What Are the Causes of the Spike in Animal-to-Human Disease Transmission in Recent Times?

April 7th is World Health Day, and while it is an opportunity to reflect on public health advances in recent decades, it is also important to address current and future health challenges.

Among the most pressing problems in recent years are disease outbreaks and their transmission from animals to humans.

From Covid-19 to monkeypox, Ebola, bird flu, Zika and HIV, the number of diseases transmitted from animals to humans has increased in recent years, raising fears of new epidemics.

What is a zoonotic disease?

A zoonotic disease is a disease or infection transmitted from vertebrate animals to humans and vice versa. The causative agents can be bacteria, viruses or parasites.

These diseases are transmitted either directly during contact between animals and humans, or indirectly through food or through vectors such as insects or spiders.

Some diseases eventually become human, like COVID-19.

According to the World Organization for Animal Health, 60% of infectious diseases affecting humans are zoonotic.

Types of comorbidities

The term “zoonosis” includes a wide range of diseases. Some affect the digestive system, such as salmonella, while others affect the respiratory system, such as bird and swine flu, as well as Covid-19 or the nervous system in the case of rabies.

The severity of these diseases in humans varies greatly depending on the disease and virulence of the pathogen, as well as on the affected person, who may be particularly sensitive to the pathogen.

animals involved

Bats serve as a reservoir for many viruses that infect humans. Some of them have been known for a long time, such as the rabies virus, but many of them have appeared in recent decades, such as Ebola, the SARS coronavirus, SARS-CoV-2 (causing COVID-19) or the Nipah virus that appeared in Asia in 1998.

Badgers, ferrets and minks often cause viral zoonotic diseases, especially those caused by coronaviruses.

Other mammals such as cattle, pigs, dogs, foxes, camels, and rodents often act as intermediate hosts.

All viruses that cause major influenza pandemics are directly or indirectly of bird origin.

Finally, insects such as ticks are carriers of many viral diseases that affect humans.

Why has the incidence of zoonoses increased?

Originating thousands of years ago, zoonotic diseases have multiplied over the past 20-30 years.

The rise in international travel allowed it to spread faster. By occupying more and more areas of the planet, people also contribute to the destruction of ecosystems and contribute to the transmission of viruses.

Industrial farming increases the risk of spreading pathogens to animals.

The wildlife trade also increases human exposure to the microbes they can carry.

Deforestation increases the risk of contact between wildlife, domestic animals and humans.

Should we be afraid of a new pandemic?

A study published in the scientific journal Nature in 2022 warns that climate change will force many animals to leave their ecosystems in search of more livable land.

By mixing more, species will transmit their viruses more, which will encourage new diseases that are likely to be transmitted to humans.

The UN Panel on Biodiversity warned in October 2020 that “without preventive strategies, pandemics will occur more frequently, spread faster, kill more people and have an increasingly devastating impact on the global economy.”

An estimated 1.7 million unknown viruses exist in mammals and birds, published in the journal Science in 2018, and between 540,000 and 850,000 of them are capable of infecting humans.

Source: Medical Express

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