Content
- What is West Nile Fever
- Causes of West Nile Fever
- West Nile Fever Symptoms
- Diagnosis of West Nile Fever in Horses
- Clinical and differential diagnosis
- laboratory diagnosis
- Horse treatments
- Prevention and Control of West Nile Fever in Horses
- West Nile Fever Vaccine in Horses
West Nile fever is a non-contagious viral disease it mainly affects birds, horses and humans and is transmitted by mosquitoes. It is a disease of African origin, but it has spread throughout the world thanks to migratory birds, which are the main hosts of the virus, maintaining a mosquito-bird-mosquito cycle that sometimes includes horses or people.
The disease causes nervous signs that can sometimes be very serious and even cause the death of those who are infected. Therefore, preventive measures must be taken for West Nile fever in horses, especially through vaccination of horses in risk areas.
If you are curious or have heard about this disease and want to know more about it, continue reading this PeritoAnimal article about West Nile Fever in Horses - Symptoms and Prevention.
What is West Nile Fever
West Nile fever is a non-contagious disease of viral origin and transmitted by a mosquito usually of the genus culex or Aedes. Wild birds, especially of the family Corvidae (crows, jays) are the main reservoir of the virus for its transmission to other beings by mosquitoes, as they develop strong viremia after the bite of an infected mosquito. The best habitat for the virus to spread are the wet areas, such as river deltas, lakes or marshy areas where migratory birds and mosquitoes abound.
The virus naturally maintains a mosquito-bird-mosquito natural cycle, with mammals sometimes being infected by the bite of a mosquito carrying the virus after it has bitten a bird with the virus in its blood. People and horses are especially sensitive and can lead to neurological symptoms more or less severe, as the virus reaches the central nervous system and spinal cord via the blood.
Transplacental transmission, breastfeeding or transplantation have also been described in people, being symptomatic in only 20% of cases. There is no horse/horse transmission, what happens is contagion from the presence of a mosquito vector of the virus among them.
Although West Nile fever is not one of the most common diseases in horses, it is very important to carry out veterinary checks to prevent this and other pathologies.
Causes of West Nile Fever
West Nile fever was once considered extinct in Brazil, but different cases have been reported in states such as São Paulo, Piauí and Ceará since 2019.[1][2][3]
The disease is caused by the West Nile virus, which is an arbovirus (arthropod-borne virus) of the family Flaviviridae and of the genre Flavivirus. It belongs to the same genus as Dengue, Zika, yellow fever, Japanese encephalitis or St. Louis encephalitis viruses. It was first identified in the year 1937 in Uganda, in the district of West Nile. The disease is distributed mainly in the Africa, Middle East, Asia, Europe and North America.
Is notifiable disease to the World Organization for Animal Health (OIE), as well as inscribed in the Terrestrial Animal Health Code of this same organization. The increased circulation of the West Nile virus is favored by the presence of floods, heavy rains, increased global temperature, population growth, extensive poultry farms and intensive irrigation.
West Nile Fever Symptoms
After the mosquito bite, Os symptoms of West Nile fever in horses can take from 3 to 15 days to appear. At other times they will never appear, because most horses that are infected will never develop the disease, so they will not show any clinical signs.
When the disease develops, it is estimated that a third of infected horses die. The signs that a horse with Nile Fever may show are:
- Fever.
- Headache.
- Inflammation of the lymph nodes.
- Anorexia.
- Lethargy.
- Depression.
- Difficulty in swallowing.
- Vision disorders with tripping when walking.
- Slow and short step.
- Head down, tilted or supported.
- Photophobia.
- Lack of coordination.
- Muscle weakness.
- Muscle tremor.
- Teeth grinding.
- Facial paralysis.
- Nervous tics.
- Circular movements.
- Inability to stand upright.
- Paralysis.
- Seizures.
- With the.
- Death.
About 80% of contagions in people do not produce symptoms and, when they present, they are nonspecific, such as moderate fever, headache, tiredness, nausea and/or vomiting, skin rash and enlarged lymph nodes. In other people, the severe form of the disease may develop with complications such as encephalitis and meningitis with neurological signs, but the percentage is usually minimal.
Diagnosis of West Nile Fever in Horses
The diagnosis of Nile Fever in horses must be made through a clinical, differential diagnosis and must be verified by collecting samples and sending them to the reference laboratory to have a definitive diagnosis.
Clinical and differential diagnosis
If a horse starts to show some of the neurological signs we have discussed, although they are very subtle, this viral disease should be suspected, especially if we are in an area of risk for viral circulation or the horse has not been vaccinated.
That's why call the equine veterinarian for any unusual behavior of the horse it is essential to treat it as quickly as possible and control possible outbreaks. must always to differentiate West Nile fever from other processes that can occur with similar signs in horses, specifically:
- Equine rabies.
