Author | Paul W. Ewald |
---|---|
Language | English |
Subject | Evolutionary biology |
Publisher | Oxford University Press |
Publication date | December 1, 1993 |
Pages | 320 |
ISBN | 0-19-506058-X |
OCLC | 27221612 |
616.9/0471 20 | |
LC Class | RC112 .E93 1994 |
Evolution of Infectious Disease is a 1993 book by the evolutionary biologist Paul W. Ewald. In this book, Ewald contests the traditional view that parasites should evolve toward benign coexistence with their hosts. He draws on various studies that contradict this dogma and asserts his theory based on fundamental evolutionary principles. This book provides one of the first in-depth presentations of insights from evolutionary biology on various fields in health science, including epidemiology and medicine.
Infectious disease are illnesses induced by another organism. [1] Such diseases range from mild to severe cases. The onset of infectious disease can be induced by bacteria, viruses, fungi, and parasites. [1] Several examples of infectious diseases are as follows: tuberculosis, chickenpox, mumps, meningitis, measles, and malaria. [2] Infectious diseases can be obtained through many routes of transmission such as inhalation, open wounds, sores, ingestion, sexual intercourse, and insect bites. [3] Author, Paul Ewald used his book to expound upon infectious diseases in humans and animals, explain various routes of transmission as well as epidemiology as a whole. [1] Epidemiology is defined as the study of the onset, distribution, and control of diseases. [4] Evolutionary epidemiology focuses on the distribution of infectious diseases whereas Darwinian epidemiology focuses on human beings as hosts of infectious diseases. [1] To fully comprehend both aspects of epidemiology, it is necessary to understand how organisms induce these diseases as well as how infected organisms counteract.
The extensive research about pathogens shows that they can evolve within a month, whereas animal hosts such as humans take centuries to make large evolutionary changes. [5] Parasite virulence and host resistance are variables that strongly impact a pathogen's ability to replicate and be distributed to many hosts. Parasite virulence is the level of harm a host endures due to a virus, bacteria, or parasite. [1] The way a host lives contributes heavily to how their body will react to pathogens. If an organism lives a moderately healthy lifestyle, including its diet, physical activity, and decreased stress, its chances of fighting off infectious diseases increase.
Host resistance pivots around how well a host's immune system can fight off a disease and rid their body of the pathogens. [6] Although a healthy lifestyle can help a host, infectious diseases seem to evolve so quickly that a new generation of a disease may have emerged before scientists have the chance to make a vaccination for the first generation. Pathogens adapt to the medications and form a resistance to them which causes the new generations of pathogens to be more detrimental than the previous generations. [7] After many generations have emerged, scientists must continuously form new vaccinations to combat the components of the disease that evolve every time a generation appears.
Two sets of experiments were performed which tested the correlation of pathogens and declining organism populations as well as zoonotic pathogens being associated with emerging infectious diseases. The first experiment focused solely on a pathogen's ability to decrease or completely wipe out a whole population of organisms. In this experiment, researchers used Daphnia magna as the host and six microparasites were vertically transmitted to the host. [8] Researchers Ebert, Lipsitch, and Mangin found that while pathogens and parasites do cause a change in a population, they do not have the ability to destroy an entire population. [7] The pathogens did however have an impact on the host's fertility. Some females involved in the experiment were unable to reproduce after being infected with the microparasites. [9]
The second experiment focused more on zoonotic pathogens being correlated with emerging infectious diseases in humans. The researchers comprised a database with separate infectious species, infectious pathogens that cause disease in patients with abnormal immune systems, and pathogens that have only been found in one case of human disease. [10] The researchers broke this database down into five portions which were viruses, bacteria, fungi, protozoa, and helminths. Direct contact, indirect contact, and vector borne were the routes of transmission used. [11] They found that 1415 zoonotic pathogen diseases have been found in humans.
A zoonosis or zoonotic disease is an infectious disease of humans caused by a pathogen that can jump from a non-human to a human and vice versa.
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable disease, is an illness resulting from an infection.
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson characterised parasites as "predators that eat prey in units of less than one". Parasites include single-celled protozoans such as the agents of malaria, sleeping sickness, and amoebic dysentery; animals such as hookworms, lice, mosquitoes, and vampire bats; fungi such as honey fungus and the agents of ringworm; and plants such as mistletoe, dodder, and the broomrapes.
An epidemic is the rapid spread of disease to a large number of hosts in a given population within a short period of time. For example, in meningococcal infections, an attack rate in excess of 15 cases per 100,000 people for two consecutive weeks is considered an epidemic.
Virulence is a pathogen's or microorganism's ability to cause damage to a host.
Viral evolution is a subfield of evolutionary biology and virology that is specifically concerned with the evolution of viruses. Viruses have short generation times, and many—in particular RNA viruses—have relatively high mutation rates. Although most viral mutations confer no benefit and often even prove deleterious to viruses, the rapid rate of viral mutation combined with natural selection allows viruses to quickly adapt to changes in their host environment. In addition, because viruses typically produce many copies in an infected host, mutated genes can be passed on to many offspring quickly. Although the chance of mutations and evolution can change depending on the type of virus, viruses overall have high chances for mutations.
