What are zoonotic diseases? Origins, examples, prevention & control

Zoonotic diseases are diseases and illnesses that pass from animals to humans. They are mainly caused by bacteria, viruses, fungi, and parasites.

People worldwide have become increasingly interested in zoonotic diseases ever since the emergence of Ebola, COVID-19, and avian influenza or bird flu.

The more we know about zoonoses, the better we will be at controlling and preventing pandemics in the future.

Origins and transmission of zoonotic diseases

In most cases, zoonotic diseases originate in wildlife, where they are maintained in what we call animal reservoirs. Reservoirs are the animals in which the disease-causing bacteria, viruses, etc., reside and multiply.

These reservoirs could be mammals, reptiles, birds, or insects. Human transmission occurs through direct contact with infected animals. We can also become infected if we consume contaminated food, have contact with animal waste, or through vectors such as ticks or mosquitoes.

The most common transmission of rabies, for example, is from an infected animal bite or scratch. Some diseases are transmitted via ticks, as is the case with Lyme disease.

Avian flu or swine flu infects humans via animal feces or respiratory droplets.

Examples of zoonosis

  • Rabies

This is a viral infection that mainly affects the central nervous system, causing severe inflammation of the spinal cord and brain. Unless treated soon after an animal bite or scratch, the patient will most likely die.

About 99% of all human infections come from domestic dogs. The other 1% come from infected cats, cattle, wolves, mongooses, raccoons, monkeys, skunks, and foxes.

  • Lyme Disease

The bacterium Borrelia burgdorferi infects humans through the bite of infected black-legged ticks while still in their nymph stage. First reports of human infections came from Lyme, in Connecticut, USA, hence the name.

  • Avian Influenza or bird flu

Caused by the influenza A virus, which in most cases infects wild birds. Some strains infect animals in poultry farms, which transmit the disease to humans. However, so far (March 2023), animal-to-human transmission is still quite rare.

  • Ebola Virus Disease

This is a rare and fatal viral disease. Humans become infected via contact with the blood, tissues, and the bodily fluids of infected primates, forest antelopes, or fruit bats.

According to the World Health Organization, Ebola virus disease has a fatality rate of about 50%.

  • COVID-19

This disease is caused by the novel coronavirus SARS-CoV-2. We are still not sure about its origins. Some people say it came from bats, possibly a pangolin, or a raccoon dog. The FBI in the US believes that it may have originated in a laboratory.

Zoonotic disease transmissions - Zoonosis

Image created by medicalvocab.com

Prevention and control of zoonotic diseases

In order to prevent and control these types of diseases, we need to target both humans and animals. Examples include:

  • Surveillance

It is crucial to report and register all occurrences of zoonotic diseases in both animals and humans.

  • Vaccination

There are shots for rabies and some other diseases that animals transmit to humans.

  • Vector control

Controlling tick and mosquito populations can help reduce the incidence of, for example, Lyme disease and dengue fever.

  • Biosecurity

Strict hygiene and security measures in animal markets, zoos, and livestock farms can help reduce the number of human infections.

  • Raising awareness

Public education is vital for combating the incidence of zoonotic diseases. Proper food handling, avoiding contact with sick animals, and thorough hand-washing can help reduce the number of human infections significantly.

The World Economic Forum says the following about zoonotic diseases:

“A growing global population, spreading urbanization, and climate change are all contributing to a higher risk of zoonotic diseases. It’s estimated that 60% of known infectious diseases and up to 75% of new or emerging infectious diseases are zoonotic in origin.”

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