Alaria species
The genus Alaria has 7 species; only A. alata is found naturally in Europe. No human illness caused by A. alata mesocercariae (infective larvae) has been reported, but concern remains because the closely related North American species A. americana has caused illnesses among humans, including 1 death. Natural infection of cats with other Alaria spp has been reported in the United States indicating biologic differences among Alaria spp.
Alariosis is a re-emerging zoonotic disease caused by infection with larval stages of trematodes of the genus Alaria. Alaria spp. infections are acquired by dogs and cats via ingestion of a wide variety of intermediate or paratenic hosts (particularly frogs and snakes) that harbor immature flukes. The prevalence was significantly higher in pregnant or lactating females cats than other intact females which might be related to increased exposure because an increase in predation by the cats during pregnancy and lactation to meet higher protein and energy demand. The infection possibly was acquired by the eating of inadequately cooked frogs, which are intermediate hosts of the worm.
Life cycle
Adult flukes, residing in the intestines of the definitive hosts, pass unembryonated eggs through the feaces of the host. After two weeks, these eggs hatch in water, releasing the miracidium. They actively penetrate and develop further in a snail host. In this first intermediate host, the miracidiae reproduction starts and after nearly a year of maturation, daughter sporocysts release cercariae provided with a fork tail (furcocercariae). They show a high motility in the water until an appropriate second intermediate host is exposed to them. This host might be a tadpole, an adult frog or other amphibian in which the furcocercariae develop into mesocercariae. The spectrum of snails, frogs, and amphibians and their preference vary depending upon Alaria species.
Pathogenesis
Alaria spp. adults develop in the small intestine and are not usually associated with intestinal illness. However, migration of immature Alaria through the lungs may result in pulmonary hemorrhage and subsequent respiratory compromise. Adults of Alaria are present in the small intestine of infected dogs and cats. Immature Alaria migrate through the lungs prior to being swallowed and developing into adult flukes in the small intestine. When infection levels are high, pulmonary damage and hemorrhage may lead to clinical disease. Alaria mesocercariae can cause severe damages within a paratenic host closely related to humans. Overall pathogenicity is correlated to high infestation densities, in particular, after repetitive intake of mesocercariae.
Clinical manifestation
There was no host reaction to the parasites. Granulomas were present in the stomach wall, lymph nodes and liver, but the worms were not identified in them. A case of fatal disease associated with systemic infection with Alaria larvae and several cases of ocular infection have been reported following ingestion of undercooked frogs legs. The causing dermatitis in humans (“swimmer’s itch”) following skin penetration.
Laboratory diagnosis
Trematode eggs are less buoyant than those of nematodes or protozoa; unless high-density sucrose flotation is used, diagnosis of infection by faecal examination requires concentrating the ova present in feces by sedimentation rather than flotation. Once identified in faecal sediment by the characteristic opercula, eggs of the different trematode species can be further differentiated by morphologic characteristics, including size. Identification of isolated mesocercariae was confirmed by PCR . The diagnosis was made by lung biopsy and confirmed at autops.
Treatment
Although albendazole has been reported to be effective in treating trematodes in dogs and cats, its use in small animals is not recommended because of potential associated side effects such as bone marrow toxicity. Tetracyclines are considered by many to be the treatment of choice.
Prevention
Zoonotic risk for A. alata infection through ingestion of cat meat is probably minimal in Europe but may be important in Asia and South America, the awareness needed where cats are occasionally consumed.
Acanthoparyphium species.
The genus Acanthoparyphium (Digenea: Echinostomatidae) is a group of minute intestinal trematodes which parasitize the small intestine of aquatic birds in marine areas of the Republic of Korea, Japan, USA, the Philippines, Kuwait, India, Puerto Rico, and Australia. Brackish water gastropods, bivalves, or oysters play the role of a first or second intermediate host, or both. A. tyosenense is the only known species belonging to Acanthoparyphium. It has been suggested that human infections with A. tyosenense were contracted by consumption of the raw flesh of intertidal bivalves, including M. veneriformi. The prevalence of A. tyosenense metacercariae was 99.5% in naturally infected.
Larval stages develop in the hepatopancreas of prosobranch snails and encyst as metacercariae in the same snail or in lamellibranchs. One- to 3-day-old juveniles and 10-day-old adults were harvested from chicks experimentally fed metacercariae from a bivalve, Mactra veneriformis. The juvenile worms were minute, curved ventrally, and had 23 collar spines characteristically arranged in a single row. The lips of the oral sucker had 7 single a ciliated sensory papillae and 4 grouped uniciliated sensory papillae. The ventral sucker had 25 a ciliated round swellings on its lip. The anterolateral surface between the 2 suckers was densely packed with tongue-shaped tegumental spines, and the ventral surface just posterior to the ventral sucker was covered with peg-like spines. Retractile, peg-like spines were seen on the anterolateral surface, whereas scale-like spines with round tips and broad bases were sparsely distributed posterior to the ventral sucker. The cirrus was characteristically protruding and armed with minute spines.
Life cycle
The natural definitive hosts of Acanthoparyphium are always aquatic birds, and the majority of them are migratory; some of them, like plovers, godwits, knots, and dotterels fly from Siberia to southern Australia. The second intermediate hosts of Acanthoparyphium species have been identified as intertidal mollusks, snails, and oysters. Among the human-infecting echinostomatid flukes, Adult trematodes are generally parasitic in the digestive tract of aquatic birds. Body elongated, tapering anteriorly, and rather elliptical at the posterior end. Five hours after infection, the cercariae tails began to separate from the bodies, and the cercariae formed cysts. Mature cysts were formed (14 days) after infection and identified as the metacercariae of A. tyosenense.
Pathogenesis
Adult Acanthoparyphium species attach to the jejunal mucosa and may provoke an inflammatory response.
Clinical manifestation
Symptoms are variable. Some patients are asymptomatic but those with heavy worm burdens may complain vague abdominal pain and diarrhoea.
Laboratory diagnosis
Diagnosis is done by the detection of eggs in the faces, the eggs are similar to that of F. hepatica and F.buski though smaller in size.
The specific diagnosis can be made only on the recovery of adult parasites. The tegumental ultrastructure of juvenile and adult Acanthoparyphium tyosenense (Digenea: Echinostomatidae) was observed by scanning electron microscopy. The surface ultrastructure of A. tyosenense was unique, especially in the number and arrangement of collar spines, shape, and distribution of tegumental spines and in distribution of sensory papillae.
Treatment
Single administrations of praziquantel in doses of up to 20 mg/kg have been reported to be effective in small numbers of patients infected
Prevention and control
Avoidance of eating raw snails will prevent transmission of infection in man.
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