Poxvirus

Poxviruses are a group of viruses that can cause pox diseases in vertebrates.

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Electron micrograph of poxvirus particles

Other names

Poxviridae

Genus

Genus Orthopoxvirus

(Ortho: from Greek orthos, “straight”)

Poxviridae

• The genus Orthopoxvirus contains a number of species that can infect animals and humans.
• The most well known member of the genus is variola virus, the causative agent of smallpox.
• Other notable members include vaccinia virus which is used in the current smallpox vaccine; cowpox virus, first introduced by Edward Jenner in the late 18th Century as the material of the first vaccine; and monkeypox virus.

Orthopoxviruses

• Camelpox virus
• Cowpox virus
• Ectromelia virus
• Horsepox virus
• Monkeypox virus
• Raccoonpox virus
• Skunkpox virus
• Taterapox virus
• Uasin Gishu virus
• Vaccinia virus (smallpox vaccine)
• Variola virus (smallpox) virus
• Volepox virus

Genus Parapoxvirus

(Para: from Greek para, “by side of”)

Parapoxviruses can infect a variety of livestock animals including sheep, goats, and cattle. Human infection is normally associated with an occupation involving sheep, goats, and cattle.

Parapoxviruses

• Bovine papular stomatitis virus
• Orf virus (sore mouth infection)
• Pseudocowpox virus
• Parapoxvirus of red deer
• Squirrel parapoxvirus

Tentative members

• Camel contagious ecthyma virus (Ausdyk virus)
• Chamois contagious ecthyma virus
• Parapoxvirus of reindeer virus
• Sealpox virus

Genus Molluscipoxvirus

Molluscum: from Latin molluscum, “clam” or “snail”)

Molluscum contagiosum is the only member of the Molluscipoxvirus genus. Molluscum contagiosum only infects humans and is a common infection of children and immunodeficient individuals.

Molluscipoxviruses

• Molluscum contagiosum virus

Genus Yatapoxviruses

(Yata: from the combination of Yaba and Tanapoxvirus)

Yatapoxviruses infect both humans and primates across equatorial Africa. Species in this genus are named for the location in which they were identified, Yaba (Lagos, Nigeria) and the Tana River Basin (Kenya). The natural host of yatapoxviruses is unknown.

Yatapoxviruses

• Tanapox virus, Yaba-like disease virus
• Yaba monkey tumor virus

Genus Capripoxviruses

(Capri: from Latin caper, “goat”)

Capripoxviruses cause infection in cattle, sheep, and goats. Infection can cause high morbidity and outbreaks of Capripoxviruses can have profound economic impact for farmers. The viruses in this genus are listed by the World Organizations for Animal Health (OIE: Office International des Epizooties) as important animal diseases that require notification.

Capripoxviruses

• Sheeppox virus
• Goatpox virus
• Lumpy skin disease virus

Genus Suipoxviruses

(Sui: from the Latin sus, “swine”)

Swinepox virus is the sole member of the Suipoxvirus genus. Swine are the only known host for this virus.

Suipoxviruses

• Swinepox

Genus Leporipoxviruses

(Lepori: from Latin lupus, “hare”)

Members of the Leporipoxvirus genus infect rabbits, hares, and squirrels. Myxoma virus was used in Australia in the 1950s as a pest control to try and eradicate feral European rabbits. Transmission of leporipoxviruses is primarily through the mosquito although other biting insects such as fleas may also transmit virus.

Leporipoxviruses

• Myxoma virus
• Shope fibroma virus (Rabbit fibroma)
• Squirrel fibroma virus
• Hare fibroma virus

Genus Avipoxviruses

(Avi: from Latin avis, “bird”)

Avipoxviruses infect a number of domestic and wild birds and can be identified as causing disease in at least 232 species in 23 orders. Transmission usually occurs by skin abrasions, inhalation, or by biting insects, such as mosquitoes.

