SALMONELLA (GASTROENTERITIS, TYPHOID FEVER, PARATYPHOID FEVER)

 

INTRODUCTION: All salmonellae are classified in the species Salmonella enterica with seven subspecies. Nearly all human pathogen salmonellae are grouped under S. enterica, subsp. enterica. Salmonellae are further subclassified in over 2000 serovars based on their O and H antigens, which used to be designated as species. Typhoid salmonelloses are caused by the serovars typhi and paratyphi A, B, and C.

MODES OF TRANSMISSION: The salmonellae are taken up orally and the invasion pathway is through the intestinal tract, from where they enter lymphatic tissue, first spreading lymphogenously, then hematogenously. A generalized septic clinical picture results. Human carriers are the only source of infection. Transmission is either direct by smear infection or indirect via food and drinking water.  Anti-infective agents are required for therapy including but not limited to; ampicillin, cotrimoxazole, 4-quinolones). An active vaccine is available to protect against typhoid fever. Enteric salmonelloses develop when pathogens are taken up with food. The primary infection source is usually livestock. These relatively frequent infections remain restricted to the gastrointestinal tract. Treatment with antiinfective agents is necessary in exceptional cases only.  It is not known why typhoid salmonellae only cause systemic disease in humans, whereas enteric salmonella infections occur in animals as well and are usually restricted to the intestinal tract.

DIAGNOSIS: The method of choice is detection of the pathogens in cultures. Selective indicator mediums are used to isolate salmonellae in stool. Identification is done using metabolic patterns. Serovar classification is determined with specific antisera in the slide agglutination test. Culturing requires at least two days. Typhoid salmonelloses can be diagnosed indirectly by measuring the titer of agglutinating antibodies to O and H antigens (according to Gruber-Widal). To provide conclusive proof the titer must rise by at least fourfold from blood sampled at disease onset to a sample taken at least one week later.

THERAPY: Typhoid salmonelloses must be treated with anti-infective agents, whereas symptomatic treatment will suffice for enteric infections. Symptomatic treatment encompasses slowing down intestinal activity (e.g., with loperamide) and replacing fluid and electrolyte losses orally as required. Eliminating the infection in chronic stool carriers of typhoid salmonellae, 2–5% of cases, presents a problem. Chronic carriers are defined as convalescents who are still eliminating pathogens three months after the end of the manifest illness. The organisms usually persist in the scarified wall of the gallbladder. Success is sometimes achieved with high-dose administration of anti-infective agents, e.g., 4-quinolones or aminopenicillins.

PREVENTION: The main method of effective prevention is to avoid exposure: this means clean drinking water, prevention of food contamination, avoidance of uncooked foods in countries where salmonellae occur frequently, disinfection of excreta containing salmonellae or from chronic carriers, etc. It is also important to report all cases to health authorities so that appropriate measures can be taken.

RELATED;

1.  BRUCELLA  

2.  GRAM NEGATIVE ENTERIC BACTERIA

3.  BACTERIOLOGY

4. MEDICAL MICROBIOLOGY

REFERENCES