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Introduction to virology
Published in Amine Kamen, Laura Cervera, Bioprocessing of Viral Vaccines, 2023
There are different degrees of a viral infection, depending on the outcome and transmission of an infection:Abortive infection: The virus would enter the host cell but cannot complete the replication successfully. This could be a result of non-permissive host cell or formation of defective virions. Example: MP strain of herpes simplex virus with canine kidney cellsAsymptomatic infection: In this type, the host is considered the carrier of the virus without experiencing any symptoms of the infection. This type of infection can also be called an inapparent or subclinical infection. Asymptomatic infections do not prompt the infected host to take proper precautions and care, leading to higher chances of transmitting the infection. Example: Most cases of Human papillomavirus infectionsSymptomatic (Active) infection: In this, the virus successfully completes its genome expression in the host cell, producing infectious virions. Symptomatic infections are clinical and apparent, showing more than one symptom related to the specific infection. Examples: Fever in most cases, cough in case of respiratory infections such as SARS, influenza A virusSelf-limiting infection: These kinds of viral infections run their course (generally seven days) and get cleared out from the host system without severe medications. Examples: Common cold, chickenpoxLatent infection: This kind of infection remains hidden or inactive or dormant. They remain static, persistent, and can exist for a very longer duration inside the host cell before becoming active. This is achieved through either escaping the cell-mediated immune response or by infecting the cells of immune-privileged sites such as the brain and eyes. The viral genome can remain as an episome or integrated into the host genome. The virus maintains its latency by expressing very few viral genes that keep the viral genome silent and hidden from the host immune system. The latency can be retracted if the host cell is introduced to stress signals. Example: Herpesvirus, retrovirus (HIV)
Legionnaires’ disease in dental offices: Quantifying aerosol risks to dental workers and patients
Published in Journal of Occupational and Environmental Hygiene, 2021
Kerry A. Hamilton, Aditya Kuppravalli, Ashley Heida, Sayalee Joshi, Charles N. Haas, Marc Verhougstraete, Daniel Gerrity
Of the available dose response models (subclinical infection and clinical severity infection), the clinical severity dose response parameter was chosen because the N50 for this model was ∼104 CFU (Armstrong and Haas 2007a; Fitzgeorge et al. 1983). This assumption is consistent with a Legionella longbeachae dose-response-time model (N50 ∼104) successfully used to reconstruct the epidemic curve of several large, well-documented outbreaks globally with good statistical fidelity without the use of a morbidity ratio (Prasad et al. 2017). In contrast, a more stringent subclinical infection model would assume an N50 of ∼101 CFU and would be considerably more conservative. Therefore, no morbidity ratio was employed, and the clinical severity infection model endpoint was considered representative of a case of Legionnaires’ disease.