Emerging and Re-emerging Infections

E&R Definitions - Genesis & Gremlins

• Emerging Infections:
  • New infections or known ones spreading geographically/to new populations.
  • Incidence ↑ in humans in past 2 decades or threatens to ↑.
  • Examples: COVID-19, Zika, Nipah.
• Re-emerging Infections:
  • Previously major health problems, declined, now ↑ again.
  • Examples: Tuberculosis (drug-resistant), Diphtheria, Measles.
• Genesis (Driving Factors - "Gremlins"):
  • Microbial adaptation (e.g., resistance).
  • Human susceptibility (e.g., HIV, aging).
  • Ecological changes (deforestation, climate change).
  • Globalization (travel, trade).
  • Public health breakdown (↓ vaccination, sanitation).
  • Human behavior (urbanization, lifestyle).

⭐ Most emerging infections are zoonotic in origin.

Emerging Diseases - Viral Villains & Bacterial Baddies

• Viral Villains:
  • Nipah Virus: Reservoir: Fruit bats (Pteropus); Amplifier: Pigs. Causes encephalitis, severe respiratory distress. Kerala outbreaks notable.
  • Zika Virus: Vector: Aedes mosquito. Linked to microcephaly in newborns, Guillain-Barré syndrome.
  • COVID-19 (SARS-CoV-2): Origin: Bats. Transmission: Respiratory droplets. Key: Pneumonia, ARDS, Variants of Concern (VOCs).
  • Mpox (Monkeypox): Reservoir: Rodents, primates. Transmission: Close contact. Symptoms: Fever, characteristic vesicular/pustular rash.
  • Avian Influenza (H5N1, H7N9): Reservoir: Wild aquatic birds. High mortality in humans. Threatens poultry industry.
  • Kyasanur Forest Disease (KFD): Vector: Haemaphysalis ticks; Hosts: Monkeys, rodents. Haemorrhagic fever. Endemic to Karnataka. 📌 KFD: "Karnataka Forest Disease".
• Bacterial Baddies:
  • Scrub Typhus (Orientia tsutsugamushi): Vector: Chiggers (larval mites). Key: Eschar at bite site, fever, rash.
  • Leptospirosis (Leptospira interrogans): Source: Rodent urine, contaminated water. Severe: Weil’s disease (jaundice, renal failure, haemorrhage).
  • Drug-Resistant TB: MDR-TB (resistant to Isoniazid & Rifampicin); XDR-TB (MDR + fluoroquinolone + second-line injectable).
  • Carbapenem-Resistant Enterobacteriaceae (CRE): E.g., Klebsiella, E. coli. Major cause of hospital-acquired infections (HAIs). High mortality.

⭐ Nipah virus encephalitis has a high case fatality rate, often 40-75%.

Re-emerging Diseases - The Unwelcome Returners

• Definition: Diseases that reappear after a significant decline in incidence, often in new geographical areas or among new populations.
• Key Drivers:
  • Waning population immunity.
  • Antimicrobial resistance (AMR).
  • Relaxation/breakdown of public health measures.
  • Ecological or environmental changes (e.g., climate change, urbanization).
• Indian Context Examples:
  • Diphtheria: Due to ↓ immunization coverage in certain pockets.
  • Pertussis: Waning immunity from acellular vaccines; resurgence in adolescents/adults.
  • Plague: Surat (1994), Beed (2002). Surveillance & rodent control vital.
  • Malaria: Drug resistance (e.g., $P. falciparum$ to Chloroquine), insecticide resistance in vectors.
  • Tuberculosis: Emergence and spread of Multi-Drug Resistant TB (MDR-TB) & Extensively Drug-Resistant TB (XDR-TB).
  • Leptospirosis: Increased outbreaks post-monsoon, associated with flooding and poor sanitation.
  • Kala-azar (Visceral Leishmaniasis): Resurgence in endemic areas, challenges with drug resistance and Post-Kala-azar Dermal Leishmaniasis (PKDL) cases acting as reservoirs.

⭐ Plague re-emerged in India in 1994 in Surat, Gujarat, after nearly 30 years of quiescence, with pneumonic plague being a significant feature of the outbreak.

Surveillance & Response - Eyes on the Enemy

• Surveillance: Continuous, systematic collection, analysis, interpretation, & dissemination of health data for action.
  • Types: Passive (routine reporting), Active (proactive case finding), Sentinel (selected sites), Syndromic (early symptom tracking).
• IDSP (India): Integrated Disease Surveillance Programme, launched 2004.
  • Key for early outbreak detection; uses S, P, L forms.
• Outbreak Response Steps:

⭐ Under IDSP, 'S' form (Syndromic surveillance) is filled by Sub-centres, 'P' form (Presumptive cases) by PHCs/CHCs, and 'L' form (Lab-confirmed cases) by laboratories.

High-Yield Points - ⚡ Biggest Takeaways

• Emerging infections: newly identified; Re-emerging: resurfacing with ↑ incidence or wider geographic spread.
• Most are zoonotic (e.g., Nipah, Avian Influenza, COVID-19), originating from animals.
• International Health Regulations (IHR) mandate global surveillance and coordinated response.
• One Health approach (human-animal-environment interface) is critical for prevention and control.
• Antimicrobial Resistance (AMR) exacerbates the threat from re-emerging pathogens.
• Notable examples: Zika virus (microcephaly), KFD (tick-borne, India), Dengue (vector-borne).