In epidemiology, infectivity is the ability of a pathogen to establish an infection. More specifically, infectivity is the extent to which the pathogen can enter, survive, and multiply in a host. It is measured by the ratio of the number of people who become infected to the total number exposed to the pathogen. [1]
Infectivity has been shown to positively correlate with virulence, in plants. This means that as a pathogen's ability to infect a greater number of hosts increases, so does the level of harm it brings to the host. [2]
A pathogen's infectivity is different from its transmissibility, which refers to a pathogen's capacity to pass from one organism to another. [1]
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.
Staphylococcus aureus is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often positive for catalase and nitrate reduction and is a facultative anaerobe that can grow without the need for oxygen. Although S. aureus usually acts as a commensal of the human microbiota, it can also become an opportunistic pathogen, being a common cause of skin infections including abscesses, respiratory infections such as sinusitis, and food poisoning. Pathogenic strains often promote infections by producing virulence factors such as potent protein toxins, and the expression of a cell-surface protein that binds and inactivates antibodies. S. aureus is one of the leading pathogens for deaths associated with antimicrobial resistance and the emergence of antibiotic-resistant strains, such as methicillin-resistant S. aureus (MRSA), is a worldwide problem in clinical medicine. Despite much research and development, no vaccine for S. aureus has been approved.
Texas root rot is a disease that is fairly common in Mexico and the southwestern United States resulting in sudden wilt and death of affected plants, usually during the warmer months. It is caused by a soil-borne fungus named Phymatotrichopsis omnivora that attacks the roots of susceptible plants. It was first discovered in 1888 by Pammel and later named by Duggar in 1916.
Virulence is a pathogen's or microorganism's ability to cause damage to a host.
Serial passage is the process of growing bacteria or a virus in iterations. For instance, a virus may be grown in one environment, and then a portion of that virus population can be removed and put into a new environment. This process is repeated with as many stages as desired, and then the final product is studied, often in comparison with the original virus.
Rickettsia rickettsii is a Gram-negative, intracellular, coccobacillus bacterium that was first discovered in 1902. R. rickettsii is the causative agent of Rocky Mountain Spotted Fever and is transferred to its host via a tick bite. It is one of the most pathogenic Rickettsia species and affects a large majority of the Western Hemisphere, most commonly the Americas.
Schistosomatidae is a family of digenetic trematodes with complex parasitic life cycles. Immature developmental stages of schistosomes are found in molluscs and adults occur in vertebrates. The best studied group, the blood flukes of the genus Schistosoma, infect and cause disease in humans. Other genera which are infective to non-human vertebrates can cause mild rashes in humans.
Adhesins are cell-surface components or appendages of bacteria that facilitate adhesion or adherence to other cells or to surfaces, usually in the host they are infecting or living in. Adhesins are a type of virulence factor.
A vertically transmitted infection is an infection caused by pathogenic bacteria or viruses that use mother-to-child transmission, that is, transmission directly from the mother to an embryo, fetus, or baby during pregnancy or childbirth. It can occur when the mother has a pre-existing disease or becomes infected during pregnancy. Nutritional deficiencies may exacerbate the risks of perinatal infections. Vertical transmission is important for the mathematical modelling of infectious diseases, especially for diseases of animals with large litter sizes, as it causes a wave of new infectious individuals.
Lysogeny, or the lysogenic cycle, is one of two cycles of viral reproduction. Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formation of a circular replicon in the bacterial cytoplasm. In this condition the bacterium continues to live and reproduce normally, while the bacteriophage lies in a dormant state in the host cell. The genetic material of the bacteriophage, called a prophage, can be transmitted to daughter cells at each subsequent cell division, and later events can release it, causing proliferation of new phages via the lytic cycle.
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.
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.
Pathogenomics is a field which uses high-throughput screening technology and bioinformatics to study encoded microbe resistance, as well as virulence factors (VFs), which enable a microorganism to infect a host and possibly cause disease. This includes studying genomes of pathogens which cannot be cultured outside of a host. In the past, researchers and medical professionals found it difficult to study and understand pathogenic traits of infectious organisms. With newer technology, pathogen genomes can be identified and sequenced in a much shorter time and at a lower cost, thus improving the ability to diagnose, treat, and even predict and prevent pathogenic infections and disease. It has also allowed researchers to better understand genome evolution events - gene loss, gain, duplication, rearrangement - and how those events impact pathogen resistance and ability to cause disease. This influx of information has created a need for bioinformatics tools and databases to analyze and make the vast amounts of data accessible to researchers, and it has raised ethical questions about the wisdom of reconstructing previously extinct and deadly pathogens in order to better understand virulence.
In biology, a pathogen, in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.
Mycoplasma penetrans is a species of Gram-positive bacteria. It is pathogenic, though many infected show no symptoms. It is a sexually transmitted disease, though an infant may be infected during birth.
When considering pathogens, host adaptation can have varying descriptions. For example, in the case of Salmonella, host adaptation is used to describe the "ability of a pathogen to circulate and cause disease in a particular host population." Another usage of host adaptation, still considering the case of Salmonella, refers to the evolution of a pathogen such that it can infect, cause disease, and circulate in another host species.
Andrew Fraser Read FRS is Evan Pugh professor of biology and entomology at Pennsylvania State University and the Director of the Huck Institutes of the Life Sciences.
This glossary of virology is a list of definitions of terms and concepts used in virology, the study of viruses, particularly in the description of viruses and their actions. Related fields include microbiology, molecular biology, and genetics.
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.
In epidemiology, particularly in the discussion of infectious disease dynamics (modeling), the latent period is the time interval between when an individual or host is infected by a pathogen and when that individual becomes infectious, i.e. capable of transmitting pathogens to other susceptible individuals.