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Protecting Your Horses from West Nile Virus: Expert Guide for Horse Owners

Updated: Dec 15, 2023


horse outside has West Nile virus vaccine for mosquito protection

Did you know that when it comes to non-human cases of West Nile Virus (WNV), horses account for a staggering 97% of affected animals? This alarming statistic highlights the significant impact of Equine West Nile Virus on the equine community.


As horse owners, the well-being and health of our equine companions are of utmost importance. Among the various diseases that can affect horses, one that demands our attention is Equine West Nile Virus (WNV). This viral infection, primarily transmitted by mosquitoes, has been a cause of concern in recent years. Understanding the nature of West Nile virus, its impact on horses, and the preventive measures available is vital for safeguarding our beloved equine partners. In this blog, we will delve into the intricacies of Equine West Nile Virus, exploring its transmission, clinical signs, diagnostic methods, treatment options, and most importantly, the preventive measures we can undertake to protect our horses from this potentially devastating disease.


Equine Nile Virus

West Nile virus in microscope
Photo credit: Britannica

Equine Nile Virus, also known as West Nile Virus (WNV), is a mosquito-borne virus that is spread by the bite of infected mosquitoes. It is a single-stranded RNA virus belonging to the family Flaviviridae and the genus Flavivirus. The virus was first identified in 1937 in the West Nile district of Uganda. Since then, it has spread throughout many parts of the world, including the United States, where it has been detected in humans, horses, and birds. Horses are particularly vulnerable to the virus. It can cause severe disease with symptoms ranging from mild fever and headache to meningitis and encephalitis.

map of the 2021 West Nile virus infections in horses
Photo credit: USDA

West Nile Virus Transmission

Horses primarily get West Nile virus (WNV) through the bite of infected mosquitoes. Mosquitoes become infected with the virus by feeding on infected birds such as crows, magpies and ravens, which serve as the primary reservoir for WNV. When an infected mosquito bites a horse, the virus is transmitted into the horse's bloodstream, leading to an infection.

It's important to note that horses are considered incidental hosts of West Nile virus, meaning they do not play a significant role in the transmission cycle of the virus. Instead, horses are considered dead-end hosts, as they do not produce enough virus in their bloodstream to infect feeding mosquitoes. Therefore, horses do not contribute to the spread of the virus to other animals or humans.

In addition to mosquito bites, there have been rare cases of horses contracting WNV through other means, such as exposure to infected birds. However, mosquito bites remain the primary mode of transmission for equine West Nile virus.

West Nile virus transmission cycle
Photo Credit: CDC

Signs and Symptoms After Contracting the West Nile Virus

After contracting the West Nile virus (WNV), horses can exhibit a range of signs and symptoms, which can vary in severity. Some infected horses may show no clinical signs at all, while others may display mild to severe symptoms. Here are some common signs and symptoms seen in horses with West Nile virus infection:

  • Fever: Horses with WNV may develop a fever, which is often the earliest and most consistent sign of infection. Elevated body temperature above the normal range (usually around 101-102.5°F or 38.3-39.2°C) can indicate the presence of the virus.

  • Loss of appetite: Infected horses may experience a decrease in appetite and show reduced interest in food or water. This can result in weight loss and a general lack of energy.

  • Depression and lethargy: Horses with WNV may appear dull, depressed, or lethargic. They may show a lack of interest in their surroundings, have a lowered head carriage, and exhibit reduced responsiveness.

horse showing neurological signs because of the equine West Nile virus
Photo credit: Horse Illustrated
  • Neurological signs: In more severe cases, horses can develop neurological symptoms due to the virus's impact on the central nervous system. These signs may include ataxia (incoordination), weakness, muscle tremors, stumbling, dragging of the toes, difficulty standing or walking, circling, head pressing, and paralysis of limbs or other body parts.


It's important to note that not all horses infected with West Nile virus will exhibit neurological signs. In fact, only a small percentage of infected horses will develop severe neurological disease.


If your horse displays any of these symptoms, it is important to contact your vet immediately. They will assess your horse and run diagnostics to determine if they have WNV. The symptoms will appear between five to fifteen days.


Diagnosis of Equine West Nile Virus

Diagnosing the Nile virus can be tricky as it can be confused with other diseases. West Nile virus (WNV) infection in horses is typically diagnosed through a combination of clinical signs, laboratory testing, and veterinary examination. Here are the common diagnostic methods used to determine if a horse has contracted West Nile virus:

horse blood being drawn for West Nile virus test
Photo credit: The Horse Hub
  • Clinical evaluation: A veterinarian will assess the horse's clinical signs and medical history. The presence of fever, neurological symptoms, and other characteristic signs can help raise suspicion of WNV infection.

  • Blood tests: Blood samples may be collected from the horse to perform laboratory tests. These tests can include:

    • Serology: Enzyme-linked immunosorbent assay (ELISA) or virus neutralization tests can detect antibodies produced by the horse's immune system in response to the virus. Detecting WNV-specific antibodies indicates exposure or infection. ELISA can detect the virus in a horse six days or one month after contracting the infection.

