Question
Read the clinical history and answer the following questions: A 15 years old boy was admitted in ward with history of fever, malaise, anorexia and adnominal discomfort. He had a coated tongue, toxemia, relative bradycardia and splenomegaly on palpation of abdomen.
- (a) What is the probable diagnosis and name the aetiological agent. 1 mark(s)
- (b) What is the pathogenesis. 2 mark(s)
- (c) What are the samples to be collected at different stages of the illness. 2 mark(s)
- (d) Describe briefly the laboratory diagnosis. 4 mark(s)
- (e) What is the prophylaxis. 1 mark(s)
Answer
a) Probable diagnosis and aetiological agent Enteric (typhoid) fever — prolonged fever, malaise, anorexia, abdominal discomfort, coated tongue, toxaemia, relative bradycardia (Faget’s sign), and splenomegaly are the classical features. Aetiological agent: Salmonella enterica serovar Typhi (and Paratyphi A/B/C for the milder paratyphoid variant).
b) Pathogenesis Ingested bacilli (in contaminated food/water) survive gastric acidity and invade the ileal mucosa via M cells overlying Peyer’s patches; they are taken up by macrophages, in which they survive and multiply (facultative intracellular pathogen), spreading to mesenteric lymph nodes and then via the thoracic duct into the bloodstream (primary bacteraemia — usually asymptomatic). The organism seeds the reticuloendothelial system (liver, spleen, bone marrow, gallbladder), multiplies there during the incubation period, and re-enters the blood (secondary bacteraemia), producing the clinical illness. Peyer’s patch hyperplasia and necrosis can progress to ulceration (classically over the ileum), risking haemorrhage or perforation. The gallbladder may harbour the organism chronically, producing the carrier state.
c) Samples at different stages
- 1st week: Blood culture (bacteraemic phase — highest yield).
- 2nd–3rd week: Stool and urine culture (organism excreted as it localizes to gut/gallbladder/kidney); blood culture yield falls.
- Throughout: Bone marrow culture — highest sensitivity at any stage, even after antibiotics have been started, since it is less affected by prior treatment.
- From ~2nd week: Serum for Widal test (antibody rises).
d) Laboratory diagnosis
- Culture — blood culture (gold standard in the first week, using bile broth to neutralise any antibacterial activity), bone marrow culture (most sensitive overall), stool/urine culture (later in the illness); isolates identified biochemically and confirmed by slide agglutination with specific O and H antisera.
- Widal test — demonstrates a rising titre of agglutinating antibody against O and H antigens in paired sera (acute and convalescent); a single high titre is only suggestive, and false positives/negatives limit its reliability.
- Newer serology — Typhidot, IgM/IgG dot-EIA for rapid diagnosis.
- Molecular methods — PCR for S. Typhi-specific genes, where available.
e) Prophylaxis Safe drinking water and food hygiene, proper sewage disposal, health education on hand hygiene; typhoid vaccination — Vi capsular polysaccharide vaccine or the newer Vi-conjugate vaccine (better immunogenicity, usable in young children), and the live attenuated oral Ty21a vaccine; identification and treatment/exclusion of chronic carriers (especially from food-handling occupations).