Coccidial Contamination of Raspberries: Mock Contamination with Eimeria acervulina as a Model for Decontamination Treatment Studies

Numerous outbreaks have been reported since 1995 in the United States and Canada that were linked to the consumption of imported fresh raspberries contaminated with Cyclospora. Because Cyclospora has no laboratory animal hosts, Eimeria acervulina, a common chicken coccidium similar in characteristics to Cyclospora, was used as a surrogate to test decontamination treatments. Raspberries were mock contaminated with E. acervulina-sporulated oocysts in a water suspension, then exposed to washing, freezing, heat, or irradiation before they were fed to chicks. The presence of oocysts in the contaminated raspberries was con rmed either by duodenal lesions or oocysts in cecal contents 5 days postinoculation (PI) or in fecal contents 6 days PI, after 24 h of fecal collection. Washing of raspberries was generally not adequate in removing coccidial contamination,but freezing and heat treatment appeared effective. Gamma irradiation of E. acervulina-sporulated oocysts at a dose of 0.5 kGy was partially effective, but it was completely effective at 1.0 kGy and higher. We suggest that E. acervulina, for mock contamination of raspberries and subsequent decontamination treatments, is easy to handle, safe, and economical to study. Numerous outbreaks caused by the coccidian protozoan, Cyclospora cayetanensis, have occurred in North America since 1995, mostly linked to the consumption of raspberries and blackberries imported from Guatemala (8, 9, 12, 15, 16, 19). In May and June of 1996 alone, 725 out of 1,465 cases of cyclosporiasis reported in the United States and Canada could be traced to 55 social events (8). Of these 55 events, raspberries were served in at least 50. In 1997, 762 out of 1,012 cases of cyclosporiasis were reported in the United States and Canada from 41 events. Raspberries were served at all 41 social events (9). Interestingly, after the U.S. Food and Drug Administration banned the importation of raspberries from Guatemala in 1998, no further outbreaks of cyclosporiasis were reported in the United States. However, because no such ban was imposed in Canada, at least two more reported outbreaks occurred that came from consumption of Guatemalan berries in Ontario: 192 cases in May 1998 from raspberries and 104 cases in the fall of 1999 from blackberries (16, 19). Although the links were still circumstantial, the evidence left little doubt that there was a cause and effect between consumption of Guatemalan berries and the outbreaks of cyclosporiasis. The most likely source for contamination of berries, which are grown aboveground, is human feces from workers in  elds, sorters touching berries from fecally soiled * Author for correspondence. Tel: 416-979-5000 x7048; Fax: 416-9795377; E-mail: mblee@acs.ryerson. ca.  ngers, sewage pits located adjacent to the berries, or pesticide mixing in soiled containers. When a team of Canadian of cials traveled to Guatemala for 1 week in April 1998, they found several opportunities for contamination but were unable to pinpoint its source. Attempts to establish patent infections for possible treatment studies in 13 laboratory animals, including chickens, rats, and monkeys, failed (4). Cyclospora cannot conveniently be studied on humans because it is a health hazard. Besides being unsafe, it is also cost-prohibitive. We have therefore chosen to work with a coccidian parasite, Eimeria acervulina, as a surrogate. Eimeria and Cyclospora are both coccidia from the same family (Eimeriidae), released from their hosts as unsporulated oocysts, and are not directly infective, needing several days to develop into infective, sporulated oocysts, and they possess an oocyst wall that is resilient to harsh environmental conditions (17). More importantly, they are like other coccidial oocysts, cleidoic in nature—i.e., they need only air and moisture to survive and therefore, can remain infective at room temperature for weeks, longer than the shelf life of most of their carriers, the fresh berries. One attractive feature in using E. acervulina is lowlevel contamination; even as low as a few oocysts, once enriched in chicken, their greatly increased progenies can easily be detected as oocysts in their feces. Besides, E. acervulina is host-speci c and does not infect humans. Toxoplasma gondii has been attempted as a surrogate for coccidial contamination on raspberries (3). However, T. gondii D ow naded rom hp://m eridianenpress.com /jfp/article-pdf/64/11/585/0362-028x-64_11_1854. pdf by gest on 27 M ay 2020 J. Food Prot. , Vol. 64, No. 11 COCCIDIAL CONTAMINATION OF RASPBERRIES 1855 TABLE 1. Effect of various decontamination treatments of raspberries with mock-contaminated Eimeria acervulina oocysts Treatment Group Gamma irradiation dose Experiment 1