    • Polymerase Chain Reaction (PCR): This test can detect the genetic material (RNA) of the virus in the horse's blood, cerebrospinal fluid, or other relevant samples. PCR is most useful in the early stages of infection.

  • Cerebrospinal fluid analysis: In cases where neurological signs are present, a sample of cerebrospinal fluid (CSF) may be collected through a procedure called a CSF tap. Analysis of the CSF can help evaluate inflammation and determine if the central nervous system is affected.

It's important to note that the diagnosis of West Nile virus in horses requires veterinary expertise and access to appropriate laboratory facilities. If you suspect your horse may have WNV, it is crucial to contact a veterinarian promptly for an accurate diagnosis and appropriate management or treatment recommendations. Early detection can improve outcomes for the animal.


Is Equine West Nile Virus Contageous?

Equine West Nile virus (WNV) is not directly contagious from horse to horse. The primary mode of transmission of WNV is through the bite of infected mosquitoes. Horses serve as dead-end hosts, meaning they do not produce enough virus in their bloodstream to infect feeding mosquitoes, and therefore they do not contribute to the spread of the virus to other horses or humans.


However, it's important to note that in rare cases, there have been reports of potential transmission of WNV between horses through non-mosquito routes. These cases are considered atypical and are not the typical mode of transmission. The virus has been detected in blood, urine, and other body fluids of infected horses, which could potentially pose a risk if there is direct contact with mucous membranes or breaks in the skin. However, the overall risk of direct horse-to-horse transmission is considered low compared to the main mode of transmission through mosquitoes.


Prevention for West Nile

Effective management of West Nile Virus in horses relies on preventative measures, as there is currently no specific treatment for the disease. Mitigating the risk of infection involves several key practices:

bucket of mosquito larvae breeding new mosquitoes
Photo credit: MMCD
  • Eliminate Standing Water: Regularly remove standing water from your property, as mosquitoes breed in such environments. Weekly emptying of birdbaths, gutters, wading pools, and other sources of stagnant water helps reduce the mosquito population around your horses.

  • Use Equine-Specific Insect Repellent: Apply insect repellent designed for horses to safeguard them from mosquito bites. This serves as an additional barrier against potential infection.

  • Implement Physical Barriers: Utilize window screens and/or mosquito netting when your horse is outdoors to minimize mosquito access. Additionally, consider using fly sheets to further reduce exposure and lower the risk of infection.

  • Avoid Peak Mosquito Hours: Refrain from taking your horse outdoors during peak mosquito activity, which typically occurs during dusk and dawn. This simple precaution helps minimize the likelihood of mosquito bites and potential virus transmission.

  • Vaccination: Vaccinate your horses against West Nile Virus as a proactive measure. Vaccination is the most effective way to build immunity and protect them from the disease.

By incorporating these preventive measures into your horse care routine, you can significantly reduce the risk of West Nile Virus infection and promote the well-being of your equine companions.


Treatment for West Nile Virus

Unfortunately, there is no specific anti-viral treatment for horses infected with the West Nile Virus. There is mainly supportive treatment that includes maintaining hydration and electrolyte balance, maintaining nutrition, and pain relief medications. Vaccination with some prevention can protect your horse from the virus and its associated complications.


The following supportive measures may be implemented:

horse in stall is resting from west nile virus
  • Rest and supportive care: Horses with WNV may require strict stall rest to minimize the risk of injury due to neurological symptoms. Providing a quiet and calm environment can help reduce stress and aid in the horse's recovery.

  • Symptom management: Depending on the specific symptoms exhibited by the horse, veterinary treatment may include the administration of non-steroidal anti-inflammatory drugs (NSAIDs) to help reduce fever and alleviate pain and inflammation. Additional medications, such as muscle relaxants or anti-seizure medications, may be prescribed if the horse experiences severe neurological symptoms.

  • Fluid therapy: Maintaining hydration is crucial for horses with WNV. Intravenous fluids may be administered to ensure adequate hydration and electrolyte balance.

  • Nutritional support: Some horses with WNV may experience a decreased appetite. Ensuring that the horse receives appropriate and balanced nutrition is essential for supporting its immune system and overall recovery. In some cases, additional nutritional support, such as tube feeding, may be necessary.


In severe cases, horses need intensive supportive care such as mechanical ventilation, nutrition support, and intensive nursing care. Since the virus affects the nervous system, it is important to provide supportive care and protect the horse from further stress. Keep the horse in a stable environment and provide plenty of rest. Keep out of direct sunlight and monitor closely for signs of illness or further neurologic signs.


It is crucial to involve a veterinarian in the diagnosis and management of West Nile virus infection in horses. They can provide guidance on the specific supportive care measures required based on the individual horse's condition.


Should I get my horse vaccinated for Equine West Nile Virus?

As mentioned before, vaccination is the best way to prevent West Nile virus in horses and should be administered before the onset of the season in which mosquitoes are most active. Vaccination helps to reduce the risk and severity of the disease in horses.


