Salmonella Infections in Humans

1. Salmonella Infections in Humans Mark Pallen

2. Salmonella infections in humans Enteric fever typhoid and paratyphoid fevers typhi, paratyphi A, B, C systemic infection infects only humans GI symptoms may not be evident Salmonella gastroenteritis non-typhi serovars zoonosis: predominantly food-borne can be complicated by septicaemia more common with some serovars, e.g. S. dublin (15% mortality rate when septicemic in the elderly) Metastatic disease, e.g. osteomyelitis

3. Overview Bacteriology Epidemiology Clinical features Diagnosis Treatment Prevention Pathogenesis

4. Bacteriology Salmonella enterica one species, ~2000 serovars Non standard nomenclature common S. enterica serovar Typhimurium or S. typhimurium rod-shaped, non-spore-forming Gram-negative bacterium belongs to the family Enterobacteriaceae close relative of E. coli Motile by peritrichous flagella (H antigen). nonmotile exceptions: S. gallinarum and S. pullorum

5. Antigenic Structure Kauffmann-White antigenic scheme agglutination reactions with specific antisera against Salmonella antigens O antigens characteristic sequence of repeating polysaccharide units in LPS. H antigens flagellar antigens (protein) and may occur in one of two phase variations. Vi antigen a capsular polysaccharide homopolymer of N-acetyl galactosamineuronic acid

6. EpidemiologyEnteric fever person-to-person spread no animal reservoir contamination with human faeces usual vehicle contaminated water. occasionally, contaminated food (usually handled by an individual who harbours S. typhi)

7. EpidemiologyNon-typhoidal serovars zoonosis with enormous animal reservoir common animal reservoirs are chickens, turkeys, pigs, and cows contaminated food is major vehicle, usually: red and white meats, raw eggs, milk & dairy products many other possibilities, from spices or chocolate to cannabis can follow direct contact with infected animals (e.g. farm trip, reptiles as pets)

8. EpidemiologyNon-typhoidal serovars outbreaks common In Catering establishments In Hospitals Stanley Royd Hospital outbreak now careful attention to hospital kitchen hygiene

9. EpidemiologyNon-typhoidal serovars Food-borne transmission by contamination of cooked food by raw food failing to achieve adequate cooking temperatures. secondary cases by person to person spread are common in outbreaks food handlers who practice good hygiene very rarely responsible for outbreaks

10. Salmonella in eggs various Salmonella serovars isolated from the outside of egg shells S. enteritidis PT4 present inside the egg, in the yolk vertical transmission deposition of the organism in the yolk by an infected layer hen prior to shell deposition.

11. Infectious dose typically about 1,000,000 bacteria much lower if the stomach pH is raised much lower if the vehicle for infection is chocolate protects the bacteria in their passage through the stomach an infectious dose of about 100 bacteria

12. Epidemiologycarrier states carrier state may last from many weeks to years with faecal shedding convalescent carrier chronic carrier ~3% of persons infected with S. typhi ~0.1% of those infected with non-typhoidal salmonellae potential for cross-contamination of foods by the infected handler �Typhoid Mary� Mallone but more common in textbooks than in real life

13. Laboratory Diagnosis Isolated from stool, blood and urine in enteric fever (blood cultures need to be taken!) Isolated from stool in gastroenteritis Appears as a non-lactose fermenter on MacConkey agar or similar selective agar

14. Laboratory Diagnosis Biochemical tests and serological tests must be done in parallel Some other bacteria, e.g. Citrobacter, may have similar serological profiles Commercial kits commonly used, e.g. API20 Phage typing done for epidemiological purposes E.g. to find source of outbreak Certain phage types predominate nationally S. typhimurium PT4 S. enteritidis DT109

15. Treatment Gastroenteritis replace fluid loss by oral and intravenous routes antibiotics are not recommended for uncomplicated gastroenteritis do not shorten illness prolong excretion. antibiotic therapy reserved for the septicaemic and metastatic disease Typhoid fever and enteric fevers should be treated with antibiotics usually ciprofloxacin rise of resistance

