Kno eosinopenia hoy in typhoid
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Eosinopenia in Typhoid Fever
What is Eosinopenia?
Eosinopenia = a reduction in circulating eosinophils below the normal count (~0.1 × 10⁹/L). It is a classic haematological finding in typhoid fever and is considered a diagnostically useful pointer.
Why Does it Occur in Typhoid?
The mechanism involves the systemic stress response triggered by Salmonella Typhi infection:
-
Cortisol / glucocorticoid surge — Severe infection stimulates the hypothalamo-pituitary-adrenal (HPA) axis, producing high endogenous cortisol levels. Cortisol is the single most potent physiological suppressor of eosinophils; it causes:
- Apoptosis of circulating eosinophils
- Sequestration of eosinophils in bone marrow (demargination into tissues rather than circulation)
- Reduced bone marrow release of eosinophil precursors
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Leukocyte sequestration in tissues — Robbins' Pathologic Basis of Disease explains the broader picture: typhoid fever (and infections caused by some viruses, rickettsiae, and protozoa) is associated with leukopenia in part because activated leukocytes (including eosinophils) are sequestered in vascular spaces and tissues rather than circulating freely. — Robbins, Cotran & Kumar Pathologic Basis of Disease
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Cytokine milieu — The dominant cytokines in the acute phase of typhoid (IL-1, TNF, IL-6) shift the bone marrow toward neutrophil and monocyte production at the expense of eosinophil production. There is no allergic/parasitic Th2 stimulus to drive eosinophilia.
Full Haematological Picture in Typhoid
| Finding | Details |
|---|---|
| Eosinopenia | Hallmark finding; present from 1st week |
| Leukopenia/neutropenia | Present in 15–25% of cases |
| Leukocytosis | Seen in children, first 10 days, or with perforation/secondary infection |
| Relative lymphocytosis | May coexist with neutropenia |
| Anaemia | Common with prolonged illness |
| Thrombocytopenia | Can occur, especially in severe disease |
— Harrison's Principles of Internal Medicine 22E
Clinical Significance of Eosinopenia
- Negative eosinophils on a peripheral smear is a useful bedside clue to typhoid fever in a febrile patient from an endemic region.
- The return of eosinophils (eosinophilia) to the blood during recovery is traditionally considered a favourable prognostic sign — it indicates the stress response is resolving and the HPA axis is normalising.
- Eosinopenia also helps distinguish typhoid from helminthic infections or allergic conditions (which cause eosinophilia), and from malaria (which more often shows thrombocytopenia with preserved eosinophil counts).
Key Mnemonic
"Eosinophils disappear in typhoid, return in recovery"
The absence of eosinophils = active typhoid stress.
The reappearance of eosinophils = a sign of convalescence.
Sources:
- Harrison's Principles of Internal Medicine 22E — Chapter 171, Diagnosis section
- Robbins, Cotran & Kumar Pathologic Basis of Disease — Systemic Effects of Inflammation
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