From Alzheimer’s to Zebrafish: Eclectic Science and Regulatory Stories 86
Prions are proteinaceous infectious particles that are one-tenth the size of viruses.
They are self-replicating but do not possess a genome. Prions are the causative agents for
transmissible spongiform encephalopathies (TSEs), a group of animal and human central
nervous system diseases with long incubation periods. These diseases are uniformly fatal.
TSEs are the only diseases that can be sporadic, genetic or infectious.14 Humans can con-
tract such diseases (kuru, Creutzfeldt-Jakob) by ingesting prion-containing material.
History
Mankind has been infected ever since human beings began evolving from our primate
ancestors. Many of the microbes responsible had also infected the mammalian ancestors
of primates and even their pre-mammalian ancestors, such as reptiles and birds. Human
diseases such as herpes infections, hepatitis A and B, malaria, yellow fever and endog-
enous retroviral infections are classified as heirloom infections, part of our birthright as
humans.15
All microbes are continuously trying to spread themselves, crossing both geographic
and species barriers. Bacteria, viruses and protozoa existed for millions of years before
animals evolved, and it is not surprising that the earliest known animals were infected
with microbes. After a microorganism crosses the species barrier, it raises major concerns
about direct transmission to humans, who tend to be in closer contact with other humans
than with animal reservoirs.
In the late Paleolithic period (about 250,000 years ago), humans began living closely
with animals to obtain meat or milk needed for sustenance. Paleolithic humans also used
animal skins and bones. With their dependence on animals and group living, humans
paid the price by being subjected to a continuing barrage of disease-causing organisms.16
Placing different animals, such as sheep and goats, within the same enclosures encour-
aged the spread of microbes across species, sometimes producing new and different
strains of microbes. These microbes were spread through the air when animals were
housed within human dwellings or through animal feces used as building materials, fuel
or fertilizer. Taenia (tapeworm), and trichinosis (roundworm), two diseases from macro-
parasite infestations, and five microbial diseases—anthrax, brucellosis, Q fever, tularemia
and glanders—infected humans for the first time during the Paleolithic era. Consuming
undercooked meat from wild cattle and wild boars was the likely cause of tapeworm,
while wild boars, horses and bears could have been the source of infestation by Trichinella
spirilli, the round worm that causes trichinosis. Anthrax, brucellosis and Q fever were
transmitted by wild ruminants, specifically the ancestors of cattle, sheep and goats.
Tularemia comes from rabbits and squirrels, while glanders is caused by bacteria carried
by horses and mules.17 It is clear that many important human diseases can be traced to
bacteria, viruses and protozoa that were first transmitted from animals to humans in the
Paleolithic era.18
Final Thoughts
According to the late Joshua Lederberg, whose work in bacterial genetics led to the Nobel
Prize in Physiology or Medicine in 1958, and a number of scientific luminaries, many gaps
remain in understanding zoonotic agents and the diseases they cause. Zoonoses involv-
ing two or more hosts, and often other vectors, illustrate some of the more interesting and
complex patterns of virulence and pathogenesis that have evolved in nature. And despite
all of the spectacular achievements in microbial genetics and genomics, there is still much
to be learned about the ecological factors that lead to human infection and its emergence.19
Prions are proteinaceous infectious particles that are one-tenth the size of viruses.
They are self-replicating but do not possess a genome. Prions are the causative agents for
transmissible spongiform encephalopathies (TSEs), a group of animal and human central
nervous system diseases with long incubation periods. These diseases are uniformly fatal.
TSEs are the only diseases that can be sporadic, genetic or infectious.14 Humans can con-
tract such diseases (kuru, Creutzfeldt-Jakob) by ingesting prion-containing material.
History
Mankind has been infected ever since human beings began evolving from our primate
ancestors. Many of the microbes responsible had also infected the mammalian ancestors
of primates and even their pre-mammalian ancestors, such as reptiles and birds. Human
diseases such as herpes infections, hepatitis A and B, malaria, yellow fever and endog-
enous retroviral infections are classified as heirloom infections, part of our birthright as
humans.15
All microbes are continuously trying to spread themselves, crossing both geographic
and species barriers. Bacteria, viruses and protozoa existed for millions of years before
animals evolved, and it is not surprising that the earliest known animals were infected
with microbes. After a microorganism crosses the species barrier, it raises major concerns
about direct transmission to humans, who tend to be in closer contact with other humans
than with animal reservoirs.
In the late Paleolithic period (about 250,000 years ago), humans began living closely
with animals to obtain meat or milk needed for sustenance. Paleolithic humans also used
animal skins and bones. With their dependence on animals and group living, humans
paid the price by being subjected to a continuing barrage of disease-causing organisms.16
Placing different animals, such as sheep and goats, within the same enclosures encour-
aged the spread of microbes across species, sometimes producing new and different
strains of microbes. These microbes were spread through the air when animals were
housed within human dwellings or through animal feces used as building materials, fuel
or fertilizer. Taenia (tapeworm), and trichinosis (roundworm), two diseases from macro-
parasite infestations, and five microbial diseases—anthrax, brucellosis, Q fever, tularemia
and glanders—infected humans for the first time during the Paleolithic era. Consuming
undercooked meat from wild cattle and wild boars was the likely cause of tapeworm,
while wild boars, horses and bears could have been the source of infestation by Trichinella
spirilli, the round worm that causes trichinosis. Anthrax, brucellosis and Q fever were
transmitted by wild ruminants, specifically the ancestors of cattle, sheep and goats.
Tularemia comes from rabbits and squirrels, while glanders is caused by bacteria carried
by horses and mules.17 It is clear that many important human diseases can be traced to
bacteria, viruses and protozoa that were first transmitted from animals to humans in the
Paleolithic era.18
Final Thoughts
According to the late Joshua Lederberg, whose work in bacterial genetics led to the Nobel
Prize in Physiology or Medicine in 1958, and a number of scientific luminaries, many gaps
remain in understanding zoonotic agents and the diseases they cause. Zoonoses involv-
ing two or more hosts, and often other vectors, illustrate some of the more interesting and
complex patterns of virulence and pathogenesis that have evolved in nature. And despite
all of the spectacular achievements in microbial genetics and genomics, there is still much
to be learned about the ecological factors that lead to human infection and its emergence.19