Cestode Development Research in China: A Review

Adult cestode is parasitic in the intestine of the vertebrate and/or Human being. It contains a series of parasites in the world. The taxonomy position of the parasites is as follows: Platyhelminthes, Cestoda. Cestodes parasitic in human and vertebrates can cause parasitic diseases. Chinese ancestors in Tang dynasty had already concerned about this. Chao Yuanfang recorded that “... the worm is an inch in length with white colour...” [“Discussion of disesase origins”, 610 A.D. From Zhao,1983] and it is infected by eating the beef that roasted by porking with mulberry twigs. So we can see that the Chinese ancestors had cestode knowledge very earlier. The little problem is that ancestors took the gravid proglottids as the whole worm and had no complete idea about this worm, nor had the lifehistory recognition. The report and research work of cestodes are just modern history and the work is a little later than foreign scientists.

Infection experiments show that Mesocyclops leuckartii Claus and Thermocyclops hyalinus (Rehberg) can serve as intermediate host of the cestodes. These 2 species of cyclops were put in the dish with the coracidium and coracidium were eaten. The hexacanth pierced into the body cavity of the cyclops and developed into a spherical larva then become narrow. 15 days later there comes a tail of the worm, 18 days later it turned to procercoid (Plate 1:  as the mature larva of the worm at the temperature of 21-23°C. Procercoid larva measured 0.40x0.18 mm in the body, and 0.24x0.07 mm for tail. The front of the body swollened with a pit, following part is narrow and slender, penetrated glands are spherical with bulbed neucleus.
After 18 days of development the procercoid become mature, measured 067×0.16 mm for the body, 0.34×0.08 mm for tail. At this time the excretory system is much more obvious. collecting pipes were 4 longitudinal ducts with small cross discharging ducts at the first 1/5 of the body. It may become the discharge ducts of the adult cestode scolex. Ducts of the tail is not clear, only 4 flamming cells. 8 pairs of granula glands and buddles of tunnels are still there. Procercoid can survive for 30 days in a cyclops by experiment observation.
Final host infection: 15 M. albus from a negative area were used as infection plan. They were fed with cyclops infected with cestode for 18 day, dissected the M. albus after 3 days of infection and a 0.53 mm worm were found with 2 and a half cycles of hooks, but it is just a little for each hook. 7 days after infection, 3 mature worms with 50 more hooks in the scolex were found. The whole life cycle is now completed.

The development process of Ophiotaenia monnigi in the copepods is as follows (Cheng, Wu et Lin, 2008)
Experimental animals: Copepods (C. leuckarti and C. prasinus) were obtained from ponds and ditches in Fuzhou with dredging nets. Snakes, Enhydris plumbae, were bought from Markets. The research was carried out in the laboratory on September in southern China.
The freshwater snakes, E. plumbae, were dissected. After the cestodes were collected, their gravid proglottids were torn into very small pieces to release the eggs if mature tapeworms were found. Then, the pieces of the gravid proglottids were cultivated with water for 4-10 days and fed to the copepods. In the cultivation processes, water should be changed everyday, otherwise the eggs would be poisoned by their metabolites. To make the copepods take in more eggs, it is necessary to stop feeding the copepods for 24 h before they were fed with the pieces of the tapeworm.
Copepods were dissected after they were fed with eggs 1, 3, 6, 8, and 11 days according to the development speed of the tapeworm's larvae, the procercoid, in their host. Shapes of the larva of different stages were drawn under the microscope (Olympus) (measurement unit is μm).
The tapeworms obtained by the authors were identified as O. monnigi Fuhrmann, 1924. Furthermore, no more species of cestodes parasitizing the same host, the water snake (E. plumbae), were found. During the experiment the temperature is around 28°C.
1. One day after infection: Hexacanths with a diameter of 0.020 μm in the eggs developed into procercoid larvae with a size of 0.027 x 0.039, and the hooks became dispersing. Embryonic cells increased apparently and were larger than those in the hexacanths (Plate 2: Figs. 1, 2). 2. Three days after infection: There appeared two parts in the procercoids. Hooks were in the larger part, which became the cercomere (tail) gradually and came off in the future. Embryonic cells luxuriantly developed, where the larger ones measured 0.010 x 0.008 and the smaller only 0.005 in diameter. The procercoid measured 0.024 x 0.020 and 0.037 x 0.029 in C. prasinus and C. leuckarti respectively, and the embryonic cells developed slower in the former host. The following description is based on the development of procercoid larvae in C. leuckarti (Plate 2: Fig. 3). 3. Five days after infection: Procercoids measured 0.041-0.082 x 0.059-0.100. An embryonic coelom, which measured as 0.019-0.063 x 0.011-0.045, appeared. In front of the coelom, embryonic cells were densely gathered; of the cells, there were four that contain a lot of granules looking like glands. Hooks were around the later edge of the embryonic coelom (Plate 2: Fig. 4). 4. Six days after infection: Procercoids were divided into body and tail parts, measuring 0.085 x 0.137 and 0.056 x 0.059, respectively. In the body part of the procercoid larvae, there was a primary apical sucker of the tapeworm (Plate 2: Fig. 5). 5. Eight days after infection: Procercoids were the same shape as that described above.
Two pairs of gland cells, whose tubules reach the front edge of the worm through the apical sucker, appeared behind the sucker. Large dark cells could be seen in the center of the body. About ten calcareous granules were in the body. The tail part was spherical and had a transparent coelom. Cells in the tail were soft and transparent. The sizes of the worm were: the body 0.096 x 0.241, the cercomere, 0.059 x 0.052 (Plate 2: Fig. 6).
Explanation to Plate 2. 1. Mature egg with a hexacanth 2. Procercoid developed after 1 day in Cyclops leuckarti 3. Procercoid of 3 days after infection 4. Procercoid of 5 days after infection 5. Procercoid of 6 days after infection 6. Procercoid of 8 days after infection 7. A mature procercoid in the copepod, Cyclops leuckarti; the cercmere had come off.
6. Eleven days after infection: Most procercoids became oval mature larvae whose cercomere dropped in the copepods. There were crowded fibers on the surface of the worm. An apical sucker was in front of the procercoid. Two pairs of gland cells were behind the sucker. Some cell might be the primitive embryonic cells that will develop in the next host. The worm measured 0.195 × 0.112, while the apical sucker is 0.091 in diameter. In a high density of infected copepods, ten mature and one immature larvae with a cercomere were found. In general, three to four procercoids were parasitizing in one copepod (Plate 2: Fig. 7).

