# Zoonosis

> Infectious disease naturally transmissible between vertebrates and humans. 60 percent of emerging infectious diseases are of animal origin; hantavirus diseases are among them.

Canonical source: https://hantatracker.fr/en/glossary/zoonosis/

**Aliases**: zoonotic, zoonotic disease, zoonosis

A **zoonosis** is an infectious disease naturally transmissible between vertebrates and humans. Zoonoses account for **60 percent of emerging infectious diseases** and **75 percent of new human pathogens** identified over the past thirty years. Hantavirus diseases, of which the MV Hondius episode is one, are an illustration.

## Definition and classifications

### WHO definition

According to the World Health Organization, a zoonosis is any disease or infection naturally transmissible between vertebrates and humans. It can be caused by viruses, bacteria, parasites, fungi or prions. Modes of transmission are multiple: direct (contact, bite), indirect (a vector such as a mosquito, tick or flea) or environmental (contaminated water, soil, food).

### Three main classes

The WHO distinguishes three categories: **endemic zoonoses** (permanently present in a given geographic area — rabies, brucellosis, leptospirosis), **epidemic zoonoses** (sporadic emergence in time and space — Ebola, hantavirus, Lassa) and **emerging or re-emerging zoonoses** (new or rapidly increasing — SARS-CoV-2, Mpox, Andes virus in 2019 and again in 2026).

## Public health importance

### Global burden

Zoonoses are estimated to cause around **1 billion human cases per year** worldwide and roughly **2.7 million annual deaths**. These figures are estimates combining endemic zoonoses with high incidence (malaria, leishmaniasis) and lower-incidence emerging episodes with high spread potential.

### Accelerated emergence

Several documented factors accelerate the emergence of zoonoses: intensified livestock farming and deforestation, which bring humans closer to wild reservoirs; international trade in live animals; international travel; climate change shifting the ranges of reservoirs and vectors; biodiversity erosion, which favours opportunistic species such as rodents and bats.

## The One Health approach

### Principle

Faced with the multi-species nature of zoonoses, since the 2000s the WHO has promoted the **One Health** approach, which integrates human, animal and environmental health in a joint effort. It is carried jointly by the WHO, the FAO (Food and Agriculture Organization of the United Nations), WOAH (formerly OIE — World Organisation for Animal Health) and UNEP (United Nations Environment Programme).

### Application to hantavirus diseases

For hantavirus diseases, One Health translates into: surveillance of rodent reservoir populations (density, viral seroprevalence), surveillance of human cases with environmental investigation around each cluster, predictive modelling of risk according to weather and rodent proliferation cycles, and coordinated communication with veterinary and agricultural authorities for prevention in rural areas.

## Relevance for the MV Hondius

The MV Hondius episode is a typical illustration of an emerging zoonosis: a pathogen usually transmitted by a wild rodent in South America (*Oligoryzomys longicaudatus*, the reservoir of Andes virus) infected humans during a trip to an endemic area, then spread on board a vessel on the high seas through human-to-human transmission. This episode simultaneously mobilises the health authorities of 10 countries and concretely illustrates the international coordination that emerging zoonoses require.