House flies carry salmonella risk for poultry
products as they are able to spread salmonella poisoning to healthy
hens, say researchers.
Peter Holt and Christopher Geden, scientists for the USDA Agricultural Research Service (ARS), found the house fly (Musca domestica) can pick up salmonella from infected hens. The disease can then be passed on to healthy hens that eat an infected fly. The experiment, described in the ARS's Agricultural Research Magazine, provides insight into one of the ways salmonella can enter the food chain. "This research shows that growers need to pay special attention to fly control using methods of surveillance and treatment that are already available," said Holt. According to the European Food Safety Authority (EFSA), 160,649 cases of human salmonellosis were reported in 2006, making it the second most common zoonotic disease in the EU. Eggs and egg products were the most frequently implicated sources, while 69 out of 179 were linked to chicken and 12 were linked to turkey. The study Healthy chickens were placed in individual, adjacent cages. Fly pupae, which were due to emerge flies in 48 hours, were placed in an open box in the same room. Three days later, the chickens were given water that contained salmonella poisoning and quickly became infected. Within 48 hours, salmonella bacteria were detected on 45 to 50 per cent of the flies, and levels remained at 50 per cent or higher over the next five days. In the next part of the experiment, the infected flies were put in the same room as uninfected hens to determine the risk flies pose as carriers of the disease. While simply being near the hens did not cause the transfer of the bacteria, intestinal colonisation with salmonella occurred in 38 per cent of the birds as a result of them eating the infected flies. Meanwhile, researchers found only minimal bacterial contamination of the hens' crops (a small sack in the digestion system that stores pre-digested food). Holt said: "We found that simple physical contact may not be the primary method of transfer of Salmonella bacteria to different surfaces in a poultry house. But a hen's eating of contaminated flies does seem to be the primary mechanism of transmission of Salmonella from flies to birds." The researchers said that while further investigation is necessary to determine the exact relationship between salmonella, flies and poultry, this study shows measure should be taken to prevent contact between the two animals.
