Influenza : A potential for another pandemic ?
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L Sausa Samson KBN
Commonly known as flu, it is a highly contagious viral respiratory infection caused primarily by influenza A and B virus.
Influenza viruses are classified as type A, B, or C by their nucleoproteins and matrix proteins. Influenza C virus infection does not cause typical influenza illness
Influenza antigens
Hemagglutinin (H) is a glycoprotein on the influenza viral surface that allows the virus to
bind to cellular sialic acid and fuse with the host
cell membrane. Neuraminidase (NA), another sur- face glycoprotein, enzy-matically removes sialic acid, promoting viral release from the infected host cell. There are 18 H types and 11 NA types, giving 198 possible combina- tions, but only a few are human pathogens.
Antigenic drift refers to relatively minor, progressive mutations in preexisting
combinations of H and NA antigens, resulting in the frequent emergence of new viral strains.
The disease is caused by the family Orthomy-xoviridae. They are enveloped viruses, spherical or pleomorphic, measuring 80-120 nm in diameter. The family contains five genera, namely: Influenza virus A, Influenza virus B, Influenza virus C, Thogotovirus, and Isavirus. Epidemiology
Influenza causes widespread sporadic illness yearly during fall and winter in temperate climates
There have been 6 major influenza pandemics, typically named after the presumed location of origin:
1889: Russian influenza (H2N2)
1900: Old Hong Kong influenza (H3N8)
1918: Spanish influenza (H1N1)
1957: Asian influenza (H2N2)
1968: Hong Kong influenza (H3N2) 2009: Swine influenza (influenza A [H1N1]pdm09)
The virus was initially referred to as a swine flu virus, but it is a combination of swine, avian, and human influenza viruses. The infection is not acquired through ingestion of pork and is acquired very rarely by contact with infected pigs.
Clinical Infection
Aquatic birds, particularly ducks, serve as reservoirs of influenza A virus, providing a genetic pool for generating new subtypes capable of infecting mammals. Migratory waterfowl disseminate the virus across international borders. The virus replicates in the intestinal tract of birds, and the faecal-oral route is considered the main route of
transmission. Influenza pandemics have been linked to the close association between concentrated human populations and domestic fowl and pigs.
Influenza viruses can be spread by
Airborne droplets, Person-to-person contact, Contact with contaminated items, Airborne spread appears to be the most important mechanism.
High-risk groups
Children, adult>65, Women in the second or
third trimester of pregnancy &People with chronic medical disorders
Symptoms and Signs of Influenza In mild cases, common cold and mild inflammation of the eye conjunctiva
Typical influenza is characterized by sudden onset of chills, fever, prostration, cough, and generalized aches and pains (especially in the back and legs). Headache is prominent. Respira- tory symptoms may be mild at first, with scratchy sore throat. Later, lower respiratory tract illness becomes dominant; cough can be persistent, raspy, and productive. Treatment of Influenza is by symptomatic treatment. Sometimes antiviral medications
Why vaccine does not work?
There are vaccine for some subtype but due to antigenic drift a new form of strain can develop ineffective to the already develop vaccine. Current commercially available influenza vaccines protect against seasonal H3N2, pandemic H1N1 influenza A, and influenza B. A vaccine for H5N1 avian influenza has been approved for people > 18 years at high risk of H5N1 exposure but is available only through public health officials. No vaccines are currently available for the other avian influenza viruses rarely associated with human disease (H7N7, H9N2, H7N3, and H7N9). Since Minor antigenic drift in H and/or NA antigens produces strains that cause seasonal epidemics more lethal strain of the virus can developed when mixed with fowl, pig and human subtype. A rare antigenic shifts resulting in new combinations of H and NA antigens can cause a pandemic with significant mortality.
Influenza Transmission Pathways
Genetic reassortment involving avian, human, and porcine subtypes
Many avian subtypes, facilitating genetic reassortment.
Birds : Occasional transfer of avian subtypes
Pigs : Occasional transfer of avian subtypes
Pigs to Humans : Periodic emergence of new virulent subtypes
Humans : Infections with established human subtypes
Humans to Pigs : Thus, pigs are considered the species in which reassortment (mixing vessel hypothesis) is most likely to occur (Shortridge). Since the genome of influenza A virus is segmented, mixed infection can lead to genetic
reassortment, resulting in the emergence of new subtypes. Such novel subtypes have been implicated in most major pandemics to date.
Because there is limited immunity to new subtypes in the human population, spread from one country to another tends to occur rapidly.
Since pigs act as a mixing vessel, which can joint the human and poultry virus together known as genetic reassortment.
It is quite possible that the reassortant virus could emerge with genetic components of human, avian, and poultry viruses, as facilitated by pig workers' more intense occupational exposure to domestic animals. Swine and poultry workers act as a bridging population often accelerating a pandemic.
