Echinococcus granulosus

ECHINOCOCCOSIS

Classification

• Class: Cestoda• Genus: Echinococcus • Species:

Species Diseases

E. granulosus Hydatid disease

Echinococcus vogeli Hydatid disease

E. multilocularis Alveolar hydatid disease

Overview

• These are tissue invasive parasites (larval Cestodes) that invade the major tissues and organs of the human body and cause a major disease called Ecchinococcosis (cystic hydatid ) disease.

• Accidental hosts: Humans (Dead end hosts)

Reservoirs Hosts Examples

Definitive hosts

Canids (canines); dogs, wolves and (fenines) cats.

Intermediate hosts

Herbivores like sheep, deer, goats, horses, cattle, wallabies, kangaroos and pigs that graze on grass infected with the eggs of the parasite.

Accidental hosts

Humans (Dead end hosts)

Farm-dog to sheep cycle Wild ‘reservoir’ cycle

In Australia……(Where it Echinococcus granulosus is most prevalent)

Disease: Cystic Ecchinococcosis

E. granulosus

Morphology

• Size (adult): Ranges in length from 2mm to 9mm

• Segments: Has 3 proglottids (segments) – immature, mature & a gravid link that is longer and wide.

• Shape: The scolex (head) has 4 suckers and a rostellium with hooks (25 – 50 )hooks with a double crown at the tip of the scolex.

Ecchinococcus Granulosus

Hydatid brood capsule with protoscolices

Scolex showing hooks

E. granulosus immature proglottid. (Source: CDC)

Immature progloid

onchosphere

Egg of E. granulossus

Epidemiology

• World widely spread in the sheep, cattle, pigs and dog rearing countries in Africa, Central Asia, southern South America, The Mediterranean, the middle East and Australia. In Africa it is found among the Turkana in Kenya, Ethiopia, Sudan, Northern Uganda and South Africa.

Mode of spread

Epidemic Areas

Central Europe South America

Mediterranean countries Middle East

Australia & New Zealand South Africa

Life Cycle

Lifecycle cont.• The disease cycle begins when the adult tapeworm gains entry and

attaches itself to the gut of the definitive host usually a carnivore and can be a canine (dog ) or the feline (cat) lineage.

• Infection begins when the dog eats wastes that contain hydatid cysts. The swallowed cysts burst and the tapeworm heads travel to the gut and attach themselves to the intestine wall. The worms are mature after about 6 weeks and an adult worm is only 6mm in length. Each mature worm grows and sheds the last segment of its body about every 2 weeks. The last segment contains immature eggs. The eggs are passed from the animal’s body in fecal material into the soil, that is eaten by an intermediate host. The eggs are resistant to weather conditions and can remain visible for months.

cont

• The intermediate host usually grazing animals in areas where canids also exist eat the grass infected with the tapeworm eggs. The eggs hatch in the animals gut into embryos called oncosphere larvae that contain hooks that travel through the blood stream and attack vital organs like the liver, lungs, brain, bones, kidney, spleen and form unilocular hydatid cysts in the host’s tissues.

Cont,• The hydatid cysts are bladder like structures

where brood (breeding) capsules are formed and are sometimes attached to a mother cyst. These cysts contain around 30 to 40 tapeworms. These cysts can grow and enlarge to the size of a softball or basket ball and may contain several smaller “balloons.” inside the main cyst via asexual reproduction they give rise to protoscolex(precursors to the head of a tapeworm) and daughter cysts. In humans protoscoleces are rarely produced in those who are infected.

E. granulossus cyst

• Slow development of cyst • Cysts have thick-walled chambers • Separated by connective tissue • Cyst is fluid filled • Cyst is free of host material

Unilocular hydratid cyst

LIFE CYCLE • Definitive host eats the infected organs and becomes

infected• After ingestion, the protoscolices evaginate, attach to the

intestinal mucosa and develop into adult stages (scolex and adult tapeworm)

• In 32-80 days, the cycle starts over when a canid eats infected meat and passes out eggs.

