[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other DNA viruses](https://durgical.com/en/microbiology/groups/other-dna-viruses/) › Other poxviruses

# Other poxviruses

- Virus
- Enveloped

## Contact?

Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

- For completeness

Large DNA viruses related to smallpox. Most come from animals and cause a few skin nodules; vaccinia, used in smallpox vaccines, can spread from the jab site.

Updated Nov 13, 2026

Also called: vaccinia virus, cowpox virus, buffalopox, orf virus, milker's nodule virus, tanapox virus, Yaba monkey tumour virus

## Quick facts

**Type**
Virus · [Other DNA viruses](https://durgical.com/en/microbiology/groups/other-dna-viruses/)

**Gram / shape**
Brick-shaped

**Spread**
Vaccinia · Cowpox · Orf and milker's nodule

**Causes**
Vaccinia vaccine complications · Orf · Cowpox

**Treatment**
Orf and the zoonotic poxviruses heal on their own

On this page

- The basics Key points
- At a glance
- Morphology
- Transmission
- Memory aid
- What the colours mean

- Clinical Virulence factors
- Diseases it causes
- Clinical picture
- Diagnosis

- Treatment Treatment
- Prevention

- Study Test yourself

- Connections Connections

## Key points

- Poxviruses: large, brick-shaped, enveloped dsDNA viruses that replicate in the cytoplasm
- Orf (parapox) comes from sheep and goats and heals on its own
- Eczema vaccinatum: vaccinia spreading over atopic skin
- Progressive vaccinia: a non-healing site in a T-cell deficiency
- Vaccinia immune globulin is first-line for serious vaccinia complications

## At a glance

**Shape**
Brick-shaped (orthopox) or ovoid with a criss-cross surface (parapox)

**Genome**
Double-stranded, linear DNA (very large)

**Envelope**
Enveloped

**Family**
Poxviridae: genera Orthopoxvirus (vaccinia, cowpox, buffalopox), Parapoxvirus (orf, pseudocowpox), Yatapoxvirus (tanapox, Yaba)

**Size**
About 200 to 300 nm, among the largest viruses

## Morphology

- Replicate in the cytoplasm, carrying their own DNA-dependent RNA polymerase
- Form cytoplasmic inclusion bodies in infected cells
- Orthopoxviruses cross-protect: immunity to one (vaccinia) protects against others (smallpox, mpox)

## Transmission

- Vaccinia: from the smallpox vaccination site to other body sites (autoinoculation) or to close contacts by touch
- Cowpox: from rodents, often through pet cats, in Europe and western Asia
- Orf and milker's nodule: contact of broken skin with sheep, goats or cattle, or contaminated objects (slaughter, milking, home butchering)
- Buffalopox: from buffaloes and cows in South Asia (a vaccinia-like virus)
- Tanapox and Yaba: from monkeys in tropical Africa, probably helped by biting insects

**Reservoir:** Rodents (cowpox); Sheep and goats (orf); Cattle (pseudocowpox); Non-human primates (tanapox, Yaba)

### Isolation precautions

What the care team adds to standard precautions.

**Contact**
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

## Virulence factors

- Viral proteins block interferon, complement and cytokine signalling, helping local spread in skin
- Infected keratinocytes proliferate, producing papules, vesicles, pustules and nodules
- Severe disseminated vaccinia occurs when T-cell immunity is weak or the skin barrier is damaged (atopic dermatitis)

## Diseases it causes

- Vaccinia vaccine complications: inadvertent inoculation, ocular vaccinia, generalized vaccinia, eczema vaccinatum, progressive vaccinia, postvaccinial encephalitis
- Myopericarditis after vaccinia-based smallpox vaccine [Myocarditis →](https://durgical.com/en/conditions/myocarditis/)
- Orf (contagious ecthyma) and milker's nodules on the hands
- Cowpox, buffalopox and tanapox: localized painful pustules or nodules with fever and lymphadenopathy

## Clinical picture

- Orf: a single or few nodules on the hands that pass from red papule to target-like nodule, weep, crust and heal in 4 to 8 weeks
- Eczema vaccinatum: widespread lesions in people with atopic dermatitis, whether or not the eczema is active
- Progressive vaccinia: a vaccination site that never heals and keeps spreading, in severe immunodeficiency; often fatal
- Cowpox: a painful black eschar-like lesion, usually on the hand or face, after contact with a cat or rodent

## Diagnosis

- Exposure history: recent smallpox vaccination (self or contact), sheep or goats, cattle, cats or rodents, travel to Africa
- PCR of lesion material distinguishes orthopox from parapox and from mpox
- Electron microscopy shows the typical brick or ovoid virions; histology shows cytoplasmic inclusions
- Orf can mimic cutaneous anthrax, pyogenic granuloma or a bacterial infection

## Treatment

Orf and the zoonotic poxviruses heal on their own with wound care. Serious vaccinia complications are treated with vaccinia immune globulin first, and antivirals such as tecovirimat, cidofovir or brincidofovir in selected cases.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Tecovirimat](https://durgical.com/en/pharmacology/tecovirimat/)
- [Cidofovir](https://durgical.com/en/pharmacology/cidofovir/)
- [Immunoglobulins and antitoxins](https://durgical.com/en/pharmacology/classes/immunoglobulins-and-antitoxins/)

## Prevention

- Cover the smallpox vaccination site and wash hands after touching it
- Screen vaccine candidates for atopic dermatitis, immunodeficiency and pregnancy, including household contacts
- Gloves when handling sheep, goats and cattle, during slaughter and home meat preparation
- Avoid touching sick wild rodents and keep pet cats with lesions under veterinary care

**Vaccine:** Vaccinia-based smallpox vaccines are no longer given routinely; they are reserved for specific laboratory and response staff. A non-replicating vaccinia vaccine is used for mpox. None is part of Colombia's PAI schedule.

## Memory aid

"Sheep give Orf, cats bring Cow": orf comes from sheep and goats, and in Europe cowpox usually reaches people through cats that hunt rodents.

## Test yourself

Think of the answer, then tap the question to see it.

## Where do poxviruses replicate, unlike most other DNA viruses?

In the cytoplasm, using their own viral DNA-dependent RNA polymerase.

## A shepherd has a weeping target-like nodule on a finger. What is the likely cause?

Orf virus (a parapoxvirus from sheep and goats), which usually heals on its own in weeks.

## Which patients are at risk of eczema vaccinatum?

People with atopic dermatitis, active or not, who receive a vaccinia vaccine or are close contacts of someone recently vaccinated.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/other-poxviruses/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

**Contact**
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

**Droplet**
Surgical mask within about a metre; single room.

**Airborne**
N95 respirator and a negative-pressure room.

## Connections

## Related 3

- [Variola virus](https://durgical.com/en/microbiology/variola-virus/)
- [Mpox virus](https://durgical.com/en/microbiology/mpox-virus/)
- [Molluscum contagiosum virus](https://durgical.com/en/microbiology/molluscum-contagiosum-virus/)

## Related conditions 1

- [Myocarditis](https://durgical.com/en/conditions/myocarditis/)

[← Back to the group: Other DNA viruses](https://durgical.com/en/microbiology/groups/other-dna-viruses/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Vaccine Adverse Events](https://www.cdc.gov/smallpox/hcp/vaccines/vaccine-adverse-events.html) (CDC, 2024); [Human Orf Virus Infection from Household Exposures — United States, 2009–2011](https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6114a3.htm) (CDC, Morbidity and Mortality Weekly Report, 2012).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/microbiology/other-poxviruses/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/other-poxviruses/