Wednesday, June 19, 2024

How Is Equine Herpes Virus Transmitted

How Is Ehv Spread

Vet Suggests People Not Overreact To Equine Herpes Outbreak

Herpesvirus is primarily spread by direct horse-to-horse contact via transfer of respiratory secretions . It is not known how far aerosolized virus can spread, although 30 yards is typically considered the maximal distance EHV-infected droplets can travel after a cough or sneeze. Virus can also be spread by contaminated hands, clothing, buckets, tack, grooming equipment, feed and trailers. The virus can live for up to 7 days in the typical environment, but it is easily killed by most disinfectants.

What Are The Signs Of Infection

In its most common form, EHV-1 causes respiratory disease in foals, yearlings and young horses in training. They show variable signs that include elevated temperature, watery nasal discharge, enlarged glands under the jaw and coughing. Some cases may progress to secondary pneumonia. In horses in training, symptoms may be mild but ‘epidemic’ loss of performance may occur. EHV-1 can cause single or multiple abortions in mares during mid to late pregnancy. Also, infected foals may be prematurely born alive but soon fade and die while others are born dead at full term. Disastrous epidemics can occur in susceptible pregnant mare populations. Also, the virus can also cause paralysis, in horses of all ages and types, often first involving weakness of the hind limbs but then progressing to involve all four limbs and resulting in death or a requirement for euthanasia.

EHV-2 does not usually cause disease on its own but is believed to cause suppression of the horse’s immunity to other viral infections and allows them to cause signs of disease, usually respiratory infection, i.e., elevated temperature, watery nasal discharge, enlarged glands under the jaw and coughing.

EHV-4 is a common cause of coughing and loss of performance in racehorses. Usually the respiratory disease is not severe but the disruption to training and performance programs and consequent economic losses can be very significant. Rarely, EHV-4 is a cause of isolated abortions in mares.

What Is The Equine Herpes Virus

Equine Herpes Virus is a contagious disease that affects horses. Although there are nine strains of the virus, Equine Herpes Virus-1 and Equine Herpes Virus-4 are most commonly seen.

The current outbreak in Europe is the EHV-1 strain.

Affected horses may suffer respiratory disease, neurological disease and abortion in pregnant mares. Young foals are also at risk and can die from the infection.

Equine Herpes Virus is found in many parts of the world and cases and outbreaks can be seen at any time of year.

Certain strains of the virus can cause severe illness in horses, which can result in their stables being placed under quarantine for several weeks so that horses cannot travel and are unable to compete.

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How Is Equine Herpesvirus Myeloencephalopathy Treated

Horses that exhibit sudden and severe neurological signs consistent with EHV-1 should be isolated immediately to prevent the spread of infection to other resident horses. Since EHV-1 is a virus, antibiotics will have no effect and antiviral drugs have shown minimal effect in already affected horses. Treatment is primarily supportive, and usually includes anti-inflammatories and fluids to maintain hydration. Slings may be used to help horses that are unable to stand on their own.

What Are Signs Your Horse Has Been Infected With Ehv

Controversies of Equine Herpesvirus

The incubation period for EHV-1 after initial infection can be as short as 24 hours but is typically around 4-6 days or longer. EVH-1 usually causes a two-phase fever spike around day 1-2 and again at day 6-7. There is often coughing and nasal discharge that accompanies a respiratory infection as well as enlargement of the lymph nodes under the jaw. If the horse develops EHM, the neurologic form of EHV-1, there are typically minimal warning signs with mild respiratory symptoms and a fever with a rectal temperature greater than 101.5 degrees. EHM appears suddenly and progresses very quickly, reaching its peak intensity within 24-48 hours of initial neurologic signs. Neurologic signs that your horse may have EHM include:

  • Incoordination
  • Leaning against walls or fencing for balance
  • Lack of energy or lethargic
  • Inability to get up

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What Is Equine Herpes Virus

There are five strains of herpes virus which affect horses, with EHV-1 and EHV-4 most commonly causing problems to horse health.

