According to recorded history, influenza (or flu) has been with us since at least the time of Hippocrates. Unfortunately, the viral disease still remains a significant challenge to both humans and animals, including horses.
For horses, flu still remains the biggest cause of viral respiratory tract infection to date, with outbreaks mostly occurring when infected animals are enclosed in close contact with healthy ones. Coughing, sneezing, licking, and contact with fomites like water buckets, grooming equipment, clothing, and tack are some of the most common ways the virus is passed from one animal to another. Infection symptoms include frequent sneezing, fever, loss of appetite, coughing, lethargy, and nasal discharge.
Most flu cases are mild and wither out within 7-14 days, though coughing may go on for longer. However, a few cases do get severe and could lead to complications such as secondary bacterial pneumonia, muscle inflammation, myocarditis, and limb edema.
Good news? Vaccination is available. Not-so-good news? Influenza is still a big threat to equine health. But why?
First, flu viruses undergo antigenic drift/evolution, a process where they build up a series of small biological transformations over time. This leads to new virus strains that the immune system often fails to recognize. This is why both humans and animals often get a second or even third bout of flu. Manufacturers must, therefore, update vaccines regularly.
Although antigenic drift can cause vaccines to potentially fail, the occasional passing of flu viral strains from other species also accounts for their large diversity in horses. When it comes to “partial host range restriction”, i.e. the ability of a particular virus to cause disease in more than one species, the flu virus is among the most notorious. The H5N1/H7N9 “bird flu” viruses and the H3N8 flu virus (from horses to dogs, and very rarely, vice versa) are other examples.
In conclusion, the flu virus threat in horses is represented by two main factors: its ability to infect more than one species and antigenic evolution. Therefore, in addition to separating infected animals from healthy ones and periodical vaccination, a regular surveillance of the disease and inclusion of viral antigens representing contemporary circulating viral strains must also remain a priority for horse owners and handlers.
Image source: Flickr.com
Disclaimer: Of Horse! and sponsors do not endorse nor validate the accuracy of a blog post. Each article is the opinion of the blogger.