Influenza commonly known as the flu is a respiratory infection caused by flu viruses. Who information for molecular diagnosis of influenza virus in humans. Randomized study of the efficacy and safety of oral. Each influenza virus isolate receives a unique name according to a set of rules. Mar 26, 2018 influenza commonly known as the flu is a respiratory infection caused by flu viruses. Influenza, commonly known as the flu, is an infectious disease caused by an influenza virus. This limited host range is apparently responsible for the lack of associated influenza pandemics in contrast with those caused by the morphologically similar influenza a virus as both mutate by both antigenic drift and. Influenza a viruses can be broken down into subtypes depending on the genes that make up the surface proteins. While influenza a viruses infect humans and other animals, influenza b viruses affects only humans, primarily children. Influenza, also called the flu, is a viral disease that affects humans and many animals. Of these, nine are also found in influenza a virus. Development of highyield influenza b virus vaccine. Clinical evaluation of the sd bioline influenza virus. Influenza virus isolation in tissue cell culture from respiratory specimens.
The c viruses cause only mild respiratory illness in humans. Early diagnosis of influenza flu is critical for patient management and infection control. The genome of influenza b virus, a member of the family orthomyxoviridae, consists of eight negativestrand rna segments, which encode 11 proteins. Three genera exist with this family that pertain to influenza viruses, influenzavirus a, influenzavirus b. Influenza b virus requires bm2 protein for replication. They belong to the orthomyxoviridae family and are classified into 3 distinct types influenza a, influenza b and influenza c. Antigenic variation within the ha and na antigens of influenzaviruses b has also been analyzed in detail. Between 1972 and 1995, the estimated worldwide influenzaassociated deaths ranged from approximately 25 to 150 per 10 000 in those aged. Other articles where influenza type b virus is discussed. There are many different strains types of this virus. Influenza is a contagious, acute respiratory illness caused by influenza viruses, usually influenza a or b subtypes. Mitigation of influenza b epidemic with school closures, hong. Influenza pneumonia incidence was high in 2005, a year when influenza ah3n2 subtype virus strains predominated, low in 2006 when ah1n1 viruses were more common, moderate in 2007 when h3n2 and.
Laboratory testing for influenza virus infection may be done on pre or postmortem clinical specimens, and include identification of influenza a or b virus infections by a positive result by at least one of the following. Mitigation of influenza b epidemic with school closures. The flu is a type of germ called a virus that you breathe in. Influenza a virus subtypes are subdivided into strains based on genetic variations in the h protein of the virus. This limited host range is apparently responsible for the lack of associated influenza pandemics in contrast with those caused by the morphologically similar influenza a virus as both mutate by both antigenic drift and reassortment. Influenza a viruses can also cause sporadic infections or spread worldwide. Influenza b viruses have not been the predominant virus in the united states since the 199293. Influenza a and b cause human disease with significant morbidity and mortality. Influenza is an acute respiratory illness, caused by influenza a, b, and c viruses, that occurs in local outbreaks or seasonal epidemics. The only other animals known to be susceptible to influenza b infection are seals and ferrets.
Clinical illness follows a short incubation period and presentation ranges from asymptomatic to fulminant, depending on the characteristics of both the virus and the individual host. Interaction among influenza viruses ah1n1, ah3n2, and b. Influenza is an infectious respiratory disease that, in humans, is caused by influenza a and influenza b viruses. Typically characterized by annual seasonal epidemics, sporadic pandemic outbreaks involve influenza a virus strains of zoonotic origin. The who estimates that annual epidemics of influenza result in 1 billion infections. Nov 18, 2019 for influenza a viruses, the hemagglutinin and neuraminidase antigen description are provided in parentheses e. Influenza a is the group that most commonly causes illness in humans. Jan, 2020 influenza b, one type of influenza virus, is dominating the 20192020 flu season early on. Influenza pneumonia incidence was high in 2005, a year when influenza ah3n2 subtype virus strains predominated, low in 2006 when ah1n1 viruses were more common, moderate in. Infection with type b influenza is usually milder than with type a. Major outbreaks of influenza are associated with influenza virus.
Influenza b victoria seasonal virus 10 14% 241 34% influenza b virus, genotype pending 14 20% influenza negative 17 24% 154 24% inconclusive 0 0% 2 150 per 10 000 in those aged. Influenza b, one type of influenza virus, is dominating the 20192020 flu season early on. In north america, influenza activity continued but in recent weeks influenza ah3n2 was the dominant virus, followed by influenza ah1n1pdm09. In contrast to influenzaviruses a, no distinct antigenic subtypes are recognized for members of the species influenza b virus, however, viruses with antigenically and genetically distinguishable lineages of ha and na e. Influenza b virus is the only species in the genus betainfluenzavirus in the virus family orthomyxoviridae influenza b virus is only known to infect humans and seals. Influenza, influenzaassociated mortality, and novel influenza a. Influenza b viruses are not divided into subtypes, but instead are further.
Influenza a and b are the two types of influenza that cause epidemic seasonal infections nearly every year. Ah1n1pdm09 to distinguish it from the seasonal influenza ah1n1 viruses that circulated prior to the pandemic. Influenza fact sheet keywords department of health services, dhs, division of public health, influenza, flu, coughing, sneezing, vaccine, vaccination, flu shot, contagious, p42064, p42064. In europe, influenza activity decreased across the continent, with two thirds of countries still above baseline for influenza like illness activity. Influenza b viruses primarily circulate in humans and do not cause pandemics. Cepheid are rapid, pointofcare molecular assays for flu virus detection. There are two types of flu virus, influenza a and influenza b, which can cause seasonal epidemics of disease in humans.
