Parapox Ovis Virus Immunomodulator

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PAIR-ah-pawks Oh-vis VEYE-ruhs - Pronunciation guide

Brand Names

  • Zylexis


Parapox Ovis Virus Immunomodulator is used in the treatment of equine herpes virus types 1 and 4. Studies indicate that this vaccine is effective in establishing an immune response that reduces the severity and duration of these viral diseases.

The parapox ovis virus activates immune cells, stimulates phagocytosis and induces expression of cytokines; the messenger proteins that stimulate production of interferon and immune cells in a number of species. The immune cells and phagocytes target the EHV and reduces the damage caused by the virus and the duration of the illness.

Clinical studies show a reduction in the number of days and amount of nasal discharge in horses that are treated with the parapox ovis virus versus a control group.


A series of intramuscular injections of the parapox ovis virus immunomodulator is called for during disease episodes, or in periods of stress such as showing, trailering, breeding, or environmental changes that increase the likelihood of EHV disease in susceptible horses or foals above 4 months in age.

Dosage and Administration

Parapox Ovis Virus Immunomodulator
Method Dosage
(click row for calculator)
Concentration Period Duration
Intramuscular injection 2 ml   Repeat dose on days 2 and 9 following the initial dose.1 NA


  • 1Retreatment is recommended during subsequent disease episodes or prior to stress-inducing situations.
  • Extra-label use of drugs in treating animals is allowable only by licensed veterinarians within the context of a valid veterinarian-client-patient relationship, and does not include drug use in treating animals by the layman (except under the supervision of a licensed veterinarian).
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your equine appears to feel better, the entire treatment plan should be completed to prevent relapse.
  • This medication may be available in forms and concentrations not noted in the above table. Always check the label and literature provided with the medication about the form and concentration and DO NOT USE the calculator if the information differs.

Side Effects

ZYLEXIS has undergone testing in a field safety trial in the US in 333 horses of various breeds ranging in age from 4 months to 20 years. No adverse events were reported.


Use entire contents when first opened. Sterilized syringes and needles should be used to administer this immunomodulator. Do not administer within 21 days before slaughter. In case of anaphylaxis, administer epinephrine or equivalent.


None reported.


No information is provided in the literature concerning accidental overdose of this vaccine. Contact the manufacturer directly for instructions should an overdose occur.


Zylexis EQ 5x1 DoseZylexis EQ 5x1 Dose



About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.