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An Introduction to Medical Entomology

For educational purposes. 

 

PENTASTOMIDA

Tongue Worms

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       The Tongue Worms have been assigned to a variety of taxa, but this section places them as a subgroup of the Crustacea.  Adult worms are elongated cylindrical or flattened with no legs (Armillifer armillatus).  Their external appearance suggests rings, which are not segments.  Their mouth has an armature that occurs before, behind or between a pair of hollowed hooks (see xxxx).  The head, thorax and abdomen are not separated, and the males are smaller than the females.  At the anterior end the hooks are conspicuous when not retracted.  Internally their structure is simple.  Behind the mouth the pharynx has muscles that serve for sucking fluids.  Circulatory or respiratory organs are absent, and the nervous system is vestigial.  Most organs may serve for reproduction.

 

       Of the two orders the Cephalobaenida have mouth hooks situated on narrow extensions or swellings of the body posterior to the mouth, whereas in the Porocephalida hooks are arranged on each side of the mouth.

 

       The Life Cycle is complex.  The larval and nymphal stages occur on one host while the adults are on another.  For example, Linguatula serrata adults occur in the nasal passages and sinuses of dogs and humans, where they suck blood.  This results in severe bleeding.  The parasite eggs are released in the mucus and infect the surrounding environment of water or vegetation.  If animals or humans consume the eggs the larvae hatch and migrate through the intestinal walls and finally locate in the liver or other organs where nymphs develop.  A larva that becomes encapsulated in host tissue then follows this, and nymphal development continues.  Nymphs mature in 5-6 months and by then they have two pairs of hooks (4-6 mm long).  Nymphs may live within cysts for 2-3 years.  Then if raw meat is consumed the nymphs access the nasal passages where they mature.  The disease in humans is referred to as "Porocephaliasis."  The severity of this disease in humans depends on how many nymphs are present.  In America infections are not common, probably because raw meat is not often consumed.

 

       Tongue worms are especially common among Europeans, and in Africa Armillifer armillatus is the species most found both in humans and wild animals, such as snakes and monkeys.  The inhabitants of some parts of Africa that consume "bush meat" are often infected.  In South America a principal problem species is Porocephalus clavatus whose alternate hosts are snakes.

 

  Key References:     <medvet.ref.htm>

 

     Matheson, R. 1950.  Medical Entomology.  Comstock Publ. Co, Inc.  610 p.

      Service, M.  2008.  Medical Entomology For Students.  Cambridge Univ. Press.  289 p