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

Overview

• This study investigated the prevalence and genetic characteristics of Cryptosporidium species in horses across four provinces in northern and eastern China, with a focus on the potential for these parasites to infect humans.
• The researchers identified zoonotic Cryptosporidium species and subtypes in horses, highlighting their role as potential reservoirs for human infection.

Introduction to Cryptosporidium and Study Rationale

• Cryptosporidium is an obligate intracellular protozoan parasite that causes diarrheal disease in both humans and animals worldwide.
• Horses have frequent close contact with humans through activities like equestrian sports, breeding, and trade, raising concerns about transmission risks.
• Despite this, there is limited molecular epidemiological data on the prevalence and types of Cryptosporidium circulating in horses in China, particularly across diverse husbandry systems.
• The study aims to fill this gap by evaluating the prevalence, molecular characterization, and zoonotic potential of Cryptosporidium spp. in horses from diverse regions in China.

Methods and Sample Collection

• A total of 412 fecal samples from horses were collected from four provinces in northern and eastern China, representing diverse equine husbandry systems.
• Detection of Cryptosporidium was performed using nested polymerase chain reaction (PCR) targeting the small subunit ribosomal RNA (SSU rRNA) gene, which allows sensitive identification of the parasite.
• For more detailed molecular characterization:
  • C. parvum and C. equi were subtyped by analyzing the 60-kDa glycoprotein gene (gp60), a common marker for strain differentiation.
  • C. andersoni was subtyped using multilocus sequence typing (MLST) at four specific loci named MS1, MS2, MS3, and MS16 to obtain finer genetic details.

Key Findings – Prevalence and Risk Factors

• Overall Cryptosporidium prevalence among the sampled horses was 4.1% (17 out of 412 samples tested positive).
• Age less than 1 year was a significant independent risk factor for Cryptosporidium infection in horses, with younger animals being about five times more likely to be infected.

Identified Cryptosporidium Species and Subtypes

• Three Cryptosporidium species with zoonotic potential were detected:
  • C. parvum (58.8% of positive samples, 10/17)
  • C. andersoni (29.4%, 5/17)
  • C. equi (11.8%, 2/17)
• Subtyping results revealed:
  • Four human-pathogenic C. parvum subtypes:
    • IIdA14G1 (found in 5 isolates)
    • IIcA5G3 (3 isolates) — uniquely detected in horses for the first time, previously mainly reported in humans
    • IIdA19G1 (1 isolate)
    • IIdA15G1 (1 isolate)
  • All C. equi isolates belonged to subtype VIaA15G4 (2 isolates).
  • For C. andersoni, four of the five isolates were assigned the MLST subtype A4A4A4A1.

Significance and Zoonotic Implications

• The presence of multiple zoonotic Cryptosporidium species and subtypes in horses indicates that these animals are potential reservoirs for transmission to humans.
• Particularly noteworthy is the detection of the IIcA5G3 subtype of C. parvum in horses, which had not been reported in equine hosts before, expanding the known host range of this human-pathogenic strain.
• Given horses’ close interactions with humans, these findings emphasize the need for monitoring and controlling Cryptosporidium infections in equine populations to reduce zoonotic risks.
• The study expands understanding of Cryptosporidium epidemiology in horses across different husbandry environments, aiding in better public health risk assessment in China.