Geographic Range
Fasciola gigantica
is found in tropical Africa, South and South-east Asia, and the Far East. In the
United States
F. gigantica
is found in Hawaii.
Habitat
The habitat of Fasciola gigantica changes with the stage of its life cycle. Adult F. gigantica live in the liver and bile ducts of its definitive hosts (sheep, cattle, and other grazing ruminant mammals). Eggs shed by adults are located in the intestinal track of mammals and also in the wild. Free swimming cercarias are found in the bodies of fresh water that are in close proximity of its definitive host. Temperatures above 10 degree Celsius are required for the development of the miracidia larvae stage. Miracidia are found in fresh water that contains intermediate snail hosts in the genus Lymnaea . Metacercaria are found encysted on vegetation and in the mammal host once ingested. Inside the snail rediae persist in the digestive gland of the mammal host, known as the hepatopancreas.
Adequate amounts of moisture are also needed, these factors can account for the intensity
and prevalence of infection in the definitive hosts. Increased numbers of incidences
are seen in the wet season.
- Habitat Regions
- tropical
- freshwater
- Aquatic Biomes
- lakes and ponds
Physical Description
Fasciola gigantica
is leaf-shaped and tapers at both ends. An adult can grow to 75 mm in length. With
the use of a scanning electron microscope the surface of
F. gigantica
appears very rough due to abundant microscopic spines and surface folding. Spines
increase in size in their middle section and are smaller on the surface near the suckers.
Spikes range from 30 μm to 58 μm and have serrated edges with anywhere from 16 to
20 sharp points. This species has both an oral and ventral sucker for feeding and
attaching to the inside of its host.
Fasciola gigantica
also has three different types of surface papillae which are used as sensory receptors.
The eggs of
F. gigantica
can reach sizes of 0.2 mm in length.
- Other Physical Features
- ectothermic
- heterothermic
- bilateral symmetry
- Sexual Dimorphism
- sexes alike
Development
Adult flukes produce eggs that are passed in the host’s feces. In the wild the eggs
hatch into miracidia and penetrate a snail host. The miracidia form into saclike sporocysts
and multiply into rediae which then develop into cercariae. Free swimming cercariae
are shed from snails, they then find aquatic plants, encyst and become metacercariae.
Metacercariae cysts wait to be taken up by other ruminant host to repeat the life
cycle. In the transmission stage the metacercariae are unknowingly ingested with aquatic
plants by humans and grazing mammals. In the mammal host metacercariae excyst in the
duodenum. Immature flukes then penetrate the liver and become mature in the biliary
track.
Reproduction
Sexually mature adults reside and presumably mate in biliary ducts of their mammalian
host.
Fasciola gigantica
reproduce sexually as adults and asexually in the other stages of its life cycle.
The flukes are in the metacercariae stage before becoming sexual adults. After residing
in their mammal host’s duodenum, the metacercariae penetrate the liver and become
mature in the biliary track. The adult flukes have both sex organs, but fertilization
between adult male and female flukes is the most common source of sexual reproduction.
Adult flukes produce eggs that are then passed in the host’s feces.
- Key Reproductive Features
- sexual
- asexual
- fertilization
Non-embryonic eggs are laid within the mammalian host and are passed through to the
intestinal tract where they are expelled in the feces.
- Parental Investment
- no parental involvement
Lifespan/Longevity
The life span for each stage of
Fasciola gigantica
varies greatly. After being ingested it takes 3-4 month for adult flukes to become
mature and begin producing eggs. Adult flukes can live for multiple years in their
definitive host. Embryos of
Fasciola
species are able to persist outside the host for several months. The free-swimming
miracidium will die soon after hatching if they do not contact a secondary host. If
conditions are favorable metacercaria are able to persist for up to a year once encysted.
Behavior
Adult
Fasciola
species produce embryos which are then shed through the digestive system with its
host’s feces. When water and temperature conditions are favorable, the embryos develop
into the ciliated larva form called, miracidium. Miracidium are able to swim and locate
its secondary snail host with help of its cilia. If the miracidium are to come in
contact with a snail it actively penetrates it. The cilia are then shed and it is
transformed in to a saclike sporocyst. The sporocyst mature and release rediae.
Inside the snail the rediae move to the snail’s digestive gland known as the hepatopancreas.
Over time this is where the rediae will form cercariae. The cercariae develop tails
and leave the snail in search for vegetation to encyst. Once the cysts are formed
Fasciola
species become metacercaria and these infect a mammal host if they are accidentally
ingested with the vegetation.
Communication and Perception
The time it takes for the shelled embryos of
Fasciola gigantica
to hatch is rapidly increased in the presence of light. If they are kept in darkness
the number of miracidia that make it to the free-swimming stage are greatly reduced.
The miracidium have extremely functional eye-spots. This is probably to prevent premature
hatching before the embryos have exited the host’s digestive track. The attack of
a proteoplytic enzyme protein controls the opening of the operculum which allows the
miracidium to exit the shelled embryo. There is evidence that the blue and violet
portion of the light spectrum triggers this attack.