EHV is widespread in the horse population with some horses carrying the virus but not showing signs of the disease as the virus can remain latent within the horse. The reactivation of the virus can occur without warning but is usually associated with stress such as transportation or weaning. Once reactivated the virus causes disease in the horse and rapidly spreads from one horse to another.

EHV-1 causes abortion in mares and also can cause neurological disease. It can also cause respiratory disease in younger horses.

EHV-4 causes respiratory disease and occasionally causes abortion in mares.

How is equine herpes spread?

Both EHV-1 and EHV-4 are spread directly via droplets in the air from coughing horses and also indirectly via people, tack, feed and equipment. In the case of EHV-1, contact with aborted foetuses and placentae associated with abortions can spread the disease.

What are the signs of equine herpes?

The signs seen with infection depend upon the strain and some horses will be infected without showing any signs. Where infected individuals do display signs these may include:

  • Respiratory Disease – rise in temperature coughing nasal discharge lack of appetite.
  • Neurological Disease- hind limb weakness incoordination paralysis and the inability to stand.
  • Abortion and death of newborn foals.

Can my horse die of herpes?

How Long Is A Cat Infectious After Getting The Virus

Once a cat is infected with FVR, they will usually show disease symptoms in 2-5 days . The cat can infect other cats during this incubation period. In most cases, once symptoms appear the active infection will last about 10-20 days.

“Stress and illness can cause the virus to become reactivated.”

All cats that have been infected with FVR will become carriers of this virus most carriers will be latent, meaning that the virus will survive in an inactive form within the cat’s body. Stress and illness can cause the virus to become reactivated, and if the virus becomes reactivated, the cat will again be infectious. In the majority of cases, the cat will show symptoms of a respiratory infection when the virus is reactivated. However, not all cats with a reactivated FVR infection will show symptoms of disease. All cats that are actively shedding virus present a risk to other cats.

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Cell Infection And Virus Replication

The lytic replication cycle of EHV-1 can be summarized as follows: entry into a permissive host cell, viral nucleocapsid uncoating, viral gene expression, viral DNA replication, virion assembly, and virion particle egress . In horses, EHV-1 can infect a diverse range of cell types, including endothelial cells of inner organs, epithelial cells of the respiratory tract, and mononuclear cells in lymphoid organs and the peripheral blood . Cells are either infected by direct contact with an infectious EHV-1 particle or by cell-to-cell spread following contact with an infected cell . Like HSV-1 and most other alphaherpesviruses, including EHV-1, efficient infection is initiated by a relatively unstable attachment to heparan sulfate molecules on the proteoglycan cell surface, mediated by gC and gB, followed by binding of gD to one of the specific receptors on the cell surface . The changes in conformation as a result of receptor engagement with gD enables intricate interactions between gB and gH/gL . However, for virus entry into host cells, EHV-1 also utilizes a unique receptor that is different from those described for other alphaherpesviruses . It has been shown that the Major Histocompatibility Complex I molecules on some equine cells serve as entry receptors for EHV-1 by binding directly to gD on the viral envelope membrane .

Respiratory Mucosal Explant Isolation And Cultivation

Six horses put down after equine herpes virus outbreak

Nasal and tracheal mucosal explants were prepared and cultivated as previously described . Lung explants were obtained following a technique described for pigs, with minor adaptations . Briefly, lung tissue was first cut up in cubes of approximately 1 cm×1 cm×5 cm . These cubes were then transferred to a 20 mL syringe containing 5 mL of 4% agarose , diluted in PBS. After filling the syringe with 5 mL of additional agarose, it was transferred to 4 °C until the agarose solidified . The tip of the syringe was cut off, before gently pushing the plunger and thereby moving the embedded lung tissue out of the barrel. Using a cryotome blade, thin lung tissues slices of 1 mm were cut and transferred to a petridish. Here, tissues were thoroughly washed to remove excess agarose and finally trimmed to a surface of approximately 25 mm2. Lung explants were transferred to 6-well plates, submerged in serum-free medium and cultivated at 37 °C and 5% CO2.