• The four stages involved in adult maturation are proglottisation, maturation, growth and segmentation. Proglottisation and maturation form the reproductive units. Growth and segmentation lengthen the body.

• Humans can be exposed to these eggs by “hand to mouth” transfer or contamination. By ingesting food, water or soil contaminated with stool from infected dog. This might include grass, herbs, greens or berries gathered from fields and by getting or handling dogs infected with the disease.

Life Cycle (cont’d)

Clinical manifestations

• Cysts may develop in any area of the body but the lungs and liver are most frequently impacted, followed by organs of the central nervous system.

• A liver cyst may produce no symptoms for 10 -20 years until its large enough to be felt by physical examination. Symptoms include:

• Pain or discomfort in the upper abdominal region or chest due to the presence of the tapeworm.

• Nausea and vomiting or coughing may occur as a result of the growing cysts.

• Unexplained weight loss.• Rupture of cyst can lead to allergic reactions, anaphylatic shock and a

hypersensitive reaction due to a flood of foreign material in the body that can result in death.

• Pressure of the cyst on surrounding tissue or bones may lead to blindness, collapse of infected bones or even sudden death if the cyst is in the heart.

Pathophysiology • Hydatid disease or echinococcosis can be either

primary (spread by ingestion) or secondary (larval tissue proliferates after spread from the primary site - usually from trauma). In primary echinococcosis larval cysts develop in a single organ in most cases (about 80% of cases). About 70% of cases involve the liver. The cysts have a wall made from both host tissue (pericyst) and larval origin (endocyst) The cysts are fluid-filled and grow very slowly (about 1 cm in diameter every year).

Cont.

• The expanding hydatid cyst causes pressure necrosis of surrounding tissues, although as growth is slow a good deal of accommodation may take place before any vital structures are compromised. This depends on the location of the cyst.

Cont.

• Slow leakage of hydatid fluid from the cyst sensitizes the patient and elicits eosinophilia.

• Rupture of an abdominal hydatid cyst either through trauma or in the course of surgery, carries with it both the risk of anaphylatic shock and the possibility of spread of the germinal epithelium which are capable of producing a new cyst.

• Rupture of a pulmonary cyst into a bronchus may be marked by severe allergic symptoms and coughing with the production of blood flecked fluid which may contain recognizable hydatid tissue. At times this results in spontaneous cure, but secondary infection may lead to chronic lung abscess.

Cystic hydratid disease

DIAGNOSIS

• C T scan for abdominal thoracic cysts.• X- ray tests.• Radiographic examination• Serological tests • Detection of Antigens in faces by Elisa is currently the

best technique.• New techniques like PCR is also used to identify the

parasite from DNA isolated from eggs or feaces.

PREVENTION• Health education in areas where the disease is known to

occur about basic hygienic practices.• De-worming dogs on a routine basis to prevent spread of

the disease.• Make it a practice to feed dogs with only commercially

prepared dog foods from reputable manufacturers• Do not feed raw or infected offal waste meats that include

organs and entrails to a dog.• Wash hands before eating, drinking and smoking and after

gardening or handling animals or their pens.• Children should avoid direct contact with dogs and

indirectly through soil, water and contaminated vegetables and teach them to wash hands.

TREATMENT

• Surgery taking special care to leave the cyst intact so that new cysts do not form.

• Mebendazole over along period of time at low dosages.

• Albendazole• Praziquantel.

Medication

Praziquantel

Arecoline

Surgery

Differences in CystsEchinococcus granulosus

• Slow development of cyst • Cysts have thick-walled

chambers • Separated by connective

tissue • Cyst is fluid filled • Cyst is free of host material

Echinococcus multilocularis

• Rapid development of cyst • Cyst has thin-walled

chambers • Not separated by

connective tissue • Cyst is gelatinous filled • Cyst is contaminated by

host material