PCR-ELISA: a new simplified tool for tracing the source of cryptosporidiosis in HIV-positive patients

Cryptosporidium parvum is a major parasitic cause of death in end-stage AIDS patients that results from both zoonotic and person-to-person transmission. Recent studies have provided evidence that parasites causing zoonotic disease and those causing anthroponotic infection are genetically distinct. Isolates carrying "animal"-type genetic markers were presumed to be the result of zoonotic spread, either directly or through contaminated food and water. The need for a genotype-specific diagnostic tool that can provide clues as to the origin and possible modes of spread of C. parvum strains has been recognised. Here, we report the development of such a tool for C. parvum based on polymerase chain reaction-enzyme linked immunosorbent assay that enables the accurate typing of isolates from HIV-seropositive and HIV-negative patients presenting with diarrhoea from the United Kingdom and Canada. This study also showed that zoonotic transmission might be predominant in the HIV-positive patient group in the United Kingdom.

Eradication of cryptosporidia and microsporidia following successful antiretroviral therapy

OBJECTIVES

Incidence of opportunistic protozoal infections causing diarrheal illnesses in patients with HIV has decreased since the introduction of highly active antiretroviral therapy (HAART). The objective of this study was to determine whether the parasites, cryptosporidia, and microsporidia were effectively eradicated or only suppressed following treatment.

DESIGN

Six HIV-positive patients with diarrheal symptoms caused by cryptosporidia or microsporidia were prospectively followed up with stool samples and duodenal biopsies. Samples were taken before HAART, between 1 to 3 months, and 6 months post-HAART.

METHODS

Duodenal samples were analyzed using routine histology and transmission electron microscopy. Stool samples were analyzed by both light microscopy and polymerase chain reaction (PCR) techniques.

RESULTS

Patients who responded successfully to HAART eradicated both cryptosporidial and microsporidial organisms. Symptoms improved within 1 month of therapy but complete eradication of the organisms was only observed after 6 months of treatment.

CONCLUSIONS

AIDs-related cryptosporidiosis and microsporidiosis can be cured following successful antiretroviral therapy.

Does Cryptosporidium parvum have a clonal population structure?

Cryptosporidiosis, the disease caused in humans by the opportunistic parasite Cryptosporidium parvum, is the result of zoonotic or anthroponotic transmission. Molecular characterization of different isolates from humans and other mammalian species has recently shown this species to be heterogeneous; this heterogeneity has been linked to the host of isolation, suggesting that the parasites causing zoonotic cryptosporidiosis and those propagated by anthroponotic transmission are genetically distinct. Here, Fatih Awad-El-Kariem provides an update on the taxonomic and epidemiological significance of these observations, and discusses evidence for and against the clonality hypothesis as a model to explain strain variation in this species.

Molecular epidemiology of cryptosporidiosis outbreaks and transmission in British Columbia, Canada

Isolates from 25 (13 sporadic and 12 outbreak) cryptosporidiosis cases, 24 of which were from British Columbia, Canada, were characterized using nested polymerase chain reaction amplification of the polymorphic internal transcribed spacer 1 locus. Two predominant Cryptosporidium parvum genotypes were found. Twelve (8 sporadic and 4 outbreak) isolates amplified with the cry7/cry21 primer pair and 12 (5 sporadic and 7 outbreak) isolates amplified with the cry7/cryITS1 primer pair. Multi-locus gene analysis using sequence polymorphisms on 3 other loci, i.e., the thrombospondin-related adhesion protein gene, the dihydrofolate reductase gene, and the 18S rRNA gene on 8 (4 outbreak and 4 sporadic) isolates showed non-random association among the human and animal alleles of the 4 different C. parvum gene loci. Associations between these 2 parasite genotypes and different routes of cryptosporidiosis transmission such as zoonotic, anthroponotic, and waterborne transmission were studied using municipal population and agricultural information, as well as detection of C. parvum oocysts in municipal drinking water specimens of the residential communities of sporadic and outbreak cases.

Differentiation between human and animal isolates of Cryptosporidium parvum using molecular and biological markers

Isolates of Cryptosporidium parvum obtained from infected humans, calves and lambs were typed using arbitrary primed polymerase chain reaction (AP-PCR) and isoenzyme electrophoresis. All animal isolates tested (n = 17) showed similar profiles in AP-PCR and isoenzyme typing. In AP-PCR assays, 9 out of 15 human isolates showed a distinct "human" profile while the remaining 6 isolates showed the "animal" profile. In isoenzyme typing, 5 human isolates which had shown "human" profiles in AP-PCR demonstrated a unique isoenzyme banding pattern, while 2 isolates which had shown "animal" profiles in AP-PCR gave the "animal" banding pattern. In a murine model of infection, all four animal isolates tested were highly infective but only one of four human isolates identified as "human" type in the AP-PCR and isoenzyme typing systems was infective. The good correlation between the data from the different typing systems supports the hypothesis that there are genetically distinct human and animal populations of C. parvum.