Leishmaniasis for 15 marks PSM answer
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LEISHMANIASIS
(Park's Textbook of Preventive and Social Medicine)
DEFINITION
Leishmaniasis is a group of protozoal diseases caused by parasites of the genus Leishmania, transmitted to man by the bite of the female phlebotomine sandfly. The disease produces various clinical syndromes - visceral leishmaniasis (kala-azar), cutaneous leishmaniasis (CL), muco-cutaneous leishmaniasis (MCL), and post-kala-azar dermal leishmaniasis (PKDL).
PROBLEM STATEMENT
World
- Visceral Leishmaniasis (VL / Kala-azar): Fatal in >95% of cases if untreated. 50,000-90,000 new cases/year worldwide. In 2018, >95% of cases came from 10 countries: Brazil, Ethiopia, India, Kenya, Somalia, South Sudan, Sudan, China, Iraq and Nepal.
- Cutaneous Leishmaniasis (CL): Most common form. 600,000-1 million new cases/year. ~95% occur in Americas, Mediterranean basin, Middle East, and Central Asia. In 2018, >85% from 8 countries: Afghanistan, Algeria, Brazil, Colombia, Iran, Pakistan, Tunisia, and Syria.
- Muco-cutaneous Leishmaniasis (MCL): >90% cases from Bolivia, Brazil, Ethiopia, and Peru.
India
- Endemic in Bihar, Jharkhand, Uttar Pradesh, and West Bengal (Darjeeling excluded).
- Kala-azar Elimination Programme targets <1 case per 10,000 population at sub-district/block level by 2023.
- India reported a significant decline in cases due to active vector control and treatment scale-up.
EPIDEMIOLOGICAL DETERMINANTS (Epidemiological Triad)
A. Agent Factors
- Causative organism: Intracellular protozoa of genus Leishmania
- L. donovani - causes Kala-azar (visceral)
- L. tropica - causes cutaneous leishmaniasis (oriental sore)
- L. braziliensis - causes muco-cutaneous leishmaniasis
- Note: This distinction is not absolute; visceral forms may produce cutaneous lesions and vice versa
- Two morphological forms:
- Amastigote (LD body): Leishman-Donovan body; intracellular form found in tissue macrophages of vertebrate host; oval, 2-3 µm
- Promastigote: Extracellular form found in sandfly gut; flagellated, elongated, 15-25 µm
B. Host Factors
- Age: All ages susceptible; children under 9 years most affected in India
- Sex: Males slightly more affected (possibly due to occupational exposure)
- Immunity: Cell-mediated immunity is the key protective mechanism; humoral response elevated but not protective
- Malnutrition increases susceptibility
- Reservoir hosts: Man is the only reservoir for Indian kala-azar (anthroponotic). In zoonotic forms, dogs, rodents and other mammals serve as reservoir hosts
C. Environmental Factors
- Vector: Female Phlebotomus argentipes (sandfly) - sole vector for Indian kala-azar
- Sandfly is small (1.5-3.5 mm), hairy, golden-colored
- Bites at dusk/night (crepuscular and nocturnal)
- Does not fly above ground floor level in most cases
- Rests in dark, damp, sheltered places (cracks, crevices, animal sheds)
- Breeds in moist organic matter (soil with high organic content near cattle sheds, walls)
- Transmission: Bite of infected female sandfly
- Season: Peaks in post-monsoon and winter months
- Housing conditions: Mud-walled, cracked houses with poor ventilation favor sandfly breeding
- Geography: Low-lying, humid, alluvial soil areas of Bihar/Jharkhand most affected
CLINICAL FEATURES
1. Visceral Leishmaniasis (Kala-azar)
- Incubation period: 3-6 months (range: 10 days to 2 years)
- Fever: Irregular, remittent, may be twice daily
- Splenomegaly (most prominent finding, may become massive - "Leishman spleen")
- Hepatomegaly
- Progressive weight loss, weakness, anemia
- Skin becomes dark (hyperpigmented) - "kala-azar" means "black fever" in Hindi
- Hypoalbuminemia, hypergammaglobulinemia
2. Cutaneous Leishmaniasis (Oriental Sore)
- Skin lesions (ulcers) on exposed parts of body; leave life-long scars
- Types: Anthroponotic (urban) CL, Zoonotic (rural) CL, Diffuse CL
3. Muco-cutaneous Leishmaniasis
- Partial or total destruction of mucous membranes of nose, mouth, throat (espundia)
4. Post-Kala-azar Dermal Leishmaniasis (PKDL)
- Skin manifestation appearing after apparent cure of kala-azar
- Hypopigmented macules, papules, nodules
- Serves as a reservoir of infection - epidemiologically significant
- Can appear months to years after treatment
DIAGNOSIS
1. RDT - rK39 Dipstick Test
- Based on detection of anti-Leishmania antibodies using a recombinant antigen (rK39)
- Simple, rapid, highly specific and sensitive for VL
- Most widely used field test in India
- Interpretation: One red line at T + C = positive; only C line = negative; no lines = invalid
- Limitation: Remains positive even after cure, so cannot distinguish past from current infection
