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An Overview of Parasite Diversity
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
Recent reviews have concluded that prominent parasite groups like trypanosomes, apicomplexans and helminths have acquired new genes through horizontal transfer and gene duplication. These processes seem to be favored and accelerated by the need to interact with a host that can fight back via its immune system and other defenses. The net result is that genome reduction is by no means the dominant theme. For instance, various protist parasites have the capacity to generate large numbers of surface molecules, which can be varied at different timepoints, stymieing any host immune response to specific parasite molecules. The phenomenon, known as antigenic variation, requires a large number of genes, each encoding a different membrane-associated molecule. Trypanosoma, Trichomonas vaginalis, Plasmodium falciparum and Giardia lamblia and others avail themselves of this immune evasion strategy, a topic that will be explored more fully in Chapter 4.
Epidemiology, Disease Transmission, Prevention, and Control
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
The infective dose is the number of organisms that must enter a host to cause an infection. It depends on the route and conditions of transmission, as well as the host′s susceptibility including the host′s immunological status. The physical properties of the organism make it either more or less susceptible to death by desiccation and other environmental affects and determine its ability to survive outside the host in soil or on an inanimate object. Host specificity may limit the availability of suitable hosts. Antigenic variation offers the organism the capability to escape or ameliorate the effects of the host′s immune response, while production of certain enzymes and toxins makes the pathogen more able to infect or cause disease.
Host Defense II: Acquired Immunity
Published in Constantin A. Bona, Francisco A. Bonilla, Textbook of Immunology, 2019
Constantin A. Bona, Francisco A. Bonilla
One of the most powerful mechanisms whereby pathogens escape specific immunity is through antigenic variation, either over long periods of time, or during an infection in a single host. Influenza viruses slowly accumulate point mutations in the surface glycoproteins hemagglutinin and neuraminidase. Occasionally these mutations will occur in areas where neutralizing antibodies bind and render them ineffective. This is called antigenic drift. Furthermore, there are animal reservoirs for influenza viruses, and occasionally one of these strains will co-infect with another influenza virus. The viruses may reassort their genetic material giving rise to new strains with surface glycoproteins radically different from those circulating previously in the human population. This is called antigenic shift. Humans exposed to influenza viruses develop immunity which protects from severe disease on re-exposure. However, mutants are not recognized by memory B and T cells because of their altered structure. Great influenza pandemics have been associated with the appearance of new virus reassortants against which humans had essentially no immunologic experience.
Understanding host immune responses to pneumococcal proteins in the upper respiratory tract to develop serotype-independent pneumococcal vaccines
Published in Expert Review of Vaccines, 2020
Theano Lagousi, Paraskevi Basdeki, Marien I De Jonge, Vana Spoulou
Significant progress has been made concerning the elucidation of the mucosal immune mechanisms induced by different pneumococcal protein antigens. Both humoral and cellular immune responses are induced against pneumococcal proteins through natural exposure, experimental carriage or immunization; however, none of the studied proteins is able to fully inhibit carriage when used as a single antigen. The combination of different proteins that are widely distributed among the majority of serotypes able to induce both arms, cellular and humoral, of immune response may further improve protection. Combinations of several antigens may impair different stages of pneumococcal infection potentially offering broad protection. Antigenic variation and level of expression variability should be taken into account while selecting combinations of protein antigens. A step forward employs the identification of highly conserved antigenic regions, or even distinct epitopes, within pneumococcal proteins with the potential to retain the benefits of protein antigens.
A profile of the Simplexa™ Bordetella Direct assay for the detection and differentiation of Bordetella pertussis and Bordetella parapertussis in nasopharyngeal swabs
Published in Expert Review of Molecular Diagnostics, 2020
The resurgence of pertussis worldwide highlights the importance of fast, reliable, and accurate diagnosis. The recent development of commercial assays with the capability of direct nucleic acid amplification and analysis of increased number of tests with a rapid turnaround is valuable for timely detection of infection and treatment. However, optimal diagnosis of pertussis depends on various factors: stage of the disease, vaccination status, and age of the patient. Therefore, a single diagnostic method cannot be used. Since PCR is the most sensitive and specific method, its use is highly recommended at any stage in addition to culture, which is often positive during the early stage, or serology at later stages. Whenever possible, culture should always be included. Bacterial strains are needed to study antigenic variation of circulating strains and the possible emergence of molecular changes involved in pathogen adaptation.
Understanding modern-day vaccines: what you need to know
Published in Annals of Medicine, 2018
Volker Vetter, Gülhan Denizer, Leonard R. Friedland, Jyothsna Krishnan, Marla Shapiro
Finally, reverse vaccinology is a new technology in which genes encoding potential antigenic proteins are identified from the entire genome of a given pathogen [41]. The identified proteins are then tested in vitro and in vivo to determine whether they are immunogenic and induce protective antibodies. Reverse vaccinology has been used to develop a vaccine against the challenging Neisseria meningitidis serogroup B [42]. Unlike other N. meningitidis serogroups, serogroup B is covered by capsular polysaccharides that have similarities to human polysaccharides. This property substantially reduces the immunogenicity of these polysaccharides and could, at least theoretically, trigger antibodies against the human host and cause auto-immune diseases [42]. In addition, a vaccine relying on recombinant proteins has been unsuccessful because of the high antigenic variation in circulating strains [42]. Reverse vaccinology helped identify four novel antigenic proteins, which have been combined in a tetravalent meningococcal B vaccine (Bexsero, GSK) [42]. By contrast, a more traditional approach of protein screening was used to develop a bivalent meningococcal B vaccine (Trumenba, Pfizer) [43].