Volume 2, Number 4—October 1996
Identification of Cyclospora in Poultry
To the Editor: Human infection with the parasitic protozoa, Cyclospora, was first described in 1979 (1), and the organism was only recently categorized as an important gastrointestinal parasite. A single species, Cyclospora cayetanensis, has been described in humans (2), while most species in the genus Cyclospora have been described only in reptiles and rodents (3). The consumption of undercooked meat and exposure to contaminated water have been considered possible sources of human infection with C. cayetanensis (1,4). Coccidia were detected in drinking water in Nepal (5), and the parasite was identified in an animal species (one duck in Peru, by Zerpa et al. ) different from those in which it was described earlier. To determine whether a domestic animal is either a host or a reservoir for C. cayetanensis, we first examined feces from cats, which are hosts and reservoirs of Toxoplasma gondii, a coccidia causing human illness, but got negative results. Because Cyclospora were recently phylogenetically linked to Eimeria mitis and E. tenella (7), coccidial parasites of chickens, we investigated the presence of Cyclospora in poultry.
We pooled feces from approximately 600 4- to 6-week-old chickens from a poultry farm near Monterrey, Mexico, and extracted feces from the caecum of 50 6- to 8-week-old chickens from a poultry market at that location. By Percoll discontinuous-gradient centrifugation (Medina-De la Garza et al., submitted), both fecal pools were positive for coccidia, mainly Eimeria species and what we regarded as C. cayetanensis oocysts. Presence of Cyclospora was confirmed by 1) characteristic morphology and size (8mm to 10mm), 2) positive staining with Kinyoun's acid-fast stain, 3) positive autofluorescence under ultraviolet light, and 4) sporulation of oocysts with formation of sporocysts after a 10-day incubation. All these are diagnostic features of C. cayetanensis (8) and to our knowledge are not described for any known poultry coccidia.
On the basis of these findings, we suggest that poultry may serve as a possible source for human infection with Cyclospora. Consumption of chicken has been reported in one infected patient in the original description by Ashford (1) and in a patient reported recently by Connor and Shlim (9). Moreover, the only existing report of C. cayetanensis found in feces from a domestic farm animal concerned a farm duck (6). Zerpa et al. suggest that besides consumption of contaminated water, other modes of transmission involving contact with domestic animals must be considered. So far, however, a possible infection route involving poultry, whether it may be direct consumption of undercooked chicken meat, contamination of food and water sources with chicken feces, or both, remains to be determined. It should be noted that sanitary standards in poultry-breeding facilities in developing countries may not be adequate. This would account for the fact that reports implicating chickens in the transmission of Cyclospora (1 9,) have occurred in, or in relation to, developing countries. The Cyclospora found in the chickens in our study have the diagnostic features of C. cayetanensis. Nevertheless, the existence of another, not yet described, Cyclospora species infecting poultry, which has similar features but is different from C. cayetanensis, cannot be excluded at this stage. In addition, the number of oocysts recovered was not large and because feces were pooled, we could not calculate the number of oocysts passed by each bird. The possibility that oocysts were acquired as a contaminant from food or water sources and were only passing though the gut of the chickens (making the chickens a paratonic host) cannot be ruled out.
The increased recognition of Cyclospora as an important cause of diarrhea in both immunocompromised and immunocompetent persons and the public health relevance of this emerging pathogen as a potential cause of diarrheal outbreaks (3,4) make prompt disclosure of the epidemiologic features and behavior of the parasite necessary. As we propose the possible participation of poultry in the epidemiologic cycle of the coccidia, we invite other Cyclospora working groups worldwide to confirm the so far putative reservoir described in this communication and to further study other possible hosts or reservoirs.
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