Avipoxviruses

• Canarypox virus
• Fowlpox virus
• Juncopox virus
• Mynahpox virus
• Pigeonpox virus
• Psittacinepox virus
• Quailpox virus
• Sparrowpox virus
• Starlingpox virus
• Turkeypox virus

Tentative members

• Crowpox virus
• Peacockpox virus
• Penguinpox virus

Lab exposure

Laboratory-acquired exposures to orthopoxviruses and subsequent infections are occasionally reported among laboratory personnel. In the United States, 14 Orthopoxvirus infections were reported during 2004–2014 among personnel working in diagnostic and research facilities. However, the true number of infections might be higher as not all Orthopoxvirus infections are reported.

Diagnostic and research facilities that handle Orthopoxviruses should therefore have established procedures instructing their staff in how to prevent and respond to occupational exposures

Signs and Symptoms

Infection with orthopoxviruses can lead to localized or generalized skin lesions, progressing from papules, to vesicles and scabs. Depending on the species and strain of orthopoxvirus involved, other signs and symptoms can include fever, swollen lymph nodes, malaise, and body aches. For information, see specific signs and symptoms for various orthopoxviruses.

Infection with Vaccinia virus generally results in a localized cutaneous lesion characterized by serous and/or purulent discharge, ulceration, and necrosis. This can be accompanied by fever and lymphadenopathy.

Persons with immunocompromising conditions or other contraindications to vaccination are at increased risk for severe disease (e.g., progressive vaccinia, generalized vaccinia, eczema vaccinatum).

Risk factors for complications

The following medical conditions may increase the risk of serious complications:

• Active skin conditions (e.g., eczema, atopic dermatitis, acne, or psoriasis)
• Immunosuppressive conditions (e.g., HIV/AIDS, steroid medication)
• Pregnancy or nursing

The clinical course of Vaccinia virus or other Orthopoxvirus infection will vary depending on the route and dose of exposure, strain, and vaccination history.

Poxvirus Genera and Strains

A majority of occupational laboratory Orthopoxvirus infections reported in the United States are caused by Vaccinia virus. However, many other wild-type orthopoxviruses (e.g., camelpox, cowpox, monkeypox) can cause infections in humans.

Replication competency

Distinguishing between replication-competent and replication-deficient poxvirus strains is required to assess the risk of infection from accidental exposure:

• Replication-deficient poxvirus strains and vectors do not produce infectious virus in humans and therefore do not cause clinical infection. These include MVA, NYVAC, TROVAC, and ALVAC strains of Vaccinia virus.
• Replication-competent poxvirus strains are capable of causing clinical infection in humans as well as producing infectious virus that can be transmitted to other people. Vaccinia virus strains commonly used in laboratories include Western Reserve, Copenhagen, NYCBOH, Lister, and Temple of Heaven. Replication-competent strains may or may not have a TK gene knockout. Indeed, a majority of reported exposures to Vaccinia virus and subsequent infections involve a TK gene knockout strain. All wild-type orthopoxviruses are replication competent.

Exposure Types

• In laboratory settings, common exposures are through accidental inoculation (needle sticks) or contact with broken skin.
• Other exposures include contact with mucous membranes (e.g., ocular splashes) or inhalation.

Pre-Exposure Vaccination and Biosafety

The Advisory Committee on Immunization Practices recommends routine vaccination with live smallpox vaccine (ACAM2000) for laboratory personnel who directly handle cultures or animals contaminated or infected with:

replication-competent vaccinia virus recombinant vaccinia viruses derived from replication-competent vaccinia strains (e.g., inserted foreign gene) other orthopoxviruses that infect humans (e.g., camelpox, cowpox, monkeypox, variola virus) Vaccination is not recommended for workers that only work with replication-deficient poxvirus strains and vectors.

Laboratory personnel working with replication-competent vaccinia viruses and recombinant viruses developed from replication-competent vaccinia viruses should be revaccinated at least every 10 years. Those who handle more virulent orthopoxviruses (e.g., Monkeypox virus) should be revaccinated every 3 years.

Also see

• Smallpox
• Moneypox

Poxvirus Resources
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