Zoonotic Diseases

Copyright Mike Brown

Animals provide important benefits to people. They provide food, fiber, livelihoods, travel, sport, companionship, and education. However, animals can sometimes carry harmful germs that can spread to people and cause illness – these are referred to as zoonotic diseases or zoonoses.

Zoonotic diseases are caused by harmful germs like viruses, bacteria, parasites, and fungi. Such germs can result in many different types of illnesses in people and animals and can also cause death. Even if animals sometimes appear healthy they can often carry germs like viruses that can make people sick, depending on the zoonotic disease.

Zoonotic diseases are very common globally. It is estimated that more than 6 out of every 10 known infectious diseases in people can be spread from animals, and 3 out of every 4 new or emerging infectious diseases in people come from animals (Centers for Disease Control and Prevention, n.d.)


How do germs spread between animals and people?

Because of the close connections that exist between people and animals, the primary ways people can get infected with germs that can cause zoonotic diseases include:

  • Direct contact: with the blood, urine, saliva, mucous, feces, or other bodily fluids of an infected animal. Examples include petting or touching animals, and bites or scratches.
  • Indirect contact: with areas where animals live or roam, or objects or surfaces that have been contaminated with germs. Examples include aquarium tank water, pet habitats, wildlife habitats, chicken coops, animal sheds, plants, and soil, in addition to pet food and water dishes.
  • Vector-borne: such as bites from a tick, or an insect like a mosquito or a flea.
  • Foodborne: such as eating or drinking something unsafe e.g. unpasteurised (raw) milk, undercooked meat or eggs, or raw fruits and vegetables contaminated with feces from infected animals. Contaminated food can cause illness in both people and animals, including pets.
  • Waterborne: including drinking or coming in contact with contaminated water that contains feces from an infected animal (Centers for Disease Control and Prevention, n.d.).

Types of zoonotic diseases

Broadly speaking, zoonotic diseases can be categorised into four key stages:

Emerging zoonotic diseases: these are diseases which newly appear in a population or have existed previously but are rapidly increasing in incidence or geographical spread.
Epidemic zoonotic diseases: these diseases affect large numbers of people within a community, population, or region. They are often caused by events such as climate change, flooding or other human/animal interactions. e.g. Ebola, bird flu, sudden acute respiratory syndrome (SARS) and Zika virus.
Pandemics: Zoonoses become pandemics when widespread infections occur within countries/globally e.g. COVID-19
Neglected zoonotic diseases: These diseases are continually present to a greater or lesser extent in certain populations, but primarily where marginalised health systems exist. Neglected zoonotic diseases are endemic in affected poor populations, but receive much less international attention and funding than emerging diseases.

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