Zoonosis

 ( Animal Diseases ) 

A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite, or prion) that can jump from a non-human (usually a vertebrate) to a human and vice versa.

Major modern diseases such as Ebola and salmonellosis are zoonoses. HIV was a zoonotic disease transmitted to humans in the early part of the 20th century, though it has now evolved into a separate human-only disease. Human infection with animal influenza viruses is rare, as they do not transmit easily to or among humans. However, Avian influenza and swine influenza viruses in particular possess high zoonotic potential, and these occasionally recombine with human strains of the flu and can cause such as the 2009 swine flu. Taenia solium infection is one of the neglected with public health and veterinary concern in endemic regions. Zoonoses can be caused by a range of disease pathogens such as , bacteria, fungi and parasites; of 1,415 pathogens known to infect humans, 61% were zoonotic. Most human diseases originated in non-humans; however, only diseases that routinely involve non-human to human transmission, such as rabies, are considered direct zoonoses.

Zoonoses have different modes of transmission. In direct zoonosis the disease is directly transmitted from non-humans to humans through media such as air (influenza) or bites and saliva (rabies). In contrast, transmission can also occur via an intermediate species (referred to as a vector), which carry the disease pathogen without getting sick. When humans infect non-humans, it is called reverse zoonosis or anthroponosis. The term is from Ancient Greek: ζῷον zoon "animal" and νόσος nosos "sickness".

Host genetics plays an important role in determining which non-human viruses will be able to make copies of themselves in the human body. Dangerous non-human viruses are those that require few mutations to begin replicating themselves in human cells. These viruses are dangerous since the required combinations of mutations might randomly arise in the natural reservoir.

Recently, there has been a rise in frequency of appearance of new zoonotic diseases. "Approximately 1.67 million undescribed viruses are thought to exist in and birds, up to half of which are estimated to have the potential to spill over into humans", says a study led by researchers at the University of California, Davis. According to a report from the United Nations Environment Programme and International Livestock Research Institute a large part of the causes are environmental like climate change, unsustainable agriculture, exploitation of wildlife, and land use change. Others are linked to changes in human society such as an increase in mobility. The organizations propose a set of measures to stop the rise.

In 2006 a conference held in Berlin focused on the issue of zoonotic pathogen effects on food safety, urging government intervention and public vigilance against the risks of catching food-borne diseases from farm-to-table dining.

Many food-borne outbreaks can be linked to zoonotic pathogens. Many different types of food that have an animal origin can become contaminated. Some common food items linked to zoonotic contaminations include eggs, seafood, meat, dairy, and even some vegetables.

Outbreaks involving contaminated food should be handled in preparedness plans to prevent widespread outbreaks and to efficiently and effectively contain outbreaks.

Veterinarians are exposed to unique occupational hazards when it comes to zoonotic disease. In the US, studies have highlighted an increased risk of injuries and lack of veterinary awareness of these hazards. Research has proved the importance for continued clinical veterinarian education on occupational risks associated with musculoskeletal injuries, animal bites, needle-sticks, and cuts.

A July 2020 report by the United Nations Environment Programme stated that the increase in zoonotic pandemics is directly attributable to anthropogenic destruction of nature and the increased global demand for meat and that the industrial farming of pigs and chickens in particular will be a primary risk factor for the spillover of zoonotic diseases in the future. Habitat loss of viral reservoir species has been identified as a significant source in at least one spillover event.

Zoonotic disease emergence is demonstrably linked to the consumption of wildlife meat, exacerbated by human encroachment into natural habitats and amplified by the unsanitary conditions of wildlife markets. These markets, where diverse species converge, facilitate the mixing and transmission of pathogens, including those responsible for outbreaks of HIV-1, Ebola, and mpox, and potentially even the COVID-19 pandemic. Notably, small mammals often harbor a vast array of zoonotic bacteria and viruses, yet endemic bacterial transmission among wildlife remains largely unexplored. Therefore, accurately determining the pathogenic landscape of traded wildlife is crucial for guiding effective measures to combat zoonotic diseases and documenting the societal and environmental costs associated with this practice.

• Rabies

• African sleeping sickness
• Dirofilariasis
• Eastern equine encephalitis
• Japanese encephalitis
• Saint Louis encephalitis
• Scrub typhus
• Tularemia
• Venezuelan equine encephalitis
• West Nile fever
• Western equine encephalitis
• Zika fever

Pets may also serve as a reservoir of viral disease and contribute to the chronic presence of certain viral diseases in the human population. For instance, approximately 20% of domestic dogs, cats, and horses carry anti-hepatitis E virus antibodies and thus these animals probably contribute to human hepatitis E burden as well. For non-vulnerable populations (e.g., people who are not immunocompromised) the associated disease burden is, however, small. Furthermore, the trade of non domestic animals such as wild animals as pets can also increase the risk of zoonosis spread.

According to the Center for Diseases Control and Prevention (CDC) hunting and consuming wild animal meat ("bushmeat") in regions like Africa can expose people to infectious diseases due to the types of animals involved, like bats and primates. Unfortunately, common preservation methods like smoking or drying aren't enough to eliminate these risks. Although bushmeat provides protein and income for many, the practice is intricately linked to numerous emerging infectious diseases like Ebola, HIV, and SARS, raising critical public health concerns.

A review published in 2022 found evidence that zoonotic spillover linked to wildmeat consumption has been reported across all continents.

Joshua Moon, Clare Wenham, and Sophie Harman said that there is evidence that decreased biodiversity has an effect on the diversity of hosts and frequency of human-animal interactions with potential for pathogenic spillover.

An April 2020 study, published in the Proceedings of the Royal Society journal, found that increased virus spillover events from animals to humans can be linked to biodiversity loss and environmental degradation, as humans further encroach on wildlands to engage in agriculture, hunting, and resource extraction they become exposed to pathogens which normally would remain in these areas. Such spillover events have been tripling every decade since 1980. An August 2020 study, published in Nature, concludes that the anthropogenic destruction of ecosystems for the purpose of expanding agriculture and human settlements reduces biodiversity and allows for smaller animals such as bats and rats, which are more adaptable to human pressures and also carry the most zoonotic diseases, to proliferate. This in turn can result in more pandemics.

In October 2020, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services published its report on the 'era of pandemics' by 22 experts in a variety of fields and concluded that anthropogenic destruction of biodiversity is paving the way to the pandemic era and could result in as many as 850,000 viruses being transmitted from animals – in particular birds and mammals – to humans. The increased pressure on ecosystems is being driven by the "exponential rise" in consumption and trade of commodities such as meat, palm oil, and metals, largely facilitated by developed nations, and by a growing human population. According to Peter Daszak, the chair of the group who produced the report, "there is no great mystery about the cause of the Covid-19 pandemic, or of any modern pandemic. The same human activities that drive climate change and biodiversity loss also drive pandemic risk through their impacts on our environment."

 ! DiseaseInformation in this table is largely compiled from: 
 ! Pathogen(s)
 ! Animals involved
 ! Mode of transmission
 ! Emergence