No abstract

No abstract

Cryptosporidium parvum and Giardia duodenalis can cause severe diarrhoea in infected individuals and their transmissive stages, oocysts and cysts, are voided in large numbers with the faeces of infected hosts. Contaminated sewage effluents are recognised as a potential source of waterborne (oo)cysts. In this investigation methods optimised for the recovery of both from a range of wastewaters were used to determine the occurrence of these organisms in influents, effluents and sludges from seven sewage treatment works in England. The data indicated the presence of small numbers of oocysts both in sewage influent and effluent samples whereas cysts were detected more frequently and at higher concentrations in both influents and effluents. Whilst sludge samples from 1/5 sites contained oocysts, cysts were detected from all five sites. These investigations indicate that discharge of sewage effluents into a watercourse, which may be used for potable water abstraction, can contaminate that watercourse with potentially infectious oocysts. In addition, the application of sludge to land can be responsible for contaminating watercourses with (oo)cysts following run-off or leaching.

We report a method for detecting Giardia duodenalis cysts on lettuce, which we subsequently use to examine salad products for the presence of Giardia cysts and Cryptosporidium oocysts. The method is based on four basic steps: extraction of cysts from the foodstuffs, concentration of the extract and separation of the cysts from food materials, staining of the cysts to allow their visualization, and identification of cysts by microscopy. The concentration and separation steps are performed by centrifugation, followed by immunomagnetic separation using proprietary kits. Cyst staining is also performed using proprietary reagents. The method recovered 46.0% ؎ 19.0% (n ‫؍‬ 30) of artificially contaminating cysts in 30 g of lettuce. We tested the method on a variety of commercially available natural foods, which we also seeded with a commercially available internal control, immediately prior to concentration of the extract. Recoveries of the Texas Red-stained Giardia cyst and Cryptosporidium oocyst internal controls were 36.5% ؎ 14.3% and 36.2% ؎ 19.7% (n ‫؍‬ 20), respectively. One natural food sample of organic watercress, spinach, and rocket salad contained one Giardia cyst 50 g ؊1 of sample as an indigenous surface contaminant.With the increasing concern about transmission of pathogenic microorganisms by foods, there is a need to control the entire food chain, from primary producer to consumer. This can be accomplished through screening and certification programs, which apply highly sensitive and cost-effective methods for detecting food-borne pathogens. These will require the use of detection methods which are robust, reproducible, and practical.The food industry is becoming increasingly aware of the potential for contamination of foodstuffs with the transmissive stages of Giardia duodenalis (9,15,17,20). Fresh produce, in particular, as it is consumed with minimal preparation, is a potential vehicle of transmission, and G. duodenalis cysts have been detected on produce in several countries (1,12,13,14). Contaminated irrigation water, especially, appears to constitute a major route of contamination of fresh produce (3, 21). Practical and reliable detection methods for monitoring foodstuffs will aid the prevention of parasitic disease outbreaks associated with contaminated food (8).The procedure developed could be used by analytical laboratories that may be asked to analyze lettuce or salad products for more than one parasite. The simultaneous elution and enumeration of Cryptosporidium oocysts and Giardia cysts from the same sample using a single extractant is the most convenient option, given that combination immunomagnetic separation (IMS) kits for both Cryptosporidium and Giardia are available commercially. Previously published methods that use IMS (12, 13, 14) used commercial kits that were developed for concentrating cysts and oocysts from water concentrates, not food matrices. These do not maximize cyst and oocyst recoveries from foods. In order to maximize cyst and oocyst recoveries from foods, the choice of ...