2. Parasitological Diagnosis (Gold Standard)
- Demonstration of LD bodies (amastigotes) in aspirates of spleen, liver, bone marrow, or lymph nodes
- Splenic aspiration: Most sensitive (98%) but carries risk of hemorrhage
- Bone marrow aspiration: Safer alternative (~80% sensitivity)
- Culture can confirm species identity
3. Aldehyde Test (Napier's Formol-gel Test)
- 1-2 ml serum + 1-2 drops of 40% formalin
- Positive: Jellification/milk-white opacity (newsprint invisible through it) within 2-20 minutes
- Becomes positive 2-3 months after onset; reverts to negative 6 months after cure
- Non-specific (positive in any chronic infection with reversed A:G ratio)
- Useful for surveillance, not diagnosis
4. Serological Tests
- DAT (Direct Agglutination Test), rK39 dipstick, ELISA, IFAT
- ELISA: Blood on filter paper can be examined in lab; useful for field surveys and epidemiology
5. Leishmanin (Montenegro) Test
- Intradermal test: 0.1 ml leishmanin (10⁶ promastigotes/ml) injected in forearm
- Read at 48-72 hours; induration ≥5 mm = positive
- Positive in CL and MCL (4-6 weeks after onset)
- Negative during active kala-azar; becomes positive in 75% within 1 year of recovery
- Used to distinguish immune from non-immune subjects; assess endemicity
6. Haematological Findings
- Progressive anemia, leukopenia, thrombocytopenia (pancytopenia)
- Elevated ESR
- Reversed albumin:globulin ratio (hypoalbuminemia + hypergammaglobulinemia)
Case Definition of Kala-azar (India)
A person from an endemic area with fever >2 weeks + splenomegaly, confirmed by RDT or biopsy.
TREATMENT
| Drug | Route | Notes |
|---|---|---|
| Amphotericin B (liposomal) | IV | First-line in India; single-dose regimen |
| Miltefosine | Oral | First oral drug for VL; avoid in pregnancy |
| Pentavalent antimonials (Sodium stibogluconate / Meglumine antimoniate) | IM/IV | Resistance developing in Bihar |
| Paromomycin (Aminosidine) | IM | Used in combination regimens |
- National Programme (India): Single dose liposomal amphotericin B (AmBisome) 10 mg/kg IV is the preferred first-line regimen
CONTROL MEASURES
In the absence of an effective vaccine, control rests on three pillars:
1. Control of Reservoir
- Indian kala-azar is anthroponotic (man = only reservoir); hence early case detection and treatment is the main reservoir control measure
- Treatment of PKDL cases is especially important as they are a major reservoir
- In zoonotic areas: destruction of infected dogs, rodent control
2. Vector Control (Sandfly Control)
- Indoor Residual Spraying (IRS): DDT/synthetic pyrethroids sprayed on interior walls and ceilings twice a year. This is the cornerstone of vector control in India.
- Insecticide-treated bed nets (ITBNs): Long-lasting insecticidal nets (LLINs) effective since sandfly bites at night
- Environmental sanitation: Filling of cracks/crevices in walls, clearing of vegetation near homes, reducing damp organic debris
- Personal protection: Repellents, protective clothing
- Sandfly does not fly higher than ground floor - spraying limited to lower portions is effective
3. Protection of Susceptible Population
- No licensed vaccine currently available
- Personal protective measures
- Awareness and health education
- Chemoprophylaxis not recommended routinely
KALA-AZAR ELIMINATION INITIATIVE (INDIA)
Target: <1 case per 10,000 population at sub-district (block/PHC) level
Key Indicators:
| Indicator | Formula |
|---|---|
| Detection rate | New KA cases/year ÷ Total population × 100 |
| Treatment completion rate | Patients completing full treatment ÷ All new KA patients started × 100 |
| Vector control coverage | Households protected ÷ All households at risk × 100 |
| Final cure rate | Patients with final cure ÷ Total started treatment × 100 |
| Treatment failure rate | (Non-response + Relapse + KA deaths) ÷ Total started × 100 |
Treatment outcomes:
- Cure: Completed full treatment with no signs/symptoms
- Non-response: Symptoms persist despite >2 weeks of treatment
- Relapse: Reappearance within 6 months of end of treatment
- Treatment failure: Non-response OR relapse
- Final cure: Symptom-free at 6 months post-treatment
SUMMARY TABLE
| Feature | Kala-azar | Cutaneous | Muco-cutaneous |
|---|---|---|---|
| Agent | L. donovani | L. tropica | L. braziliensis |
| Vector | P. argentipes | Sandfly | Sandfly |
| Reservoir | Man (India) | Man/rodents | Rodents |
| Main feature | Splenomegaly, fever | Skin ulcers | Mucosal destruction |
| Leishmanin test | Negative (active) | Positive | Positive |
| Fatal if untreated | Yes (>95%) | No | Rarely |
Source: Park's Textbook of Preventive and Social Medicine, Chapter on Protozoal Infections (pp. 351-354).
