Fasciola: Introduction, Morphology, Life Cycle, Pathogenecity, Laboratory

Fasciola: Introduction, Morphology, Life Cycle, Pathogenecity, Laboratory Diagnosis and Treatment

Egg of Fasciola hepatica in saline preparation

An egg of Fasciola hepatica in saline preparation of feces as shown above picture having following properties and they are-

Large ( having size of 140 X 80 µm)
Hen’s egg-shaped
Ovoid in shape
Operculated
Bile stained ( brownish-yellow in color) and
Unsegmented ovum in a mass of yolk cells

Fasciola hepatica was first discovered by Jehan de Brie in 1379 and its common name is a liver fluke. Fascioliasis is a zoonotic disease and its causative agents are parasites, Fasciola hepatica, and F. gigantica, flatworms, or trematodes that mainly affect the liver. They are leaf-shaped worms, large enough to be visible to the naked eye i.e. adult F. hepatica measure 2–3 cm x 1.3 cm while adult F. gigantica measure 2.5–7.5 cm x 1.2 cm). The disease they both cause is similar. WHO estimates that at least 2.4 million people are infected in more than 70 countries worldwide, with several million at risk.

Scientific Classification of Fasciola

(Linnaeus, 1758)

Kingdom: Animalia
Phylum: Platyhelminthes
Class: Trematoda
Subclass: Digenea (“two generations”)
Order: Echinostomida
Family: Fasciolidae
Genus: Fasciola
Species: F. hepatica
Binomial name: Fasciola hepatica, F. gigantica

Geographical Distribution: Cosmopolitan in distribution

Habitat: A parasite of herbivorous animals, living in the biliary passage of the liver and it is occasionally found in man.

Morphology of Fasciola

Fasciola hepatica possesses mainly three stages of life egg, larva ( in snail), and adult worm. The adult worm has following properties –

Large, broad, flat body

Leaf-shaped

Anterior end forms a prominent cephalic cone

Small oral and ventral suckers

Long and highly branched intestinal caeca

The life span of the adult worm in sheep is 5 years and in men 9 to 13 years.

Female adult: 25,000 eggs/day

Egg: The characteristics of the egg are as follows-

Large ( having size of 140 X 80 µm)
Hen’s egg-shaped
Ovoid in shape
Operculated
Bile stained ( brownish-yellow in color) and
Unsegmented ovum in a mass of yolk cells
Excreted with the bile into the duodenum and then passed out along with stool
It does not float in the saturated solution of common salt.
It can develop only in water.

Larval Stage: It may be of following phase- miracidium, cercaria, and metacercaria

Life cycle of Fasciola

It completes its life cycle in two different hosts. Definite host- Sheep, goat, cattle, or man. Adult worm in the biliary passages of the liver and reservoir host is primarily the sheep. Intermediate host (where the larval stages of the worm develop)-Snails of the genus Lymnaea and larval development proceeds in this snail and a carrier (entailing suitable aquatic plants). The process starts when infected animals defecate in fresh-water sources. Since the worm lives in the bile ducts of such animals, its eggs are evacuated in feces and hatch into larvae that lodge in a particular type of water snail. Once in the snail, the larvae reproduce and eventually release more larvae into the water. These larvae swim to nearby aquatic or semi-aquatic plants, where they attach to the leaves and stems and form small cysts (metacercariae). When the plants with the small cysts attached are ingested, they act as carriers of the infection. Watercress and water-mint are good plants for transmitting fascioliasis, but encysted larvae may also be found on many other salad vegetables. Ingestion of free metacercariae floating on water may also be a possible mode of transmission. Metacercariae excsts in the duodenum or jejunum and liberate the juvenile fluke. Juvenile fluke penetrates the intestinal wall and reaches the liver capsule. The parasite burrows into the liver parenchyma where it grows and develops. It becomes sexually mature in the bile ducts. The eggs are liberated in the feces through the bile in about 3-4 months after infection. The cycle is then repeated.

Mode of transmission

Ingestion of freshwater plants with metacercaria or by drinking water with floating metacercariae.