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Clinical Signs And Symptoms Of Equine Herpesvirus

Clinical signs and symptoms of respiratory disease associated with EHV include:

Fever in two phases,

peaking once on days 12 and again on days 67

Discharge from the eyes and nose,

with minimal coughing

Enlarged lymph nodes

The neurological disease associated with EHV is also known as Equine HerpesVirus Myeloencephalopathy . EHM is usually sudden-onset and rapidly progressing.

Clinical signs and symptoms may include:

Nasal discharge,


In typical cases, the outcome is usually favourable, with recovery in a matter of weeks.

In cases of more advanced neurological disease, however, such as with horses who are unable to urinate or stand, the prognosis is poor.

Treatment for horses infected with EHV is a combination of supportive care and symptom management. Fever, pain, and inflammation are often treated with non-steroidal anti-inflammatories, and some horses may require IV fluids. Antiviral drugs may be used to decrease the risk of developing EHM in horses infected with or exposed to EHV.

Preventative measures can be taken to reduce the risk of EHV transmission and outbreak. These include:

VaccinationVaccines are available to help prevent respiratory disease and abortions associated with EHV and reduce viremia . Since EHV is a risk-based vaccine, talk to your veterinarian to help decide if your horse is at risk.

Is My Family At Risk

The upper respiratory infection that is caused by feline viral rhinotracheitis is only infectious to other cats. However, upper respiratory infections in cats can be caused by or complicated by bacterial infections, some of which might be contagious to humans. If you follow good hygiene practices including proper hand washing after handling any cat, you will minimize the chance that you can get an illness from this or any other infectious disease. Consult your family physician if anyone in your family develops signs of a respiratory infection if your cat is ill.

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Herpes Virus In Horses

The herpes virus is a large family of viruses. Most mammalian species are susceptible to at least one type of herpes virus. Fortunately, this virus is very species-specific, meaning that humans do not catch equine herpes virus, and vise versa. There are five known subtypes in horses, but Equine Herpes Virus-1 and EHV-4 are the two severest forms of the virus. EHV-3 is another type of major herpes virus, although it is normally associated with coital exanthema, a venereal disease that can be transmitted to horses.

The different classifications of equine herpes virus affect different systems one affects the reproductive and neurological systems, whereas another causes respiratory issues. The virus type will also determine the symptoms the horse displays.

Vaccination With Duvaxyn Ehv

Michael Porter, Equine Veterinarian: Equine Herpes Virus

You can vaccinate your horse against equine herpes virus with Duvaxyn® EHV-1,4, available from your vet.

Vaccination reduces the clinical signs of respiratory diseases caused by both strains of the virus, EHV-1 and EHV-4.

It also helps to control EHV-1 abortion when used in conjunction with appropriate management practices, as advised by your vet.

Your horse can get this vaccination from 5 months of age, or from 3 months if at high risk of infection. Your horse will need a second dose 46 weeks after the first dose, followed by a booster every 6 months.

Breeding mares should receive doses at 5, 7 and 9 months of pregnancy.

For more details about Duvaxyn® EHV-1,4 and correct dosing information, visit the Products section of this site.

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Infection By Other Herpesviruses:

Equine herpesvirus 2 is ubiquitous in respiratory mucosa, conjunctiva, and WBCs of normal horses of all ages. The pathogenic significance remains obscure. It has been suggested that EHV-2 is the cause of herpetic keratoconjunctivitis and inflammatory airway disease in young horses. Equine herpesvirus 3 is the cause of equine coital exanthema , a benign, progenital exanthematous disease.

Equine gamma herpesvirus 5 has emerged as the pathogen associated with equine multinodular pulmonary fibrosis . The role of EHV-5 in EMPF is unclear . Clinical signs include weight loss, cough, fever , and respiratory difficulty. EMPF is seen primarily in middle-aged horses, although it has been reported in young horses. Physical examination findings include tachycardia, tachypnea, increased respiratory effort , and poor body condition. Wheezes and crackles are often ausculted without a rebreathing procedure. In early cases, EMPF may be mistaken as heaves. In addition to EMPF, EHV-5 has been associated with lymphoproliferative disease and lymphoma. One unusual case report describes a 21-yr-old horse with profound pancytopenia and pulmonary fibrosis EHV-5 was isolated from the bone marrow of this horse.