Standardized mortality rate for 5 marks psm park
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STANDARDIZED (ADJUSTED) MORTALITY RATE
(Park's Textbook of Preventive and Social Medicine, pp. 71-72)
WHY STANDARDIZATION IS NEEDED
When comparing the death rates of two populations with different age compositions, the crude death rate (CDR) is not a valid yardstick - because rates are only comparable if the populations upon which they are based are comparable.
For example, a city with more elderly people will always show a higher CDR than a younger city, even if the younger city has worse health. Using a series of age-specific death rates is accurate but cumbersome.
Solution: Age standardization (age adjustment) - removes the confounding effect of different age structures and yields a single standardized/adjusted rate by which mortality experience of different populations can be directly compared. Adjustment can be made for age, sex, race, parity, etc.
METHODS OF STANDARDIZATION
Standardization is carried out by one of two methods: Direct or Indirect. Both begin by selecting a "standard population."
1. DIRECT STANDARDIZATION
Principle
Apply the age-specific death rates of the study population to a chosen standard population to calculate the number of deaths that would have occurred if the study population had the standard age structure.
Steps
- Calculate age-specific death rates for the study population
- Select a standard population (known age-group numbers)
- Multiply each age-specific rate by the corresponding standard population number → Expected deaths per age group
- Sum all expected deaths
- Divide total expected deaths by total standard population
Standardized Death Rate = Total Expected Deaths / Total Standard Population × 1000
Example (City X - from Park's)
Step 1: Age-specific death rates for City X
| Age | Mid-year pop | Deaths | Rate per 1000 |
|---|---|---|---|
| 0 | 4,000 | 60 | 15.0 |
| 1-4 | 4,500 | 20 | 4.4 |
| 5-14 | 4,000 | 12 | 3.0 |
| ... | ... | ... | ... |
| 55-64 | 7,000 | 150 | 21.4 |
| Total | 53,500 | 446 | CDR = 8.3 |
Step 2: Apply age-specific rates to standard population → get Expected Deaths
Step 3: Standardized Death Rate = Total Expected Deaths / Total Standard Population × 1000
This gives a rate that can be directly compared with the standardized rate of another city computed using the same standard population.
Limitation of Direct Method
- Requires age-specific death rates for each population being compared - these may be unavailable or unreliable when population numbers are small
2. INDIRECT STANDARDIZATION - STANDARDIZED MORTALITY RATIO (SMR)
Principle
Instead of applying study population's rates to a standard population, apply the standard population's (national) age-specific rates to the study population to get expected deaths, then compare with observed deaths.
Definition
SMR is a ratio (usually expressed as a percentage) of:
- Observed deaths in the study group
- Expected deaths (calculated by applying national/reference age-specific death rates to the study group's age structure)
SMR = (Observed Deaths / Expected Deaths) × 100
Interpretation
| SMR Value | Meaning |
|---|---|
| = 100 | Same mortality as reference population |
| > 100 | Greater mortality risk than reference population (unfavorable) |
| < 100 | Lower mortality risk than reference population (favorable) |
Example - Coal Workers (from Park's)
| Age | National rate/1000 | Coal workers | Expected deaths |
|---|---|---|---|
| 25-34 | 3.0 | 300 | 0.9 |
| 35-44 | 5.0 | 400 | 2.0 |
| 45-54 | 8.0 | 200 | 1.6 |
| 55-64 | 25.0 | 100 | 2.5 |
| Total | 1,000 | 7.0 |
Observed deaths = 9; Expected deaths = 7
SMR = 9/7 × 100 = 129
This means coal workers had 29% more mortality than the national population - an unfavorable experience. This measures the excess risk of mortality due to occupation.
Advantages of Indirect Method (SMR) over Direct Method
- Does not require age-specific death rates of the study population (only needs age distribution)
- More useful when study group numbers are small (age-specific rates unstable)
- Uses more stable rates of the larger (national) population applied to the smaller study group
- Can also be used if the event of interest is occurrence of disease (not just death) → called Standardized Incidence Ratio (SIR)
COMPARISON: DIRECT vs. INDIRECT STANDARDIZATION
| Feature | Direct Method | Indirect Method (SMR) |
|---|---|---|
| What is applied to standard population | Study population's age-specific rates | Standard population's age-specific rates applied to study group |
| Result | Standardized Death Rate | SMR (ratio, ×100) |
| Data needed | Age-specific rates of study population | Only age-group numbers of study group |
| Best used when | Large populations, stable rates | Small populations, rates unavailable |
| Allows direct comparison | Yes, between populations | Not directly between multiple populations |
Source: Park's Textbook of Preventive and Social Medicine, Chapter 2 - Epidemiology (pp. 71-72)
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