Prevalence, molecular characterization and zoonotic potential of Cryptosporidium spp. in horses from diverse husbandry systems across four provinces of northern and eastern China.

Cryptosporidium is an obligate intracellular zoonotic protozoan causing diarrheal disease in humans and animals globally. Horses have more frequent close contact with humans through equestrian sports, breeding, and cross-regional trade. However, comprehensive molecular epidemiological data on diverse equine husbandry systems in China are limited. We tested 412 fecal samples from horses across four Chinese provinces via small subunit ribosomal RNA (SSU rRNA) nested polymerase chain reaction (PCR). C. parvum and C. equi were subtyped using the 60 kDa glycoprotein (gp60) gene, and C. andersoni was subtyped via multilocus sequence typing (MLST) at four loci (MS1, MS2, MS3, MS16). The overall Cryptosporidium prevalence was 4.1% (17/412). Age < 1 year was a significant independent risk factor for infection (adjusted PR = 4.92, 95% CI: 1.08-22.41, P = 0.039). Three zoonotic Cryptosporidium species were identified: C. parvum (10/17, 58.8%), C. andersoni (5/17, 29.4%), and C. equi (2/17, 11.8%). Four human-pathogenic subtypes of C. parvum were identified, including IIdA14G1 (n = 5), IIcA5G3 (n = 3), IIdA19G1 (n = 1), and IIdA15G1 (n = 1). Notably, the IIcA5G3 subtype, which has previously been reported mainly in humans, was detected for the first time in equine hosts. All C. equi isolates were subtyped as VIaA15G4 (n = 2), and four of the five C. andersoni isolates were assigned the MLST subtype A4A4A4A1 (n = 4). These findings indicate that horses in China carry multiple high-risk zoonotic Cryptosporidium species and subtypes, suggesting they may serve as potential reservoir hosts for human infection.