Question
A 50-year-old woman, an agriculture worker came with complaints of fever, malaise, headache with yellow discolouration of sclera in eyes for the past 5 days. O/E microalbuminuria. There were floods in her place in the previous week. (
- (a) What is your diagnosis ( 2 mark(s)
- (b) Describe the pathogenesis ( 3 mark(s)
- (c) Lab diagnosis ( 6 mark(s)
- (d) Classify various causes of bloodstream infection with examples. 4 mark(s)
Answer
a) Diagnosis Leptospirosis (Weil’s disease) — agricultural occupation with flood-water exposure, fever, jaundice, and renal involvement (microalbuminuria) are the classic picture.
b) Pathogenesis Leptospira interrogans enters through cuts/abrasions in skin or through intact mucosa (conjunctiva, oropharynx) on contact with water or soil contaminated with the urine of infected rodents (or other reservoir animals) — the flood-water exposure in this case is the classic transmission setting.
- Leptospiremic phase: the organism disseminates hematogenously to multiple organs, its endotoxin-like lipopolysaccharide and outer-membrane proteins directly damaging vascular endothelium, producing widespread vasculitis and capillary leak — the basis of the disease’s multi-organ character.
- Organ involvement: hepatic — jaundice out of proportion to the relatively mild hepatocellular necrosis seen on biopsy (canalicular cholestasis predominates); renal — interstitial nephritis and acute tubular necrosis producing the microalbuminuria/renal impairment seen here; pulmonary — capillary hemorrhage in severe (Weil’s) disease; muscular — myositis causing myalgia.
- Immune phase: after an interval of relative improvement, an immune-mediated second phase may follow, driving aseptic meningitis and uveitis as antibody-antigen complexes deposit in these tissues.
c) Laboratory diagnosis
- Direct demonstration (first week, leptospiremic phase): dark-field microscopy of blood/CSF for the characteristic hook-ended spirochete; culture on Fletcher’s or EMJH (Ellinghausen-McCullough-Johnson-Harris) semisolid medium — slow-growing (up to 4–6 weeks), so rarely useful for immediate management; PCR on blood/urine — most sensitive method in the early leptospiremic phase, before antibodies appear.
- Serology (from the second week, leptospiruric phase): Microscopic Agglutination Test (MAT) — the gold standard, using live leptospiral antigens against paired sera to demonstrate a rising titre, but technically demanding and available only in reference laboratories; IgM-ELISA — rapid, widely used screening test suitable for bedside decision-making.
- Supportive findings: deranged liver function tests (raised bilirubin with only mildly raised transaminases — a discriminating pattern from viral hepatitis), raised blood urea/serum creatinine, urine microscopy showing microalbuminuria and granular casts, thrombocytopenia, and raised CPK (reflecting myositis).
d) Classification of causes of bloodstream infection
- Bacterial — Gram-positive (Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus), Gram-negative (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhi — enteric fever bacteremia), spirochetal (Leptospira interrogans, relapsing-fever Borrelia).
- Viral — Dengue, Chikungunya, Cytomegalovirus, HIV (during acute retroviral syndrome).
- Fungal — Candida species (catheter-related fungemia), Cryptococcus neoformans (in the immunocompromised).
- Parasitic — Plasmodium species (malaria), Trypanosoma.
- By clinical source — catheter/device-related bacteremia, infective endocarditis, urosepsis, intra-abdominal/biliary sepsis, and primary bacteremia without an identifiable focus.