Question
A 25 years old male comes to a medical outpatient department with complaints of high fever with relative bradycardia for the past one week, he has headache, coated tongue and hepatosplenomegaly. Answer the following:
- (a) What is the probable diagnosis. 1 mark(s)
- (b) What is the causative organism. 1 mark(s)
- (c) Describe the pathogenesis of this disease. 3 mark(s)
- (d) Discuss the laboratory diagnosis of this disease. 3 mark(s)
- (e) Discuss the vaccines used for prevention of this disease. 2 mark(s)
Answer
a) Probable diagnosis: Enteric (typhoid) fever.
b) Causative organism: Salmonella enterica serovar Typhi (Paratyphi A/B/C cause the milder paratyphoid variant).
c) Pathogenesis Ingested bacilli survive gastric acid and invade ileal mucosa through M cells overlying Peyer’s patches; taken up by macrophages, in which the organism survives and multiplies (facultative intracellular pathogen), it spreads to mesenteric lymph nodes and then via the thoracic duct into the 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 — fever, relative bradycardia (Faget’s sign), coated tongue, and hepatosplenomegaly (from RE-system involvement). Peyer’s patch hyperplasia can progress to necrosis and ulceration, risking intestinal haemorrhage/perforation; the gallbladder may harbour the organism chronically (carrier state).
d) Laboratory diagnosis
- Blood culture — highest yield in the first week (bacteraemic phase).
- Bone marrow culture — most sensitive at any stage, even after antibiotics.
- Stool and urine culture — useful from the second/third week as the organism localizes to the gut/gallbladder/kidney.
- Widal test — demonstrates a rising titre of O and H agglutinins in paired sera; limited by false positives/negatives.
- Newer rapid serology (Typhidot, IgM dot-EIA) and PCR where available.
e) Vaccines
- Vi capsular polysaccharide vaccine — injectable, single dose, protects for ~3 years, usable from 2 years of age.
- Vi-conjugate (typhoid conjugate) vaccine — improved immunogenicity, usable in infants from 6 months, longer-lasting protection, now WHO-preferred.
- Live attenuated oral Ty21a vaccine — 3–4 oral doses on alternate days, not for immunocompromised individuals or children under 6 years.