Water-borne diseases

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     Water-borne diseases are infections transmitted through the ingestion of contaminated water, often containing pathogenic microorganisms, chemicals, or toxic substances.

  • Main transmission route: Fecal-oral
  • Contaminants include: Bacteria, viruses, protozoa, helminths, and toxic chemicals.

Historical Perspective

  • 1854 London Cholera Outbreak: John Snow linked cholera to contaminated water, founding modern epidemiology.
  • 19th-20th Century: Water filtration and chlorination drastically reduced waterborne diseases in developed nations.
  • 21st Century Challenges: Climate change, urbanization, and antibiotic resistance exacerbate risks.

Classification of Water-Borne Diseases

  • Bacteria- Cholera, Typhoid, Paratyphoid, Shigellosis
  • Viruses-  Hepatitis A, Hepatitis E, Polio, Norovirus
  • Protozoa-  Amoebiasis, Giardiasis, Cryptosporidiosis
  • Helminths - Dracunculiasis (Guinea worm), Schistosomiasis
  • Chemical - Fluorosis, Arsenicosis, Nitrate poisoning

Bacterial Infections

(a) Cholera (Vibrio cholerae)

  • Transmission: Fecal-oral route, contaminated seafood.
  • Symptoms:
    • Profuse "rice-water" diarrhea (up to 20L/day loss).
    • Severe dehydration, sunken eyes, hypovolemic shock.
  • Treatment:
    • Oral Rehydration Solution (ORS) (WHO standard: NaCl + glucose + KCl).
    • IV fluids in severe cases.
    • Antibiotics (doxycycline, azithromycin) for severe infections.
  • Prevention:
    • Vaccination (Dukoral, Shanchol).
    • Water chlorination (0.5–2 mg/L free chlorine).

(b) Typhoid Fever (Salmonella Typhi)

  • Transmission: Contaminated water/food (e.g., street food).
  • Symptoms:
    • Step-ladder fever (gradual increase).
    • Rose spots (rash on abdomen).
    • Hepatosplenomegaly (enlarged liver/spleen).
  • Treatment:
    • Ceftriaxone (1st line for resistant strains).
    • Azithromycin for uncomplicated cases.
  • Prevention:
    • Typhoid conjugate vaccine (TCV) (85% efficacy).
    • Food hygiene (avoid raw vegetables in endemic areas).

(c) Shigellosis (Bacillary Dysentery)

Causative Agent: Shigella dysenteriae (most severe), S. flexneri.

  • Symptoms:
    • Bloody diarrhea (dysentery), fever, tenesmus.
  • Complications:
    • Hemolytic Uremic Syndrome (HUS) (S. dysenteriae type 1).
  • Treatment:
    • Ciprofloxacin (resistance rising).
    • Azithromycin as alternative.

Viral Infections

(a) Hepatitis A (HAV)

  • Transmission: Fecal-oral, raw shellfish.
  • Symptoms:
    • Jaundice, fatigue, nausea (lasts weeks to months).
  • Prevention:
    • HAV vaccine (2-dose series, lifelong immunity).

(b) Rotavirus

  • Leading cause of severe childhood diarrhea.
  • Symptoms:
    • Watery diarrhea, vomiting, dehydration.
  • Prevention:
    • Rotavirus vaccine (85% effective against severe cases).

 (c) Poliomyelitis

  • Agent: Poliovirus (Picornaviridae)
  • Infection path: Oropharyngeal → GI tract → CNS (rare)
  • Rare Fact: Wild poliovirus types 2 and 3 are eradicated, only type 1 remains in circulation (2025 update).

Protozoan Diseases

(a) Amoebiasis (Entamoeba histolytica)

  • Forms: Cyst (infective), trophozoite (invasive)
  • Complication: Liver abscess, rarely brain abscess
  • Rare Fact: Trophozoites phagocytose RBCs — diagnostic feature.

(b) Cryptosporidiosis (Cryptosporidium parvum)

  • Transmission: Chlorine-resistant cysts
  • At-risk groups: Immunocompromised (e.g., HIV/AIDS)
  • Rare Fact: Causes prolonged diarrhea in AIDS patients (persistent infection).

(c) Giardiasis (Giardia lamblia)

  • Symptoms:
    • Sulfur-smelling diarrhea, bloating, malabsorption.
  • Treatment:
    • Metronidazole (250 mg TDS for 5–7 days).

Helminthic Diseases

(a) Dracunculiasis (Guinea Worm)

  • Agent: Dracunculus medinensis
  • Intermediate host: Copepod (Cyclops)
  • Transmission: Drinking water with infected copepods
  • Rare Fact: Considered nearly eradicated by WHO; <20 cases globally (2024 data).