- Equine herpesvirus type 1.
- Alphavirus encephalomyelitis.
- Equine protozoal encephalomyelitis.
- Eastern and Western equine encephalitis.
- Venezuelan equine encephalitis.
- Verminosis encephalitis.
- Bacterial meningoencephalitis.
- Botulism.
- Poisonings.
- Hypocalcaemia.
laboratory diagnosis
The definitive diagnosis and its differentiation from other diseases are given by the laboratory. Should be taken samples to perform tests and, thus, detect antibodies or virus antigens for the diagnosis of the disease.
Tests to directly diagnose the virus, specifically antigens, are performed with samples of cerebrospinal fluid, brain, kidney or heart from the autopsy if the horse died, with polymerase chain reaction or RT-PCR, immunofluorescence or immunohistochemistry in the brain and spinal cord being useful.
However, the tests commonly used to diagnose this disease in live horses are the serological ones, from blood, serum or cerebrospinal fluid, where instead of the virus antibodies will be detected that the horse produced against him. Specifically, these antibodies are immunoglobulins M or G (IgM or IgG). IgG increases later than IgM and when clinical signs are sufficiently present then only detection of serum IgM is diagnosed. You serological tests available for the detection of Nile Fever in horses are:
- IgM capture ELISA (MAC-ELISA).
- IgG ELISA.
- Inhibition of hemagglutination.
- Seroneutralization: is used to confirm positive or confusing ELISA tests, as this test may cross-react with other flaviviruses..
The definitive diagnosis of West Nile fever in all species is made using the virus isolation, but it is not generally practiced because it requires a Biosafety Level 3. It can be isolated in VERO (African green monkey liver cells) or RK-13 (rabbit kidney cells), as well as in chicken cell lines or embryos.
Horse treatments
The treatment of West Nile Fever in horses is based on symptom treatment that occur, since there is no specific antiviral, so the supportive therapy will be as follows:
- Antipyretics, analgesics and anti-inflammatory drugs to reduce fever, pain and internal inflammation.
- Fixation to maintain posture.
- Fluid therapy if the horse cannot properly hydrate itself.
- Tube nutrition if ingestion is difficult.
- Hospitalization with a safe place, padded walls, comfortable bed and head protector to prevent injuries from knocks and control neurological signs.
Most of the horses that are infected recovers by developing specific immunity. Sometimes, although the horse outgrows the disease, there can be sequelae due to permanent damage to the nervous system.
Prevention and Control of West Nile Fever in Horses
West Nile fever is a notifiable disease, but it is not subject to an eradication program, as it is not contagious among horses, but requires a mosquito to mediate between them, so it is not mandatory to slaughter infected horses, except for humanitarian reasons if they are no longer of quality of life.
It is essential to apply preventive measures for Nile fever for good control of the disease through epidemiological surveillance of mosquitoes as vectors, birds as main hosts and horses or humans as accidental.
The program's objectives are to detect the presence of viral circulation, assess the risk of its appearance and implement specific measures. Wetlands must be specially watched and surveillance in birds is carried out on their carcasses, as many of the infected ones die, or by sampling from suspects; in mosquitoes, through their capture and identification, and in horses, through sentry sampling or by suspected cases.
As there is no specific treatment, vaccination and reducing exposure to transmitting mosquitoes are essential to reduce the risk of horses contracting the disease. O preventive mosquito control program is based on the application of the following measures:
- Use of topical repellents on horses.
- Place the horses in stables, avoiding outdoor activities during times of greater exposure to mosquitoes.
- Fans, insecticides and mosquito traps.
- Eliminate mosquito breeding sites by cleaning and changing the drinking water daily.
- Turn off the lights in the stable where the horse is to avoid attracting mosquitoes.
- Put mosquito nets in the stables, as well as mosquito nets on the windows.
West Nile Fever Vaccine in Horses
On horses, unlike people, there are vaccines which are used in areas of greatest risk or incidence of the virus. The great use of vaccines is to reduce the number of horses with viremia, that is, horses that have the virus in their blood, and to reduce the severity of the disease by showing immunity if infected.
Inactivated virus vaccines are used from 6 months of age of the horse, administered intramuscularly and require two doses. The first is at six months of age, revaccinating after four or six weeks and then once a year.
We emphasize once again that if the horse has any of the symptoms mentioned in this article, see a horse veterinarian as soon as possible.
We also have this other article on horse tick home remedies that might interest you.
This article is for information purposes only, at PeritoAnimal.com.br we are not able to prescribe veterinary treatments or perform any type of diagnosis. We suggest that you take your pet to the veterinarian in case it has any type of condition or discomfort.
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