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Which Fluke Eggs Have Shoulders?

Flukes, or trematodes, are parasitic flatworms that infect the blood, lungs, liver or intestines of vertebrates. A common method of diagnosing an infection is the identification of fluke eggs in the victim's stool. Whether the fluke egg has "shoulders" or not is a sign to use in identification. While there are many species of flukes, each of which infects a different part of the body, only a few species commonly infect humans.

  1. Liver Flukes

    • Fasciola hepatica is the primary species of fluke to infect the bile ducts of human livers. They live on watercress, water chestnuts and other water plants. Their eggs are oval with thin shells and no shoulders. Clonorchis sinensis, known as the Chinese Liver Fluke, also infects the liver, but it is contracted through eating undercooked freshwater fish. Though symptoms and complications are similar for both varieties of liver fluke, Clonorchis sinensis are smaller, with very prominent shoulders. Opisthorchis viverrini, a species of liver fluke primarily from Thailand, also has a very prominent shoulder.

    Lung Flukes

    • The fluke that most commonly infects human lungs is Paragonimus westermani. P. westermani eggs are asymmetrical, with thick shells and shoulders. This fluke is usually caught by eating infected crustaceans; in very rare cases it can migrate to the brain, causing seizures and possibly fatal inflammation.

    Intestinal Flukes

    • The most common intestinal fluke to infect humans is Fasciolopsis buski, which is found mainly in East Asia. In life cycle and physical characteristics it is very similar to F. hepatica, and they are both contracted through eating infected water plants. Like F. hepatica, the eggs of this species are large and oval, with thin shells and no shoulders. However, there are other species of intestinal flukes that do have shoulders, including Heterophyes heterophyes and Metagonimus yokogawai, both of which live primarily in the Far East, have prominent shoulders, and infect the small intestine.

    Blood Flukes

    • The Schistosomes include all species of trematodes that infect the blood stream, and they are the only types of flukes that have separate sexes. Though there are several others, the most common three species of blood fluke to infect humans are Schistosoma haematobium, S. mansoni and S. japonicum. No Schistosome eggs have shoulders, though all have distinct spines that distinguish them from other types of fluke eggs.

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