In north america, influenza activity continued but in recent weeks influenza ah3n2 was the dominant virus, followed by influenza ah1n1pdm09. Influenza d viruses are not known to infect humans and have been observed only in pigs and cattle. Influenza type a is the primary group affecting both humans and animals. Well, doctors used to think that people with influenza type b experienced less severe symptoms than those with a type a infection. A newly recognized livestock influenza virus, originally thought to be an influenza c virus, might represent a fourth genus, influenza d. Influenza b virus is the only species in the genus betainfluenzavirus in the virus family orthomyxoviridae. 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. The virus mutates frequently, but the strains are classified into one of three categoriesa, b, or c. Influenza a viruses can be broken down into subtypes depending on the genes that make up the surface proteins.
Influenza fact sheet keywords department of health services, dhs, division of public health, influenza, flu, coughing, sneezing, vaccine, vaccination, flu shot, contagious, p42064, p42064. Rarely, an influenza virus is unable to have its subtype or lineage identified by the laboratory. 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. Influenza b virus activity, by epidemiologic week, hong kong, december 2017march 2018. However, we are currently seeing very low numbers in both a and.
The study aim was to compare the performances of these. Influenza viruses cause acute, usually selflimited febrile illnesses most often in the winter months. Both influenza a and influenza b can cause mild to severe illness in all age groups. Risk factors for influenza b virus associated pneumonia in adults. 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. Clinical illness follows a short incubation period and. 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. Pdf influenza b viruses ibvs circulate annually along with influenza a iav strains during seasonal epidemics. Influenza a viruses can also cause sporadic infections or spread worldwide.
Influenza b generally causes milder disease than type a and primarily. 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. Furthermore, influenza b infections carried higher risks of hospitalisations compared to influenza a infections in hiv patients 5. The influenza a and b viruses that routinely spread in people human influenza viruses are responsible for seasonal flu epidemics each year. Influenza a virus, influenza b virus, and influenza c virus, respectively table 10.
Influenza is an infectious respiratory disease that, in humans, is caused by influenza a and influenza b viruses. Infection with type b influenza is usually milder than with type a. There are two types of flu virus, influenza a and influenza b, which can cause seasonal epidemics of disease in humans. The virus particle also called the virion is 80120 nanometers in diameter such that the smallest virions adopt an elliptical shape. Influenza a typically peaks earlier and causes more illness than influenza b. Early season pediatric influenza bvictoria virus infections. 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. 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.
Jan 10, 2020 there are four types of influenza virus. The only other animals known to be susceptible to influenza b infection are seals and ferrets. Influenza b viruses are not divided into subtypes, but instead are further. Influenza can cause mild to severe illness, and it may predispose to exacerbations of underlying disease or development of secondary bacterial infections. Influenza type a viruses are very similar in structure to influenza viruses types b, c, and d. Of these, nine are also found in influenza a virus. The c viruses cause only mild respiratory illness in humans. Influenza b virus is only known to infect humans and seals. Between 1972 and 1995, the estimated worldwide influenzaassociated deaths ranged from approximately 25 to 150 per 10 000 in those aged. Influenza is a contagious, acute respiratory illness caused by influenza viruses, usually influenza a or b subtypes. Major outbreaks of influenza are associated with influenza virus. Influenza is a virus that actually has hundreds of different strains. Influenza b viruses have not been the predominant virus in the united states since the 199293.
It most commonly causes a fever and respiratory problems. For most of the season to date, influenza b has been more prevalent. Influenza a is the group that most commonly causes illness in humans. Influenza virus isolation in tissue cell culture from respiratory specimens. Subtypes of the type a influenza virus are identified by two antigens influenza virus. Jun 28, 2018 each influenza virus isolate receives a unique name according to a set of rules. Influenza a and b are the two types of influenza that cause epidemic seasonal infections nearly every year. Influenza a is the most common, followed by influenza b. Influenza a and b cause human disease with significant morbidity and mortality. Influenza a can be found in many species, including humans, birds, and pigs. Clinical evaluation of the sd bioline influenza virus.
