adult worm & remain invaginated within a vesicular body After entering the definitive host, the scolex with suckers & rostellar hooklets becomes exvaginated and develops into adult worm

11. Life cycle The worms completes its life cycle in two hosts E. granulosus : dogs E . multilocularis : foxes, Other canids including domestic dogs, wolves, and raccoon dogs. Echinococcus granulosus : sheep, cattle, goats, and pigs E. multilocularis : rodents Definitive host Intermediate host Human is an accidental intermediate host also considered as a dead end host

12. Mode of Infection Ingestion of eggs due to intimate handling of infected dogs or by eating raw vegetables or other food contaminated with dog feces

13. Ova ingested by man (or sheep, cattle), and liberated the embryo ( oncosphere) by destruction of chitinous wall of egg by gastric juice The oncosphere penetrate the intestinal wall & enter portal venules to liver and develops “hydatid cyst” Some embryo pass through liver and enter right side of heart to pulmonary capillaries to form “pulmonary hydatid cyst” Development in Man Development in Dog Dog may eat the caracasses or offal containing the cyst of infected sheep or cattle Inside the intestine of dogs, the scolices develop into adult worms that mature in 6-7 weeks and produce eggs to repeat the cycle

14. Cyst structure At gross examination , the vesicles resemble a bunch of grapes Site : liver 65%, lung 25%, muscle, spleen, kidney, heart, bone, brain etc. Slow-growing: 2-3cm/year Grow slowly often taking 20 years or more to become big enough to cause clinical illness

15. The cyst wall is formed by Consists of compressed liver parenchyma and fibrous tissue laid down by host fibroblast & new blood vessels Merges with adjacent host tissue Nutrition derived via this layer Pericyst Secreted by embryo Tough, acellular, laminated, elastic hyaline membrane, 1mm Resembles white of a hard boiled egg, easily separable from the adventitia Non-infective Ectocyst Is a germinal layer Single layer of cells lining the inner aspects of the cyst Is the only living element, being responsible for the formation of the other layers and brood capsules & scolices within the cyst. Secretes the hydatid fluid Endocyst

16. Pathogenesis Hydatid cyst represent larval form Gradual displacement of vital host tissue, vessels or parts of organ-damage & dysfunction. At the site of deposition, the embryo slowly develops into a hollow bladder or cyst filled with fluid. This become the hydatid cyst. Enlarge slowly and reachs a diameter of 0.5-1 cm in about 6 months. Growing cyst evoke host tissue reaction leading to the deposition of fibrous capsule around it.

17. Hydatid fluid Fig: Clean and clear cyst fluid from a diagnostic puncture [Rinaldi F, Brunetti E, Neumayr A, Maestri M, Goblirsch S, Tamarozzi F. Cystic echinococcosis of the liver: A primer for hepatologists.  World J Hepatol 2014; 6(5): 293-305] Clear, colourless or pale yellow. Slightly acidic, pH-6.7 Contain salts like sodium chloride, sodium phosphate and sodium & calcium salt of succinic acid and proteins Antigenic, used for Casoni’s test Anaphylactic shock on absorption Centrifuged deposit shows hydatid sand, brood capsules, free protoscolices and hooklets

18. From the germinal layer, small knob like excrescences protrude into the lumen of the cyst. These enlarge, become vacuolated & filled with fluid called brood capsules Inner wall of broods capsule protoscolices develop, complete with invaginated scolex bearing sucker & hooklets Several thousands of protoscolices develop into a mature hydatid cyst Inside mature hydatid cyst further generation of daughter cyst & grand daughter cyst develops Brood Capsules

19. Hydatid Sand A granular deposit or hydatid sand is found at the bottom of the cyst, consisting of free brood capsules and protoscolices and loose hooklets

20. Some cyst are sterile & may never produce brood capsules, while some brood capsule may not produces scolices called Acephalocysts Acephalocysts Sometimes a fragment of germinal layer detach and develop daughter cyst inside the mother cyst Endogenous daughter cyst Herniation and rupture of germinal and laminated layer may occur through some weaker part of the bone in case of hydatid disease of bone Exogenous cyst

21. Fate of hydatid cyst 1 2 3 4

22. Classification of cyst Type I Type III Type IV Type II Cyst with daughter cyst(s) and matrix

23. Clinical features Many hydatid cysts remain asymptomatic, even into advanced age Theoretically, echinococcosis can involve any organ The liver is the most common organ involved, followed by the lungs. These two organs account for 90% of cases of echinococcosis

24. In Cystic Echinococcosis (CE) Symptoms due to the pressure effect of the cyst Most symptomatic cysts are larger than 5 cm in diameter Organs affected by E. granulosus are the liver (63%), lungs (25%), muscles (5%), bones (3%), kidneys (2%), brain (1%), & spleen (1%) In the liver, the pressure effect of the cyst can produce symptoms of obstructive jaundice and abdominal pain Involvement of the lungs produces chronic cough, dyspnea, pleuritic chest pain, and hemoptysis Cerebral involvement causes h eadache, dizziness, and a decreased level of consciousness Secondary complications may occur as a result of infection of the cyst or leakage of the cyst

