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Evaluation and Risk Assessment of Zoonotic Transmission of Cryptosporidium


The project aims, within 6 objectives, to investigate the relationship between isolates of Cryptosporidium in human disease and in animal and environmental contacts, and to establish the host range of Cryptosporidium species and genotypes.
<OL> <LI> Estimate the prevalence of zoonotic cryptosporidiosis in humans and quantify the oocyst load from human, animal and environmental sources.
<LI> Investigate the relationships between isolates obtained in objective 1 (and other selected isolates from the CRU’s bank of isolates)
<LI>Using a case control study, explore the role of non-farmed animals in the zoonotic transmission of cryptosporidiosis.
<LI>Develop an epidemiological-derived population frame work to aid the investigation and surveillance data analysis of zoonotic cryptosporidiosis.
<LI> Using animal infectivity studies, identify Cryptosporidium isolates of human origin with the ability to colonise different animal host species over time.
<LI>Expand the quantitative risk assessment (QRA) for the transmission of zoonotic cryptosporidiosis.

More information

Progress: Year 1 of the project was primarily focussed upon the complex organisation of such an enhanced study involving a wide number of collaborating organizations (VLA, NPHS for Wales, HPA, Local Authorities). Decisions on how the project is to be run from the additional questions on the questionnaires through to sample strategies, sample handling and identification, case-control design, harmonisation of molecular and microscopical techniques have all been collaboratively agreed and at all levels of involvement. Project meetings have been held regularly and all decisions have been approved by a panel of experts and lay people at a steering group meeting. Training of appropriate staff in microscopy and molecular techniques has taken place. Harmonisation of DNA extraction techniques, microscopy techniques and molecular detection techniques has been agreed and additional quality control measures have been designed to act as validation of the results of each collaborating laboratory. <P>

Enhanced surveillance comprises identification of human cases of cryptosporidiosis, via a specifically designed, EHO-administered questionnaire as part of existing routine case follow-up. Consent for further sampling will be obtained from cases reporting animal or relevant environmental exposures. EHOs will then inform the regional VLA of all cases by faxing the questionnaire, with case name and address deleted. The regional VLA will send trained scientific personnel to sample the suspected sources or vehicles of Cryptosporidium as indicated on the questionnaire. Samples will be investigated for the presence of Cryptosporidium oocysts by IFAT microscopy. The animal faecal samples DNA will be subjected to molecular analysis at the VLA and human case samples at the Cryptosporidium Reference Unit in Swansea submitted from the local diagnostic laboratories. The environmental samples (including private water samples) will be tested for the presence of Cryptrosporidium at CREH Analytical Limited and typed at the CRU in Swansea. These epidemiologically-linked isolates will be typed using molecular methods now harmonised between the CRU and VLA Weybridge. DNA exchange and confirmation by DNA sequence analysis of the ssu rDNA gene will be undertaken for quality control purposes. Further sub-typing will be undertaken using molecular methods selected from the GP60 sequence-based tool, microsatellite DNA markers; and single strand conformation polymorphism analysis.
A case control study to investigate the role of pets in human cryptosporidiosis has been designed and approved by project management and steering groups and ethical approval is being sought from the Central Office for Research Ethics Committee. This CC study will establish whether pets in households where human cases of cryptosporidiosis are reported are more likely to excrete Cryptosporidium than those in non-case households. The incidence of diarrhoea among pets will also be measured. Molecular techniques as above will be employed.
Animal infectivity studies have been designed and agreed upon to study the ability of human isolates to colonise calves, lambs, piglets, chickens and turkeys. Provision has been implemented to focus, in particular, on isolates previously not investigated in this way. In addition the design of the study has allowed for serial infectivity studies to crucially examine the viability and stability of the isolates after passage through animal models.
Finally, a VLA database has been established to collate all data from the enhanced epidemiological studies, the case-control studies and the animal infectivity studies. Access has been arranged for, but limited to, all vital personnel. This database has been arranged to allow back up every 24hours minimum to help ensure minimal data loss.
It is too near the beginning in the project to draw any conclusions regarding the transmission potential and evaluation of the zoonotic nature of Cryptosporidium species. It has been demonstrated that this research is welcome across the HPA, NPHS for Wales, VLA and EHD as there is scant knowledge of Cryptosporidium prevention and control.


Veterinary Laboratories Agency, UK
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