Twice as many viruses pass from humans to animals than from animals to people

Roughly twice as many viruses pass from humans to animals than from animals to people (findings of a recent study – see below for summary)

Surprisingly, we find that humans are as much a source as a sink for viral spillover events, insofar as we infer more viral host jumps from humans to other animals than from animals to humans. 

The study report

In an anthropocentric world (a world in which humans speak about themselves and refer to themselves as the center of everything) it is unsurprising that when we speak about acquiring diseases we tend to write more about acquiring those diseases from animals rather than animals aquiring a disease from us. News media may present a slightly distorted view on this topic as a consequence.

Humans get twice as many viral infections from other humans than from animals
Humans get twice as many viral infections from other humans than from animals
Until September 7th I will give 10 cents to an animal charity for every comment. It is a way to help animal welfare without much effort at no cost. Comments help this website too, which is about animal welfare.

In a nice balancing act, and a return to reality, the study’s findings should not surprise anybody. It does not surprise me. To put it in scientific language, anthroponotic diseases are twice as common as zoonotic diseases.

We’ve just survived the Covid-19 pandemic which was caused by the transference of a virus from an animal to the human race. Although its source may have been the Wuhan bio lab rather than an animal slaughtered at they will hand wet market.

The research took place at University College London (UCL). They developed methods to enable them to analyse almost 12 million viral genomes in public databases.

They were able to reconstruct evolutionary histories to enable them to analyse which genomes develop mutations. Across most viral species there was a prevalence of human-animal transmission i.e. most often humans gave animals diseases rather than in the other direction.

And they discovered that there were more animal-to-animal disease transmission than, as I understand it, previously thought.

They found that when there were more genetic mutations there were more transmissions between different hosts of different species.

Prof Francois Balloux, a co-author of the study from the UCL Genetics Institute, said:

“We should consider humans just as one node in a vast network of hosts endlessly exchanging pathogens, rather than a sink for zoonotic bugs.

Prof Francois Balloux

“By surveying and monitoring transmission of viruses between animals and humans, in either direction, we can better understand viral evolution and hopefully be more prepared for future outbreaks and epidemics of novel illnesses, while also aiding conservation efforts.”

Prof Francois Balloux

Source and thanks to MRCVS online.

RELATED: Truth about Toxoplasmosis and Cats

Summarising the findings of the study: “The evolutionary drivers and correlates of viral host jumps”

This is quite technical for obvious reasons but it is simplified here and it is here for completeness.

In the study titled “Crossing host boundaries: the evolutionary drivers and correlates of viral host jumps,” researchers investigated the factors underlying the transition of viruses from non-human vertebrates to humans. Here are the key findings:

  1. Directionality of Host Jumps:
    • Contrary to conventional assumptions, humans are not only recipients but also sources of viral spillover events. In fact, more viruses are inferred to have jumped from humans to other animals than vice versa.
    • This challenges the prevailing view that host jumps primarily occur from animals to humans.
  2. Increased Genetic Changes:
    • Viral host jumps are associated with an increase in genetic changes (mutations) relative to viruses evolving alongside a single host animal.
    • These mutations reflect the adaptation of viruses to exploit their new hosts effectively.
  3. Evolutionary Mechanisms:
    • Viral lineages involved in putative host jumps exhibit heightened evolution.
    • The mutational threshold for a host jump is lower for viruses with broad host ranges.
  4. Genomic Targets of Natural Selection:
    • Different viral families show distinct genomic targets of natural selection following a successful host jump.
    • Structural or auxiliary genes are often prime targets for selection.

In summary, understanding the evolutionary drivers of viral host jumps can contribute to mitigating viral threats across species boundaries. 🦠🌍

What are the implications of these findings?

Let’s delve into the implications of the study’s findings on the evolutionary drivers and correlates of viral host jumps:

  1. Public Health Preparedness:
    • Recognizing that humans can be both recipients and sources of viral spillover events is crucial for public health preparedness.
    • Surveillance systems should monitor not only animal-to-human transmission but also human-to-animal transmission to prevent potential outbreaks.
  2. Viral Adaptation and Mutation:
    • The observed increase in genetic changes during host jumps highlights the adaptability of viruses.
    • Understanding these mutations can aid in predicting which viruses are likely to cross species boundaries and cause disease.
  3. One Health Approach:
    • The findings emphasize the interconnectedness of human, animal, and environmental health.
    • Implementing a “One Health” approach—integrating human, animal, and ecosystem health—is essential for preventing zoonotic diseases.
  4. Targeted Interventions:
    • Different viral families exhibit distinct genomic targets of natural selection post-host jump.
    • Tailoring interventions based on these targets can enhance our ability to control emerging infectious diseases.
  5. Conservation and Biodiversity:
    • Studying host jumps sheds light on the dynamics of virus-host interactions.
    • Conservation efforts should consider the role of wildlife as reservoirs for potential zoonotic viruses.

In summary, these findings underscore the need for interdisciplinary collaboration, vigilant surveillance, and proactive measures to mitigate the risks posed by viral host jumps across species boundaries. 🌏🔬🦠

Sources: various including:, Science Daily, Eurekalert and more.

List the zoonotic diseases carried by cats

This is a list of some zoonoses that can pass from domestic cats to humans. It is here to complete the page. These are rare. Toxoplasmosis is far more commonly acquired from undercooked foods than from cats for instance.

Cats can potentially transmit several zoonotic diseases to humans. Here are some common ones:

  1. Cat Scratch Disease (CSD):
    • Cause: CSD is caused by the bacterium Bartonella henselae, which may be carried in the saliva of infected cats and in the bodies of cat fleas.
    • Transmission: Usually transmitted via scratches, but bites and contact with open wounds can also spread the bacteria.
    • Symptoms in Humans: Swelling, blistering, painful lymph nodes, fever, headache, sore muscles, and fatigue. Severe cases can affect the eyes, brain, and heart.
    • Precautions: Avoid rough play with cats, wash hands after handling them, control fleas, and keep cats indoors to reduce the risk of CSD.
  2. Ringworm:
    • Cause: Ringworm is a fungal infection.
    • Transmission: It can be transmitted from humans to cats and vice versa.
    • Symptoms in Humans: Circular, itchy skin lesions.
    • Precautions: Maintain good hygiene and seek treatment if infected.
  3. Salmonella:
    • Cause: Salmonella bacteria.
    • Transmission: Cats can contract it from contaminated food or surfaces.
    • Symptoms in Humans: Gastrointestinal illness.
    • Precautions: Proper food handling and hygiene are essential.
  4. Toxoplasmosis:
    • Cause: Caused by the parasite Toxoplasma gondii.
    • Transmission: Cats can shed the parasite in their feces.
    • Symptoms in Humans: Usually mild, but can be severe in immunocompromised individuals.
    • Precautions: Pregnant women should avoid handling cat litter and raw meat.
  5. Giardiasis:
    • Cause: Caused by the parasite Giardia.
    • Transmission: Cats can carry it without showing symptoms.
    • Symptoms in Humans: Diarrhea and abdominal discomfort.
    • Precautions: Wear gloves when changing litter and maintain cleanliness.

Remember that while the likelihood of contracting these diseases from cats is generally low for healthy individuals, those with weakened immune systems need to take extra precautions. 🐱🤲🦠

Sources: Cornell, Better Vet,, Wikipedia

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