Molecular Analysis of the 18S rRNA Gene of Cryptosporidium Parasites from Patients with or without Human Immunodeficiency Virus Infections Living in Kenya, Malawi, Brazil, the United Kingdom, and Vietnam

Abstract

An 840-bp fragment of the 18S rRNA gene was used to identify Cryptosporidium spp. recovered from human immunodeficiency virus (HIV)-infected and -uninfected patients from Kenya, Malawi, Brazil, the United Kingdom, and Vietnam. Initial identification was by Ziehl-Neelsen acid-fast staining. Confirmation was by nested PCR, targeting the most polymorphic region of the 18S rRNA gene. Genotyping was by restriction endonuclease digestion of the PCR product followed by nucleotide sequencing. Among 63 isolates analyzed, four genotypes of Cryptosporidium were identified; 75% of the isolates were of the C. parvum human genotype, while the potentially zoonotic species were of the C. parvum bovine genotype (21.7%), the C. meleagridis genotype (1.6% [one isolate]), and the C. muris genotype (1.6% [one case]). HIV-infected individuals were more likely to have zoonotic genotypes than the HIV-uninfected individuals. Among the C. parvum group, strains clustered distinctly into either human or bovine genotypes regardless of the geographical origin, age, or HIV status of the patients. The intragenotypic variation observed in the C. parvum human genotype was extensive compared to that within the C. parvum bovine genotype group. The variation within genotypes was conserved in all geographical regions regardless of the patients' HIV status. The extensive diversity within genotypes at the 18S rRNA gene locus may limit its application to phylogenetic analyses.The use of molecular methods in the taxonomy of Cryptosporidium spp. has led to increased recognition of the diversity of the species infecting humans. The main causative agents of human cryptosporidiosis are strains of human and bovine genotypes of the species C. parvum (also called genotype 1 and genotype 2, respectively) (3). Recent reports document human infections with zoonotic species, including C. parvum dog and cat types (now renamed C. canis and C. felis, respectively) and C. meleagridis and C. muris (mainly avian and murine parasites, respectively) (4,5,11,13,24). A recently recognized Cryptosporidium cervine genotype has been identified in both immunocompromised and immunocompetent people (9). However, the prevalence and significance of the different species and genotypes in both immunocompetent and immunodeficient people are not yet clear. Experimental studies of both humans and animals suggest that diverse species and genotypes show different levels of infectivity and virulence (8). Others have pointed out that zoonotic strains of C. parvum produce more severe infections in humans than the strains found only in humans (7). Moreover, the potential reservoir hosts and transmission pathways for the novel species infecting humans are unclear (3). These issues underscore the importance of the precise identification of species recovered from humans.So far, a limited number of isolates have been typed from developing countries and especially from human immunodeficiency virus (HIV)-infected people (5,12,16,17,19,20,24), yet cryptosporidiosis is endemic in most tropical region...

Unexpected results from large-scale cryptosporidiosis screening study in calves in Tanzania

“…For example, Cryptosporidium hominis is particularly associated with human infections, and C. bovis and C. andersoni particularly associated with infections in cattle (Xiao, 2010). Severe diarrhea occurs in young and immunocompromised animals and humans (Gatei et al, 2003;Ramirez et al, 2004). However, self-limiting or subclinical disease also occurs, predominantly in adults and immunocompetent animals and humans (Ramirez et al, 2004).…”

Prevalence and genetic characterization of Cryptosporidium spp. and Cystoisospora belli in HIV-infected patients

“…that infect humans 21 . Although more than five Cryptosporidium species/genotypes have been described in humans, C. parvum and C. hominis are the species responsible for most cases of cryptosporidiosis in the world 4,5,10 . Genetic analysis of the two clinical isolates of Cryptosporidium spp.…”

Evidence Supporting Zoonotic Transmission of Cryptosporidium spp. in Wisconsin

“…Geographic differences in the human incidence of C. parvum and C. hominis have been identified. For example, C. parvum is generally reported to be more common in the United Kingdom (8,9,16,17), while C. hominis is reportedly more common in the United States (26,34). To date, U.S. studies identifying the causative species of cryptosporidiosis have been limited to outbreaks and sporadic cases occurring in AIDS patients from urban areas (34).…”