Alaria alata
General Information
- 1.
Name: Latin: ala = wing; alaris = belonging to the wing.
- 2.
Geographic distribution/epidemiology: Worldwide, especially in regions with wild dogs, foxes, wolves, and martens. Prevalences of Alaria species in dogs in the USA (A. canis, A. americana) and in foxes in Germany are up to 30 %.
- 3.
Morphology/life cycle: The life cycle is diagrammatically represented in Fig. 1. It runs similarly in the different species: A. canis (syn. A. americana), A. mustelae (marten), and A. marcianae (cats). The hermaphroditic adult worms, which belong to the digenetic trematodes of the family Diplostomatidae, reach a size of 2.5–6 mm × 0.5–2 mm and live in the intestine mainly of wild canids. Their brownish eggs, which measure 98–125 μm × 62–81 μm, possess an operculum, but do not contain a miracidium, when they are excreted in feces. The latter develops inside the egg outside of its host, when the egg reached water. Two intermediate host types become involved as can be seen in Fig. 1.
- 4.
Symptoms of disease: Depending on the number of parasites in a host, an infection may run symptomless, whereas heavy infections may lead to catarrhal enteritis or even as a consequence to death of the final host. Since pigs and wild boars as well as humans may become infected, too, they also may suffer from symptoms of disease. They become paratenic hosts in case they ingest mesocercariae of A. alata within tissues of one of the second intermediate hosts (Fig. 1).
- 5.
Diagnosis: Coproscopic investigation after use of SAFC, MIFC, or flotation techniques for concentration of eggs within feces is the method of choice.
- 6.
Infection: Final hosts (i.e., canids) become infested when ingesting infected intermediate hosts of the second type (Fig. 1). In the USA, raccoons were also found to act as intermediate hosts (Fig. 2).
- 7.
Prophylaxis: Domestic dogs or other canids should not be fed with raw meat from wild animals.
- 8.
Incubation period: 4–6 weeks.
- 9.
Prepatent period: 19–21 days.
- 10.
Patency: Years.
- 11.Treatment: Praziquantel (5 mg/kg bodyweight, 1× oral application).Alaria alata, Fig. 1
Life cycle of Alaria canis (A. americana). 1 The adults (2.5–4,2 mm long) live in the anterior third of the small intestine of the final hosts (canids). 2 The operculate eggs are unembryonated when laid. 3 Larvae (miracidia) hatch in about 2 weeks after reaching water. 4 Miracidia swim actively and enter several species of helisomid snail (first intermediate host), inside which mother sporocyst and daughter sporocyst are produced. The latter gives rise to cercariae. 5 The furcocercous cercariae leave the snail during daylight hours and swim to the water surface, where they hang upside down. 6 If tadpoles (as intermediate hosts of the second type) pass by, the cercariae penetrate the skin. In about 2 weeks, the cercariae become transformed into mesocercariae (6.1, 6.2 show surface view). 7–9 2 weeks after infection, the mesocercariae are infectious for a series of paratenic hosts or directly for the final host (canids) if this host ingests an infected tadpole (or an adult frog after its metamorphosis). Inside the paratenic host, the mesocercariae are accumulated (8) in various tissues without further development. Large numbers of mesocercariae are very pathogenic for their hosts. If humans become accidentally infected, severe damage or death may occur. Mesocercariae which have reached the intestine of the final host penetrate into the body cavity and pass through the diaphragm into the lungs by the end of 2–3 weeks. Here, they transform into diplostomula (metacercariae) in about 5–6 weeks. The diplostomula migrate up the trachea and are finally swallowed. Inside the intestine, they mature in about 4 weeks and cause severe enteritis. FB forebody, FT forked tail, GP genital pore, HB hindbody, HF holdfast organ, IN intestine, OP operculum, OS oral sucker, OV ovary, PH pharynx, TE testis, UT uterus with eggs, VI vitellarium, VS ventral sucker
Alaria alata, Fig. 2Lightmicroscopic picture of an adult worm of Alaria sp.
Further Reading
- Möhlk et al (2009) Biology of Alaria spp. and human exposition risk to Alaria mesocercariae – a review. Parasitol Res 105:1–15CrossRefGoogle Scholar
- Portier J et al (2011) New data on the trematode Alaria alata (Goeze 1792) obtained during Trichinella inspections. Parasite 18:271–275PubMedPubMedCentralCrossRefGoogle Scholar
- Ríehn et al (2011) Development of a PCR approach for differentiation of Alaria spp. mesocercariae. Parasitol Res 108:1327–1332PubMedCrossRefGoogle Scholar