Ірі бауыр құрты: сипаттамасы, таралған аймақтары және өмірлік циклы

Species of fluke

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 in length × 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.

Fascioloides magna is essentially of North American origin but the parasite was introduced into Europe with imported game animals at the second half of the 19th century. In spite of being native to North America the fluke was first described in Italy. In 1875, Bassi observed massive deaths of red deer in the Royal Park (now La Mandria Regional Park) near Torino, Italy. The signs were similar to well known fasciolosis in sheep. He named it Distomum magnum. The author believed that the parasite was introduced into the park in wapiti imported from the United States in 1865. Most workers did not accept Bassi’s species because of his poor description. From 1882 to 1892, the fluke was recorded from different areas of the United States and described separately by many authors. Later, Stiles (1894) pointed out that the American findings are identical with species described previously by Bassi. Stiles made a complete morphological description of the adult fluke and named it Fasciola magna (Bassi 1875) Stiles 1894. In 1895, Stiles suggested that the life cycle of the fluke is very similar to Fasciola hepatica, i. e. it includes an aquatic snail as an intermediate host. He gave a comparative description of the egg and miracidium of the fluke. However, first reported intermediate hosts of F. magna were not published until 1930’s. The complete life cycle of F. magna, including a description of all the larval stages, was described by Swales (1935) in Canada.

Dead end hosts are represented by large bovids, suids, llamas, horses and some Old World cervids. Infections in dead end hosts are characterized by excessive fibrosis, thick walled encapsulation of flukes within hepatic parenchyma, and black pigmentation of various tissues. While American authors have not observed any clinical symptoms in cattle,

Aberrant hosts of F. magna are sheep and goats. However, the course of infection is similar in guinea pigs, and chamois (Rupicapra rupicapra) In aberrant hosts, flukes do not mature and migrate until the host dies. Hepatic lesions in aberrant hosts generally include firm adhesions of the liver to the diaphragm, black pigmentation, hematomas, necroses, and haemorrhagic tracts in which juvenile flukes are located.

While the eggs of F. magna resemble those of F. hepatica, this similarity is of limited use; eggs usually are not passed in cattle and sheep. Recovery of the parasites at necropsy, as well as proper identification of F. hepatica or F. gigantica is necessary for definite diagnosis. When domestic ruminants and deer share the same grazing areas, the presence of disease due to F. magna should be kept in mind. Mixed infections with F. hepatica occur in cattle.

For control of fascioloidosis in wild ruminants, successful application of anthelminthics in feed is necessary. The drug has to have flavour and smell that do not prevent animals from eating medicated feed. In addition, there should adequate therapeutic scope, i. e. span between therapeutic and minimal toxic dose. Therefore, only some of anthelminthics that are efficient in domestic ruminants have been tested in wild ruminants infected with F. magna. Fascioloidosis of cervids was successfully controlled with triclabendazole in the United States, and triclabendazole with levamizole in Hungary, Austria, In contrast, rafoxanide is commonly used in treatment in Czech Republic

In North America, especially in Wisconsin, flukes found inside deer livers are sometimes consumed by humans, sautéed in butter. They are served as "liver butterflies", "little livers" or "little flapjacks".