Molecular Epidemiology of Cryptosporidiosis in Children in Malawi

Abstract

Few studies have examined the molecular epidemiology of cryptosporidiosis in developing countries. In this study, DNA of 69 microscopy-positive human fecal samples collected from Malawi were examined by multilocus genetic analyses. From 43, 27 and 28 of the samples, the SSU rRNA, 70 kDa heat shock protein (HSP70) and 60 kDa glycoprotein (GP60) genes, respectively, were successfully PCR-amplified. Restriction analysis of the SSU PCR products showed that 41 of the 43 PCR-positive samples had C. hominis and 2 had C. parvum. Sequence analysis of the HSP70 and GP60 gene confirmed the species identification by SSU rRNA PCR-RFLP analysis, but also revealed high intraspecific variations. Altogether, six HSP70 subtypes and six GP60 subtypes (belonging to four subtype alleles) of C. hominis were found. Linkage disequilibrum analysis of the two genetic loci showed possible intraspecific recombination. Thus, cryptosporidiosis in the study area was largely caused by anthroponotic transmission. The high intraspecific variation and existence of genetic recombination were probably results of high transmission of cryptosporidiosis in this area.

Identification of a High Diversity of Cryptosporidium Species Genotypes and Subtypes in a Pediatric Population in Nigeria

“…16 Cryptosporidium hominis was the dominant species identified in our study. High levels of C. hominis are consistent with studies from other developing countries such as Peru, 18 Kenya, 16 India, 14 Malawi, 5,7 and Uganda, 4,15 which indicate that anthroponotic transmission may play a major role in the epidemiology of Cryptosporidium in these areas. A relatively high level of C. parvum was also found in the current study and this finding is in contrast to those of studies from other developing regions where C. parvum infections are generally much lower than that of C. hominis .…”

“…In contrast, other studies in the tropics have indicated that prevalence of infection is highest in months with the greatest rainfall. [4][5][6][7] However, prevalence was highest during the dry season in Kenya. 16 In Venezuela no seasonal variation was detected.…”

“…3,4 Studies indicate that prevalence varies geographically, with increased prevalence in developing countries, and temporally, with higher rates reported during the rainy season in many tropical countries. [4][5][6][7] A range of Cryptosporidium species, genotypes, and subtypes infect humans, and each may have different sources of infection, transmission routes, and pathogenicity. [8][9][10] Thus, identifying the species present in a population is crucial for identifying risk factors for transmission and implementing control programs to limit exposure to infectious oocysts.…”

“…[11][12][13] Cryptosporidium hominis and C. parvum are the most frequently detected, and C. hominis infections are more common in developing countries. 5,7,[14][15][16][17][18] Both species have different host ranges. Although C. hominis is confined mostly to humans, C. parvum infects humans and ruminants.…”

“…20,21 Although cryptosporidiosis is prevalent in developing countries, genetic characterization of species is lacking, especially in Africa, where only four subgenotyping studies have been conducted in Uganda, Malawi, Kenya, and South Africa. 7,15,22,23 Cryptosporidium meleagridis , although not found as commonly as C. hominis and C. parvum , is the third most common infection in humans. 4,5,14,18,24,25 Two subtypes of C. meleagridis have been identified at the small subunit (SSU) ribosomal RNA (rRNA) gene locus, and six 6 subtypes have been identified at the GP60 gene locus, 26 which indicate possible heterogeneity in host range, and therefore routes of transmission, for C. meleagridis .…”