本省自來水中梨形鞭毛蟲及隱孢子蟲存在性調查及其分析方法之評估

Abstract

梨形鞭毛蟲及隱孢子蟲是常見的腸道寄生性原生動物。梨形鞭毛蟲能寄生在人類及多種哺乳動物的小腸而引起梨形鞭毛蟲症；其症狀有腹瀉、胃絞痛、頭暈、噁心等。至於隱孢子蟲則會導致人類及哺乳動物感染隱孢子蟲症，其症狀與梨形鞭毛蟲症類似，這兩種原蟲通常經由飲水進入宿主體內。近幾年美國及英國已爆發多起梨形鞭毛蟲症與隱孢子蟲症的流行；這兩種原蟲之外壁有厚夾膜，因此對水廠的消毒劑具有抗性。目前水廠的消毒方法並不能有效抑制隱孢子蟲卵囊體的生長；同樣的，在偏遠地區，若只用簡單的消毒設備，也不足以去除水中梨形鞭毛蟲的囊體。當務之急乃應建立飲用水水源中致病原生動物存在情形以確保民眾健康。 水體中梨形鞭毛蟲及隱孢子蟲的檢測方法包括三個步驟：水樣的收集與濃縮、原蟲與其他雜質顆粒分離以及原蟲的檢測。ICR原蟲分析法是美國所公告第一個檢測梨形鞭毛蟲與隱孢子蟲的標準方法，但此法的原蟲回收率過低，一直為人所詬病。因此，另一原蟲分析法-Method 1622已在1997年提出。近十年來，國外已爆發多起飲用自來水而引起梨形鞭毛蟲症和隱孢子蟲症的大型感染案例，因此希望藉由檢測本省自來水原水及清水之致病性原生動物及相關水質，了解原蟲之分佈狀況，進而採取必要之行政及技術管制措施，以保障大眾健康。 本研究乃對國內十一處淨水場原水與清水及十三處簡易自來水進行梨形鞭毛蟲、隱孢子蟲及相關水質參數之調查，以了解原蟲在水體中之含量及其與水質參數間之相關性。另外，本研究也對ICR原蟲分析法各個操作步驟的原蟲回收率進行分析，並評估四種市售之飲水機濾心對原蟲的去除效率。 研究結果顯示，國內十一處淨水場之原水中，梨形鞭毛蟲及隱孢子蟲的檢出率分別為79%與69%，平均含量為380.5 cysts/ 100L與184.8 oocysts/ 100L。淨水場的清水中，梨形鞭毛蟲及隱孢子蟲檢出率分別為66%與40%，平均含量為16.4 cysts/ 100L與9.3 oocysts/ 100L。至於十三處簡易自來水設施，梨形鞭毛蟲的檢出率為37%，隱孢子蟲的檢出率為37%。在相關性的比較上，除了梨形鞭毛蟲與隱孢子蟲含量彼此具有相關性外，與濁度及總菌落數亦具相關性。另外梨形鞭毛蟲含量和糞便大腸菌具相關性。十一處淨水廠之整體梨形鞭毛蟲平均感染風險度為0.0296/年，隱孢子蟲之平均感染風險度則為0.0878/年。以聚丙烯濾管進行原水之原蟲回收率分析時，梨形鞭毛蟲與隱孢子蟲的整體回收率都較Polycarbonate濾膜低。四種市售飲水機濾心中，T/C濾心的原蟲截留率最差，而Sediment Filter和聚丙烯管的截留效率最好。目前國內亟需訂定相關議題之指導規範，並對水廠操作提出建議，來防止致病性原生動物的感染，使其感染風險降至最低。

The protozoan parasites Giardia and Cryptosporidium have been recognized as the most common pathogenic protozoa of the gastrointestinal tract. Members of the genus Giardia infect the upper portions of the small intestine in humans and in several other mammals, causing giardiasis with diarrhea, stomach cramps, nausea, and fatigue. Many outbreaks of giardiasis have been reported in the last few decades. Members of the genus Cryptosporidium also cause gastroenteritis in humans and animals and are often responsible for waterborne outbreaks, which are associated with the consumption of surface water or inadequately removing protozoa in water supplies. In the United States and Great Britain, Giardia and Cryptosporidium have been involved in several outbreaks of waterborne gastroenteritis. The thick-walled cysts and oocysts are extremely resistant to commonly used disinfectants such as chlorine. The disinfection method applied currently in the water treatment plant failed to deactivated effectively the growth of Cryptospordium oocyts. Meanwhile, the simple disinfection process used in the retired area is unable to remove completely Giardia cysts. It is important to investigate the outbreak of Giardia and Cryptospordium in the source water to protect the public health. Methods available for the detection of Giardia and Cryptosporidium in water sample involve three stages: sample collection and concentration; separation of protozoan parasites from other debris; and detection of the parasites. The Information Collection Rule (ICR) protozoan method of USA is the first standard method for detecting Giardia and Cryptosporidium in water samples by a fluorescent antibody procedure. However, this method has been heavily scrutinized for the low recoveries. Method 1622, as improved procedure by adopting the immunomagnetic separation (IMS) is propounded in 1997. Many outbreaks of giardiasis and cryptosporidiosis have been reported in the last decade. Therefore, there is an urgent need to survey the occurrence of protozoan parasites though understanding the relationship between protozoa and water quality parameters in drinking water in order to provide the information for concerning human health. The research has conducted the sampling and measurement of Giardia and Cryptosporidium in water samples. The sampling sites include 11 major water treatment plants and 13 simple water facilities. The values of water quality parameter from various sampling points were determined for the evaluation of correlation to protozoan parasites. The concentrations of cysts and oocysts in the treated water were applied to the risk analysis equation to calculate the risk of human infection of Giardia and Cryptosporidium in drinking water supplies. The efficiencies of concentration, elution and purification techniques in ICR protozoan method for recovering cysts and oocysts were also evaluated in this research. In addition, we collected four blanks of filter cartridges for water fountain and their removal efficiencies were assayed for Giardia and Cryptosporidium. It was discovered that the percentage positive of Giardia and Cryptosporidium in the raw water samples from 11 water treatment plants were 79% and 69%, and the average counts were 380.5 cysts/ 100L and 184.8 oocysts/ 100L, respectively. In treated waters, the percentage positive was 66% for Giardia and 40% for Cryptosporidium, while the average counts were 16.4 cysts/ 100L and 9.3 oocysts/ 100L, respectively. In water samples from simple water facilities, the occurrences for both were 37%. Positive correlations were discovered in the following inter-relationships: concentrations of both parasites, parasite concentrations and turbidity level, parasite and heterotrophic bacteria concentrations, and Giardia and fecal coliforms concentrations. The annual risk of infecting parasites from treated water samples in five different plants were 2.96’10-2 for giardiasis and 8.78’10-2 for cryptosporidiosis, respectively. The overall recovery efficiencies of cysts and oocysts were sampled with polypropylene filter higher than these sampled with polycarbonate membrane. When the removal efficiencies by four filter cartridges used in the water fountain were compared, the Sediment filter and polypropylene filter showed the better removal efficiency than the other filters. The results of investigation confirm the need for more stringent regulation. In the mean time, recommendations must be made optimizing treatment process in order to lower the risk of infecting protozoa and the outbreak of waterborne diseases.