TRICHOCEPHALIASIS. 557 



The ova are barrel-shaped and are characterized, as are those of Trichosoma, by 

 the little colorless plug which closes each end of the brownish shell. 



Habitat. — The caecum and, less frequently, the colon and ileum of certain 

 mammals. 



Several species of Trichuris are recognized for different hosts, namely, Trichuris 

 trichiura of man and apes ; T. affimis of sheep, goats, and cattle ; T. depressinsculus 

 of the dog and fox; T. unginculatus of the rabbit; T. crenatus of the pig. These 

 species are distinguished morphologically chiefly by the size and structure of 

 the spicule and its sheath. 



Trichuris trichiura (Linnaeus, 1761). 



Male, 40 to 45 millimeters long; spicule, 2.5 millimeters long; sheath covered 

 with small, evenly distributed papillae. Female 40 to 50 millimeters long, length 

 of slender anterior portion to length of thick posterior portion as 3 to 2. Mouth 

 opening simple and with appendages. Ova yellow to brown, 50 to 54 millimeters 

 long by 23 millimeters broad; unsegmented in fresh faeces. 



Habitat. — Caecum and, less frequently, colon and ileum of man, apes, and the 

 lemur. 



Development. — Simple, without intermediate host. Embryo develops in water 

 or moist earth in from 3 to 6 months or longer and will remain alive in its shell 

 for several years unless ingested by its final host when it hatches and reaches 

 sexual maturity in the caecum after about 16 days. 



The resistance to the action of physical and chemical agents shown by both 

 the parent and eggs is remarkable. The parasite is the most difficult of any to 

 destroy in the intestine. The ordinary anthelmintics as a rule have little or no 

 effect upon it. The eggs may be frozen or completely dried without doing them 

 permanent injury. 



Modes of transmission. — Direct: Inasmuch as an intermediate host is not 

 necessary for the propagation of this parasite, and inasmuch as contact with faecal 

 discharges is necessary in order to receive the eggs into the gastro-intestinal canal, 

 infection proves a closer personal contact with filth than is true of many other 

 parasitic infections. However, because of the slow development of the eggs under 

 outside influences, immediate transmission from person to person or auto-reinfection 

 can not occur. 



Water when contaminated with faecal discharges, directly or indirectly, may 

 become a transmitter of infection, but because of the rapidity with which the 

 eggs are sedimented in water, it would seem as if this were a much less important 

 medium of transmission than it is generally considered to be. 



Food, particularly uncooked vegetables, and to a less extent, fruits, are un- 

 doubtedly a means of transmission in a considerable number of instances. On two 

 occasions during our study of the washing from fresh vegetables for the presence 

 of amoebae, ova of Trichuris were found in the sedimented material. The danger 

 from fresh vegetables is great in those countries where human faeces are used 

 as fertilizer for the vegetable gardens. Although this procedure is a violation of 

 the law, it is certainly practiced to a considerable extent by Chinese gardeners 

 in the Philippines, as it is in several other oriental countries. 



Insects, such as flies, water bugs, roaches, etc., may be factors of some impor- 

 tance as transmitters of the infection by mechanically carrying it from infected 

 faeces to food and water supplies. 



Soil, in localities where methods of sewage disposal are primitive, surely 

 becomes infected and because of the great viability of the eggs in earth, such places 

 become a menace in many obvious ways. So-called clay eaters would be especially 

 liable to infection. 



