Molecular identification and biological characterization of Cryptosporidium muris from a naturally infected cat ( Felis catus )

Abstract Cryptosporidium muris is a gastric species primarily infecting rodents, whereas natural infections in cats are rarely documented and biologically poorly characterized. Oocysts of C. muris were detected in a cat and monitored for 120 days. Molecular characterization was performed on the small subunit rRNA, actin, 70-kDa heat shock protein , Cryptosporidium oocyst wall protein and thrombospondin-related adhesive protein of Cryptosporidium -1 loci. Oocyst morphology was evaluated microscopically. Infectivity and shedding dynamics were assessed in BALB/c mice and compared with C. muris RN66 and C. proliferans . Oocyst integrity during storage at 4°C was monitored for 60 days at 15-day intervals using flow cytometry and viability assays. The infected cat shed oocysts for 97 days, with a maximum intensity of 371 200 oocysts per gram (OPG), yet remained clinically asymptomatic. Developmental stages were confirmed histologically in gastric biopsy specimens. Haematological and biochemical parameters remained within reference ranges, and no concurrent parasitic, bacterial or viral infections were detected; only seropositivity to Toxoplasma gondii was recorded. All analysed loci showed 100% identity with C. muris RN66. Oocyst morphology did not differ from reference isolates. However, oocysts originating from the cat exhibited markedly reduced environmental stability, with a 90% decline in integrity within 60 days. Experimental infection of mice confirmed infectivity, but total oocyst output (32 300 OPG/days) was several orders of magnitude lower than that of C. muris RN66. Although genetically identical to rodent isolates, the feline-derived C. muris displayed altered biological properties, including reduced oocyst stability and transmission fitness. Cats may serve as susceptible but epidemiologically inefficient hosts.