Cholera psm
Reading File
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Reading File
Reading File
Reading File
I now have comprehensive information from both Park's PSM and Harrison's. Let me compile the full detailed answer on Cholera as covered in PSM (Park's Textbook of Preventive and Social Medicine).
Cholera - PSM (Park's Textbook of Preventive and Social Medicine)
Definition
Cholera is an acute infectious disease of the intestinal tract caused by Vibrio cholerae O1 or O139, characterized by profuse watery diarrhoea ("rice-water stools"), vomiting, severe dehydration, and potentially death if untreated.
Epidemiological Determinants
1. Agent Factors
Causative organism: Vibrio cholerae O Group 1 (O1) and O139. Non-agglutinating (NAG) vibrios / non-cholera vibrios (NCV) are non-epidemic strains.
Biotypes of O1:
| Feature | Classical | El Tor |
|---|---|---|
| Agglutinate chicken/sheep RBCs | No | Yes |
| Resistant to phage IV | No | Yes |
| Resistant to polymyxin B 50-unit disc | No | Yes |
| VP reaction / haemolytic test | Positive | Inconsistent |
- Serotypes (both biotypes): Inaba, Ogawa, Hikojima
- Most El Tor strains in India belong to the Ogawa serotype
- El Tor was first isolated at the El Tor quarantine station, Egypt (1905)
- Cholera today is caused mostly by El Tor biotype and O139
Resistance of the organism:
- Killed at 56°C in 30 min; killed instantly by boiling
- Survives in ice for 4-6 weeks
- Destroyed in a few hours by drying and sunshine
- Easily killed by coal tar disinfectants (cresol) and bleaching powder (6 mg/L kills instantly)
- El Tor biotype is more resistant than classical vibrios
Toxin production: Vibrios multiply in the lumen of the small intestine and produce an exotoxin (enterotoxin) consisting of:
- L toxin (light/B subunit): binds to gangliosides on epithelial cell membrane - irreversible binding
- H toxin (heavy/A subunit): activates adenylate cyclase → raises cyclic AMP (cAMP) → drives fluid and ions into intestinal lumen → profuse watery diarrhoea
- The toxin has no effect on any tissue other than intestinal epithelial cells
Reservoir of infection: The human being is the only known reservoir
- ~75% of infected persons are asymptomatic (but shed vibrios for 7-14 days)
- ~20% develop acute watery diarrhoea with severe dehydration
- Mild and asymptomatic cases maintain the endemic reservoir
- Carriers are usually temporary (rarely chronic)
2. Host Factors
- Age: El Tor cholera predominantly affects all ages; in endemic areas it is a pediatric disease
- Immunity: Acquired natural immunity is temporary
- Nutrition: Malnourished children and HIV-infected persons are at greater risk of death
- Gastric acid: Low gastric acidity (hypochlorhydria, antacids, or food intake) markedly increases susceptibility - the infectious dose is normally relatively high
3. Environmental Factors
- Contaminated water is the most important vehicle of transmission
- Seasonal fluctuations: In India, peak incidence varies - in some regions it peaks in August
- El Tor has greater "endemic tendency" causing higher infection-to-case ratios
- Free-living V. cholerae in coastal waters/estuaries (associated with plankton) contributes to inter-epidemic persistence
Pandemic History
- Seven global pandemics since 1817, all originating from the Ganges delta
- The 7th pandemic (current): started in Indonesia in 1961, caused by El Tor biotype
- Classical biotype is now thought to be extinct
- O139 serogroup emerged in southeastern India in October 1992 - distinct LPS, has a polysaccharide capsule (unlike O1), and immunity to O1 is not protective against O139
Incubation Period
A few hours to 5 days - commonly 1-2 days
Pathogenesis (PSM)
- Vibrio penetrates the mucus layer (secretes mucinase)
- Adheres to intestinal epithelial cells via surface adherence factor
- Produces enterotoxin - L toxin binds gangliosides (irreversible); H toxin activates adenylate cyclase
- cAMP rises → drives isotonic fluid and ions into intestinal lumen from all segments of small intestine
- Profuse diarrhoea results - not increased peristalsis, not tissue invasion
Clinical Features (PSM)
90% of El Tor cholera cases are mild and clinically indistinguishable from other diarrhoeas. Severe ("cholera gravis") occurs in only 5-10%.