- Communication Channels
- tactile
Food Habits
When the adult
Fasciola
are in the bile ducts of a host it obtains a small portion of its nutrients from
active bloodsucking. In a day’s time, a single adult fluke can take in about 0.2 ml
of blood. There is evidence that adult flukes need around 100 times the amount of
glucose than
Fasciola
receives from active ingestion. Therefore, adult flukes also receive nutrients by
absorption of glucose through their tegument.
The free-swimming miracidia were once thought to be a non-feeding stage, but it has
been shown they metabolize glucose when it is present.
- Primary Diet
- carnivore
- Animal Foods
- mammals
- blood
Predation
A variety of general aquatic predators are known to feed on the free-living stages
of
Fasciola gigantica
, including the miracidia and the cercariae stages.
Ecosystem Roles
Fasciola spp.
have a negative impact on its definitive host and are capable of causing mortality
if infection is severe.
Fasciola gigantica
parasitizes
lymnaeid
snails, which are intermediate hosts, and cows, sheep and other ruminants, which
are definitive hosts. In some instances humans are also infected.
- Ecosystem Impact
- parasite
- lymnaeid snails, Lymnaea
- sheep, Caprinae
- cows, Bovinae
- humans, Homo sapiens
Economic Importance for Humans: Positive
These are no known positive effects of Fasciola gigantica on humans.
Economic Importance for Humans: Negative
Fasciola spp.
cause a disease known as fascioliasis, which can cause significant economic loss
when it infects livestock. This parasite reduces the amount of meat that a cow will
produce when slaughtered, and leaves the liver inedible. This parasite also reduces
milk production and can causes mortality in chronic infections. In some developing
countries fascioliasis is the second leading cause of economical loss, costing 10
million dollars annually. Immunization of livestock also adds to the cost of fascioliasis.
Few human infections with
F. gigantica
have been reported but are seen in Asia, Africa, and Hawaii.
- Negative Impacts
- injures humans
- causes or carries domestic animal disease
Conservation Status
Other Comments
In countries that
Fasciola gigantica
is present, the prevalence of infected animals is extremely high. In certain areas
of Africa prevalence can range from 30-90%, 25-90% in Indonesia and 4-24% in Thailand.
Additional Links
Contributors
Marcus Carmona (author), Radford University, Renee Mulcrone (editor), Special Projects.
- Palearctic
-
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- oriental
-
found in the oriental region of the world. In other words, India and southeast Asia.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Ethiopian
-
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- freshwater
-
mainly lives in water that is not salty.
- marsh
-
marshes are wetland areas often dominated by grasses and reeds.
- swamp
-
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- heterothermic
-
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
- bilateral symmetry
-
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- asexual
-
reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents
- fertilization
-
union of egg and spermatozoan
- internal fertilization
-
fertilization takes place within the female's body
- parasite
-
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
- sessile
-
non-motile; permanently attached at the base.
Attached to substratum and moving little or not at all. Synapomorphy of the Anthozoa
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- tactile
-
uses touch to communicate
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
- parasite
-
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
- causes disease in humans
-
an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).
- causes or carries domestic animal disease
-
either directly causes, or indirectly transmits, a disease to a domestic animal
- carnivore
-
an animal that mainly eats meat
- sanguivore
-
an animal that mainly eats blood
References
Cheesbrough, M. 2005. District Laboratory Practice in Tropical Countries, Volume 1 . Cambridge, England: Cambridge University Press.
Dangprasert, T., W. Khawsuk, A. Meepool, C. Wanichanon, V. Viyanant, E. Upatham, S. Wongratanacheevin, P. Sobhon. 2001. Fasciola gigantica : Surface topography of the adult tegument. Journal of Helminthology , 75: 43-50.
Johnson, P., D. Thieltges. 2009. Diversity, decoys and the dilution effect: How ecological communities affect disease risk. Journal of Experimental Biology , 213: 961-970.
Kumar, V. 1998. Trematode Infections and Diseases of Man and Animals . AA Dordrecht , The Netherlands: Kluwer Academic Publishers.
Miliotis, M., J. Bier. 2003. International Handbook of Foodborne Pathogens . Imprint, New York: Marcel Dekker Inc.
Read, C. 1973. Animal Parasitism . Englewood Cliffs, New Jersey: Prentice-Hall, Inc.
Saleha, A. 1991. "Southeast Asian J Trop Med Public Health" (On-line pdf). Liver fluke disease (fascioliasis) : Epidemiology, economic impact and public health significance. Accessed January 19, 2013 at http://www.tm.mahidol.ac.th/seameo/1991-22-suppl/84-361-364.pdf .
Sobhon, P., T. Dangprasert, S. Chuanchaiyakul, A. Meepool, W. Khawsuk, C. Wanichanon, V. Viyanant, E. Upathamb. 2000. Fasciola gigantica : Ultrastructure of the adult tegument. Science Asia , 26: 137-148.
2009. "Fascioliasis" (On-line). Parasites and Health. Accessed January 19, 2013 at http://www.dpd.cdc.gov/dpdx/html/fascioliasis.htm .