This writer is a BVSC student at the College of Veterinary Science and Animal Husbandry, Mizoram
Commonly known as flu, it is a highly contagious viral respiratory infection caused primarily by influenza A and B virus.
Influenza viruses are classified as type A, B, or C by their nucleoproteins and matrix proteins. Influenza C virus infection does not cause typical influenza illness
Influenza antigens
Hemagglutinin (H) is a glycoprotein on the influenza viral surface that allows the virus to
bind to cellular sialic acid and fuse with the host
cell membrane. Neuraminidase (NA), another sur- face glycoprotein, enzy-matically removes sialic acid, promoting viral release from the infected host cell. There are 18 H types and 11 NA types, giving 198 possible combina- tions, but only a few are human pathogens.
Antigenic drift refers to relatively minor, progressive mutations in preexisting
combinations of H and NA antigens, resulting in the frequent emergence of new viral strains.
The disease is caused by the family Orthomy-xoviridae. They are enveloped viruses, spherical or pleomorphic, measuring 80-120 nm in diameter. The family contains five genera, namely: Influenza virus A, Influenza virus B, Influenza virus C, Thogotovirus, and Isavirus. Epidemiology
Influenza causes widespread sporadic illness yearly during fall and winter in temperate climates
There have been 6 major influenza pandemics, typically named after the presumed location of origin:
1889: Russian influenza (H2N2)
1900: Old Hong Kong influenza (H3N8)
1918: Spanish influenza (H1N1)
1957: Asian influenza (H2N2)
1968: Hong Kong influenza (H3N2) 2009: Swine influenza (influenza A [H1N1]pdm09)
The virus was initially referred to as a swine flu virus, but it is a combination of swine, avian, and human influenza viruses. The infection is not acquired through ingestion of pork and is acquired very rarely by contact with infected pigs.
Clinical Infection
Aquatic birds, particularly ducks, serve as reservoirs of influenza A virus, providing a genetic pool for generating new subtypes capable of infecting mammals. Migratory waterfowl disseminate the virus across international borders. The virus replicates in the intestinal tract of birds, and the faecal-oral route is considered the main route of
transmission. Influenza pandemics have been linked to the close association between concentrated human populations and domestic fowl and pigs.
Influenza viruses can be spread by
Airborne droplets, Person-to-person contact, Contact with contaminated items, Airborne spread appears to be the most important mechanism.
High-risk groups
Children, adult>65, Women in the second or
third trimester of pregnancy &People with chronic medical disorders
Symptoms and Signs of Influenza In mild cases, common cold and mild inflammation of the eye conjunctiva
Typical influenza is characterized by sudden onset of chills, fever, prostration, cough, and generalized aches and pains (especially in the back and legs). Headache is prominent. Respira- tory symptoms may be mild at first, with scratchy sore throat. Later, lower respiratory tract illness becomes dominant; cough can be persistent, raspy, and productive. Treatment of Influenza is by symptomatic treatment. Sometimes antiviral medications
Why vaccine does not work?
There are vaccine for some subtype but due to antigenic drift a new form of strain can develop ineffective to the already develop vaccine. Current commercially available influenza vaccines protect against seasonal H3N2, pandemic H1N1 influenza A, and influenza B. A vaccine for H5N1 avian influenza has been approved for people > 18 years at high risk of H5N1 exposure but is available only through public health officials. No vaccines are currently available for the other avian influenza viruses rarely associated with human disease (H7N7, H9N2, H7N3, and H7N9). Since Minor antigenic drift in H and/or NA antigens produces strains that cause seasonal epidemics more lethal strain of the virus can developed when mixed with fowl, pig and human subtype. A rare antigenic shifts resulting in new combinations of H and NA antigens can cause a pandemic with significant mortality.
Influenza Transmission Pathways
Genetic reassortment involving avian, human, and porcine subtypes
Many avian subtypes, facilitating genetic reassortment.
Birds : Occasional transfer of avian subtypes
Pigs : Occasional transfer of avian subtypes
Pigs to Humans : Periodic emergence of new virulent subtypes
Humans : Infections with established human subtypes
Humans to Pigs : Thus, pigs are considered the species in which reassortment (mixing vessel hypothesis) is most likely to occur (Shortridge). Since the genome of influenza A virus is segmented, mixed infection can lead to genetic
reassortment, resulting in the emergence of new subtypes. Such novel subtypes have been implicated in most major pandemics to date.
Because there is limited immunity to new subtypes in the human population, spread from one country to another tends to occur rapidly.
Since pigs act as a mixing vessel, which can joint the human and poultry virus together known as genetic reassortment.
It is quite possible that the reassortant virus could emerge with genetic components of human, avian, and poultry viruses, as facilitated by pig workers' more intense occupational exposure to domestic animals. Swine and poultry workers act as a bridging population often accelerating a pandemic.
This writer is a BVSC student at the College of Veterinary Science and Animal Husbandry, Mizoram