Equine rhinopneumonitis is a complex disease of viral origin that can produce a wide variety of clinical signs in our horses. It is especially important in foals and pregnant mares, in which it produces abortions or foals born with a death sentence. However, any horse can be affected, so it is necessary for every horse caretaker to know about this disease in order to act as soon as possible against it, as well as to vaccinate the horses and control the new horses that enter.
What is equine rhinopneumonitis?
Equine rhinopneumonitis is a infectious disease of viral origin that affects equids all over the world, foals being highly susceptible among 4 months and two years of age. It is produced by different types of herpesviruses, mainly causing respiratory and reproductive processes. Rhinopneumonitis has a high economic and he alth importance for horses, because:
- It is characterized by a high prevalence and worldwide distribution.
- It has a high mortality.
- It causes a lot of veterinary expenses for its treatment and prevention (vaccination).
- Produces total abortions of practically all the pregnant mares.
What causes equine rhinopneumonitis?
The causes of rhinopneumonitis in horses are double-stranded DNA viruses of the herpesviridae family and the Varicellovirus genus, specifically Equine herpesvirus type 1(EHV-1) and the Equine herpesvirus type 4 (EHV-4). In addition, EHV-1 is considered notifiable as it is included in the "Single List of Notifiable Diseases" of the OIE (World Organization for Animal He alth), therefore, it is mandatory to notify confirmed cases to this global entity..
Latency is characteristic of herpesviruses. Thus, equine rhinopneumonitis occurs in up to 70% of horses, when after infection the virus is not recognized or destroyed by the immune system, remaining in the body throughout the life of the horse by inserting its genetic material (DNA) in the cells of the trigeminal ganglion and lymph nodes of the head and thorax. Under stressful conditions, the virus can reactivate and produce symptoms, contributing to the spread of the disease among horses.
Equine coital rash
Equines can also be affected by Equine herpesvirus type 3, which is the cause of a highly contagious disease known as coital exanthema equine, whose contagion is venereal through riding. Generally, this disease has a good prognosis, within two days the papules caused by the virus on the genitals of horses and mares turn into blisters made up of a yellowish liquid that break causing ulcers that usually disappear within 2- 3 weeks without treatment, leaving just white spots on the skin.
Recovered animals usually remain carriers throughout their lives, the virus enters latency and, as in rhinopneumonitis, reactivates when our horse is subjected to stress or immunosuppression. It is recommended to use antiseptic lotions and ointments to prevent secondary infections and not to breed affected horses.
Equine rhinopneumonitis symptoms
EHV-4 enters through the respiratory tract, replicates in the nasal cavity, pharynx and trachea, and in the mucosa and tissue lymphoid in this area. However, EHV-1 can spread from the respiratory tract through its ability to invade the cells of the horse's blood vessels, anddisseminate to other organs even without producing clinical manifestations of respiratory disease. Thus, after EHV-1 infection, other alterations may appear such as abortions, death of newborns, neurological signs or ocular alterations.
The symptoms that infected horses may present, depending on the type of herpesvirus and its spread, are:
Respiratory symptoms (EHV-4 and EHV-1)
Both EHV-4 and EHV-2 rhinopneumonitis can manifest respiratory signs such as these:
- Fever (39-41ºC).
- Moderate cough.
- Lethargy.
- Anorexy.
- Inflammation of the trachea and bronchi.
- Swollen lymph nodes.
- Mucous congestion (dark coloration).
- Very abundant watery nasal discharge from both nostrils.
- The watery discharge may become mucopurulent by colonizing bacteria and causing secondary infection.
Perinatal mortality (EHV-1)
Only equine EHV-1 rhinopneumonitis causes:
- Abortions: they mainly occur in the last months of the mares' gestation (between month 7 and 11), it is common that It occurs after the respiratory process and can sometimes also occur in less advanced moments of gestation. If you have several mares and the virus enters, it is common for abortions to occur in waves, which is known as an "abortion storm", because they all tend to gestate at the same interval. The virus passes from the respiratory system to the blood vessels of the uterus, where it produces thrombi or blood clots, continues through the allantochorionic and umbilical circulation until it colonizes the fetus, causing cell death in various organs and tissues, which ends with placental abruption and death. of the fetus causing an abortion.
- Foals born with pneumonia: When pregnant mares are exposed to EHV-1 late in pregnancy, the consequence is not the abortion, but the birth of an infected foal. The foal is born with a viral pneumonia that ends in almost 100% of the cases causing its death in a short time, since they are weak, unable to get up and suck, with fever and serious respiratory distress due to the pneumonia that leave without oxygen.
