Sneaking viruses? Equine influenza
How the bird flu broke its barrier to horses and infected them with horse flu.
Equine influenza (horse flu) has its origin as being a bird flu virus sneaking to horses and slowly spreading among them as EIV(H3N8).
Symptoms are similar to seasonal flu virus in people, horses infected with EIV experience fever and dry cough.
More severe symptoms can include wheezing while breathing. Loss of appetite, runny nose and fatigue (tiredness) may also be seen.
Equine Influenza majorly affects nose, throat and lungs.
Structure and classification of the virus.
Equine influenza is classified as orthomyxovirus, single stranded, segmented RNA genome.
Categorized as type A influenza virus on the basis of their internal protein structure.
Subdivided into two categories namely H (Hemagglutinin) and N (Neuraminidase) on the basis of antigenicity of surface protein. H and N comprise 25% and 10% of viral protein mass.
Influenza viruses are codified according to type, host species, subtype, place and year of isolation. Often followed in parenthesis by H and N subtypes. H and N mutate frequently known as Antigenic Drift.
Influenza viruses are also prone to major changes in antigenic composition caused due to reassortment of the H and N genes known as Antigenic Shift. Antigenic drift has been observed for many years while Antigenic shift has not been documented till date.
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Influenza A virus belong to two subtypes
· H7N7- Designated as A/Equine/Prague 56
· H3N8- Designated as A/Equine/Miami 63
Influenza A virus is the only known virus to cause pandemic (occurs when a new and different virus infects us to which we have little or no immunity).
Now let’s talk about how these viruses crossed barriers to infect other species.
· Avian Influenza A (H3N8) circulating in birds first infected horses, adapted to them and eventually started to spread amongst them as EIV(H3N8). These infections occur through exposure to mucus and saliva from infected animals.
· EIV (equine influenza virus) H3N8 infected dogs adapted to them and started regularly spreading as Canine Influenza A (H3N8) virus.
The A (H3N8) adapted to their respective host and continued to spread among horses, birds and dogs. Where AIV and EIV currently persists, CIV is now extinct in dogs.
Studies have shown that EIV is not capable to cause illness in humans. Though under experimental conditions humans are observed to develop antibodies against EIV which can be considered as a sign of infection.
In the current scenario EIV viruses are not well adapted to humans but in the coming years there is a possibility that the virus may change in such a way that it starts to infect and spread easily among humans.
Tracking these genetic changes in viruses is very important to prevent the emergence of new viruses.
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