Describe the emerging and re-emerging infections and the factors responsible.

Emerging and Re-emerging Infections

• Examples of emerging infections — HIV, SARS, MERS, COVID-19, Ebola, NIPAH, ZIKA, avian and pandemic influenza, Chikungunya and Kyasanur Forest disease
• Examples of RE-emerging infections — tuberculosis, particularly drug-resistant forms; malaria; dengue; cholera; diphtheria and measles where immunisation coverage has fallen; and plague
• The factors responsible, which form the substance of the answer:
• 1. Ecological and environmental change — deforestation and encroachment on wildlife habitat, bringing humans into contact with novel pathogens; dam and irrigation projects; climate change, extending the range of vectors to higher altitudes and latitudes; and flooding and natural disasters
• 2. Human demography and behaviour — rapid unplanned urbanisation and slum growth; population growth and crowding; sexual behaviour and injecting drug use; and an ageing and increasingly immunocompromised population
• 3. International travel and trade — a pathogen can now reach any city on earth within its incubation period, which is the single most important change from the historical situation and makes national containment inadequate by itself
• 4. Technology and industry — intensive livestock farming, which creates dense susceptible animal populations; mass food processing and global food distribution, which turn a local contamination into a multi-country outbreak; blood products and transplantation; and invasive medical devices
• 5. Microbial adaptation — mutation, antigenic drift and shift in influenza, recombination and gene transfer, and antimicrobial resistance
• 6. Breakdown of public health measures — falling immunisation coverage and vaccine hesitancy; deteriorating sanitation and water supply; collapse of vector control programmes after early success; war, conflict and displacement; and complacency following apparent victory
• The pattern of complacency deserves emphasis — malaria and dengue both resurged in India after control programmes were scaled back following early success, which is the recurring lesson of the topic
• 7. Zoonotic spillover — the wildlife trade and live animal markets, with bats being a particularly important reservoir for rabies, Nipah, Ebola and coronaviruses
• The response required:
• Strong surveillance with early warning, including syndromic and event-based surveillance that can detect the unusual before it is identified
• Laboratory capacity, including genomic sequencing
• Rapid response teams and outbreak preparedness plans
• The international health regulations (2005), which oblige countries to develop core capacities and to notify WHO of any public health emergency of international concern
• The one health approach, integrating human, animal and environmental surveillance
• Research into vaccines, diagnostics and therapeutics, with platforms ready before the next outbreak
• Risk communication and community engagement, without which measures are not adopted and misinformation fills the gap
• The lessons of COVID-19 — the speed of global spread; the value of prior investment in surveillance and laboratories; the importance of clear, honest communication; the enormous indirect harm to other health services, immunisation and tuberculosis programmes; and the inequity of vaccine distribution between rich and poor countries
• A pathogen crosses the world within its incubation period, which makes purely national containment inadequate
• Complacency after victory causes re-emergence, as malaria and dengue both demonstrated in India
• Deforestation brings novel pathogens to people, which is the commonest ecological driver of emergence
• Bats are a particularly important reservoir, for rabies, Nipah, Ebola and coronaviruses alike
• Intensive livestock farming creates dense susceptible populations, which is how influenza reassorts
• Global food distribution spreads local contamination into multi-country outbreaks within days
• Climate change extends vector range to higher altitudes and latitudes, bringing disease to new populations
• Event-based surveillance detects the unusual before it has been identified, which routine reporting cannot
• The IHR oblige countries to build core capacities and to notify events of international concern
• Risk communication is part of the response, since misinformation fills any gap left by official silence
• COVID-19 harmed other services badly, interrupting immunisation and tuberculosis programmes for months
• Vaccine distribution was inequitable, which is a lesson about global governance rather than about science
• Falling immunisation coverage brings back measles and diphtheria, which is re-emergence by our own hand