Parapox ovis virus immunomodulator
Inactivated Parapox ovis virus
Also known as: Zylexis · PPOV · PIND-ORF · Baypamune
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Aid in reducing upper airway disease caused by herpesvirus types 1 and 4 | 2 mL IM | IM | Repeat doses on days 2 and 9 following the initial dose | 3 doses total | 🌎 NA |
| Hyper-responding or delayed uterine clearance (DUC) broodmares | A single IM dose | IM | Once | The day before breeding | 🌎 NA |
- Aid in reducing upper airway disease caused by herpesvirus types 1 and 4: Retreatment is recommended during subsequent disease episodes or prior to stress inducing situations.
- Hyper-responding or delayed uterine clearance (DUC) broodmares: Followed by 12 mg of dexamethasone sodium phosphate IV at the time of breeding and 1 mL (20 Units) oxytocin and 1 mL (250 micrograms) estradiol with or without uterine lavage 6 hours later.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Parapox ovis virus immunomodulator is a biologic immunostimulant primarily used in veterinary medicine to boost the non-specific immune response.
Key characteristics include:
- Paramunity Inducer: It utilizes an inactivated (killed) virus that originally causes 'orf' (contagious pustular dermatitis) in sheep.
- Equine Application: In the US, it is labeled for healthy horses (4 months and older) to aid in reducing upper respiratory disease caused by Equine Herpesvirus types 1 and 4 (EHV-1 and EHV-4).
- Reproductive Use: Off-label, it is utilized in equine reproduction protocols for broodmares with delayed uterine clearance (DUC) or hyper-responsive uteri.
- Small Animal Use: While not labeled in the US for small animals, similar products (e.g., Baypamun®) have been used in Europe for dogs and cats to stimulate non-specific immunity during viral infections or stress.
Clinical Pearl: Because the virus is inactivated, it cannot cause disease in the treated animal. It serves purely as a decoy to wake up the host's innate immune system.
Mechanism of action
The drug acts as a paramunity inducer through a process known as viral interference.
- Mechanism: The inactivated parapoxvirus "infects" host cells with a defective, non-replicating viral particle.
- Immune Activation: This pseudo-infection $\rightarrow$ triggers the host's innate immune system $\rightarrow$ leading to the induction and release of interferons, cytokines, and colony-stimulating factors.
- Cellular Response: It also stimulates the activation of natural killer (NK) cells, which help clear pathogenic viruses before they can establish a robust infection.
Safety & warnings
Contraindications
- Prior hypersensitivity to the agent
Adverse effects
- Anaphylaxis (rare but possible)
Precautions
Hypersensitivity Risk: As with any biologic product, anaphylaxis is possible. Epinephrine (or an equivalent) should be readily available when administering this product.
Regulatory Warning: This is a USDA-licensed biologic, not an FDA-approved drug. Do not administer to horses within 21 days of slaughter.
Monitoring
- Clinical efficacy (improvement in respiratory infection signs or uterine clearance)
- Signs of anaphylaxis or hypersensitivity immediately post-injection
Pharmacokinetics
Absorption
Effects on the immune system are reported to occur 4-6 hours after treatment.
Elimination
Immunomodulatory effects persist for 1-2 weeks.
Overdose
No specific information is available regarding acute toxicity or overdosage. Given its nature as an inactivated biologic, massive toxicity is unlikely, though the risk of immune-mediated or injection-site reactions may increase.
Available products
Formulations
- Injection: Freeze-dried inactivated virus powder for reconstitution with sterile diluent
Veterinary
- Zylexis® Injection: Boxes of 5-single dose vials for reconstitution with 5-2mL vials of sterile diluent
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store refrigerated (2-8°C). Do not freeze. After reconstituting with the provided diluent, the entire contents should be used immediately.
Client information
Your veterinarian has prescribed an immunostimulant for your horse.
- What it does: This medication acts like a "wake-up call" to your horse's immune system, helping it fight off specific respiratory viruses (like Equine Herpesvirus) or assisting in reproductive therapies for breeding mares.
- How it works: It contains a killed virus that cannot cause disease, but tricks the body into mounting a strong, natural immune defense.
- What to watch for: While generally very safe, any injected biologic can rarely cause an allergic reaction. Monitor your horse for signs of facial swelling, hives, difficulty breathing, or severe lethargy shortly after the injection, and contact your veterinarian immediately if these occur.
- Slaughter warning: Do not use in horses intended for human consumption within 21 days of administration.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.