Here are some reasons why you should consider vaccinating your horse against WNV:

  • Disease prevention: WNV can cause severe illness and neurological complications in horses. Vaccination is an effective preventive measure to reduce the risk of infection and the potential for serious disease.

  • Safety for your horse: Horses that are not vaccinated against WNV are more susceptible to contracting the virus if exposed to infected mosquitoes or other potential sources of infection. Vaccinating your horse helps provide an extra layer of protection and can contribute to their overall well-being.

  • Public health considerations: While horses are considered dead-end hosts for WNV and do not directly transmit the virus to humans or other animals, the disease serves as an indicator of local virus activity. By vaccinating horses, you contribute to efforts in controlling the spread of WNV and protecting public health.

  • Peace of mind: Vaccination provides peace of mind for horse owners, knowing that they have taken proactive steps to protect their horses from a potentially serious and preventable disease.


When considering WNV vaccination for your horse, it's important to consult with a veterinarian. They can evaluate your horse's individual risk factors, local disease prevalence, and recommend an appropriate vaccination protocol tailored to your horse's needs.

Additionally, remember that vaccination is just one aspect of a comprehensive approach to WNV prevention. Implementing mosquito control measures, such as removing standing water and using insect repellents, is also essential to minimize the risk of exposure to mosquitoes carrying the virus.


In what season the West Nile Virus is most likely to occur in horses?

horses grazing outside in summer could get West Nile virus

West Nile virus is a seasonal virus that typically occurs during the warm summer months in North America. The peak activity of the virus occurs between late July and early September. During this time, mosquitoes are most likely to feed on the blood of birds and other animals, including horses. As the weather turns cooler, the activity of the virus will decrease and eventually die off, but there is still a chance that an infected mosquito could remain active into the early fall months.


It's crucial to remember that the risk of WNV infection can vary from year to year and between different regions. Factors such as local mosquito populations, bird migration patterns, and environmental conditions can influence the prevalence and timing of WNV activity in a particular area.


Can a horse survive the Equine West Nile Virus?

Yes, most horses that become infected with the West Nile virus will survive, though they may develop long-term health problems as a result. The outcome of WNV infection in horses can vary depending on several factors, including the horse's overall health, age, immune response, and the severity of the infection.


horse grazing after surviving the West Nile virus

While WNV can cause severe illness and neurological symptoms in some horses, it's important to note that not all infected horses will develop severe disease. In fact, many horses that contract WNV may only exhibit mild or no clinical signs at all and can recover with appropriate supportive care. The disease is rarely fatal.


However, in more severe cases, horses may experience neurological symptoms such as ataxia, muscle weakness, paralysis, and other neurological deficits. These cases can be more challenging, and the prognosis may vary depending on the extent of the neurological damage and the individual horse's response to treatment. Horses that experience neurological symptoms due to the virus are more likely to experience death or severe disability.


Can I get West Nile virus from my horse?

No, direct transmission of West Nile virus (WNV) from horses to humans is extremely rare. Horses are considered dead-end hosts for WNV, meaning they do not produce enough virus in their bloodstream to effectively infect feeding mosquitoes and thus cannot contribute to the spread of the virus to humans or other animals.


mosquito on a leaf could be caring West Nile virus

The primary mode of transmission of WNV to humans is through the bite of infected mosquitoes. Mosquitoes acquire the virus by feeding on infected birds, which serve as the primary reservoir for WNV. Humans can become infected when bitten by an infected mosquito, but direct contact with an infected horse does not pose a significant risk of transmission.


However, it's important to note that proper precautions should still be taken when handling or caring for an infected horse. This includes following general hygiene practices such as wearing gloves when handling bodily fluids, practicing good hand hygiene, and avoiding direct contact with open wounds or mucous membranes.

If you have concerns about West Nile virus or any other infectious disease, it is always advisable to consult with a healthcare professional or veterinarian for the most accurate and up-to-date information.


Final Thoughts about Equine West Nile Virus

In conclusion, Equine West Nile Virus is a significant concern for horse owners, as it can lead to severe illness and neurological complications in affected horses. Understanding the nature of the virus, its transmission, clinical signs, and available preventive measures is crucial for protecting our equine companions.


Prevention plays a crucial role in mitigating the risk of West Nile Virus in horses. Vaccination is highly recommended as part of routine equine healthcare, as it can significantly reduce the severity of the disease if infection occurs. Implementing mosquito control measures, such as removing standing water, using insect repellents formulated for equine use, and employing protective measures like fly sheets and blankets, can further minimize the risk of mosquito bites and exposure to the virus.


Early detection and prompt veterinary care are vital if West Nile Virus is suspected in a horse. Diagnosis involves a combination of clinical evaluation, laboratory testing, and veterinary expertise. Supportive care, including rest, medication for symptom management, fluid therapy, and nutritional support, can help improve the horse's chances of recovery.


By staying informed, working closely with veterinarians, and implementing appropriate preventive measures, we can help protect our horses from Equine West Nile Virus and ensure their well-being. Remember, timely action and proactive measures are key to safeguarding our equine companions from this potentially devastating disease.

happy horse running outside protected from West Nile virus
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