Three stages of a typical case:
| Stage | Features |
|---|---|
| Stage of Evacuation | Abrupt onset, profuse painless watery diarrhoea ("rice-water stools"), vomiting; up to 40 stools/day |
| Stage of Collapse | Sunken eyes, hollow cheeks, scaphoid abdomen, sub-normal temperature, washerman's hands/feet, absent pulse, unrecordable BP, absent skin turgor, oliguria → anuria; intense thirst, cramps in legs and abdomen |
| Stage of Recovery | BP rises, temperature normalises, urine re-established; if anuria persists → renal failure and death |
Mild cases recover in 1-3 days.
Treatment
Cornerstone: Fluid and electrolyte replacement
Oral Rehydration Solution (ORS)
- Works via the hexose-Na⁺ co-transport mechanism (glucose/galactose carries Na⁺ across gut mucosa even when cholera toxin is active)
- WHO ORS: glucose, NaCl, KCl, trisodium citrate in safe water
| Dehydration | Treatment |
|---|---|
| None/Mild | ORS orally (age-based volumes) |
| Moderate | ORS 200-4000 mL depending on age/weight over 4 hours |
| Severe | IV Ringer's Lactate 100 mL/kg (first 3h for adults; 6h for children <12 months) |
Antibiotics
- Reduce duration and severity of illness; decrease vibrio shedding
- Doxycycline (single dose, adults) - drug of choice
- Tetracycline, azithromycin, ciprofloxacin are alternatives
- Antibiotic resistance (especially to tetracycline) is increasingly reported
Epidemiology in India (PSM)
- Since introduction of El Tor biotype in 1964, geographic distribution in India changed considerably
- West Bengal lost its former reputation as the "home of cholera"
- Many previously cholera-free states now affected
- Peak incidence in many parts of India occurs in August
- Seasonal pattern has shifted in Kolkata and Bangladesh - now most frequent in autumn
Principles of Control (PSM)
- Safe water supply - most important
- Sanitation - proper sewage disposal
- Food hygiene - especially cooked rice and seafood
- Case detection and treatment - to reduce vibrio shedding from reservoir
- Contact tracing and chemoprophylaxis
- Vaccination:
- WC-rBS oral cholera vaccine (killed whole cells + recombinant B subunit) - 2 doses, 85% protection for 6 months, 50-60% for 3 years
- Used in outbreak settings and for travellers
- Health education - handwashing, boiling water, avoiding raw seafood
- Reporting - cholera is a notifiable disease under International Health Regulations (IHR); international surveillance mandated by WHO
Cholera epidemics are self-limiting due to acquisition of temporary immunity and large numbers of subclinical cases that exhaust the susceptible pool.
Key sources:
- Park's Textbook of Preventive and Social Medicine, Cholera chapter (Agent factors, Pathogenesis, Clinical Features, Control)
- Harrison's Principles of Internal Medicine 22E (2025), Chapter 173 - Cholera
Maleria according to park in short
Finding Sources
Reading File
Reading File
Reading File
Reading File
Reading File
I have enough content for a concise PSM summary. Here it is:
Malaria - Park's PSM (Short Notes)
Definition
A protozoal disease caused by Plasmodium spp., transmitted by infected female Anopheles mosquito. A typical attack has 3 stages: cold stage, hot stage, sweating stage, with febrile paroxysms at definite intermittent periodicity.