How Is This Infection Diagnosed

Several different infectious agents can cause upper respiratory disease in cats , with subtle differences in examination findings between the different diseases. A presumptive diagnosis of feline viral rhinotracheitis is based primarily on a cat’s medical history and clinical signs combined with the findings on physical examination, particularly if the cat has evidence of a corneal infection. Corneal staining with fluorescein dye is often performed to look for any ulcers that may have developed. A Schirmer tear test to assess tear production may be supportive of a diagnosis of FVR, since decreased tear production has been associated with FVR conjunctivitis.

Specific identification of FVR virus particles may be made by collecting samples of cells and discharges from the nose, eyes, or back of the throat. Identification of feline herpesvirus DNA by polymerase chain reaction amplification is the most sensitive test available for diagnosing infection by FHV-1. Unfortunately, if the virus is in a latent state , diagnostic testing is usually not rewarding.

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Recommendations For Participants At Equine Events

CDFA Animal Health Officials are continually monitoring for EHV-1 cases. CDFA reminds horse owners traveling with horses to participate in an equine event, that there is always disease risk when horses of unknown health status are commingled for a show or competition. CDFA strongly recommends that horse owners practice proper biosecurity when attending an equine event. Compliance with basic biosecurity practices is an important factor in reducing risk of exposure to all contagious equine diseases. Basic biosecurity measures to follow to decrease potential disease spread at equine events include:

  • Limit horse-to-horse contact
  • Avoid use of communal water sources
  • Avoid sharing of equipment unless thoroughly cleaned and disinfected between uses
  • Monitor your horse for clinical signs of disease and report any temperature over 102°F to a veterinarian

Diagnosis Of Equine Herpes Virus

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Your vet will base their diagnosis on clinical history and signs, followed by tests to isolate the virus on nasal swabs taken as early as possible after infection is suspected.

In addition blood samples will be taken to measure the levels of antibodies in the blood when the horse is first examined by the vet and then again two to three weeks later. An increase in the levels of antibodies seen in the blood will confirm recent exposure to the virus.

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What Do I Do If Ehv Is Confirmed

Your vet will advise specifically on how to isolate affected horses and on the hygiene/cleaning procedures to be followed, but in general…

  • If an abortion has occurred, special procedures must be followed your vet will specify what these need to be. Isolation will need to be for at least 28 days after the last abortion, so be prepared for some crucial short term changes to yard routine.
  • Thoroughly clean equipment, surfaces and vehicles with a steam cleaner and apply an appropriate disinfectant that destroys viruses. This should be done in between occupants. The disinfectant needs to be applied in the correct dilution to be effective.
  • Use separate equipment and change outer clothes between unaffected and affected horses. See to affected horses last. Make sure that everyone washes their hands between horses.
  • You need to have and follow a proper yard hygiene and disinfection policy. Please see our separate factsheet.
  • Epidemiology And Transmission Of Ehv

    Exposure of horses to either EHV-1 or its close relative EHV-4 occurs very early in life. It has been reported that between 80 to 90% of horses are infected, with either pathogen, by the time they are 2 years of age . The great level of antigenic relatedness between EHV-1 and EHV-4 often complicates seroepidemiological findings as a result of a lack of type-specific antibodies and extensive antigenic cross-reactivity that exists in natural infection . In the early 1990s, evidence became available that the envelope glycoprotein, gG, of EHV-4 elicits a type-specific antibody response, which enabled the differentiation between antibodies present in polyclonal sera from mixed cases of infection involving both EHV-1 and EHV-4 . The antigenic determinants in the carboxyl domain of the gGs of EHV-1 and EHV-4 have been described as useful tools for differentiating between these viruses based on distinct humoral responses that they elicit in their natural hosts . The annual incidence of EHV-1 is not well defined, as a result of mixed infection with EHV-4 and the ability of both viruses to undergo latency. Latency is an important survival strategy employed by alphaherpesviruses for continuous persistence and dissemination within their natural host population . Virus reactivation in an infected host, following latency, could occur at any time to promote a clinical course of the disease and virus shedding.

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