Salmonella transmission

Present scientific evidence indicates that transmission of enteric pathogens (particularly Campylobacter) is mainly horizontal, while vertical transmission from parent to progeny via the egg is considered much less likely. Studies have shown that that the majority of Salmonella and Campylobacter strains do not cause disease symptoms in poultry and that between 40% and 80% of chicken flocks are Campylobacter positive. 

Holmberg, S. D., J. G. Wells, M, L. Cohen, 1984, Animal-to-Man Transmission of Antimicrobial-Resistant Salmonella ... 

Similar to E. coli, the main transmission route of Salmonella to vegetables is through fecal contamination, cross-contamination and food handling. In a 12-month abattoir study, Milnes et al. (2007) determined the fecal carriage of Salmonella to be 23.4% in swine 1.4% in cattle, and... 

Salmonella typhimurium DT104 is usually resistant to ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline. An outbreak of 25 culture-confirmed cases of multidrug-resistant S. typhimurium DT104 has been identified in Denmark (54). The strain was resistant to the above-mentioned antibiotics and nalidixic acid and had reduced susceptibility to fluoroquinolones. A swineherd was identified as the primary source (54). The DT104 strain was also found in cases of salmonellosis in Washington State, and soft cheese made with unpasteurized milk was identified as an important vehicle of its transmission (55). 

Salmonella usually remains in the intestines for up to 5 weeks - and in some cases for many months. Be aware that some individuals can become chronic carriers of Salmonella bacteria and 2% may develop chronic arthritis. Good personal hygiene and handwashing techniques would prevent the majority of transmissions. Wash hands thoroughly with warm, soapy water after visits to the restroom and before food preparation. 

Propagated outbreaks of infection relate to the direct transmission of an infective agent from a diseased individual to a healthy, susceptible one. Mechanisms of such transmission were described in Chapter 7 and include inhalation of infective aerosols (measles, mumps, diphtheria), direct physical contact (syphilis, herpes virus) and, where sanitation standards are poor, through the introduction of infected faecal material into drinking water (cholera, typhoid) or onto food (Salmonella, Campylobacter). The ease of transmission, and hence the rate of onset of an epidemic (Fig. 9.3) relates not only to the susceptibility status and general state of health of the individuals concerned but also to the virulence properties of the organism, the route of transmission, the duration of the infective period associated with the disease, behavioural patterns, age of the population group and the population density (i.e. urban versus rural). 

Transmission of Salmonellosis occurs in the majority of cases by contaminated food. The most common sources are poultry, eggs, fruits, vegetables, dairy products and shellfish. Peanut butter has been also implicated in an outbreak of salmonellosis in the USA and powdered infant formula in two outbreaks with Salmonella enteric in infants in France. 

Transmission of Salmonella infection may also occur from man to man and animal to man. Salmonellosis outbreaks have been reported in person handling chicken, ducks, kittens and hedgehogs. 

As already indicated, the main source of Salmonella infection and transmission is by food, the main reservoir being poultry, eggs and egg products (Maki 2009). 

Salmonella typhi is a human pathogen. The mode of transmission is by contamination of water by fecal excretion, but it is also transmitted from person to person by hands and contact with infected patients. Food handlers who carry Salmonella typhi pose an increased risk of transmission of infection. Salmonella typhi are excreted in the stool of chronic carriers who may be asymptomatic as well as in the stool and urine in patients with active disease. Outbreaks of typhoid fever are associated with inadequate sanitary infrastructures in developing countries due to inadequate measures of hygiene. Contamination of water in the community is the main source of infection in endemic areas. In developed countries the main source of contamination is by food supplies infected by carriers. Flies and lack of adequate standards of proper disposal of waste may also account for the spread of infection. 

Transmission of Salmonella typhi may also occur in day care centers and schools by direct contact with the fecal-oral route. Particularly attention should be taken by nursing and medical personnel in infectious units who care for patients with Salmonellosis and typhoid fever. 