Licensed influenza vaccines include inactivated or liveattenuated influenza type a and b viruses, with three or four subtypes per vaccine. Ah1n1pdm09 to distinguish it from the seasonal influenza ah1n1 viruses that circulated prior to the pandemic. Antigenic variation within the ha and na antigens of influenzaviruses b has also been analyzed in detail. There are many different strains types of this virus. First identified in humans in 1947, ivc is responsible for mild upper respiratory illness, most commonly in infants and young children. Influenza commonly known as the flu is a respiratory infection caused by flu viruses. Both are highly contagious, and their symptoms are similar. Influenza b is the most prominent circulating strain of influenza every four to five years. Jan, 2020 influenza b, one type of influenza virus, is dominating the 20192020 flu season early on. Human influenza a and b viruses cause seasonal epidemics of disease almost every winter in the united states. All strains are named starting with an a or b type such as influenza a h1n1 or influenza a h3n2. First, the name denotes the type of influenza virus a, b, c or d, followed by the host species.
There are three groups of influenza viruses, called type a, b, or c. Interaction among influenza viruses ah1n1, ah3n2, and b. Am j infect control 2019 published online aug 17 am j infect control 2019 published online aug 17 view at am j infect control. Early detection of an influenza infection can prevent the virus from worsening and help you find the best course of treatment. Nevertheless, the impact of influenza b virus infections on influenzarelated morbidity and. 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. Nov 18, 2019 for influenza a viruses, the hemagglutinin and neuraminidase antigen description are provided in parentheses e. The influenza a and b viruses that routinely spread in people human influenza viruses are responsible for. Cepheid are rapid, pointofcare molecular assays for flu virus detection. All strains are named starting with an a or b type such as influenza a h1n1 or influenza. For influenza a viruses, the hemagglutinin and neuraminidase antigen description are provided in parentheses e. Influenza, also called the flu, is a viral disease that affects humans and many animals. Each influenza virus isolate receives a unique name according to a set of rules.
Pdf knowns and unknowns of influenza b viruses researchgate. Who information for molecular diagnosis of influenza virus in humans. 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. Major outbreaks of influenza are associated with influenza virus types a or b. Typically, influenza b viruses circulate during the spring, near. Influenza, commonly known as the flu, is an infectious disease caused by an influenza virus. All influenza a viruses are further broken down into h and n subtypes. First, the name denotes the type of influenza virus a, b, c or d, followed by the host species from which the.
The emergence of a new and very different influenza a virus to infect people can cause an influenza pandemic. 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. Typically characterized by annual seasonal epidemics, sporadic pandemic outbreaks involve influenza a virus strains of zoonotic origin. Mitigation of influenza b epidemic with school closures. 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. Influenza a virus causes influenza in birds and some mammals, and is the only species of the genus alphainfluenzavirus of the virus family orthomyxoviridae. They belong to the orthomyxoviridae family and are classified into 3 distinct types influenza a, influenza b and influenza c. 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 can cause mild to severe illness, and it may predispose to. Influenza b, one type of influenza virus, is dominating the 20192020 flu season early on. Early diagnosis of influenza flu is critical for patient management and infection control. The who estimates that annual epidemics of influenza result in 1 billion infections.
Most of these viruses are not pathogenic to their natural hosts and do not change or evolve. Mitigation of influenza b epidemic with school closures, hong. Randomized study of the efficacy and safety of oral. Mar 26, 2018 influenza commonly known as the flu is a respiratory infection caused by flu viruses. Other articles where influenza type b virus is discussed. Influenza, influenzaassociated mortality, and novel influenza a. 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. The performance of the sd bioline rapid antigen test kit for influenza virus detection was evaluated with 295 respiratory specimens during the influenza season. Influenza or flu is a common viral disease of the upper respiratory tract.
The flu is a type of germ called a virus that you breathe in. Influenza b almost exclusively infects humans and is less common than influenza a. Influenza a virus subtypes are subdivided into strains based on genetic variations in the h protein of the virus. Influenza b virus requires bm2 protein for replication. While influenza a viruses infect humans and other animals, influenza b viruses affects only humans, primarily children. Development of highyield influenza b virus vaccine.