Influenza or Flu is an infectious or contagious respiratory disease caused by influenza viruses that infect the throat, nose, and sometimes the lungs.
Influenza or flu viruses are from the family Orthomyxoviridae, and these families represent enveloped viruses, and the genome consists of eight segments of negative-sense single-strand RNA.
Influenza or flu viruses are categorized as influenza A viruses, influenza B viruses, influenza C viruses, and influenza D viruses. Influenza A, B, and C can affect human beings, and among the three influenzas, A is very severe than B, and C. Type B influenza is moderate, and C is not so critical. Influenza D mainly affects animals like cattle.
People who are affected by influenza virus show mild to moderate symptoms and in some case people have died.
Influenza viruses are mainly transmitted from animals to humans and not transmitted between humans to humans. Flu or influenza is either seasonal or zoonotic.
Seasonal means some are spared or effect during a particular season (seasonal flu), and zoonotic means disease, which is transmitted from animal to human (zoonotic influenza).
Terminology
When animal viruses infect their natural animal hosts, they’re named for that host so, when an avian influenza virus infects a bird, it’s called avian influenza.
Similarly, when a swine influenza virus infects a pig, it’s referred to as swine flu. It’s incorrect then to call a seasonal H1N1 virus infection of a person swine flu because it’s infecting a human it’s not infecting a pig.
Type of Influenza virus or Flu Virus
Influenza viruses are categorized as influenza A virus, influenza B virus, influenza C virus, and influenza D virus.
Influenza A virus or Flu Virs A
Influenza A virus causes epidemics and pandemics and can affect many species like pigs, birds, humans, horses, etc. Influenza A virus can be subtype according to the combinations of the hemagglutinin (HA) and the neuraminidase (NA).
The viruses that we consider as zoonotic influenza viruses are viruses that are circulating in animal populations, so for example, there are avian influenza viruses, H5N1, H7N9 or H5N6.
Pigs or swine also have their influenza viruses and, they are typical subtypes H1N1, H1N2 or H3N2. Again, not to be confused with seasonal viruses that may look the same as H1N1 and H3N2.
Human cases with these known zoonotic influenza viruses have been reported from about 20 countries around the world.
Evolution of influenza A
Influenza A consists of Two varieties of surface glycoproteins namely Haemagglutinin (HA) = site for attachment to infect host cells, 18 types and Neuraminidase (NA) = release of new viruses from the cell, 11 types.
An essential characteristic of influenza A is constant transformation or mutation of the viral RNA. Nucleotide changes can lead to changes in the haemagglutinin and neuraminidase surface proteins.
Changes can be Small (the same subtype -antigenic DRIFT causing seasonal influenza epidemics) and Large or rare (new subtype -antigenic SHIFT causing epizootics and pandemics).
Influenza B virus
Type B can also cause epidemics (less severe than A). It is responsible for substantial outbreaks every 2-3 years, but it has not caused pandemics.
Influenza C virus
Type C influenza causes mild illness in humans, and No epidemics or pandemics take place.
How to Flu Spread or mode of transmission of influenza
There are two modes of transmission one from animal to human and, second is from human to human.
Luckily most of the human cases with these zoonotic influenza viruses occur from animal to human transmission. Meaning the person is infected with the influenza virus from contact with an infected animal.
Contact meaning touching the birds; contact with the body of the bird during slaughtering or processing, coming into contact with the blood the faeces or any other secretions from infected animals.
The second mode of transmission again very rare is that one human is infected with these viruses and can spread that virus directly to another human.
Seasonal influenza or Seasonal Flu
The small changes in the same subtype which we called antigenic drift they are the cause of seasonal epidemic influenza. And in temperate climates, these seasonal epidemics mainly occur during the winter.
In tropical climates, they can occur throughout the year, and we often have still one or two peaks and in tropical climates. The severity is the morbidity and mortality of seasonal influenza viruses also vary from year to year.
And the varying seasonal severity is reflecting in the ability of pre-existing immunity to combat a changed virus, also the increasing level of immunity to a changing virus over seasons and differences in viral virulence the ability so to cause disease and complications.
Seasonal influenza is spreading very quickly. It spread by aerosol droplets, infected person coughing and sneezing, and contaminated surfaces which are touched by an infected people.