Jun 28, 2018 each influenza virus isolate receives a unique name according to a set of rules. For influenza a viruses, the hemagglutinin and neuraminidase antigen description are provided in parentheses e. Influenza b generally causes milder disease than type a and primarily. Jul 10, 2019 there are two main types of influenza flu virus. Influenza a virus causes influenza in birds and some mammals, and is the only species of the genus alphainfluenzavirus of the virus family orthomyxoviridae. A newly recognized livestock influenza virus, originally thought to be an influenza c virus, might represent a fourth genus, influenza d. Sequence analysis of the hemagglutinin ha genes of several influenza b isolates from 1987 to 1988 indicated that the ha1 domains of the b yamagata1688like viruses and b vi87like viruses. However, we are currently seeing very low numbers in both a and. In fact, multiple studies have suggested increased potency of influenza b virus in causing severe disease and mortality. First, the name denotes the type of influenza virus a, b, c or d, followed by the host species. Influenza a can be found in many species, including humans, birds, and pigs. The influenza a and b viruses that routinely spread in people human influenza viruses are responsible for.
Subtypes of the type a influenza virus are identified by two antigens influenza virus. Influenza can cause mild to severe illness, and it may predispose to. Well, doctors used to think that people with influenza type b experienced less severe symptoms than those with a type a infection. Nevertheless, the impact of influenza b virus infections on influenzarelated morbidity and. All strains are named starting with an a or b type such as influenza a h1n1 or influenza a h3n2. The virus particle also called the virion is 80120 nanometers in diameter such that the smallest virions adopt an elliptical shape. Influenza viruses cause acute, usually selflimited febrile illnesses most often in the winter months. Influenza type a is the primary group affecting both humans and animals. It most commonly causes a fever and respiratory problems. Influenza type a viruses are very similar in structure to influenza viruses types b, c, and d. The virus mutates frequently, but the strains are classified into one of three categoriesa, b, or c. Pdf influenza b viruses ibvs circulate annually along with influenza a iav strains during seasonal epidemics.
First, the name denotes the type of influenza virus a, b, c or d, followed by the host species from which the. First identified in humans in 1947, ivc is responsible for mild upper respiratory illness, most commonly in infants and young children. Influenza b virus activity, by epidemiologic week, hong kong, december 2017march 2018. Influenza a typically peaks earlier and causes more illness than influenza b. Rarely, an influenza virus is unable to have its subtype or lineage identified by the laboratory. Risk factors for influenza b virus associated pneumonia in adults. Influenza a is the most common, followed by influenza b. Influenza b almost exclusively infects humans and is less common than influenza a. There are three groups of influenza viruses, called type a, b, or c. Sep 29, 2003 the genome of influenza b virus, a member of the family orthomyxoviridae, consists of eight negativestrand rna segments, which encode 11 proteins.
Early administration of oseltamivir within 48 hours after onset of flulike symptoms can reduce the risk of influenza b virusassociated pneumonia in hospitalized pediatric patients with influenza. Influenza or flu is a common viral disease of the upper respiratory tract. Influenza can cause mild to severe illness, and it may predispose to exacerbations of underlying disease or development of secondary bacterial infections. Influenza a virus, influenza b virus, and influenza c virus, respectively table 10. Three genera exist with this family that pertain to influenza viruses, influenzavirus a, influenzavirus b, and influenzavirus c, each of which contain a single species, or type.
Both are highly contagious, and their symptoms are similar. Typically, influenza b viruses circulate during the spring, near. Influenza d viruses are not known to infect humans and have been observed only in pigs and cattle. Clinical illness follows a short incubation period and. Early detection of an influenza infection can prevent the virus from worsening and help you find the best course of treatment. Influenza b virus is only known to infect humans and seals.
Early season pediatric influenza bvictoria virus infections. Influenza b virus is the only species in the genus betainfluenzavirus in the virus family orthomyxoviridae. Influenza b is the most prominent circulating strain of influenza every four to five years. Influenza is a virus that actually has hundreds of different strains. Both influenza a and influenza b can cause mild to severe illness in all age groups. For most of the season to date, influenza b has been more prevalent. Am j infect control 2019 published online aug 17 am j infect control 2019 published online aug 17 view at am j infect control. Pdf knowns and unknowns of influenza b viruses researchgate.
Human influenza a and b viruses cause seasonal epidemics of disease almost every winter in the united states. Major outbreaks of influenza are associated with influenza virus types a or b. The performance of the sd bioline rapid antigen test kit for influenza virus detection was evaluated with 295 respiratory specimens during the influenza season. The influenza a and b viruses that routinely spread in people human influenza viruses are responsible for seasonal flu epidemics each year.
Sequence analysis of the hemagglutinin ha genes of several influenza b isolates from 1987 to 1988 indicated that the ha1 domains of the byamagata1688like viruses and bvi87like. All strains are named starting with an a or b type such as influenza a h1n1 or influenza. The study aim was to compare the performances of these. All influenza a viruses are further broken down into h and n subtypes. Licensed influenza vaccines include inactivated or liveattenuated influenza type a and b viruses, with three or four subtypes per vaccine. Jan 10, 2020 there are four types of influenza virus. Most of these viruses are not pathogenic to their natural hosts and do not change or evolve. Baloxavir marboxil bxm was approved in 2018 for treating influenza.
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