The equine influenza is, according to the latest findings in our latitudes, caused by the virus strains Influenza A/Equi-2/Newmarket/2/93 and A/Equi-2/Ohio/03. While the influenza viruses are related to the pathogen of human influenza, fortunately, no infections have (as yet) occurred from horse to human (and vice versa).
Transfer
The animals contract the viruses via droplet infection of the mucous membranes of the upper and lower respiratory tract. From here, the virus spreads throughout the entire respiratory tract in a very short time. However, the virus can also spread via the bloodstream.
This leads to viral damage of the lung tissue, which is accompanied by coughing. With each cough, large amounts of the virus are released into the environment within a radius of up to 40 metres. Viral shedding occurs mainly during the incubation period (twelve hours to three days) and during the first five days after the onset of clinical symptoms. However, it can also be shed by animals for seven to ten days after they appear to have recovered.
Typical of influenza is the extremely short incubation period. If an infected horse enters a non-immune herd, the disease spreads within a few days to up to 100% of the animals.
The virus spreads not only through the air but also via carriers such as dust, feed, cleaning materials, animals, and contact persons.
Clinical course
Equine influenza is a highly contagious, febrile infectious disease of the respiratory tract, preferentially settling in the lower respiratory organs. Typical of this disease is a sudden onset of recurring fever, which can rise to 42°C.
After a few days, a strong, but dry and painful cough sets in. Furthermore, clear, watery to slimy nasal discharge can be observed as a result of inflammation of the nasal mucous membrane. In addition, inflammation of the conjunctiva with increased tear flow can occur. The subsequent fever-free phase can last for hours or even days, then fever sets in again.
Usually, three or more bouts of fever are typical with an infection of equine influenza viruses. A continuously elevated body temperature, as well as purulent nasal discharge, conversely, is a sign of an additional bacterial infection. Furthermore, particularly with severe cases, reduced feed intake, lethargy, apathy, and general or local muscle tremors can occur. Heart weakness and swollen limbs are also possible.
The danger of this illness lies in the potential for chronic damage to the lung tissue, which can lead to a long-term reduction in performance.
Therapy
The therapy consists of immediate immobilisation of the animals and calling in the vet for treatment. After the fever subsides, the horses should not be ridden for approximately three weeks to prevent chronic bronchitis.
During the recovery phase, in addition to rest, conditions relating to posture and feeding play a crucial role: fresh air, high-quality, dust-free feed. Even if the illness subsides without bacteria being able to establish themselves in the mucous membranes damaged by the viruses, the body's own lung cleaning mechanisms remain impaired for a good four weeks. If horses are worked too soon (it is recommended to have one week of rest for each day with a fever), permanent respiratory diseases often remain. Furthermore, muscle damage (including in the heart) can be a consequence of an influenza infection and lead to performance limitations.
Prophylaxis
The most important hand tool against this really very contagious disease is preventive vaccination. Because of the long-term health risks for their horse from the consequences of an influenza infection, protective vaccinations against influenza are not only indicated because events are put at risk by so-called flu waves, but also because the required weeks of rest and the same possible long-term consequences can thus be avoided. Admittedly, influenza cases or even epidemics have hardly been seen in Germany for years, but this can again be attributed to the consistent vaccination of all horses.