25. In Alveolar Echinococcosis (AE) T he liver is the primary site of infection, and it closely mimics cirrhosis or carcinoma Progressive liver dysfunction that ultimately leads to liver failure Distant metastasis is possible, and involvement of other organs ( eg , lung, brain, bone) can occur in as many as 13% of the patients

26. Fluid from the cyst: Hydatid cyst fluid can be aspirated for microscopic examination Serum: Collected for serological tests to detect specific antibodies Tissue samples: Cyst wall tissues from surgery can be used for histopathology and molecular studies Specimen

27. 1. Microscopy Wet, unstained mounts of hydatid fluid sediment are examined Examination of cyst fluid for 'hydatid sand’ reveals: Protoscolices , Brood capsule and Hooklets

28. Centrifugation Filtration Method of concentration of Hydatid cyst fluid Practical for high-volume samples Difficult with viscous samples Most effective technique Reliable for any samples but inconvenient for high-volume, clear samples

29. 2. Imaging Study Ultrasonography is the diagnostic procedure of choice

30. Plain X-rays permit the detection of hydatid cyst in lung and bones. In cases where long bones are involved, a mottled appearance is seen in the skiagram CT scan is superior for the detection of extrahepatic disease MRI appears to add diagnostic benefit for cysts, especially at difficult sites such as spinal vertebrae and cardiac cysts

31. 3. Serology Antibody detection Antibody against Ag B from hydatid fluid by- Indirect hemagglutination test (IHA) Indirect immunofluorescence ELISA Western blot Specific Echinococcal antigen in serum, urine and CSF can be detected by- Double diffusion Counter immunoelectrophoresis Antigen detection

32. 4. Casoni’s test The antigen in hydatid fluid is collected from animal or human cysts and is sterilized by membrane filtration A large wheal of about 5 cm in diameter with multiple pseudopodia like projections appears within half an hour at the test side and fades in about an hour Positive Edema and induration appears after 8 hours The fluid is injected (0.2 mL) intradermally in one arm and an equal volume of saline as control is injected in the other arm Secondary reaction

33. 5. Others Blood: Eosinophilia Histopathology : After surgical removal of cyst, Giemsa stain or PAS stain can be done to demonstrate cyst wall Molecular methods: Can be done by DNA probes and PCR, but their application is limited by their technical complexity

34. Management Traditionally, surgical removal was considered as the best mode of treatment of cyst Currently, USG staging is recommended and management depends on the stage In early stages, the treatment of choice is “PAIR” (Puncture, aspiration, injection and reaspiration) Great care is taken to avoid spillage and cavities are sterilized with 0.5% silver nitrite or 2% NaCl Albendazole (15mg/Kg in two divided doses) is initiated 4 days before the procedure and continued for 4 weeks afterwards

35. Basic steps of “PAIR” USG or CT guided puncture of the cyst Aspiration of the cyst fluid Infusion of scolicidal agents (cetrimide, 95% Alcohol etc ) Reaspiration of the fluid after 5-10 minutes “PAIRD” (D=drainage) is a variant of PAIR that includes insertion of catheter at the end of the procedure

36. 10% Formalin Hydrogen peroxide (15-20)% Hypertonic saline 5% Chlorhexidine 95% Alcohol Cetrimide Scolicidal agents include:

37. Surgery Treatment of choice for complicated stages Partial or total pericystectomy preferred For pulmonary cyst- wedge resection or lobectomy required Recurrence is common Pre and postoperative chemotherapy with albendazole for 2 years after curative surgery is recommended Chemotherapy Chemotherapy with benzimidazole agents are restricted to residual, postsurgical and inoperable cysts. Albendazole (400mg BD for 3 months) & Praziquantel (20mg/kg/day for 2 weeks) have proved beneficial

38. Complications of hydatid cyst Include two main categories: Rupture of the hydatid cyst More frequent, occurring in 20-50% of cases Anaphylaxis can occur followed by severe hypotension and death Transbronchial spread to other lobes Secondary bacterial infection Appears in only 5-8 % of cases Septicaemia Compression causes restrictive and obstructive changes Calcification- Rare

39. Prevention Prevent dogs from feeding on the carcasses of infected sheep Periodic deworming of pet dogs Restrict home slaughter of sheep and other livestock Do not consume any food or water that may have been contaminated by fecal mater from dogs Washing hands with soap and warm water after handling dogs, and before handling food Teach children the importance of washing hands to prevent infection

40. In this retrospective study in SSMC, from 2002 to 2011, total 130 cases of hepatic and abdominal CE was recorded

41. Question What parasite causes hydatid cyst ? Pathogenesis and fate of hydatid cyst? S.N.-Hydatid cyst