Flies as vectors for Salmonella spp. and their control in pork butcheries in Kampala, Uganda – A contribution to improve public health
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Heilmann, M. 2016. Flies as vectors for Salmonella spp. and their control in pork butcheries in Kampala, Uganda – A contribution to improve public health. PhD thesis. Berlin, Germany: Freie Universitaet Berlin.
Permanent link to this item: http://hdl.handle.net/10568/78107
Synanthropic flies live close to humans and their animals, feed on their food and breed in faeces and other organic material. As such, they are known vectors for Salmonella spp., which are among the most common causes for foodborne diseases worldwide, especially in the developing world due to poorer sanitary conditions. Given that pork consumption in Uganda is rapidly increasing, while good food safety practices remain absent, this study aimed to assess the occurrence of Salmonella spp. in pork joints and to investigate the impact of insecticide-treated fence material on the number of flies in selected pork joints Kampala, Uganda. From June – October 2014 a baseline study was conducted in Kampala with 60 randomly selected pork joints, including interviews with 60 butchers and 240 customers. Best-worst (BW) method was used during face-to-face interviews to assess key practices of pork butchers in Kampala and their perception of what’s important to their customers when buying pork. Samples of houseflies, foodstuff and equipment were taken once in all butcheries and tested for Salmonella (S.) spp. Cultural isolation was performed according to ISO 6579:2002. After the baseline, a pilot study was done to investigate the impact of insecticide-treated fence material allocating 18 pork joints to an intervention and 5 to a control arm. A biphasic weekly monitoring using sticky traps with pre-intervention and following intervention was done from August to November 2014. Butchers’ answers indicate that raw pork is the most commonly sold form of meat (53%) followed by fried (30%), roasted (15%) and cooked (2%) pork. This is in line with customers’ answers which reveal raw pork as the most commonly bought form of meat (48%) followed by fried (38%), roasted (9%) and cooked (5%) pork. Pork is the second most common meat consumed at home after beef. A high proportion of butchers (87%) stated that they serve cooked pork with raw accompaniments like avocado, onions, tomatoes or cabbage. Half of the butchers buy pork from the local city abattoir; the rest obtain their meat from other sources. Flies were observed in 80% of pork joints and 43% had other pest animals, such as rodents, birds and other insects according to the enumerator’s observation. The majority of butchers (92%) believed that flies can transmit diseases. The vast majority of butchers (85%) and customers (97%) dislike flies and associate them with health and hygiene issues. By asking sixty butchers what they consider as the most and the least important attribute to their clients, this study revealed that butchers believe that customers care most about “Meat from the same day” and “Cleanliness in the butchery” while “Fat layer of the meat”, “Pest animals in/around the butchery” and “Presence of flies in the butchery” are the least important attributes. Among 693 samples, 8.8% were tested positive for Salmonella spp. Thereby, 7.9% were tested positive for S. Enteritidis. These cases rank from 31.2% for raw pork (24/77), 22.1% for houseflies, 9.1% for water, 5.2% for tomatoes and 3.9% for cabbage. Further, S. Gallinarum was found in 0.9% of cases including 2.6% for tomatoes, 2.6% for onions, 1.3% for cabbage as well as 1.3% for roasted pork. All 154 samples from either butchers’ hands or their equipment were negative. Fly monitoring during intervention has led to a total of 7,953 flies containing 85% M. domestica, 14% Calliphoridae and 0.4% Sarcophagidae. Medians of caught flies in the netted group before and after intervention corresponds with a reduction in catches of 48% (p=0.002), while a slight increase in the control group was observed. Both the high fly abundance and prevalence of S. Enteritidis illustrates the need for improving food safety in pork joints. This accounts in particular for raw vegetables given that interviews indicate that they are mostly served raw. According to butchers’ opinions, flies are less important to customers. However, both customers and butchers dislike flies and the majority associate them with diseases. For establishing an effective and affordable implementation on markets social behaviour and butchers’ knowledge, attitudes and practices should be taken into account when improving food safety including vector control. Insecticide-treated fence material provide a practical, affordable and sustainable solution in controlling flies and are therefore recommended as a complementary strategy to food safety and improve public health.