Nervous symptoms (HVE-1)
When the virus targets the nervous system, it can cause neurological symptoms such as:
- Incoordination of movements.
- Inability to get up.
- Urinary incontinence.
- Faecal retention.
- Paralyzed tongue.
Ocular symptoms (HVE-1)
This is the symptom that occurs less frequently. The alterations that can be seen are: uveitis, chorioretinitis and, sometimes, permanent blindness if the damage to the retina is severe.
Pulmonary vascular disease (PHV-1)
This clinical form occurs when EHV-1 targets the circulation of the lung, where it invades blood vessel cells smaller, which causes acute respiratory distress due to lack of oxygen in the lungs that causes the death of the horse.
Equine rhinopneumonitis diagnosis
According to the symptoms that rhinopneumonitis produces in our horses, it can be confused with other diseases that affect equids such as:
- Respiratory symptoms: equine influenza, equine viral arteritis, horse sickness.
- Reproductive signs: equine infectious anemia, equine viral arteriris, leptospirosis, salmonellosis, non-infectious abortions.
- Nervous symptoms: West Nile virus or rabies.
Lab Diagnosis
In order to confirm the diagnosis, it is necessary to detect the DNA of the virus or the antigen of the virus (its surface proteins). To do this, the samples can be:
- Tracheobronchial lavages.
- Nasopharyngeal swabs.
- Blood when there is a fever.
- Abortions (fetuses or appendages).
The tests to perform can be:
- PCR: the most useful of all, it allows to differentiate the different types of herpesvirus in horses.
- Viral isolation: by culture of animal tissues.
- ELISA: to detect antibodies (which may be due to infection or vaccination, but are not usually detected before 60 days after both processes).
Treatment of equine rhinopneumonitis
Because it is a disease caused by a virus and not a bacteria, antibiotics are not effective, they can be given when there are or to avoid secondary bacterial complications, so the treatment and control of disease should be based on vaccination, treatment of the horse's symptoms, as well as its hydration status and daily caloric needs, and measures to prevent the spread of the virus.
The treatment of rhinopneumonitis in horses that is carried out, therefore, is supportive or symptomatic to palliate the clinical signs that our horse, such as:
- Fever reducers if you have a fever.
- Anti-inflammatories (phenylbutazone or flunixin meglumine).
- Infected horse rest up to 18 days after the last period of fever has passed.
- Reducing crowding and stress.
- Avoid letting the horse lie down for a long time, which is common in this disease, as it can cause decubitus ulcers.
- Antitussives if there is a cough.
- Mucolytics and bronchodilators.
Prevention measures for rhinopneumonitis in horses
Due to the speed with which this virus spreads among horses, to avoid new cases of rhinopneumonitis in places where several horses live, measures must be taken to prevent and control possible outbreaks of the disease, through good management and good hygiene. These measures consist of:
- Isolate sick people from other non-infected animals or non-contaminated areas.
- New horses entering must have been vaccinated two weeks prior to transport and quarantined for four weeks upon entry.
- Periodic disinfections of the places where the horse has contact.
- Removal of fetuses and placentas.
- Vaccination to decrease the clinic and elimination.
Vaccine for equine rhinopneumonitis
Due to the wide distribution of the virus throughout the world, it is important to maintain our horses with an adequate level of immunity through vaccination against equine herpesvirus type 1 and 4In addition, as we have mentioned, it is a measure to be required before the entry of a new horse. Vaccination does not prevent the onset of the disease or contagion, but it lessens its severity by reducing the amount of virus spread by horses.
There is not really a standardized vaccination protocol, the vaccine that can be used is an inactivated one that protects against Herpesvirus type 1 and type 4. In general, the following vaccination protocol is recommended:
- Vaccination of foals: first vaccination when they are 4-6 months old, revaccination a month and annual reminder.
- Vaccination of non-breeding adults: application of three doses separated by one month each, not vaccinating again if there is no risk.
- Vaccination of sport horses: vaccination every three or four months.
- Vaccination of pregnant mares: in general, in the 5th, 7th and 9th months, sometimes it may also be necessary in the month 3 and calving.
- Vaccination of non-pregnant mares: in those places intended for horse breeding, vaccination should be done at the beginning of the breeding season and revaccinate according to risk.
