In 1928 Curt demonstrated that non-human schistosome cercariae are capable of producing dermatitis in man. Since then many species of avian and mammalian schistosomes have been shown to produce similar disease in different parts of the world. In 1958 a kind of schistosome dermatitis locally known as 'Ya-Mu-Lan' (meaning duck-saliva-disease) was discovered in Foochow, Fukien Province. The infection occurred among farmers who waded in canals and ditches, while taking care of ducks in their natural environment. The same dermatitis was reported from Yung-siao district bordering Kwangtung. In Szechwan a similar disease was reported by T. C. Pap (1957) where it was known as 'Ya-Si-Feng' (meaning duck-feces-disease). From the endemic area in Foochow, 10, 145 snails belong to the species Lymnaea (Radix) plicatula Benson were examined and a kind of ocellated fork-tailed cercaria was discovered. Another closely related snail, Lymnaea (Fossaria) ollula Gould was also found infected but the incidence of infection was somewhat lower. Experiments were conducted to infect laboratory reared ducklings and full grown ducks, the feces of which were examined to be free from schistosome eggs. Ten to twelve days later edult worms were recovered in the mesenteric and portal veins and a few specimens were found in the lungs and heart. Lymnaea (Radix) plicatula were also experimentally infected with miracidia hatching out from eggs secured from the infected duck.Studies on the morphology of both the adult worms and the developmental larval stages were made and the details are reported in the present communication.Our observation indicates that the worm belongs to a species of Trichobilharzia different from any other known species. The name Trichobilharzia paoi sp. nov. is proposed after Prof. T. C. Pap of Chungking Medical College, Szechwan.Description of the adult worm:Male: Body slender, total length 5.35-7.31mm. width 0.076-0.095mm. Oral sucker measures 0.051-0.060ram×0.043-0.060mm in diameter. Ventral sucker, the surface of which is armed with small spines, measures 0.051-0.060mm in diameter. Oesophagus. bifurcates anterior to the ventral sucker at a distance about anterior two-thirds between oral sucker and acetabulum. Intestinal caeca iun posteriorly on two sides and reunite behind the gynaecophoric canal, which is a longitudinal slit 0.237-0.380mm in length and 0.123-0.152mm in width. Gynaecophoric canal is foimed by inward folding of two lateral sides of the body bearing numerous spines. Testes round, 70-90 in number arranged in a single longitudinal row. Their diameter ranges 0.051-0.064mm. Seminal vesicle occupies an area from a level immediately posterior to the ventral sucker to the fore margin of gyneacophoric canal. It measures 0.172-0.447mm in length and 0.038-0.055mm in width.Female: More delicate than male, length 3.38-4.89mm, greatest width 0.076-0.114mm. Oral sucker terminal with mouth openning on its ventral aspect, diameter 0.051-0.056mm×0.038-0.051mm. Ventral sucker, a small solid organ, measures 0.030-0.040mm×0.035-0.043mm in diameter. Oesophagus bifurcates at some distance before the acetabulum. Intestinal ceaca reunite behind the ovary, forming a single caecum passing to near the posterior end of body. Ovary spiral in shape with a length 0.253-0.352mm and a width 0.021-0.025mm. Seminal receptacle elongated in form, is connected to the ovary on its posterior aspect. A Laurer's canal is present. It originates from Seminal receptacle and opens to the exterior. The oviduct starts from the ovary, runs parallel with the vitalline duct to the anterior of ovary, where they unite together forming the ootype, surrounded on all sides by a cluster of unicellular Mehlis glands. The uterus is short and contains only one egg. Female genital pore is immediately postacetabular. Egg is spindle or elongate oval in shape with a sharp curved spine at one end. Egg measures 0.236-0.316mm×0.068-0.112mm. Avian schistosomes parasitising domestic and wild ducks and other birds belong to the subfamily Bilharziellinae Price, 1929, and family Schistosomatidae Looss, 1899. They were formerly considered to belong to two genera, namely Pseudobilharxiella Eismont, 1929 and Trichobilharzia Skrjabin and Zkharow, 1920. Yamaguti (1958) consideted Pseudobilharziella to be the synonym of Trichobilharzia and listed 22 species in his "Systema helminthum". Recent additions of some new species made up the total of about 25 species. In comparing the structure, it is found that the Chinese species belongs to those duck schistosomes with spindle-shaped eggs. Among them the most closely related is T. yokogawai (Oiso, 1927), from which it differs in several important aspects, such as the size of the worm, the extent of gynaecophoric canal, number of testes and size of eggs. Their different characters are tabulated as follows:T. yokogawai T. paoi n. sp. Male Body length 2.0-2.75mm 5.35-7.31mm (Foochow specimen)average 2.336mm 4.0-10.3mm (Chungking