Diagnostic Stage: Ova

Infective Stage: Metacercaria

Pathogenicity and Clinical Features

It causes zoonotic disease fascioliasis. After the larvae are ingested with contaminated food or water, a symptom-less incubation period starts, lasting for a few days to a few months. The disease may be in the following phases acute or invasive phase and Chronic or latent phase.

Asymptomatic phase

It can cause fever.
Right upper quadrant abdominal pain
Hypereosinophilia

Acute or invasive phase

The acute phase, lasting 2-4 months.
Migration from the intestine to the liver
Traumatic and necrotic lesions in liver parenchyma
Typical symptoms include fever, nausea, a swollen liver, skin rashes, and extreme abdominal pain.

Chronic or latent phase

The parasite has reached the bile ducts
Obstruction
Stimulates inflammation in the biliary epithelium leading to fibrosis
Obstruction causes biliary sepsis
Symptoms include intermittent pain, jaundice, and anemia. Pancreatitis, gallstones, and bacterial super-infections may also occur. Patients with chronic infections experience hardening of the liver (fibrosis) as a result of long-term inflammation.

Laboratory Diagnosis of Fasciola

Specimens: Stool, duodenal or biliary aspirates, blood

Microscopy: Demonstration of eggs in the feces.

Serological test: Complement fixation test (CFT), haemagglutination test, immunofluorescence assay, immunodiffusion, immunoelectrophoresis, counter-current electrophoresis (CCIE -most sensitive) whereas testing using an immunoblot assay that detects IgG antibody to FhSAP2, a recombinant antigen derived from Fasciola hepatica is also most sensitive specific test.

Molecular Test: RFLP(restriction Fragment Length Polymorphism ): PCR-RFLP, is a technique that exploits variations in homologous DNA sequences. It refers to a difference between samples of homologous DNA molecules that come from differing locations of restriction enzyme sites, and to a related laboratory technique by which these segments can be illustrated.

Complete blood cell (CBC) count and biochemical test: High to moderate eosinophilia and elevated liver function tests.

Additional types of testing: Abdominal imaging, such as USG, computerized axial tomography (CAT scan), magnetic resonance imaging (MRI) scan, and endoscopic retrograde cholangiopancreatography (ERCP as shown below); and histopathologic examination of a biopsy specimen of liver or other pertinent tissue.

Treatment of Fasciola

The drug of choice for the treatment of fascioliasis is Triclabendazole, a benzimidazole compound active against immature and adult Fasciola parasites. The recommended due to having following properties-

Efficacy
Safety
Ease of use

Other drugs are-

Bithionol
Nitazoxanide

Note-Praziquantel, which is active against most trematodes (flukes), typically is not active against Fasciola parasites, and therefore, praziquantel therapy is not recommended for fascioliasis.

In some patients who have biliary tract obstruction, manual extraction of adult flukes e.g., via endoscopic retrograde cholangiopancreatography (ERCP) may be indicated as shown below-

Fasciola gigantica

It is also called the giant liver fluke, a parasite of herbivorous animals and human cases have also been reported. The life cycle, pathogenicity, and clinical features are similar to those of Fasciola hepatica but intermediate hosts are different snails. It is larger than F. hepatica and lives in the biliary passage of its host. Its egg is hard to make difference from F. hepatica, F. buski, and Echinostomes species.

Epidemiology

They are worldwide distribution in distribution and economic importance in livestock raising. Few human cases have been reported locally.

Prevention of Fasciola

The prevention can be achieved by using the following steps-

Inspecting the plants, especially watercress, very carefully for the metacercariae or more effectively by not eating plants grown in areas where herbivorous mammals (especially sheep) are found.
The contamination of water with feces from infected animals or people in areas where the aquatic plants are used for food should be prevented.
Water-grown vegetables should be washed with 6% vinegar or potassium permanganate( KMnO4) for 5-10 minutes, which kills the encysted metacercariae.
This approach is more successful than attempts to halt the consumption of raw vegetables.
Cook water-grown vegetables thoroughly before eating.
Avoid sewage contamination of growing areas.
The use of molluscicides is the most frequent public health intervention, as it prevents the transmission of many other trematodes, including Schistosoma species.

universe84a