It is estimated that 3-5% of untreated patients become carriers of S. typhi. Chronic carriers pose a significant pool of infected individuals with Salmonella typhi, because they shed bacilli for a long period. The risk is enhanced since these carriers are difficult to identify because the majority are asymptomatic. Furthermore, Salmonella typhi colonize the gallbladder and biliary tree and they are excreted in the stool by the enterohepatic circulation. Even the removed of the gallbladder is not always an effective measure to abolish the carrier state, since Salmonella typhi spread to the intrahepatic bile ducts. Identification of carriers is important in order to contain and limit the transmission to healthy individuals. Carrier s state is confirmed by isolation of Salmonella typhi in stool culture. Treatment of carriers with amoxicilhn, trimethoprim-sulfamethoxazole or ciprofloxacin is indicated. 

Agent Index A340 Class Index C26 Typhoid Feve Salmonella typhi Type Bacteria Insidious onset of sustained fever, severe headache, malaise, loss of appetite, and usually constipation (although it may cause diarrhea). Individuals may become asymptomatic carriers capable of spreading the disease (e.g. Typhoid Mary). Routes Ingestion Secondary Hazards Fecal Vector (mechanical) Incubation 3 to 90 days Mortality Rate < 10% Reservoir Humans Direct Person-to-Person Transmission is possible (fecal/oral). 

Salmonella paratyphi is a bacterial enteric (intestinal) infection with an abrupt outbreak, which produces the following symptoms continued fever, headache, malaise, enlarged spleen, rose spots on the trunk of the body, and diarrhea. These symptoms are similar to those of typhoid fever, but the death rate is much lower. Mild and asymptomatic infections may also occur upon exposure. Outbreaks and locations are similar to those of the other salmonella bacteria. The infectious dose is 1000 organisms by ingestion. Transmission occurs by direct or indirect contact with feces or, in rare cases, urine of patients or carriers. It is spread by food, especially miUc and dairy products, shellfish, and in some isolated cases, water supplies. Incubation depends on the strength of the dose, but usually 1-3 weeks for enteric fever and 1-10 days for gastroenteritis. Antibiotic treatment with chloramphenicol, ampicillin, or TMP-SMX is usually effective. 

Sosinsky, G.E., Francis, N.R., DeRosier, D.J., Wall, J.S., Simon, M.N. and Hainfeld, J. (1992). Mass determination and estimation of subunit stoichiometiy of the bacterial hook-basal body flagellar complex of Salmonella typhimurium by scanning transmission electron microscopy. Proc. Natl. Acad. Sci. U.S.A. 89,4801-4805. 

Beeause Salmonella spp. are ubiquitous, transmission can occur through contact with soil, wild birds, rodents, insects, pet animals, and water. In humans, a simple handshake ean spread the bacterium. Feed (figure 1) is always a main suspect, since ingredients are harvested with little regard to possible eontamination by wildlife. In recent years, concerns have been raised because many strains of Salmonella spp. have become resistant to several of the antibiotics traditionally used for treatment, in both animals and humans. An effective prevention strategy is required to limit exposure to this pathogen on the farm. It is necessary to monitor animals, visitors, equipment. 

Humphrey, T.J. and Banning, D.G. (1988) The vertical transmission of salmonellas and formic acid treatment of chicken feed. A possible strategy for control. Epidemiology and Infection 100 43-49. 

Pathogens (no. per 100 ml) Total coll, salmonella, etc. 10 -10 Disease transmission... 

Our laboratories have investigated NAD metabolism in both prokaryotic and eukaryotic systems. Background information in this area has previously been reviewed (1-3). The work we describe here on eukaiyotic systems is initial experiments to examine the possible role of ADP-ribosylation in modulating synaptic transmission in die nervous system, hi this article, we also summarize our present understanding of NAD metabolism and its regulation in the bacterium Salmonella typhimurium, and present preliminary data for a link between NAD turnover cycles and DNA repair in this bacterium. 

Other approaches to the proper assessment of R-factor effects include (a) a survey of the incidence in I967 of antibiotic resistance in Salmonella from clinical sources in the United States showing no significant increase during the past five years (b) a study of the incidence of resistance (present) and transmissible factors (not present) in drug-free primitive human and animal communities (c) analysis of pre-antibiotic era isolates (some resistance) and (d) the search for and the mode of action of agents (acridines) which prevent effective transfer of R-factors. 

---