Zoonotic or other Influenza or Flu Virus
Avian influenza or flu virus
The primary risk factor for the human being is direct and indirect contamination with the infected alive or dead bird or poultry and contaminated environments, such as live bird markets.
For avian influenza virus A(H5N1) infections in humans, the incubation period is 2-5 days ranging up to 17 days. And for A(H7N9) virus, the incubation period ranges from 1 to 10 with an average incubation period is five days (For both the virus the incubation period is more than seasonal influenza that is two days).
Swine Flu or influenza virus
In the case of swine influenza virus, the risk factor is direct or indirect contamination with infected pig or visiting locations where pigs are exhibited. And in some case, a limited human to human transmission has occurred.
The incubation period of swine flu influenza ranges from 2-7 days.
Older people with compromised immune systems and those with underlying medical conditions such as heart disease, kidney disease, diabetes, chronic lung disease, and cancer are at higher risk of severe illness.
Sign and Symptoms of Influenza or Flu
Seasonal influenza is showing a sudden onset of -:
- fever
- cough (usually dry),
- headache,
- muscle and joint pain
- severe malaise (feeling unwell),
- sore throat,
- and a runny nose.
The incubation period is two days, but it can be as short as 1 – 5 days.
Avian, swine and other zoonotic influenza diseases in humans may range from mild upper respiratory infection to severe pneumonia, acute respiratory distress syndrome, shock and in some case causes death also.
Patients who are infected by A(H5) or A(H7N9) avian influenza viruses show aggressive symptoms. Initially show high fever and cough followed by signs of lower respiratory tract involvement, including difficulty breathing and dyspnoea.
Upper respiratory tract symptoms include coryza, and sore throat is less common. Other symptoms include diarrhoea, vomiting, abdominal pain, bleeding from the nose or gums, encephalitis, and chest pain etc.
And in case of severe case symptoms reported pneumonia, septic shock, multi-organ dysfunction, hypoxemic respiratory failure, and secondary bacterial and fungal infections.
Prevention Of Flu or Influenza
Vaccination is a very important tool for seasonal influenza, but there is no good vaccine for these non-seasonal influenza viruses. For a few sub-types, there are vaccines, but they’re not widely available.
Practice good hygiene, especially regular hand washing, before and after touching animals at farms, markets, or other places where animals may be present.
Avoid direct and indirect contact.
Avoid the consumption of under-cooked and raw animal products.cover mouth during coughing and sneezing.
Wash hands with soap and with hand wash.
Avoid touching nose and eyes.
Avoid eating raw animal food.
Summery
- Influenza or Flu is an infectious or contagious respiratory disease caused by influenza viruses that infect the throat, nose, and sometimes the lungs.
- Influenza viruses or flu are from the family Orthomyxoviridae.
- Influenza viruses are categorized as influenza A viruses, influenza B viruses, influenza C viruses and influenza D viruses.
- Influenza viruses or flu are mainly transmitted from animal to human and not transmitted between human to human. Influenza or flu is either seasonal or zoonotic.
- The incubation period is two days, but it can be as short as 1 – 5 days.
- Influenza A virus causes epidemics and pandemics and can affect many species like pigs, birds, humans, horses, etc.
- The small changes in the same subtype which we called antigenic drift they are the cause of seasonal epidemic influenza. And in temperate climates, these seasonal epidemics mainly occur during the winter.
- Seasonal influenza or flu is spreading very quickly. It spread by aerosol droplets, infected person coughing and sneezing, and contaminated surfaces which are touched by an infected people.
- Seasonal influenza or flu is showing a sudden onset of -: fever, cough (usually dry), headache, muscle and joint pain severe malaise (feeling unwell), sore throat, and a runny nose.
For avian influenza virus A(H5N1) infections in humans, the incubation period is 2-5 days ranging up to 17 days.
- And for A(H7N9) virus, the incubation period ranges from 1 to 10 with an average incubation period is five days.
- Avian, swine and other zoonotic influenza or flu diseases in humans may range from mild upper respiratory infection to r severe pneumonia, acute respiratory distress syndrome, shock and in some case causes death also.
- Vaccination is a very important tool for seasonal influenza or flu, but there is no good vaccine for these non-seasonal influenza viruses. For a few subtypes, there are vaccines, but they’re not widely available.