Age-related detection and molecular characterization of Cryptosporidium suis and Cryptosporidium scrofarum in pre- and post-weaned piglets and adult pigs in Japan.

We investigated the distribution of Cryptosporidium in pigs in Japan by immunofluorescence staining of fecal samples and characterization of isolates by multilocus sequencing. The 344 animals sampled on eight farms included pre-weaned piglets (<1 month old; n = 55), weaned piglets (1-2 months old; n = 65), finished pigs (2-4 months old, n = 105) and of 4-6 months old (n = 67), sows (n = 36), and boars (n = 16). Average prevalence of Cryptosporidium on farms was 32.6%, ranging from 4.9 to 58.1%, decreasing with animal age (prevalences of <1 month old, 1-2 months old, 2-4 months old, 4-6 months old, sows, and boars were 27.3, 47.7, 41.9, 22.4, 11.1, 18.8%, respectively). Piglets (<1 and 1-2 months old) showing signs of diarrhea shed relatively more oocysts (5.28 in average log scale of oocysts per gram) in feces than piglets with normal or loose stools (those of 4.90). Thirty seven successful sequencing of the 18S ribosomal RNA gene among 62 examined samples revealed that all of the identified isolates were Cryptosporidium suis or Cryptosporidium scrofarum, which are generally specific to pigs, and that other species, such as zoonotic Cryptosporidium parvum, were absent. Interestingly, C. suis was frequently found in piglets younger than 2 months old, while C. scrofarum infection was more prevalent in older pigs which also showed increased prevalence of mixed C. suis and C. scrofarum infections. Sequencing of actin gene loci revealed the existence of variants of both Cryptosporidium species in pigs in Japan. Although the number of pigs examined in this study was relatively low, our results suggest that Cryptosporidium infection is widespread among pigs in Japan. In addition, the possibility of age-related specificity and pathogenicity in pig infections is also suggested.