Zoonoses Are More Common Than You Might Believe!
July 13, 2020 at 4:48 p.m.
By Max [email protected]
Rabies is a zoonosis, a disease caused by a pathogen transmitted from animals to humans. According to David Quammen in his book “Spillover: Animal Infections and the Next Human Pandemic,” there are more human diseases transmitted from animals that you might expect. COVID19 is one, AIDS is another. AIDS is a disease of zoonotic origin caused by a virus that, having reached humans through just a few accidental events in western and central Africa, now passes human-to-human by the millions. Influenza is a whole category of others as is measles, which is likely the result of a spillover of a virus from cattle to humans.
The list is seemingly endless, including Ebola and the bubonic plague. The Spanish influenza of 1918-19 had its ultimate source in a wild aquatic bird, and after passing through some combination of domesticated animals emerged to kill as many as 50 million people. Pondering them as a group tends to reaffirm the old Darwinian truth (the darkest of his truths, well known and persistently forgotten) that humanity is a kind of animal, inextricably connected with other animals: in origin and in descent, in sickness and in health.
The list of zoonotic diseases also includes monkeypox, bovine tuberculosis, Lyme disease, West Nile fever, Marburg virus disease, hantavirus pulmonary syndrome, anthrax, Lassa fever, Rift Valley fever, ocular larva migrans, scrub typhus, Bolivian hemorrhagic fever, Kyasanur forest disease and a strange new affliction called Nipah encephalitis, which has killed pigs and pig farmers in Malaysia. Each of them reflects the action of a pathogen that can cross into people from other animals.
Many of these diseases have something in common, they jumped to humans after we started destroying habitats and ruining ecosystems. Unfortunately, new zoonotic diseases are emerging and re-emerging at an exponentially increasing rate.
The Lancet medical journal reports that Democratic Republic of Congo has had 11 Ebola virus outbreaks since the 1970s, but six have occurred in the past decade. Coronavirus infections are also emerging more frequently: from SARS to MERS, and now COVID-19. Not all zoonotic diseases become pandemics, but most pandemics are caused by zoonoses and they have become characteristic of the Anthropocene era (the current geological age).
Zoonotic diseases are more treacherous than non-zoonotic diseases. Smallpox is one example of the latter, it is caused by variola virus, which under natural conditions infects only humans. Smallpox could be eradicated because that virus, lacking ability to reside and reproduce anywhere but in a human body (or a carefully watched lab animal), couldn’t hide. (Hiding is what makes zoonotic diseases so interesting, so complicated, and so problematic.) Poliomyelitis is another nonzoonotic disease. It has afflicted humans for millennia but that (for counterintuitive reasons involving improved hygiene and delayed exposure of children to the virus) became a fearsome epidemic threat during the first half of the twentieth century, especially in Europe and North America.
In the United States, the polio problem peaked in 1952 with an outbreak that killed more than three thousand victims, many of them children, and left 21,000 atleast partially paralyzed. Like smallpox, polio has been virtually eliminated by inactive or oral vaccination.
The New York Times recently described a possible means by which COVID-19 made the transition from animals to humans. It may have started somewhere in China’s mountainous Yunnan province when a hunter entered a limestone cave. He was there to trap horseshoe bats using specially designed nets. He was successful in capturing a dozen or so and took them to vendors at a nearby wildlife market where they were stored in cages along side peacocks, bullfrogs, rat snakes, soft-shell turtles, mouse deer, ferret badgers and foxes, all being sold for their meat, fur or medicinal properties. The hunter also took the plumpest bats to restaurants he had been supplying. What the hunter didn’t know was that the bats were teeming with invisible ecosystems of fungi, bacterial and viruses. Many of the viruses multiplying within bats had circulated among their hosts for thousands of years, using bat cells to replicate but rarely causing severe illness.
Through chance mutations and the frequent exchange of genes, one virus had acquired the ability to infect the cells of certain other mammals in addition to bats, should the opportunity ever arise. When the hunter entered the cave, he provided the virus with a new path to follow, one that led out of the damp crevices it had always known, out of the country side, into the world at large. Of course, the virus might have initially jumped from bats to another caged creature in the market as well. When chefs of other buyers browsed the market, they may have inhaled infectious droplets or touched contaminated surfaces and spread the virus to others. Modern transportation has dispersed these dangerous microbes across the world in record time.
Max Sherman is a medical writer and pharmacist retired from the medical device industry. He has taught college courses on regulatory and compliance issues at Ivy Tech, Grace College and Butler University. Sherman has an unquenchable thirst for knowledge on all levels. Eclectic Science, the title of his column, touches on famed doctors and scientists, human senses, aging, various diseases, and little-known facts about many species, including their contributions to scientific research. His new book “Science Snippets” is available from Amazon and other book sellers. He can be reached by email at [email protected].
