6io 



CESTOIDEA 



Hymenolepis (Hymenolepis) nana von Siebold, 1852. 



Synonyms. — -Tcenia murina Dujardin, 1845, nec Gmelin, 1790; 

 T. nana von Siebold, 1852, nec van Beneden, 1867; T. cegyptiaca 

 Bilharz, 1852; Diplacanthus nanus Weinland, 1858. 



This is the dwarf tapeworm of man, and was discovered by 

 Bilharz in the ileum of a boy who died of meningitis in Cairo. It 

 is found in Egypt, Europe, North and South America, Siam, and 

 Japan, and is by no means a rare parasite in man. Calandruccio 

 estimates that lu per cent, of the children in Sicily are affected. Stiles 

 reports 4-8 per cent, for 125 children in Washington. The number 

 found varies from one or two to several thousands in one individual. 



There is doubt as to whether this worm is or is not identical with 

 Hymenolepis nana var.fraterna Stiles, 1906, which is common in rats 

 and mice. Probably it is distinct from this parasite, because Grassi 

 and Looss were unable to transmit it to mice. 



Morphology. — ^It is the smallest tapeworm in man, measuring 

 only 10 to 15 millimetres in length, and from 0-5 to 0-7 millimetre 

 in breadth. 



The head is globular, and provided with a rostellum with one ring 

 of twenty-four to thirty hooks, which are very small, 14 to 18 /j, in 

 length. The neck is relatively long. * 



There are about 150 proglottides, 0-4 to 0-9 millimetre in breadth 

 and 0-014 to 0-030 millimetre in length. The genital pore is 

 marginal. The mature uterus contains about thirty or more eggs, 

 which are oval, and measure 30 to 48 p,, and contain onchospheres 

 measuring 16 to 19 fj, in diameter. 



Life-History. — It is believed that the cysticercus will be found in 

 some insect. 



The nearly related T. nana var.fraterna completes its development 

 entirely in the rat, for the cysticercus develops in the villus, while 

 the adult lies in the lumen of the intestine. 



Pathogenicity. — Owing to its small size it is apt to be overlooked, 

 but there is no doubt that it spreads in crowded institutions and 

 poorer families. Apparently, when the parasite occurs in small 

 numbers no symptoms result, but in considerable numbers dis- 

 turbance may occur, which has been assigned by Mingazzini to the 

 effects of toxins. 



Treatment. — Male-fern is the best treatment (w^?^ Chapter LXXV.). 



Prophylaxis. — While it is doubtful whether T. nana and T. nana 

 var. fraterna are the same or different species, it will be necessary to 

 guard against the contamination of food by rats and mice. More- 

 over, it must be remembered that the infection spreads in crowded 

 dwellings, and therefore isolation of the infected^child should be 

 insisted upon, 



Subgenus 2. Drepanidotsenia Railliet, 1892. 



With the characters of the genus, but the hooks have a dorsal root much 

 larger than the ventral, and are only eight to twenty in number. -Proglottis 

 broad, testes three, alongside which lies female genitalia. 



