Zoonoses

Zoonoses and the Human-Animal-Ecosystems Interface

Any disease or infection that is naturally transmissible from vertebrate animals to humans and vice-versa is classified as a zoonosis according to the PAHO publication "Zoonoses and communicable diseases common to man and animals". Zoonoses have been recognized for many centuries, and over 200 have been described. They are caused by all types of pathogenic agents, including bacteria, parasites, fungi, and viruses.

Reducing public health risks from zoonoses and other health threats at the human-animal-ecosystems interface (such as antimicrobial resistance) is not straightforward. Management and reduction of these risks must consider the complexity of interactions among humans, animals, and the various environments they live in, requiring communication and collaboration among the sectors responsible for human health, animal health, and the environment.

The WHO is engaging in an ever-increasing number of cross sectoral activities to address health threats at the human-animal-ecosystem interface. These threats include existing and emerging zoonoses as well as antimicrobial resistance, food-borne zoonoses, and other threats to food safety.

Some examples of zoonoses, classified according to the type of causative agent, are given hereafter.

Bacteria

Every year millions of people get sick because of foodborne zoonoses such as Salmonellosis and Campylobacteriosis which cause fever, diarrhoea, abdominal pain, malaise and nausea. Other bacterial zoonoses are anthrax, brucellosis, infection by verotoxigenic Escherichia coli, leptospirosis, plague, Q fever, shigellosis and tularaemia.

Parasites

Cysticercosis/Taeniasis is caused by a parasite which infects swine and can cause seizures, headache and many other symptoms in humans. In Latin America for example, 100 out of 100 000 inhabitants suffer from this disease (estimation). Other parasitic zoonoses are trematodosis, echinococcosis/hydatidosis, toxoplasmosis and trichinellosis.

Viruses

Rabies is a disease of carnivores and bats mainly transmissible to humans by bites. Almost all persons infected by rabid animals will die if not treated. An estimated number of 55 000 persons, mainly children, die of this disease in the world every year. Dogs are responsible for most human deaths. Other viral zoonoses are avian influenza, Crimean-Congo hemorrhagic fever, Ebola and Rift Valley fever.

Fungi

Dermatophytoses are superficial mycoses that may be acquired from infected animals and affect the skin, hair and nails of humans, causing itching, redness, scaling and hair loss. Another mycotic infection that can be zoonotic is sporotrichosis.



Unconventional agents

The agent of Bovine Spongiform Encephalopathy is thought to be the cause of variant Creutzfeldt-Jakob Disease (vCJD) which is a degenerative neurological disease different from CJD, at present inevitably lethal in humans.

Zoonoses still represent significant public health threats, but many of them are neglected, i.e. they are not prioritized by health systems at national and international levels. They affect hundreds of thousands of people especially in developing countries, although most of them can be prevented.

Influenza at the Human-Animal Interface (HAI)

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Global Early Warning System for Major Animal Diseases, including Zoonoses (GLEWS)

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