Environmental transmission pathways for cryptosporidium parvum in urban small holder dairy

Abstract

A study was carried out to obtain an understanding of the role of environmental transmission pathways for Cryptosporidium parvum from dairy farming households to humans in Dagoretti Division, Nairobi. Household questionnaires were administered to capture the household members in contact with cattle, cattle dung and the frequency of such contact. A previous study had positively associated Crptosporidia in cattle with households having shallow wells. Cattle faecal samples were collected and stained for Cryptosporidia by Modified Ziehl Neelsen and Immuno-fluorescent assay and households with cattle found positive were selected for this study. Further selection was based on the presence of shallow well, and weighted on the number of cattle that were positive. From each household a total of 22 samples were collected; 1 sample of heaped manure and 8 from a manure heap made for purposes of viability study, 6 soil samples from around the cattle shed and 2 from well margins, 3 samples of slurry from shed, 1 sample of tap water and 1 sample of shallow well water. The manure, slurry and soil samples were assessed for presence and isolation of Cryptosporidium spp. oocysts. In addition, manure and slurry samples were characterized for pH and temperature for manure heaps on the day of sampling. Soil samples were analyzed for both pH and gravimetric moisture content. Water samples were tested for presence of fecal coliforms which were used as indicator organisms for faecal contamination and as proxies for C. parvum. Viability of Cryptosporidia oocysts in stacked manure was determined by isolation of oocysts and their viability determined using infant mice models. The soil moisture content 20.53% (Range 35.76, SD. 6.51), was favourable to survival of oocysts while the average manure temperature 26.2OC, (Range 18, SD 4.91) and pH values were 8.1 for manure, 7.8 for slurry, and 7.7 for soil were potentially unfavourable to viability of oocysts. Three percent (5/160) of the soil samples were positive, seven percent of slurry samples (4/60), fifteen percent of the heaped manure (3/20) and four percent (7/160) of manure we heaped for infectivity study. Twenty five percent (1/4) of treated well water, eighty eight percent (15/17) of untreated well water, and fourty two percent (5/12) of Nairobi City Council (NCC) water in storage facilities were positive for fecal coliforms while none was detected in the two samples of rain water and the three samples of NCC water sampled directly from the tap. Two samples of manure heaped for infectivity study from the first and second week respectively were positive on Immunochromatographic test indicating that they had viable C. parvum oocysts. A quantitative risk assessment was carried out to assess the risk of infection with C. parvum using the Codex Alimentarius framework, which comprises hazard identification, hazard characterization, exposure assessment, and risk characterization. Five major transmission pathways were identified and an event tree constructed to assess disease exposure in the two most vulnerable populations (malnourished children and people living with HIV/AIDSPLWAs). From these observations, a probabilistic quantitative risk assessment model was developed and parameterised with data from the survey questionnaire, detailed mapping and secondary data which gave a daily risk of 2 cases per 10,000 people. Although cattle are the source of C. parvum, the risk from eating raw vegetables was three times higher than that associated with consuming milk. This was largely explained by good milk-handling and poor manure-handling practices. Information on risks associated with different pathways was used to develop community-based interventions for decreasing risks associated with urban cattle.