What Is Equine Influenza?
The term equine influenza refers to a highly contagious viral disease of the upper respiratory tract in horses. Its symptoms appear in the form of cough, conjunctivitis, fever and runny nose, but usually do not lead to death. Interestingly, it is estimated that 100% of horses that have not been vaccinated or exposed to the virus will be infected at some point.
In any case, although the infection rate is alarming, the mortality rate from this infection does not exceed 4%. In other words, only foals and horses with a delicate state of health before infection are at real risk. If you want to know more about equine influenza, read on.
Is equine influenza caused by a virus?
Equine influenza goes by several names in the veterinary field, including horse flu or equine flu. These terms may sound familiar as they are also applicable in human medicine. No wonder: the pathogen belongs to the group of Influenza A viruses , which also cause diseases in people, birds and other mammals.
As indicated by the Sinobioligical website , it is estimated that there could be 144 subtypes of the Influenza A virus , although only 2 of them seem to specialize in infecting horses. So far, strains H7N7 (equine-1) and H3N8 (equine-2) have been detected. In any case, it is believed that H7N7 may have disappeared from the natural environment, as it has not been detected for over 20 years.
Thus, the main suspect in all cases of flu in horses is the H3N8 subtype. However, it is known that this pathogen can also infect birds, dogs, cats and even seals, according to the BBC.
Virus Characteristics
These microorganisms are very simple, like all viruses. Its genetic information consists of RNA segments, which are in turn protected from the environment by a lipid bilayer, which gives shape to the pathogen. Specifically, Influenza- type viruses are categorized into different variants according to the proteins expressed in their membrane.
As viruses lack almost all the characteristics necessary to be considered cells, they are rarely included in the group of living beings. To replicate, they need to infiltrate the host cell, “hijack” its replicative machinery and generate copies. When the new viruses go out into the extracellular environment, the infected cell dies (lysis).
Equine Flu Symptoms
According to the MSD Veterinary Manual website , the incubation period lasts from 1 to 3 days after infection. After this short interval, the following symptoms usually appear:
- High fever, up to 41°C.
- Serous nasal discharge.
- Strong, dry cough.
- General weakness and worse performance at work.
- Difficulty breathing (dyspnoea).
- Muscle pain and stiffness of the musculoskeletal system.
The most obvious clinical signs last for a very short time, about 2 or 3 days, in immunocompetent horses, as they are able to face the infection quickly and get rid of it. However, as the virus invades the wall of the respiratory epithelium, local destruction of some bronchial structures may occur. Because of this, the cough sometimes lasts a few more weeks.
Possible complications
Due to the damage caused by viral expansion and replication, it usually takes about 21 days for the respiratory epithelium to completely heal. During this time, horses are likely to be infected by other opportunistic pathogens, and may then present conditions such as pneumonia, pleuropneumonia and chronic bronchitis. Therefore, it is best to let the horse rest until it fully recovers.
How does contagion occur?
As the journal Frontiers of Microbiology points out , this condition is transmitted through droplets, which can be expelled by the sick animal during a cough, sneeze or whinny. The effectiveness of this virus lies in its resistance, as it can be transmitted through the air over distances of 1 to 2 kilometers.
Furthermore, the microorganism remains viable for up to 3 days outside the host. Brushes, chairs, caregivers’ clothing, haystacks, drinking fountains and all facility materials can contain pathogens. If a healthy horse comes into direct contact with any of these elements, it will be infected.
Equine influenza diagnosis
Ideally, it is necessary to call the veterinarian when only one horse has the aforementioned clinical signs. In any case, due to the rapidity of the contagion, most of the stable members, or all of them, certainly fall ill at the same time. This situation is more than enough to suspect an outbreak of equine influenza.
The first step is always to obtain samples from the animal’s oral and nasal mucosa. These samples are taken to the laboratory and, through genetic information amplification techniques , such as PCR, it is possible to detect the virus genome. Circulating blood antibody tests are also very useful for this task.
Treatment and Prevention
Horses that do not develop severe clinical signs do not need specific treatment, only supportive care. In any case, ideally, each sick horse should have 1 week of rest for each day of fever, usually 3 weeks. Animals that have a high fever can be treated with non-steroidal anti-inflammatory drugs ( NSAIDs ), always at the doses indicated by the veterinarian.
On the other hand, it may also be necessary to prescribe antibiotics to the animal, especially if the fever lasts more than 4 days and the runny nose is accompanied by purulent solutions. Thus, secondary infections that could endanger the life of the sick horse are avoided.
a very common disease
As we stated at the outset, up to 100% of unvaccinated horses are infected with equine influenza at some point in their lives. Although the condition generates very uncomfortable symptoms, within 2 or 3 weeks the pathology usually resolves itself and the horse returns to its previous state of health. The mortality rate does not exceed 4%, therefore, it is not a fatal condition.
In any case, special care must be given to immunocompromised specimens and foals in the herd. These weaker animals can develop much more severe infectious conditions, so to protect them, the best option is to vaccinate everyone in the stable.