Species & Periodicity
| Species | Periodicity | Fever Cycle | Special Feature |
|---|---|---|---|
| P. vivax | Benign tertian | Every 48 hrs | Relapses (hypnozoites in liver) |
| P. falciparum | Malignant tertian | Every 48 hrs | Most dangerous; no relapses but recrudescence |
| P. malariae | Quartan | Every 72 hrs | Recrudescence for years |
| P. ovale | Ovale tertian | Every 48 hrs | Mild; relapses |
Life Cycle
1. Human cycle (asexual - schizogony):
- Sporozoites injected → liver (pre-erythrocytic schizogony, 5-16 days)
- P. vivax/ovale form hypnozoites (dormant liver forms → cause relapses)
- Merozoites released → enter RBCs (erythrocytic schizogony) → rupture → fever paroxysm
- Some merozoites form gametocytes (sexual forms)
2. Mosquito cycle (sexual - sporogony):
- Mosquito ingests gametocytes → fertilization in stomach → ookinete → oocyst → sporozoites → salivary glands
- Extrinsic incubation period: 10-20 days
Epidemiological Determinants
Agent
- 4 species of Plasmodium; P. falciparum causes most deaths
Reservoir
- Humans only (except P. malariae in chimpanzees in Africa)
- Person is a reservoir only when they harbour mature, viable gametocytes of both sexes at density ≥12/mm³ blood
- Children are better reservoirs than adults (more gametocyte carriers)
- In vivax: gametocytes appear 4-5 days after asexual parasites
- In falciparum: gametocytes appear 10-12 days after asexual parasites
Period of Communicability
- As long as mature viable gametocytes circulate in sufficient density
- Relapses: Vivax/ovale can relapse >3 years after first attack
Vector
- Female Anopheles mosquito
- Bites usually at night (dusk to dawn)
- Breeds in clean, stagnant water
Host Factors
- All ages susceptible; children and pregnant women most at risk
- Sickle cell trait, G6PD deficiency confer some protection
Incubation Period
| Species | Incubation |
|---|---|
| P. vivax | 10-17 days |
| P. falciparum | 7-14 days |
| P. malariae | 18-40 days |
| P. ovale | 11-16 days |
Clinical Features
Three stages of febrile paroxysm:
- Cold stage - rigors, chills, feeling cold (15-60 min)
- Hot stage - high fever, headache, nausea (2-6 hrs)
- Sweating stage - profuse sweating, temperature falls, patient feels relieved
Complications of P. falciparum: Cerebral malaria, acute renal failure, liver damage, blackwater fever, severe anaemia, hypoglycaemia, ARDS, collapse
Complications of P. vivax/ovale/malariae: Anaemia, splenomegaly, hepatomegaly, herpes, renal complications
Diagnosis
| Method | Feature |
|---|---|
| Thick blood smear | Screening - detects parasite even when scanty (~20x more sensitive than thin film) |
| Thin blood smear | Species identification |
| Serology (FAT) | Becomes positive 2 weeks after infection; useful for epidemiological studies, not for current infection |
| RDT (Rapid Diagnostic Test) | Dipstick format; detects circulating parasite antigens; field-applicable |
Malaria Indices (Surveillance)
| Index | Definition |
|---|---|
| API (Annual Parasite Incidence) | Confirmed malaria cases per 1000 population/year |
| ABER (Annual Blood Exam Rate) | Blood smears examined per 100 population/year (target: ≥10%) |
| SPR (Slide Positivity Rate) | % of slides positive for malaria |
| SFR (Slide Falciparum Rate) | % of slides positive for P. falciparum |
| Pf% | % of total cases due to P. falciparum |
Treatment (India Guidelines 2013)
No presumptive treatment - all cases must be confirmed by microscopy or RDT first.
| Case | Treatment |
|---|---|
| P. vivax | Chloroquine × 3 days + Primaquine 0.25 mg/kg/day × 14 days (radical cure for relapses) |
| P. falciparum | ACT (Artemisinin Combination Therapy) - Artesunate + SP (sulfadoxine-pyrimethamine) × 3 days + Primaquine single dose (gametocytocidal) |
| Severe malaria | Injectable artesunate or quinine IV |
Control Strategies (NVBDCP)
1. Surveillance & Case Management
- Active & passive case detection
- Early diagnosis and complete treatment
- Sentinel surveillance
2. Integrated Vector Management (IVM)
- Indoor Residual Spray (IRS) - DDT, malathion, synthetic pyrethroids
- Insecticide Treated Bed Nets (ITNs) / LLINs (Long-Lasting Insecticidal Nets)
- Anti-larval measures - source reduction, biological control (larvivorous fish like Gambusia)
- Environmental management - drainage, filling of breeding sites
3. Epidemic Preparedness
4. Supportive Interventions
- BCC (Behaviour Change Communication)
- Intersectoral collaboration, operational research
Special Malaria Types in India (PSM)
- Forest malaria - forests/deforested areas; highly efficient vectors
- Border malaria - high transmission belts along international/state borders; difficult to control
Malaria Vaccines
- RTS,S (Mosquirix) - first malaria vaccine; targets P. falciparum pre-erythrocytic stage; limited efficacy (~30-40%); recommended by WHO for sub-Saharan Africa
Source: Park's Textbook of Preventive and Social Medicine, Malaria chapter
This is a shared conversation. Sign in to Orris to start your own chat.