16. Prevention Remove source Salmonella free life-stock Vaccinate chicks Interrupt transmission Good food hygiene Cook food properly Keep raw and cooked foods apart Public Health: clean water Strengthen host vaccination

17. Salmonella vaccines Vaccination of travellers against typhoid recommended, but does not remove need for good hygiene Three licensed vaccines Traditional heat-killed very reactogenic Vi subunit vaccine live oral vaccine, S. typhi Ty21A Salmonellas can act as live attenuated carriers for other antigens So far only experimental No vaccines for gastroenteritis

18. Clinical FeaturesEnteric Fever incubation period 10 to 14 days septicaemic illness myalgia and headache fever splenomegaly leukopenia abdominal pain Rose spots (macular rash on abdomen) 10% fatal positive blood, urine, and stool cultures Sequelae: intestinal haemorrhage and perforation

19. Clinical featuresGastroenteritis incubation period depends on dose symptoms usually begin within 6 to 48 hours Nausea and Vomiting Diarrhoea Abdominal pain Myalgia and headache Fever duration varies, usually 2 to 7 days seldom fatal, except in elderly or immunocompromised

20. Pathogenesis Gastroenteritis Pathogenic salmonellae ingested in food survive passage through the gastric acid barrier invade intestinal mucosa invasion of epithelial cells stimulates the release of proinflammatory cytokines induces an inflammatory reaction causes diarrhoea and may lead to ulceration and destruction of the mucosa

21. PathogenesisEnteric Fever Bacteria invade mucosa or Peyer's patches of small intestine (?M cells), pass into mesenteric lymph nodes where they multiply and then enter the blood stream via the thoracic duct Primary bacteraemia cleared by RES, bacteria multiply in RES cells and destroy them Facultative intracellular parasites

22. PathogenesisEnteric fever Secondary bacteraemia occurs and results in spread to other organs. Infection of the biliary tract. Multiplication in biliary tract leads to seeding the intestine with large numbers of bacteria. Involvement of intestinal lymphoid tissue may lead to necrosis and ulceration. In untreated nonfatal cases, temperature drops in 3 to 4 weeks (onset on immunity?)

23. S. typhimurium in the mouse S. typhimurium causes gastroenteritis in humans causes typhoid-like disease in mice infection can be established orally or systemically used as model of typhoid primary mechanisms of pathogenesis invasion of the intestine survival and growth in macrophages

25. Invasion membrane ruffling depends on Spi1 Type III secretion system Spi1 effectors SopE affects actin cytoskeleton SipA binds to actin, inhibits depolymerization SopB inositol phosphate phosphatase SptP: PTPase, disrupts the actin cytoskeleton

27. Invasion Salmonella enters host cells by inducing host cell membrane ruffling membrane ruffles non-specifically wrap around the bacteria and pull them into the cell Salmonella end up in membrane-bound vesicles called Salmonella-containing vacuoles (SCV).� SCVs are unique environments within the cell defined by the bacteria within them As they mature, SCVs do not follow the defined routes of cellular trafficking of vesicles and differ in their composition from normal phagosomes

28. Survival in cells Spi2 Type III secretion system expressed in cells activated by acidic pH in phagosome mutants severely attenuated in mice currently under intense investigation PhoP/PhoQ Pags Prgs

30. Salmonella can also trigger apoptosis through Spi1

31. Salmonella cellular subversion

32. Salmonella cellular subversion

38. Salmonella Genome Sequencing Projects Completed S. typhiumurium LT2 at WashU Multi-resistant S. typhi from Vietnam at Sanger Centre Ongoing Salmonella five-pack at Sanger

39. Online bibliography http://www.hhmi.org/lectures/1999/index.htm http://www.sanger.ac.uk/Projects/ http://genome.wustl.edu/gsc/bacterial/salmonella.shtml http://www.salmonella.org/ http://www.who.int/inf-fs/en/fact149.html http://www.bmj.com/cgi/content/full/313/7065/1094 http://vm.cfsan.fda.gov/~mow/chap1.html http://129.109.112.248/microbook/ch021.htm