Question
A thirty two years old lady presented with complaints of step ladder type of high fever, headache and coated tongue for the past ten days. She had hepatosplenomegaly and bradycardia. Blood count showed leucopoenia. Answer the following: What is the diagnosis of this condition Name the species of bacteria causing this condition Discuss about the pathogenesis of this disease How will you confirm the diagnosis in the laboratory Name the vaccines used for prevention of this disease (1+1+3+3+2)
Answer
Diagnosis: Enteric (typhoid) fever — the characteristic step-ladder pattern of high fever (stepwise rise over successive days), headache, coated tongue, hepatosplenomegaly, relative bradycardia, and leucopoenia (unusual among bacterial infections, which typically cause leucocytosis — a useful distinguishing clue) is classical.
Species of bacteria: Salmonella enterica serovar Typhi (Paratyphi A/B/C cause the milder, related paratyphoid fever).
Pathogenesis Ingested bacilli survive gastric acidity and invade ileal mucosa via M cells overlying Peyer’s patches; taken up by macrophages, in which the facultative intracellular organism survives and multiplies, it spreads to mesenteric lymph nodes and then via the thoracic duct into blood (primary bacteraemia, usually asymptomatic). The organism seeds the reticuloendothelial system (liver, spleen, bone marrow, gallbladder), multiplies during the incubation period, and re-enters the blood (secondary bacteraemia), producing the clinical illness — the step-ladder fever reflects successive waves of bacteraemic seeding. Peyer’s patch hyperplasia can progress to necrosis and ulceration over the terminal ileum, risking haemorrhage/perforation; the gallbladder may harbour the organism chronically (carrier state). Bone-marrow/reticuloendothelial suppression of granulopoiesis by the organism’s endotoxin is thought to contribute to the characteristic leucopoenia.
Laboratory confirmation
- Blood culture — best yield in the first week (bacteraemic phase); bile broth neutralises antibacterial serum activity.
- Bone marrow culture — most sensitive at any stage, even after antibiotics have begun.
- Stool and urine culture — become positive from the second/third week as the organism localizes to the gut and gallbladder/kidney.
- Widal test — demonstrates a rising titre of O and H agglutinating antibody in paired sera; limited by cross-reactions/background titres, so a single titre is only suggestive.
- Newer methods — Typhidot/IgM dot-EIA and PCR where available.
Vaccines for prevention
- Vi capsular polysaccharide vaccine — injectable, single dose, ~3 years’ protection, usable from 2 years of age.
- Vi-conjugate (typhoid conjugate) vaccine — improved immunogenicity, usable in infants from 6 months, longer-lasting, now WHO-preferred.
- Live attenuated oral Ty21a vaccine — 3–4 oral doses on alternate days, not for immunocompromised individuals or young children.