Severe Influenza Pneumonia and Its Mimics in the Critical Care Unit
Cheston B. Cunha, Burke A. Cunha in Infectious Diseases and Antimicrobial Stewardship in Critical Care Medicine, 2020
Influenza viruses are members of the family Orthomyxoviridae, with three known types: A, B, and C. They all possess single-stranded ribonucleic acid (RNA) segments to replicate. Different genomic RNA segments facilitate reassortment and swapping between different influenza virus strains. This leads to the rapid exchange of RNA segments and to new influenza subtypes. A strain such as the novel H1N1, the pandemic influenza A (H1N1) 2009, or swine influenza H1N1 virus rapidly spread from person to person because of its absence of immunity. Every new influenza subtype resulted after a genome reassortment was capable of causing an unpredictable pandemic in term of spreading, difficulty treating infection, and mortality rates. This phenomenon is called “antigenic shift” and is observed only in influenza virus A. In contrast, the “antigenic drift” involves all influenza types, and the new virus is usually easy to treat [6,7].
Influenza neurologic complications
Avindra Nath, Joseph R. Berger in Clinical Neurovirology, 2020
Influenza viruses are members of the Orthomyxoviridae family. There are three types of influenza viruses that can infect humans: A, B, and C. Influenza types B and C primarily infect humans, whereas influenza A viruses infect a wide variety of mammals (including humans, horses, pigs, ferrets, cats, and dogs) as well as avian species. The ability of influenza A viruses to infect such a wide variety of host species that frequently come into close contact with one another permits the occurrence of co-infections with multiple influenza A viruses in permissive hosts that can serve mix the different influenza RNA segments. The genome of influenza viruses consists of seven to eight segments of negative-sense single-stranded RNA contained within an envelope to form a virus particle (virion) that is polymorphic and can be spherical or filamentous in morphology [1]. Co-infections can result in genetic reassortant viruses that express novel antigenic properties, which can cause periodic epidemics in immunologically naive populations. In some instances, these new viruses cause epidemics and can spread rapidly and widely enough to be considered as a pandemic.
Influenza
James M. Rippe in Lifestyle Medicine, 2019
Influenza viruses are members of the family Orthomyxoviridae. There are three types of influenza virus: influenza A, influenza B, and influenza C. Influenza viruses have been divided into these three types on the basis of major antigenic differences in the nucleoprotein (NP) and matrix (M) protein antigens. Influenza A viruses are the most virulent of the three influenza viruses and are the etiologic agents of all known influenza pandemics. Influenza B virus tends to cause milder disease than influenza A.2 Influenza C virus causes infection in humans only infrequently, and its pattern of infection follows no seasonal variation. All three types of virus exhibit a host-cell-derived lipid envelope and a genome of segmented, negative sense single-stranded RNA. Influenza viral particles are variable in shape, from irregular spheres that measure 80–120 nm in diameter to long filamentous particles. Only influenza A viruses are subtyped. Influenza A is subtyped on the basis of two major surface proteins, neuraminidase (NA) and hemagglutinin (HA). These surface proteins project like spikes, densely covering the surface of the virus, and are important for cell entry. One additional protein, membrane protein M2, is also present in small amounts on the viral envelope. Influenza A viruses are named for their HA and NA surface proteins, for example, a virus called H3N2 will contain HA type 3 and NA type 2. In addition to subtype, influenza A viruses are further characterized on the basis of the place and time that the virus was first isolated (e.g., A/California/7/2009) (H1N1).
Effector mechanisms of influenza-specific antibodies: neutralization and beyond
Published in Expert Review of Vaccines, 2018
Federica Sicca, Sam Neppelenbroek, Anke Huckriede
Influenza viruses are enveloped viruses which belong to the Orthomyxoviridae family. The two clinically relevant genera of the Orthomyxoviruses are influenza virus A and influenza virus B. Among the influenza A viruses, different subtypes can be distinguished based on the subtypes of hemagglutinin (HA) and neuraminidase (NA) [2]. So far, 18 different subtypes of the HA protein (H1-H18) and 11 different subtypes of the NA protein (N1-N11) have been identified [3]. Influenza B viruses form two lineages, the B/Victoria/2/87-like lineage and the B/Yamagata/16/88-like lineage, but are not further divided into subtypes [4]. The genome of influenza viruses is composed of single-stranded RNA organized in separate segments [5]. This genome make-up enables rapid evolution of influenza virus since replication of RNA is highly error-prone resulting in frequent point mutations. Moreover, the segmented nature of the genome enables the swap of entire segments if two different viruses infect a given cell simultaneously. This phenomenon is observed mainly for influenza A viruses which circulate in a number of animal species, in contrast to influenza B viruses which are with few exceptions restricted to humans. If point mutations or segment swap affect the HA glycoprotein, the major antigen of influenza virus, they can lead to antigenic drift and antigenic shift, respectively, thus enabling the virus to escape immune responses evoked by prior infection or vaccination [6,7].
Intranasal inactivated influenza vaccines for the prevention of seasonal influenza epidemics
Published in Expert Review of Vaccines, 2018
Kaori Sano, Akira Ainai, Tadaki Suzuki, Hideki Hasegawa
Seasonal influenza is a highly contagious infectious disease with a vast number of people infected worldwide, causing over one million deaths annually [1]. The main causative infectious agents of influenza are influenza A and B viruses, which are classified in the Orthomyxoviridae family, defined by viruses that possess single-stranded, segmented, and negative-sense RNA genomes. The major surface glycoproteins of this influenza virus are hemagglutinin (HA) and neuraminidase (NA). Influenza A viruses are further classified based on the antigenicity of the two surface glycoproteins (e.g. H1N1 and H3N2), and influenza B viruses are divided into two lineages based on the antigenicity of HA (i.e. Yamagata lineage and Victoria lineage) [2]. The two surface glycoproteins are continuously under strong evolutionary pressure and thus subject to frequent mutations. These mutations cause successive changes in the antigenic sites of HA and NA, which phenomenon is referred to as ‘antigenic drift’ [3]. This antigenic drift enables the virus to evade preexisting immunity in the human population, which is the cause of seasonal influenza epidemics worldwide [4].
Variant influenza: connecting the missing dots
Published in Expert Review of Anti-infective Therapy, 2022
Vivek Chavda, Rajashri Bezbaruah, Tutumoni Kalita, Anupam Sarma, Juti Rani Devi, Ratnali Bania, Vasso Apostolopoulos
Global pandemics with many deaths and morbidity ensue with the emergence of novel strains of viruses for which no immunity has developed in the human population [45]. These viruses were the main culprit of the Asian flu, Spanish flu, and Hong Kong flu outbreaks in the 19th century in 1957, 1918, and 1968, respectively (Figure 3) [46–48]. Viral flu outbreaks occur regularly with variations in severity. Swine flu is caused by influenza A strains including subtypes such as H1N1, H1N2, H2N1, H2N3, H3N1, and H3N2 [49,50]. Influenza type A belongs to the genus Orthomyxovirus in the family Orthomyxoviridae. It is an eight-segmented single-stranded RNA virus with a diameter of approximately 120 nm [51–54].
Related Knowledge Centers
- Influenza A Virus
- Influenza C Virus
- Mucus
- Influenza
- Negative-Strand Rna Virus
- Rna Virus
- Influenza B Virus
- Influenza D Virus
- Thogotovirus
- Quaranjavirus