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The Challenge of Parasite Control
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
Regardless of parasite type—viral, bacterial or eukaryotic—vaccines tend to fall into one of several categories. Until recently, almost all vaccines could be accurately described as either killed or live, attenuated vaccines (Table 9.5). Killed vaccines (also called inactivated vaccines), as the name suggests, consist of inactivated virus or dead organisms. The Salk polio vaccine and the injected, inactivated influenza vaccines are examples of killed vaccines. Attenuated vaccines contain a weakened strain of the parasite, which although able to infect and replicate in the host, is unable to cause disease. The oral Sabin polio vaccine and the more recent attenuated influenza vaccine inhaled as a nasal mist both consist of an attenuated virus. Both types of vaccines have advantages and disadvantages. An attenuated vaccine more closely mimics natural disease and is more likely to stimulate both humoral and cell-mediated immunity. Furthermore, such vaccines are administered through the normal portal of entry and are therefore more likely to generate immunity at the exact site where the parasite is found in the body. There is, however, a low but often significant probability that the attenuated organisms in a live vaccine will revert to virulence if they undergo random mutation. Attenuated poliovirus in the Sabin vaccine, for instance, reverts to virulence in about one in each 2.6 million vaccinated individuals, causing symptoms of polio.
Introduction to Vaccination
Published in Mesut Karahan, Synthetic Peptide Vaccine Models, 2021
Nezih Pişkinpaşa, Ömer Faruk Karasakal
Conventional (classical) vaccines are prepared by inactivation of viruses or bacteria replicated in cell cultures and by physical comparison of an adjuvant (aluminum hydroxide and/or fat adjuvant). Conventional vaccines are discussed in two groups: live attenuated vaccine and inactive vaccine (Lee et al. 2012).
Disease Prediction and Drug Development
Published in Arvind Kumar Bansal, Javed Iqbal Khan, S. Kaisar Alam, Introduction to Computational Health Informatics, 2019
Arvind Kumar Bansal, Javed Iqbal Khan, S. Kaisar Alam
Many types of vaccines are used. The traditional approach was to use attenuated virulent genes (disease-causing genes in pathogens) that are too weak to cause the disease but strong enough to invoke the immune response to counter the disease. Traditional vaccines can be: 1) live attenuated vaccine; 2) inactivated vaccine; 3) component vaccines; 4) VLP (virus-like particle) vaccine; 5) liposomal vaccines; 6) adjuvanted vaccines; 7) conjugate vaccine and 8) toxoid vaccine.
Insight into the current Toxoplasma gondii DNA vaccine: a review article
Published in Expert Review of Vaccines, 2023
Xirui Zhang, Hao Yuan, Yasser S. Mahmmod, Zipeng Yang, Mengpo Zhao, Yining Song, Shengjun Luo, Xiu-Xiang Zhang, Zi-Guo Yuan
Attenuated T. gondii vaccines are now considered the most promising type of vaccine which provides complete protection. Toxovax, the only commercial T. gondii vaccine, is also an attenuated vaccine made from live T. gondii S48 strain to protect susceptible breeding ewes. Attenuated vaccines are often made using life cycle defective mutants, virulence factor deletion mutants, or nutrient auxotrophic mutants. Among them, attenuated vaccines made from auxotrophic mutants are considered more promising [12]. However, although the attenuated vaccine has an excellent immune effect, the risk of reverting back to a complete virulence strain cannot be ignored [10]. Together with the disadvantage of short-shelf life and its inefficiency in protecting against different Toxoplasma strains resulted in labeling it as none an ideal vaccine for wide application.
Approaches in broadening the neutralizing antibody response of the influenza vaccine
Published in Expert Review of Vaccines, 2021
Ruiqi Zhang, Ivan Fan-Ngai Hung
The seed virus for live attenuated vaccine is cold-adapted and only cultured in chicken embryonated eggs [32–34]. The live attenuated vaccines are approved in North America and part of Europe, and administrated through intranasal route [25]. Currently, the nasal spray vaccines are quadrivalent and made up of an influenza A(H1N1) virus, an influenza A(H3N2) virus and two influenza B viruses [35]. Vaccination with this vaccine can induce immune response and elicit IgA and IgG antibodies as influenza infection [36,37]. Although the live attenuated vaccine has high safety and cannot replicate efficiently at body temperature, pregnant women, children less than 2 years old, and people with immunodeficiency are not suggested to be vaccinated with this vaccine [25,38]. Like an inactivated vaccine, the live attenuated vaccine may also induce allergies associated with chicken embryos.
From infection to vaccination: reviewing the global burden, history of vaccine development, and recurring challenges in global leishmaniasis protection
Published in Expert Review of Vaccines, 2021
Greta Volpedo, Ryan H Huston, Erin A Holcomb, Thalia Pacheco-Fernandez, Sreenivas Gannavaram, Parna Bhattacharya, Hira L Nakhasi, Abhay R Satoskar
First, there is a concern about the balance between safety and efficacy. Live attenuated vaccines can achieve attenuation by either physicochemical methods (i.e. long-term invitro culture, mutagenesis, or irradiation) or by genetic modifications. In the first case, there is the concern that the parasites could regain virulence; this is also possible for parasites with mutations in just one allele of the genes [203]. Laboratory-generated Leishmania mutants are also antibiotic resistant, which is a useful and practical method for parasite selection during scientific research. Some parasites may retain those genes, which can also lead to antibiotic resistance within Leishmania populations, making this type of vaccine not feasible for clinical use [234]. Thus, homozygous mutants without antibiotic resistance genes would be ideal candidates for safe use in humans. Additionally, live attenuated vaccines should be designed to be safe for immunocompromised patients, since vaccination is also necessary in regions with high rates of HIV-positive individuals [203]. On that regard, killed parasites may appear as a safer alternative, providing a broad range of antigens without the risk of virulence. However, they fail to provide significant protection, suggesting that a carefully designed live attenuated vaccine could be a better option [131].