Equine influenza — why vaccination and biosecurity together protect the herd

Equine influenza, colloquially horse flu, is one of the most contagious respiratory diseases of the horse. It is caused by an influenza virus and spreads extremely fast via coughing in the finest droplets as well as via contaminated hands, clothing and equipment. Where many horses come together — competitions, transports, large stables — a single infected animal can infect a whole group before the disease is even noticed.

Leading signs — fever and dry cough

Classic is a sudden, high rise in fever, accompanied by a dry, hard, often paroxysmal cough and watery to later viscous nasal discharge. Added to this are dullness, reluctance to eat and in part swollen lymph nodes. Unlike with some other respiratory infections, the dry cough stands at the forefront early on. The disease is for healthy adult horses usually well survivable, but can run more severely in foals, old or weakened animals, and above all an irritated respiratory system entails a long recovery phase in which exertion does harm.

Why vaccination protects via the herd

With such a contagious pathogen, vaccination works not only for the individual horse but for the whole herd. If a high proportion of the horses is protected, the virus finds fewer susceptible animals, the spread slows down and outbreaks turn out milder — the principle of herd immunity. Vaccinated horses fall severely ill less often and as a rule shed less virus, which in turn protects the remaining animals. Precisely for this reason many competition rulebooks and the LPO tie a valid influenza vaccination to participation: where many horses from different herds meet one another, a high vaccination protection is the shared insurance of all involved.

How the vaccination scheme is built up in principle

A robust protection does not arise with a single shot. The principle of common schemes provides first a primary immunisation of several vaccinations at defined intervals, which builds up the immune system step by step, followed by regular boosters, because the protection wanes over time and the circulating virus strains change. For horses with frequent contact to unfamiliar animals — for example in competition sport — tighter booster intervals are recommended than for horses in a closed herd. Which vaccine, which scheme and which intervals apply to an individual horse depends on its living environment, the applicable competition rules and veterinary recommendation — the determination and execution belongs in veterinary hands.

Vaccination and biosecurity belong together

As important as the vaccination is, it does not replace the hygiene. The complete protection is carried by both pillars together: new arrivals and horses returning from competitions are observed and isolated in case of suspicion, fever is measured, buckets and grooming kit stay horse-specific, hands are disinfected between the animals. Whoever isolates coughing or feverish horses early and does not bring them together with healthy ones interrupts the chain of infection where the vaccination alone reaches its limits. Vaccination and biosecurity are not alternatives, but two halves of the same protection concept.