Zoonotic diseases: classification, global burden and the one health imperative

Abstract

Zoonotic diseases infections that pass naturally between vertebrate animals and humans are among the most pervasive and consequential of all health threats, accounting for roughly six in ten human infectious diseases and the great majority of those that have emerged in recent decades. This review provides a structured overview of zoonoses for a veterinary and allied-sciences readership. We begin with definitions and terminology, then classify zoonoses by causative agent (viral, bacterial, parasitic, fungal and prion), by route of transmission (direct contact, food- and water-borne, vector-borne and airborne), and by epidemiological pattern (endemic, epidemic and emerging). We summarise the staggering global and Indian burden, noting that a small group of zoonoses cause billions of human illnesses and millions of deaths each year, concentrated among the rural poor, and that India ranks among the world’s principal hotspots. Representative diseases are reviewed across the major agent groups rabies, avian influenza, Nipah, Ebola and COVID-19 among the viruses; brucellosis, leptospirosis, anthrax and bovine tuberculosis among the bacteria; toxoplasmosis, echinococcosis and cysticercosis among the parasites—alongside the food-borne and vector-borne dimensions of the problem. We then examine the ecological and socio-economic drivers of emergence, the principles of diagnosis, surveillance, prevention and control, and the central role of the One Health approach and of veterinarians within it. The recurring message is that animal, human and environmental health are inseparable, and that managing zoonoses is therefore a shared, cross-sectoral responsibility.