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Rabies is a zoonosis, a disease caused by a pathogen transmitted from animals to humans. According to David Quammen in his book “Spillover: Animal Infections and the Next Human Pandemic,” there are more human diseases transmitted from animals that you might expect. COVID19 is one, AIDS is another. AIDS is a disease of zoonotic origin caused by a virus that, having reached humans through just a few accidental events in western and central Africa, now passes human-to-human by the millions. Influenza is a whole category of others as is measles, which is likely the result of a spillover of a virus from cattle to humans.
The list is seemingly endless, including Ebola and the bubonic plague. The Spanish influenza of 1918-19 had its ultimate source in a wild aquatic bird, and after passing through some combination of domesticated animals emerged to kill as many as 50 million people. Pondering them as a group tends to reaffirm the old Darwinian truth (the darkest of his truths, well known and persistently forgotten) that humanity is a kind of animal, inextricably connected with other animals: in origin and in descent, in sickness and in health.
The list of zoonotic diseases also includes monkeypox, bovine tuberculosis, Lyme disease, West Nile fever, Marburg virus disease, hantavirus pulmonary syndrome, anthrax, Lassa fever, Rift Valley fever, ocular larva migrans, scrub typhus, Bolivian hemorrhagic fever, Kyasanur forest disease and a strange new affliction called Nipah encephalitis, which has killed pigs and pig farmers in Malaysia. Each of them reflects the action of a pathogen that can cross into people from other animals.
Many of these diseases have something in common, they jumped to humans after we started destroying habitats and ruining ecosystems. Unfortunately, new zoonotic diseases are emerging and re-emerging at an exponentially increasing rate.
The Lancet medical journal reports that Democratic Republic of Congo has had 11 Ebola virus outbreaks since the 1970s, but six have occurred in the past decade. Coronavirus infections are also emerging more frequently: from SARS to MERS, and now COVID-19. Not all zoonotic diseases become pandemics, but most pandemics are caused by zoonoses and they have become characteristic of the Anthropocene era (the current geological age).
Zoonotic diseases are more treacherous than non-zoonotic diseases. Smallpox is one example of the latter, it is caused by variola virus, which under natural conditions infects only humans. Smallpox could be eradicated because that virus, lacking ability to reside and reproduce anywhere but in a human body (or a carefully watched lab animal), couldn’t hide. (Hiding is what makes zoonotic diseases so interesting, so complicated, and so problematic.) Poliomyelitis is another nonzoonotic disease. It has afflicted humans for millennia but that (for counterintuitive reasons involving improved hygiene and delayed exposure of children to the virus) became a fearsome epidemic threat during the first half of the twentieth century, especially in Europe and North America.
In the United States, the polio problem peaked in 1952 with an outbreak that killed more than three thousand victims, many of them children, and left 21,000 atleast partially paralyzed. Like smallpox, polio has been virtually eliminated by inactive or oral vaccination.
The New York Times recently described a possible means by which COVID-19 made the transition from animals to humans. It may have started somewhere in China’s mountainous Yunnan province when a hunter entered a limestone cave. He was there to trap horseshoe bats using specially designed nets. He was successful in capturing a dozen or so and took them to vendors at a nearby wildlife market where they were stored in cages along side peacocks, bullfrogs, rat snakes, soft-shell turtles, mouse deer, ferret badgers and foxes, all being sold for their meat, fur or medicinal properties. The hunter also took the plumpest bats to restaurants he had been supplying. What the hunter didn’t know was that the bats were teeming with invisible ecosystems of fungi, bacterial and viruses. Many of the viruses multiplying within bats had circulated among their hosts for thousands of years, using bat cells to replicate but rarely causing severe illness.
Through chance mutations and the frequent exchange of genes, one virus had acquired the ability to infect the cells of certain other mammals in addition to bats, should the opportunity ever arise. When the hunter entered the cave, he provided the virus with a new path to follow, one that led out of the damp crevices it had always known, out of the country side, into the world at large. Of course, the virus might have initially jumped from bats to another caged creature in the market as well. When chefs of other buyers browsed the market, they may have inhaled infectious droplets or touched contaminated surfaces and spread the virus to others. Modern transportation has dispersed these dangerous microbes across the world in record time.
Max Sherman is a medical writer and pharmacist retired from the medical device industry. He has taught college courses on regulatory and compliance issues at Ivy Tech, Grace College and Butler University. Sherman has an unquenchable thirst for knowledge on all levels. Eclectic Science, the title of his column, touches on famed doctors and scientists, human senses, aging, various diseases, and little-known facts about many species, including their contributions to scientific research. His new book “Science Snippets” is available from Amazon and other book sellers. He can be reached by email at [email protected].
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