In medicine, public health, and biology, transmission is the passing of a pathogen causing communicable disease from an infected host individual or group to a particular individual or group, regardless of whether the other individual was previously infected. The term strictly refers to the transmission of microorganisms directly from one individual to another by one or more of the following means:
In infectious disease ecology and epidemiology, a natural reservoir, also known as a disease reservoir or a reservoir of infection, is the population of organisms or the specific environment in which an infectious pathogen naturally lives and reproduces, or upon which the pathogen primarily depends for its survival. A reservoir is usually a living host of a certain species, such as an animal or a plant, inside of which a pathogen survives, often without causing disease for the reservoir itself. By some definitions a reservoir may also be an environment external to an organism, such as a volume of contaminated air or water.
Paul W. Ewald is an American evolutionary biologist, specializing in the evolutionary ecology of parasitism, evolutionary medicine, agonistic behavior, and pollination biology. He is the author of Evolution of Infectious Disease (1994) and Plague Time: The New Germ Theory of Disease (2002), and is currently director of the program in Evolutionary Medicine at the Biology Department of the University of Louisville.
Optimal virulence is a concept relating to the ecology of hosts and parasites. One definition of virulence is the host's parasite-induced loss of fitness. The parasite's fitness is determined by its success in transmitting offspring to other hosts. For about 100 years, the consensus was that virulence decreased and parasitic relationships evolved toward symbiosis. This was even called the law of declining virulence despite being a hypothesis, not even a theory. It has been challenged since the 1980s and has been disproved.
An emergent virus is a virus that is either newly appeared, notably increasing in incidence/geographic range or has the potential to increase in the near future. Emergent viruses are a leading cause of emerging infectious diseases and raise public health challenges globally, given their potential to cause outbreaks of disease which can lead to epidemics and pandemics. As well as causing disease, emergent viruses can also have severe economic implications. Recent examples include the SARS-related coronaviruses, which have caused the 2002-2004 outbreak of SARS (SARS-CoV-1) and the 2019–21 pandemic of COVID-19 (SARS-CoV-2). Other examples include the human immunodeficiency virus which causes HIV/AIDS; the viruses responsible for Ebola; the H5N1 influenza virus responsible for avian flu; and H1N1/09, which caused the 2009 swine flu pandemic. Viral emergence in humans is often a consequence of zoonosis, which involves a cross-species jump of a viral disease into humans from other animals. As zoonotic viruses exist in animal reservoirs, they are much more difficult to eradicate and can therefore establish persistent infections in human populations.
In epidemiology, a disease vector is any living agent that carries and transmits an infectious pathogen to another living organism; agents regarded as vectors are organisms, such as parasites or microbes. The first major discovery of a disease vector came from Ronald Ross in 1897, who discovered the malaria pathogen when he dissected a mosquito.
Daphnia magna is a small planktonic crustacean that belongs to the subclass Phyllopoda.
Host–parasite coevolution is a special case of coevolution, where a host and a parasite continually adapt to each other. This can create an evolutionary arms race between them. A more benign possibility is of an evolutionary trade-off between transmission and virulence in the parasite, as if it kills its host too quickly, the parasite will not be able to reproduce either. Another theory, the Red Queen hypothesis, proposes that since both host and parasite have to keep on evolving to keep up with each other, and since sexual reproduction continually creates new combinations of genes, parasitism favours sexual reproduction in the host.
Spillover infection, also known as pathogen spillover and spillover event, occurs when a reservoir population with a high pathogen prevalence comes into contact with a novel host population. The pathogen is transmitted from the reservoir population and may or may not be transmitted within the host population. Due to climate change and land use expansion, the risk of viral spillover is predicted to significantly increase.
Hamiltosporidium is a genus of Microsporidia, which are intracellular and unicellular parasites. The genus, proposed by Haag et al. in 2010, contains two species; Hamiltosporidium tvaerminnensis, and Hamiltosporidium magnivora. Both species infect only the crustacean Daphnia magna (Waterflea).
In parasitology and epidemiology, a host switch is an evolutionary change of the host specificity of a parasite or pathogen. For example, the human immunodeficiency virus used to infect and circulate in non-human primates in West-central Africa, but switched to humans in the early 20th century.
The study of gene-for-gene interactions uncovers genetic components, evolutionary impacts, and ecological/economic implications between rust fungi and plants. Rust fungi utilize the gene-for-gene interaction to invade host plants. Conversely, host plants utilize the gene-for-gene interaction to prevent invasion of rust fungi.
Disease ecology is a sub-discipline of ecology concerned with the mechanisms, patterns, and effects of host-pathogen interactions, particularly those of infectious diseases. For example, it examines how parasites spread through and influence wildlife populations and communities. By studying the flow of diseases within the natural environment, scientists seek to better understand how changes within our environment can shape how pathogens, and other diseases, travel. Therefore, diseases ecology seeks to understand the links between ecological interactions and disease evolution. New emerging and re-emerging infectious diseases are increasing at unprecedented rates which can have lasting impacts on public health, ecosystem health, and biodiversity.
Dieter Ebert is professor for Zoology and Evolutionary Biology at the Zoological Institute at the University of Basel in Basel, Switzerland. He is an evolutionary ecologist and geneticist, known for his research on host–pathogen interaction and coevolution, mainly using the model system Daphnia and its parasites.