Chicken and duckcestode lifecycle (Su et Lin, 1987)
During 1981~1984,a total of 250 ducks and geese were examined in Xiamen,Fujian. and Diochis stefanskii were also studied, and the specific characters of each stage of larvae, especially their cysticercoids, were carefully studied and compared. It was revealed that they had a general pattern in the course of their oncogenesis. The process of larval growth can be divided into five stages: a.oncosphere stage,b.lacuna stage, c. cysticavity stage, d.scolex formation stage,and e.cysticercoid stage. Based on their observations, the features of these hymenolepidae cysticercoids, including the shape and size of cysticercoid, the cystic wall and fibrous membrane, the shape, size and number of rostellar hooks etc. can be identified as the specific diagnostic characters of species.Take H. venusta as an example to explain the development process of these cestodes.
Egg of H. venusta is with a feeble, transparent shell, roundish, 51-61×39-46μm, with a oval out embryomembrane, then innermembrane which enclosed the hexacanth.The intermediate host of the cestode is freshwater Heterocypris sp.The egg can developed into a cysticercoid in 11 days at the temperature of 26-30°C (average, 28°C) after infected with its host. At least 15 days is needed to become whole mature cysticercoid which is infective. 5 development stages can be seen in the whole developmental course.
1. stage of hexacanth (Plate 3: Fig 2-4). After 24 hours the egg is taken by its host (it is called infection, thereafter), the hexacanth can get through the gut and enter the body cavity of Heterocypris sp. It takes 2-3 days for the development of this stage. The worm is roundish or oval, with a diameter of 20-50μm. Sometimes the worms moved like an amoeba. The measurement for cells in it is variously changed but the cells' membrane and nucleus are very clear. The 6 hooks become to leave their position and arranged irregularly. 2. Lacunna stage (Plate 3: Fig 5-8). 4-6 days after infection hexacanth becomes bigger, 60-180μm. A transparent cavity comes out in the center of the worm and it is the primitive cavity. It increased with the growth of the worm, and become a ball body with empty center. The 6 hooks arranged in surface of the cavity, arranged irregularly. The characteristics of the stage are the worm growing fast and the primitive cavity formation. 3. cysticcavity stage (Plate 3: Fig 9). From 5 to 8 days after infection, the growth of the worm toward to 2 ends. The first part of the worm grows more fast with quite often cell division and become sturdy tissue then comes a cavity called cysticavity. Another part of the worm with little growth and showed sag states, the hooks and the primitive cavity stay there. So the worm can be divided into 2 parts, and 2 cavities at this time. In the beginning the two cavities are communicating with each other, after development, the primitive cavity with hooks is blocked with cells and it becomes the tail part of the worm. The first part of the worm developed well with fast cell division and form the organs of suckers, and rostellum etc. The length of worm is 250-330μm.  Fig 10-11). 9 days after infection the worm comes to this stage. In front of the worm there comes the scolex, then in the middle there is the roundish or oval cavity body, after then there is a slender tail part. 4 oval suckers can be seen in the scolex, then rostellum come into being, then hooks come at the top of the rostellum. After the scolex the neck present, there are many calcium carbonate granules. At the center of the cavity body part there is the cavity and it connected with the neck at the front. The cavity wall is composed of several layer of cells arranged tidily. The tail part is slender and with 6 hooks. Sometimes the primitive cavity still can be seen in the tail. The measurement of the worm at the time is as follows: scolex width,90-110μm; suckers, 40-50x70-72μm; cavity body width, 130-200μm; tail length, 300-400μm; rostellum 50-60μm; hooks, 14-15μm. 5. cysticercoid stage (Plate 3: Fig 12). After 11 days of infection the scolex of the worm retracted into the cavity body part and the cysticercoid is formed. It is not infective unless after 15 day of infection it becomes mature enough. The mature cysticercoid 210-237x187-205μm, is composed of three layers of body wall. Outside it is transparent cuticle, 3-5μm; the middle layer is composed of soft cells with one line of mast cells and several lines of round cells, 3.5-18μm; inner layer is with fibers, 9-15μm. The scolex is retracted in the cavity, 4 suckers, 62-64x77-81μm. Outside the rostellum there is a rostellum sac. At the top of rostellum there are 8 hooks, 39-42μm. Calcium carbonate granules ever at the neck is now around the scolex. The tail, 300-400μm. With the developedment of the worm to mature calcium carbonate granules increased with those fibers and the cysticercoid become more and more infective.
Other 4 species of cestode developed in the same course mainly but with different host, egg, development time as well as characteristics. 1. Materials and Method: a. Selection of the pregnant segments: take few of the pregnant proglottids to dissect and release the eggs and observe under microscopes. To prove them is full mature by that the embryo is developed enough with quite active hexacanth. And take 5-10 pregnant proglottids to do the experiment. The pregnant segments from feces of Marmorta himalayana can also be used to infect the mites. b. Collection, isolation and feed with soil mites. Same as Lin Yuguang (1962Yuguang ( ,1975 (Fig 1:12