Sporadic Human Cryptosporidiosis Caused by Cryptosporidium cuniculus, United Kingdom, 2007–2008

To investigate sporadic human cryptosporidiosis trends in the United Kingdom, we tested 3,030 Cryptosporidium spp.–positive fecal samples, submitted for routine typing in 2007–2008, for C. cuniculus. C. cuniculus prevalence was 1.2%; cases were mostly indigenous and occurred across all age groups. Most occurred during August–October and may be linked to exposure opportunities.

More C. cuniculus cases were detected in the late summer and autumn than in the winter and spring, similar to infections with C. hominis but not C. parvum ( Figure  2). Three C. cuniculus cases were identifi ed in the East Midlands, the outbreak affected region, but none were found in Northamptonshire, the outbreak-affected area. Most cases (24%) were in the Eastern region of England. Two case-patients had traveled outside the UK, one to Spain and the other destination not known, during the incubation period.
Occupational and environmental exposure data were available for 14 C. cuniculus case-patients from patient questionnaires administered by local Environmental Health Departments. No occupational risks were linked to rabbits. One patient (a 9-year-old boy) reported direct contact with rabbits (a pet), and 2 patients had potential environmental contact (a 63-year-old woman played golf, and a 36-yearold man sat on grass during a walking holiday). Two casepatients reported diarrhea in other residential contacts. None of the patients reported links with (lived in, had visited or received visitors from) the outbreak-affected area. Available clinical details were insuffi cient for all cryptosporidiosis case-patients for comparative purposes. One C. cuniculus case-patient was an immunosuppressed child who had received a kidney transplant.
Two GP60 subtype families, Va (n = 18) and Vb (n = 19), were detected in sporadic C. cuniculus isolates, linked to patient sex; 10/14 (71.4%) female patients had Va subtype, compared with 7/22 (31.8%) male patients (χ 2 = 5.24, df = 1, p = 0.022). No signifi cant difference in age or regional distribution was found, but cases with Va occurred only in August through December, while Vb cases occurred all year but mostly in August ( Figure 2).

Conclusions
C. cuniculus was fi rst identifi ed as a human pathogen during a waterborne outbreak, and its epidemiology has now been described for sporadic cases in the United Kingdom. Although the numbers are small, and the data need to be interpreted with caution, it was the third most commonly identifi ed Cryptosporidium species in patients with diarrhea during the study period, after C. parvum and C. hominis. All C. cuniculus isolates identifi ed by PCR-RFLP were confi rmed by sequence analysis, indicating the reliability of the test algorithm used, although the development of specifi c probes will enhance testing capability. All ages were infected with little age delimitation <50 years, after which numbers declined. Contrast this to C. parvum and C. hominis, which are both linked to young age. C. cuniculus distribution is seasonal, peaking in August through November, and differences in seasonal distribution of GP60 subtypes were marked.
Rabbits are the natural hosts for C. cuniculus (5), and seasonal distribution and variation in humans may refl ect rabbit breeding seasons and infections, although good epidemiologic studies of Cryptosporidium spp. in wild rabbits are lacking (7). Studies of farmed and wild rabbits so far indicate that GP60 subtype Vb predominates (7-9), although the outbreak was caused by Va (4). Unlike with C. hominis, seasonal distribution of cases was not linked to foreign travel. The C. cuniculus outbreak had occurred in July when few sporadic cases were detected. The distribution of sporadic cases was the opposite of the outbreak in which more case-patients were female (6). The association between GP60 subtypes and patient sex is intriguing. A small number of case-patients had possible exposure risks, although this requires further  investigation. The only known hosts of C. cuniculus are humans and European rabbits (Oryctolagus cuniculus) (5,(7)(8)(9), and until population-based studies of rabbits are undertaken, the risks cannot be fully evaluated, nor the human epidemiology fully explained.