Brucellosis
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Direct answer
Undulant fever with drenching night sweats, arthralgia, hepatosplenomegaly and a history of raw milk, close contact with goats, sheep or cattle, or laboratory exposure should put brucellosis at the top of the differential — an intracellular infection by Brucella species that can involve almost any organ while the patient looks deceptively well between fever spikes. Diagnosis rests on serology (Rose Bengal plate test as a screen, serum agglutination titres of 1:160 or higher in endemic settings, or a single four-fold rise) and on blood or bone-marrow culture, the marrow being the more sensitive source. Treatment is combination therapy — doxycycline 100 mg twice daily plus streptomycin or rifampicin for six weeks, longer for endocarditis, osteoarticular or neurobrucellosis.
What you must remember
- Species and host: B. melitensis (goats, sheep — most virulent), B. abortus (cattle), B. suis (pigs), B. canis (dogs); India's cases cluster in Uttar Pradesh, Gujarat, Rajasthan, Punjab, Haryana and the southern states where raw milk and unpasteurised dairy are consumed.
- Why undulant: brucellae survive inside macrophages, seeding and reseeding from the reticuloendothelial system, so fever undulates over weeks with malaise, sweats and sacroiliitis or peripheral arthritis (the commonest osteoarticular manifestation in India).
- Classic exam triad: fever, profuse sweating (often described as smelling of wet hay), and arthralgia with hepatosplenomegaly and relative lymphocytosis with normal white cell count.
- Complications map: spondylitis of the lumbar spine (Pedro Pons sign — tenderness at L4), orchitis or epididymo-orchitis, neurobrucellosis, uveitis, and the rarest but deadliest — brucella endocarditis of the aortic valve.
- Serology ladder: Rose Bengal screening; serum agglutination test with prozone phenomenon at very high titres; 2-mercaptoethanol test to detect IgG indicating active disease; ELISA for IgM and IgG. Culture uses Castaneda double-phase medium and carries a laboratory hazard warning — alert the microbiologist.
- Regimens: doxycycline 100 mg twice daily plus streptomycin 1 g intramuscularly daily for two to three weeks (doxycycline-streptomycin preferred for spondylitis) or doxycycline plus rifampicin 600-900 mg daily for six weeks, per WHO-endorsed options; doxycycline in combination remains the backbone in pregnancy alternatives or paediatrics.
- Relapse and response: defervescence within a week is expected; relapse in the first year, usually from spondylitis or inadequate compliance, demands re-treatment with a streptomycin-containing regimen.
A walked-through diagnostic path
Picture a 34-year-old dairy worker from Anand with six weeks of evening fever, sweats and low-back pain, already treated empirically for typhoid without response. Blood counts show mild anaemia with relative lymphocytosis and a mildly raised C-reactive protein. Step one widens the differential against enteric fever, tuberculosis and typhus — all common in the same belt. Step two sends Rose Bengal and serum agglutination; a titre of 1:320 with a positive 2-mercaptoethanol test marks active infection, and bone-marrow culture is requested if the initial blood cultures in Castaneda medium stay negative at six weeks. Step three stages the disease: examination of the spine, testes and heart, an echocardiogram for vegetations, and an MRI if lumbar tenderness persists, because spondylitis extends treatment beyond the standard course. Step four starts doxycycline with streptomycin, monitoring for defervescence, gentamicin-equivalent nephrotoxicity and tinnitus. The same ladder — screen, confirm, stage the focus, treat and watch for relapse — is what a viva examiner wants articulated.
How the exam frames it
NEET-PG rarely asks brucellosis straight; it wraps it in a dairy farmer with "fever not responding to ceftriaxone" and relative lymphocytosis, expecting you to pick serum agglutination over Widal. Two traps recur. First, the prozone phenomenon — a falsely negative agglutination in overwhelming infection, so a negative test with strong suspicion means dilute and repeat. Second, the endocarditis question: brucella endocarditis is one of the few indications where medical cure is unreliable and valve replacement plus prolonged combination therapy is the standard answer. Students also forget the laboratory hazard angle — brucella is among the commonest causes of laboratory-acquired infection, and stating "inform the lab when you suspect it" earns marks in infection-control vivas.
Frequently asked questions
Which serological test screens for brucellosis and what titre is significant?
The Rose Bengal plate test screens; serum agglutination at 1:160 or above in an endemic setting, or a four-fold rise in paired sera, supports active brucellosis.
What is the Pedro Pons sign?
Tenderness over the fourth lumbar vertebra, described with brucella spondylitis — a classic spot-diagnosis clue in Indian PG examinations.
Why does brucella culture carry a laboratory hazard?
The organism is highly infectious by aerosol, so cultures are handled in biosafety cabinets and clinicians must warn microbiology when brucellosis is suspected.
Which drug combination is first-line for uncomplicated brucellosis?
Doxycycline 100 mg twice daily with either streptomycin 1 g daily or rifampicin for about six weeks — monotherapy is avoided because relapse rates rise.
How does brucella endocarditis change management?
It is an indication for surgical valve replacement combined with prolonged multi-drug therapy, since medical therapy alone is frequently curatively inadequate.