Flatworms

Platyhelminths: Flatworms

Distinct Structures
- Flat, wrinkled edges
- Mechanism of Feeding
- The process of attachment and disposal of waste through the mouth

General Lifecycle Description
- Involve two or more intermediate hosts (specific details vary by species)
Miracidium: First larval stage
- Characteristics: Ciliated, free swimming, lacks mouth
- First Intermediate Host: Freshwater snails
In Snail Host: Asexual reproduction occurs
- Sporocyst: Sac-like structures may produce either daughter sporocysts or radiae
- Redia: Contains pharynx, rudimentary intestines, and a tail; may produce more radiae or cercariae
- Development details vary by species, yet precise steps may not need to be memorized due to complexity

Cercaria: Final larval stage
- Characteristics: Tail shed, secretes protective coatings, encyst to develop in vegetation or other intermediate hosts
- Blood flukes can directly infect humans
- Hundreds of cercariae can be produced from one miracidium
Metacercaria:
- Encyst in the intestinal wall
- Migrate to tissues and mature into adults
- Eggs are produced and can be detected in feces, urine, or sputum

Intermediate Hosts:
- Snails of the genera Hippeutis and Segmentina
- Vegetation including bamboo and water chestnuts
Definitive Hosts:
- Humans and hogs found primarily in Asia and the Indian subcontinent
- Ingest metacercariae on plants leading to encystment in the duodenum
Adult Characteristics:
- Development occurs over 3 months with a lifespan of 1 year
- Adults range from 20-80 mm in length
Symptoms:
- Typically mild or asymptomatic, but can include abdominal pain, fever, and diarrhea
- Heavy infections may lead to intestinal obstruction and edema

Diagnostic Eggs:
- Dimensions: 130-140 µm long and 50-70 µm wide
- Brown-yellow, unembryonated, with an indistinct operculum and terminal knob
- Closely resembles Fasciola hepatica, difficult to distinguish based on location and size

Encysts in the duodenum of definitive hosts
Ingested metacercaria reside on water plants (infective stage)
Attachment occurs in the small intestine, leading to adulthood and egg production
Egg Characteristics:
- Diagnostic stage: unembryonated eggs found in feces
- Indistinct operculum with yolk sacs
Life Cycle Stages:
- Miracidium hatches from egg; penetrates snail
- Redia stage occurs in snail tissue
- Sporocyst formation leads to more cercaria development

Found on all continents, hybridization may occur between F. hepatica and F. gigantica
Definitive Hosts:
- Include sheep, goats, horses, and humans
Intermediate Hosts:
- Slow-moving aquatic snails and water vegetation
Infection & Diagnostic Examination
- Eggs: Largest operculated eggs in humans, measuring 130-140 µm x 70-90 µm
- Commonly found in stool or biliary drainage

Geographic Distribution: East Asia and Far Eastern Russia, with cases in the US via immigrants and imported fish
Symptoms range from mild and asymptomatic to severe including abdominal pain, diarrhea, and jaundice
Diagnostic Eggs:
- Dimensions: 27-35 µm x 11-20 µm, oval with a convex operculum
- Miracidium is visible; small knob present on abopercular end
Life Cycle
- Adults reside in biliary duct
- Eggs ingested by snails (first intermediate host), releasing cercariae to infect fish

Hosts: Common hosts include humans, dogs, pigs, and sheep
Pulmonary paragonimiasis: most prominent infection observed
- May occur extraneously affecting the brain or abdomen
Life Cycle
- Eggs are released in sputum and can hatch upon environmental contact
- Encystment occurs in crabs or crayfish; maturation phases involve the lungs as the final site

Habitat: Reside in blood vessels of the definitive host, often the mesenteric venules
Infection Types: Schistosomiasis, bilharziasis, and swamp fever
Dioecious: possess separate sexes, prominent sexual dimorphism where males encapsulate females
Symptoms and Diagnostic Features
- Eggs are ejected through stool or urine depending on species; diagnostic eggs are found in excretions
Life Cycle
- Involves freshwaters and intermediate snail hosts
- Cercariae penetrate human skin leading to various pathological conditions

Egg Sizes:
- S. mansoni: 110-170 µm x 45-75 µm found in stool
- S. japonicum: 55-85 µm x 40-60 µm found in urine or stool
- S. haematobium: 110-170 µm x 40-70 µm found in urine

Final Development:
- Adults mature in portal blood vessels specific to respective species and primarily release eggs into urine or feces as the diagnostic stage
Significance of Identification:
- Proper identification crucial due to concurrent life cycle complexities and associated infection symptoms.