(b) Schistosomiasis (Bilharzia)

  • Agent: Schistosoma spp.
  • Infective form: Cercariae from snail hosts
  • Rare Fact: Eggs trapped in tissues cause granulomas and fibrosis, not the worms directly.

Non-Infectious Water-Borne Illnesses

(a)  Fluorosis

  • Cause: High fluoride (>1.5 mg/L)
  • Symptoms: Dental mottling, skeletal deformities
  • Endemic areas: Rajasthan, Andhra Pradesh, parts of Africa
  • Rare Fact: Fluoride also affects the thyroid and may impair intelligence in children.
(b)  Arsenicosis
  • Cause: Ingestion of arsenic-contaminated water
  • Sources: Groundwater (Bangladesh, West Bengal, Bihar)
  • Symptoms: Hyperpigmentation, keratosis, cancers
  • Rare Fact: Arsenic alters gene expression via epigenetic mechanisms. 

Diagnostics

  • Bacteria: Culture (MacConkey, TCBS for cholera), PCR
  • Viruses: ELISA, RT-PCR
  • Protozoa: Microscopy, antigen detection
  • Water testing: MPN (Most Probable Number), membrane filtration, PCR for pathogens

Prevention Strategies

(a) Household-Level Interventions

  • Boiling water (1+ minute at 100°C kills most pathogens).
  • Ceramic filters (0.2 µm pores remove Cryptosporidium).
  • Solar disinfection (SODIS): PET bottles + 6 hrs sunlight.

(b) Community & Policy Measures

  • WASH programs (Water, Sanitation, Hygiene).
  • Vaccination campaigns (e.g., oral cholera vaccine in Haiti).
  • Sanitation laws (e.g., India’s Swachh Bharat Mission).
MCQ's:

Q1. Which of the following statements about Cryptosporidium parvum is INCORRECT?
A. It is resistant to standard chlorination protocols
B. It infects immunocompetent individuals but causes chronic infection in immunodeficient hosts
C. It forms oocysts that are highly stable in the environment
D. It multiplies extracellularly in the intestinal lumen

Q2. Which of the following correctly matches the disease with its causative agent and mode of transmission?
A. Schistosomiasis – Schistosoma haematobium – Ingestion of eggs
B. Amoebiasis – Entamoeba histolytica – Cercarial skin penetration
C. Typhoid – Salmonella typhi – Fecal-oral route
D. Dracunculiasis – Wuchereria bancrofti – Ingestion of L3 larvae

Q3. A child in an endemic area presents with hepatomegaly, bloody diarrhea, and flask-shaped ulcers in the colon. The most likely cause is:

A. Giardia lamblia
B. Entamoeba histolytica
C. Strongyloides stercoralis
D. Vibrio cholerae

Q4. Which of the following waterborne diseases is most likely to present with prolonged cholestatic jaundice in pregnant women, especially in the third trimester?
A. Hepatitis A
B. Hepatitis B
C. Hepatitis E
D. Leptospirosis

Q5. Which of the following BEST explains the persistence of Vibrio cholerae in aquatic environments during interepidemic periods?
A. Sporulation
B. Formation of conjugative plasmids
C. Biofilm formation on plankton and chitin
D. Transformation into resistant endospores

Q6. Which of the following pathogens associated with waterborne disease is most likely to survive in viable but non-culturable (VBNC) form under environmental stress?
A. Salmonella typhi
B. Vibrio cholerae
C. Poliovirus
D. Entamoeba histolytica

Q7. Which of the following conditions is most likely to be endemic in a region where drinking water is sourced from arsenic-rich groundwater aquifers?
A. Keratomalacia
B. Hyperkeratosis with skin melanosis
C. Skeletal fluorosis
D. Cirrhosis of the liver due to Hepatitis B

Q8. Which of the following statements about Dracunculus medinensis is TRUE?

A. Human becomes infected by cercarial skin penetration
B. Male worm is released in the urine
C. Eradication is possible as the parasite has no animal reservoir
D. Vector control with insecticides is effective

Q9. Which of the following is NOT used as a biological indicator of fecal contamination in water quality testing?
A. Escherichia coli
B. Fecal streptococci
C. Clostridium perfringens
D. Vibrio cholerae

Q10. Which of the following mechanisms is MOST responsible for the increased frequency of waterborne outbreaks post-heavy rainfall and flooding events?
A. Enhanced UV penetration of surface water
B. Dilution of pathogenic load
C. Overwhelming of sewage treatment infrastructure
D. Increase in water pH leading to inactivation of pathogens

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