specimen) Position of immediately behind 0.371-0.495mm behind gynaecophoric Acetabulum acetabulum (Foochow specimen) canal 0.35-0.57mm behindacetabulum (Chungking specimen) T. yokogawai T. paoi n. spLength of 0.2mm 0.247-038mm (Foochow specimen)gynaecophoric 0.35-0.41mm (Chungking specimen)canalNumber of 50-70 70-90 (Foochow specimen)testes 50-85 (Chungking specimen)Size of eggs Length 0.204-0.238mm 0.236-0.316mmWidth 0.051-0.068mm 0.068-0.112mm (Foochow specimen)0.215mm0.075mm (Chungking specimen)From the above table it can be noticed that these two species can be distinguished by these essential differences.T. paoi is, furthermore, differentiated from T. physellae, another closely related species by the number of testes, which is about 210-240 in the latter and are arranged in two to three rows. Tanaka (1960) reported another duck schistosome from Oki Island, which he identified as T. physellae. According to this auther, the male has only 52-78 testes, the seminal vesicle is much shorter reaching only about half distance between gyaaecophoric canal and the acetabulum. Another striking difference is that the intestinal ceaca of T. physellae from Oki Island reunite at the region anterior to the seminal vesicle, while in T. paoi they reunite behind the Seminal receptacle at the level anterior to the gynaecophoric canal.Macfarlane (1944, 1949) and Olivier (1949) have shown that the dermatitis produced by avian schistosomes is a sensitization phenomenon. They have demonstrated striking differences in the reaction of skin of infected animals to the penetration of cercariae in the initial and subsequent infections, and presented evidence for the ideathat human cases also become increasingly allergic to the protein of invading schistosome cercariae. In order to make further inquiries on this problem and to investigate whether Chinese species of Trichobilharzia will induce similar reactions in the mammalean host, experiments were conducted to infect laboratory-reared white mice and biopsies made of the skin in the first and also after a series of repeated infections It is with the purpese to observe the behavior of the cercariae after having penetrated into the body of an abnormal host, and to trace the course of their migration and destiny.1. Tissue reaction in primary infection: Histological sections were made on biopsies on various intervals after infection, one and half hour, 3 hours, 5 hours, 8 hours, 21 hours etc. At one and half to three hours after exposure, the cercariae already penetrated the epidermis. Some of them were in the hair follicles. A few arrived at the corium. Those just penetrated Corneum stratum were found lying there horizontally, and usually there was a small tunnel or cavity, formed among the epithelial cells, surrounding each cercaria. Such phenomenon is similar to that as observed by Gordon and Griffiths (1951) on the behavior of the cercaria of Schistosoma mansoni. Olivier and Weinstein (1953) also observed the same in Trichobilharzia ocellata. During early hours of invasion there was apparently very little cellular response to the cercariae. Those, which invaded the corium, were surrounded by a small number of leucocytes. Apparently the cercariae were still in good condition. They were probably living at the time of biopsy as indicated by their intact cell structure being well stained, 21 hours after infection, the tissue shows more infiltration of white cells and histiocytes. More of them gathered around the cercariae, some of which appeared as having signs of histolysis, while others seem still quite normal. Observations made on tissues fixed at later hours after infection indicated that even in the primary exposure, great majority of the invading cercariae were already arrested and immobilized in the epidermis and not able to invade further into the body.A small part of the cercariae, however, were found to migrate to the lung tissue. They were evidently being carried by the blood stream to the new site, where they produced considerable tissue damage and hemmorrhage. In our experiments with mice infected 20 hours previously, petechial hemorrhages were present on the surface of the lung. Infection experiments were conducted on 19 mice, each of which was infected with 80 to 250 cercariae. Dissections of the animals were made at various intervals from one day to about a month since exposure. The largest number of worms and hemorrhagic spots were found on the lung tissue during the second and third day after infection. Of the 19 mice, 15 were found to show pulmonary lesions. The number for each mouse ranges from one to 86. From eleven of them, worms were recovered from the tissue and from each mouse from one to 15 worms were counted. When the dissections were made during the first three days, the worms were still living. As time elasped, only formation of nodules were found. Sectioned nodules contained worms which were either dead or moribund.2. Tissue reaction in repeated infections: A
