Paper II
Question
List four bacterial zoonotic infections. Describe the laboratory diagnosis of any one of them (2+4)
Answer
Four bacterial zoonotic infections:
- Anthrax (Bacillus anthracis, from livestock/animal products).
- Leptospirosis (Leptospira species, from rodent urine-contaminated water/soil).
- Brucellosis (Brucella species, from unpasteurized dairy/contact with infected livestock).
- Plague (Yersinia pestis, from rodent fleas).
Laboratory diagnosis of leptospirosis (detailed): Leptospira species are thin, tightly coiled, motile spirochetes; transmission occurs via direct or indirect contact with urine of infected rodents/animals, typically through contaminated water/soil entering the body via cuts, abrasions, or mucous membranes (a genuinely important zoonotic hazard following flooding, as rodent-contaminated water spreads widely — a classical epidemiological association).
- Direct microscopy: dark-field microscopy of blood (during the early leptospiraemic phase, first ~7–10 days) or urine (later, leptospiruric phase) can demonstrate motile spirochetes, though sensitivity is limited and requires expertise.
- Culture: on specialized media (e.g., Fletcher’s or EMJH medium), technically demanding and slow (can take weeks), not useful for acute diagnosis.
- Serology: Microscopic Agglutination Test (MAT) — the reference standard serological test, detecting agglutinating antibody against a panel of Leptospira serovars, typically requiring paired acute/convalescent sera for a rising titre; IgM ELISA — a more rapid, widely used screening test, positive from about the second week of illness.
- Molecular methods: PCR — detects leptospiral DNA in blood (early) or urine (later), useful for early diagnosis before antibody has developed.
- Rapid diagnostic tests: point-of-care immunochromatographic strip tests for IgM antibody, useful in field/outbreak settings.