Baghiatollah University of Medical Sciences, Department of Anatomy, and Iran University of Medical Sciences, Tehran, Iran.
Ascaris Lumbricoides is the largest of the common nematode parasites of the human digestive system. It has a world-wide distribution and is very common in regions with poor sanitation. Because of this association with man, Ascaris' impact on human health is taught in medical institutions around the world. Different techniques are used to prepare Ascaris for educational purposes in medical colleges. One method is immersion and storage of the nemotode specimens in formaldehyde. A second less common method is preservation in alcohol. Histological cross sections are also utilized in some teaching laboratories . The disadvantages to teaching with specimens stored in formaldehyde or alcohol is that they are wet and these solutions are associated with noxious odors and potential health problems in humans. Additionally, specimens stored in formaldehyde or alcohol often present problems in transportation for use outside institutions . The disadvantage of histologic specimens is their limitation in scope. The purpose of this study was to perform plastination of Ascaris Lumbricoides specimens using the S10 technique. This procedure produced specimens which are dry, odorless and easy to handle while maintaining the natural shape of the specimen. Ascaris Lumbricoides preserved in this manner can be easily used for demonstration in educational courses working with medical students as well as public health education of the general population.
plastination; silicone; S10; Ascaris
M.H. ASADI: Fax: 0098 21 66956253; E-mail: asadiamh@yahoo.com
Infection with Ascaris lumbricoides continues to be a significant health problem throughout the world (Lynne and Garcis, 2001). Ascaris occurs in about 22 percent of the world population (Muller and Baker, 1990). Depending upon poor sanitation for its spread, human Ascarids have been described as a household and backyard infection (Bogitsh and Cheng, 1998). Ascaris is contacted by ingesting mature eggs from contaminated soil which occurs most often among children who play on the ground. Food, mainly vegetables, and drinking water may be contaminated and become the source of infection (Tsieh, 1999). In educational courses in medical colleges, specimens of Ascaris are utilized for demonstration purposes. The form most widely used is formalin fixed worms. This approach to teaching has some disadvantages , among the most undesirable are odor and dampness. This investigation was designed to employ S10 method instead of formalin to produce more desirable teaching specimens. It was assumed that using the S10 plastination technique would produce specimens which are dry, odorless, and preserve the natural shape and appearance of the parasite .
The Ascarid specimens used in this study had been fixed in 5% formaldehyde for an extended period of time. These specimens were rinsed in cold tap water to remove as much formaldehyde as possible. The specimens were subsequently cooled to 5°C prior to dehydration. Several specimens of Ascaris were submerged in at least three baths of one hundred percent acetone at -20°C. The ratio volume of acetone to the specimens approximately was 10:1. The low temperature fixes the shape of specimens . When the acetone concentration remained at 99%, after approximately three weeks, dehydration was deemed complete. The Ascarids were then submerged in a mixture of S10/ S3 (100:1) for at least one day at -20°C. Longer immersion at this stage serves to shorten the impregnation time for the specimens and also reduces the shrinkage of the worms ' cuticles. The volume ratio of silicone to the specimens was 3: 1. In this stage the specimens immersed in silicone were placed under vacuum for 14 to 18 days at -20°C. The pressure was slowly decreased to 5mm Hg. Ascaris cuticles are somewhat impermeable to large molecules and surrounds a very small visceral space. For this reason, a slow decrease in pressure helps to prevent shrinkage of the specimens (Table 1). After forced impregnation, the Ascarids were removed from the polymer and excess polymer was drained from their surfaces for three days. The specimens were then placed in a single layer on a grid in the Biodur HH, 0 gas curing unit and exposed to S6 gas cure vapors for 3 days at room temperature (von Hagens, 1985).
| Pressure | Time |
| 85mm Hg | 1-2 days |
| 75mm Hg | 2 days |
| 65mm Hg | 1-2 days |
| 55mrn Hg | 2 days |
| 45mm Hg | 1-2 days |
| 35mm Hg | 2 days |
| 25mm Hg | 1-2 days |
| 15mm Hg | 2 days |
| 5mm Hg | 2 days |
After plastination, the Ascarid specimens retained their original shapes (Fig. 1). The Ascarids retained some flexibility. The plastinated specimens are odorless, non-toxic and dry to the touch (von Hagens et al., 1987).
Figure 1. Plastinated Ascarid.
Plastination of animal and fish are reported in some articles (Asadi, 1998; Zhong et al., 2000), but in this research, it was the first trial of plastination in parasitology . Not only were the resulting specimens dry and odorless, but the color of the plastinated worms was more aesthetic than that of specimens stored in formaldehyde. Because of the good results for teaching, it was suggested that in the future that plastination in the teaching of parasitology be considered as an alternative to traditional preservation methods. It should be mentioned that S10 plastination is recommended for considerably large size parasites like Ascaris and Teania and it may not be suitable for smaller nematodes .
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