Fayer R, Graczyk T K, Lewis E J, Trout J M, Farley C A
Immunology and Disease Resistance Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705-2350, USA.
Appl Environ Microbiol. 1998 Mar;64(3):1070-4. doi: 10.1128/AEM.64.3.1070-1074.1998.
Oocysts of Cryptosporidium parvum placed in artificial seawater at salinities of 10, 20, and 30 ppt at 10 degrees C and at 10 ppt at 20 degrees C were infectious after 12 weeks. Those placed in seawater at 20 ppt and 30 ppt at 20 degrees C were infectious for 8 and 4 weeks, respectively. These findings suggested that oocysts could survive in estuarine waters long enough to be removed by filter feeders such as oysters. Thereafter, 30 Eastern oysters, Crassostrea virginica, were collected with a dredge or with hand tongs at each of six sites within Maryland tributaries of the Chesapeake Bay in May and June and in August and September of 1997. Hemocytes and gill washings from all oysters were examined for the presence of Cryptosporidium oocysts and Giardia cysts by immunofluorescence microscopy utilizing a commercially available kit containing fluorescein isothiocyanate-conjugated monoclonal antibodies. Giardia was not detected by this method from any of the 360 oysters examined. Presumptive identification of Cryptosporidium oocysts was made in either hemocytes or gill washings of oysters from all six sites both times that surveys were conducted. In addition, during August and September, for each of the six sites, hemocytes from the 30 oysters were pooled and gill washings from the oysters were pooled. Each pool was delivered by gastric intubation to a litter of neonatal mice to produce a bioassay for oocyst infectivity. Intestinal tissue from two of three mice that received gill washings from oysters collected at a site near a large cattle farm and shoreline homes with septic tanks was positive for developmental stages of C. parvum. These findings demonstrate for the first time that oysters in natural waters harbor infectious C. parvum oocysts and can serve as mechanical vectors of this pathogen.
将微小隐孢子虫的卵囊置于10℃下盐度为10、20和30 ppt的人工海水中，以及20℃下盐度为10 ppt的人工海水中，12周后具有感染性。置于20℃下盐度为20 ppt和30 ppt海水中的卵囊，分别在8周和4周后具有感染性。这些发现表明，卵囊能够在河口水中存活足够长的时间，以便被诸如牡蛎等滤食性动物清除。此后，1997年5月、6月以及8月、9月，在切萨皮克湾马里兰州支流的六个地点，用拖网或手钳采集了30只东部牡蛎（美洲牡蛎）。利用含有异硫氰酸荧光素偶联单克隆抗体的市售试剂盒，通过免疫荧光显微镜检查所有牡蛎的血细胞和鳃冲洗液，以检测隐孢子虫卵囊和贾第虫包囊的存在。在所检查的360只牡蛎中，均未通过该方法检测到贾第虫。在进行调查的两次中，在所有六个地点的牡蛎的血细胞或鳃冲洗液中均初步鉴定出隐孢子虫卵囊。此外，在8月和9月，对于六个地点中的每个地点，将30只牡蛎的血细胞汇集在一起，将牡蛎的鳃冲洗液汇集在一起。通过胃插管将每个汇集物投喂给一窝新生小鼠，以进行卵囊感染性的生物测定。从一个靠近大型养牛场和带有化粪池的海滨住宅的地点采集的牡蛎的鳃冲洗液投喂给三只小鼠中的两只，其肠道组织中微小隐孢子虫发育阶段呈阳性。这些发现首次证明，天然水域中的牡蛎携带具有感染性的微小隐孢子虫卵囊，并且可以作为这种病原体的机械传播媒介。
