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An Introduction to Parasitism
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
Most parasites are obligate parasites and need a host organism to provide the basics for existence (Figure 1.10). According to Combes (1991), a host is a living environment that is “discontinuous, because individual hosts resemble islands; reproducing, because hosts produce hosts; variable when hosts evolve; and transient when hosts die.” Parasites depend metabolically or physiologically on a host, a characteristic that for many lies at the heart of the concept of parasitism (for more see Chapter 3). Parasites might rely on the host for nutrition, a key digestive enzyme, or a developmental cue that enables them to mature in synchrony with their hosts. Several important terms used to describe particular kinds of hosts relevant to a parasite’s interests are briefly presented in this section and will be revisited in later chapters as well.
Host-Parasite Relationships
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
One may contrast the life-style of a free-living organism which may accidentally or only occasionally colonize a host with the life-style of an organism that can live only as a parasite. These latter are called obligate parasites. All viruses are obligate parasites, but obligate parasitism occurs among all classes of parasites. Plasmodia that cause malaria are obliga tely parasitic protozoa, trichinella are obligately parasitic worms, and dodder is an obligately parasitic plant. There are some parasites that are obligate parasites during some stages of their life cycles and are free-living in others. The common flea, for example, is free-living in its larval stage but is parasitic as an adult.
Factors Controlling the Microflora of the Healthy Mouth
Published in Michael J. Hill, Philip D. Marsh, Human Microbial Ecology, 2020
For cultivation, the dispersed samples are usually serially diluted in transport fluid, and aliquots are spread on various nonselective and selective agar media for incubation under different atmospheric conditions, depending on the microorganisms being cultivated.52,53 Since the majority of species are facultative or obligate anaerobes and several require carbon dioxide for growth, a gas mixture of H2/N2/CO2 is often used for incubation in an anaerobic jar or cabinet (Figure 12). A catalyst removes residual oxygen by combining it with hydrogen to form water. Some obligate anaerobes die very rapidly if exposed to oxygen. Therefore, oxygen-free conditions are essential not only for incubation, but also during the various technical procedures. Rubber-stoppered tubes may be kept anaerobic by flushing them with such a gas mixture whenever they are opened.54 If such tubes containing melted agar are rolled horizontally while cooling, they will be coated with agar on which colonies can grow (roll tubes). Alternatively, all procedures may be carried out in an anaerobic chamber (Figure 12). The recoveries of periodontal bacteria with various anaerobic techniques and culture media have recently been reviewed.55,56
Using chronobiology-based second-generation artificial intelligence digital system for overcoming antimicrobial drug resistance in chronic infections
Published in Annals of Medicine, 2023
Yotam Kolben, Henny Azmanov, Ram Gelman, Danna Dror, Yaron Ilan
The circadian clock regulates various aspects of viral replication, host responses, and associated pathogenesis. A disrupted circadian clock has been linked to increased susceptibility to several viral-associated diseases. Viruses are obligate parasites reliant on their hosts for replication and dissemination. As more than 80% of protein-coding genes in various tissues show daily rhythmic expression, and given the dependency of virus replication on cellular pathways, host clock components directly or indirectly influence virus replication [44]. Numerous factors that synchronize peripheral clocks, including the autonomic nervous system, body temperature, fasting/feeding cycles, and cytokines and hormones, may impact viral-mediated pathologies [44]. Viruses can reprogramme cellular metabolism, affecting the mechanisms involved in circadian rhythm [45]. Chronobiology is important for designing therapeutic strategies against SARS-CoV-2 and COVID-19, and other viruses [46].
“Me and ‘that’ machine”: the lived experiences of people with neuromuscular disorders using non-invasive ventilation
Published in Disability and Rehabilitation, 2023
Meredith A. Perry, Matthew Jenkins, Bernadette Jones, Jarrod Bowick, Hannah Shaw, Emma Robinson, Morgan Rowan, Kate Spencer, Alister Neill, Tristram Ingham
This is the first study to explore these perceptions of control and identity in the relationship between people with NMD and their NIV machine. In this instance, the relationship reflects a physical and psychological interaction between the human body and NIV machine to augment the user’s residual function [54]. While symbiosis usually refers to living organism, the concept of symbiosis between human-machine has been evident for over half a century [55] and is usually an obligate relationship, that is, with humans dependent on the machine for survival. To date, only a few studies have described the relationship developed between people with a chronic illness and the machines that keep them alive. Patients with kidney disease have described relationships with their dialyzer as being ‘one’ with the machine or being a machine themselves [56]. While these patients relished the independence provided by dialysis, they were acutely aware of their dependence on and the control the machine held over their life. Another study has described the symbiotic relationship patients with diabetes developed with their insulin pump, whereby participants were one with the machine and had subsequently created adjusted identities that incorporated the machine into their lives [57].
Forget-me-not: Lemierre’s syndrome, a case report
Published in Journal of American College Health, 2023
Benjamin Silverberg, Melinda J Sharon, Devan Makati, Mariah Mott, William D Rose
The great majority of cases follow infection of the palatine tonsils or peritonsillar tissue,16,17 and there may be an association with other bacterial and viral infections such as Strep throat and Epstein-Barr mononucleosis, though this has yet to be proved conclusively.7,11,16–18,23,28 Less than 2% of cases result from ear or dental infections (e.g., otitis media, sinusitis, mastoiditis, sialadenitis).13,20 These infections are thought to cause immunosuppression and disruption of mucosal barriers, spurning the gram-negative bacillus Fusobacterium necrophorum (an obligate anaerobe previously known as Bacillus fundiliformis) to become pathogenic.9,11,31 High-grade bacteremia and septic seeding of vital organs ensues.