page_title: Fascioloides magna
section_title: Life cycle
hierarchical_section_title: Fascioloides magna / Life cycle
caption_attribution_description: The egg of Fascioloides magna
context_page_description: Fascioloides magna, also known as giant liver fluke, large American liver fluke or deer fluke, is trematode parasite that occurs in wild and domestic ruminants in North America and Europe. Adult flukes occur in the liver of the definitive host and feed on blood. Mature flukes measure 4 to 10 cm in length × 2 to 3.5 cm in width, and have an oval dorso-ventrally flattened body with oral and ventral sucker. The flukes are reddish-brown in colour and are covered by tegument. As with other digenean trematodes, the life cycle includes intramolluscan phase in snails. The parasite is currently distributed in wild ruminants in North America and Europe, including Austria, Canada, the Czech Republic, Croatia, Germany, Hungary, Italy, Poland, Serbia, Slovakia, and the United States.
context_section_description: The life cycle of F. magna is relatively complex and is similar to the development of the related fluke, F. hepatica. A detailed account of the F. magna life cycle was given by Swales (1935), Erhardová-Kotrlá (1971), and reviewed by Pybus (2001).
  Adult flukes occur in pairs or groups within a fibrous capsule in the liver parenchyma of the definitive host. Mature flukes release eggs which are collected in the cavity of the capsule. The capsule contains a great mass of eggs and has duct connections to bile ducts. The eggs are passed together with bile into the bile collecting system, enter the small intestine, and leave the definitive host along with the faeces. The eggs which are passed out in the faeces into the environment are undeveloped and undergo embryonation outside the host. Several physical-chemical factors, especially temperature, humidity and oxygen tension, are known to influence embryonation. During the embryonation of the egg, a larva called a miracidium develops from germinal cells. Fully developed miracidium releases the operculum of the egg using several proteases. The embryonation period varies from 27 to 44 days in natural conditions. Ciliated miracidia hatch in water and actively seek suitable intermediate hosts that are freshwater snails from family Lymnaeidae. After attaching to a suitable snail host, the miracidium penetrates into the snail body. After shedding its ciliated cell layer it is called a sporocyst. The sporocysts are found in the foot, the snail body, digestive glands, reproductive organs, and in the pulmonary sac of the snail. The sporocysts contain germinal cells that give rise to 1-6 mother rediae (a trematode larval form with an oral sucker). Developed mother rediae are released from the sporocyst and migrate into digestive glands, renal organ, reproductive organs, and pulmonary sac of the snail body. Each mother redia can asexually produce up to 10 daughter rediae. However, only 3 to 6 daughter rediae complete their development and leave the mother rediae. In turn, each daughter redia may produce 1-6 Trematode lifecycle stages#Typical lifecyle stagescercariae in experimentally infected snails and 16-22 cercariae under natural conditions. Cercariae emerge from the rediae and mature usually in digestive glands of the snail. Mature cercarie spontaneously emerge from the snail host and swim actively in water for up to two hours before encysting on vegetation. After encystment the flukes are called metacercariae. Development within the snail takes 40 to 69 days depending upon the temperature and the species of snail. The definitive host ingests vegetation containing the metacercariae. In the stomach and the intestine, the metacercariae are stimulated to emerge from the cyst (excystation). Newly excysted juvenile flukes penetrate the wall of the intestine and migrate in the abdominal cavity. Juvenile flukes penetrate the Glisson’s capsule of the liver and continue migrating in the liver tissue. Rarely juvenile flukes penetrate other organs, such as lungs or kidneys. In these organs, however, flukes do not survive and not attain maturity. In the liver, flukes migrate within the parenchyma to search another fluke. If the fluke meet another one, they stop moving, and the fibrous capsule is formed around them. In the capsule, the parasite completes its development and starts egg-laying. Prepatent period varies 3–7 months and is dependent on host species. Adult F. magna can survive in the liver of the host up to 7 years.
caption: The egg of F. magna.
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