Orthopoxvirus
Encyclopedia
Orthopoxvirus is a genus
of poxvirus
es that includes many species
isolated from mammal
s, such as Camelpox virus, Cowpox virus, Ectromelia virus
, Monkeypox virus
, and Volepox virus, which causes mousepox. The most famous member of the genus is Variola virus, which causes smallpox
. It was wiped out using another orthopoxvirus, the Vaccinia virus, as a vaccine.
, are very specific for their hosts.
, malaise
, head and body aches, and sometimes vomiting
. Lesions that developed into crater-like ulcers surrounded by inflammatory tissue and eventually covered by thick black crusts are the characteristic indicators of orthopox infection. Severe edema
and erythema
may affect large areas in cases of severe infection. Encephalitis
(alteration of mental status and focal neurologic deficits), myelitis
(upper- and lower-motor neuron dysfunction, sensory level and bowel and bladder dysfunction), or both may result from Orthopoxvirus infection. Rarely, orthopoxviruses may be detected in cerebrospinal fluid
. Some mammalian orthopox infections are known to result in high instances of mortality.
from persons vaccinated with vaccinia vaccine. It is effective for treatment of eczema vaccinatum and certain cases of progressive vaccinia. However, VIG is contraindicated for the treatment of vaccinial keratitis. VIG is recommended for severe generalized vaccinia if the patient is extremely ill or has a serious underlying disease. VIG provides no benefit in the treatment of postvaccinal encephalitis and has no role in the treatment of smallpox. Current supplies of VIG are limited, and its use should be reserved for treatment of vaccine complications with serious clinical manifestations. The recommended dosage of the currently available VIG for treatment of complications is 0.6 ml/kg of body weight. VIG must be administered intramuscularly and should be administered as early as possible after the onset of symptoms. Because therapeutic doses of VIG might be substantial (e.g., 42 ml for a person weighing 70 kg), the product should be administered in divided doses over a 24- to 36-hour period. Doses can be repeated, usually at intervals of 2–3 days, until recovery begins (e.g., no new lesions appear). Future reformulations of VIG might require intravenous administration, and health-care providers should refer to the manufacturer's package insert for correct dosages and route of administration. CDC is currently the only source of VIG for civilians (see Vaccinia Vaccine Availability for contact information). The Food and Drug Administration
has not approved the use of any antiviral compound for the treatment of vaccinia virus infections or other Orthopoxvirus infections, including smallpox. Certain antiviral compounds (ST-246) have been reported to be 100% active against vaccinia virus or other Orthopoxviruses in vitro and among test animals. ST-246 has been granted orphan drug status by the FDA and is currently under study to determine the safety and effectiveness in humans . Gleevec, a compound FDA approved for cancer treatment limits the release of enveloped extracellular virions and protects mice from a lethal challenge with vaccinia . Currently Gleevec and related compounds are being evaluated by the CDC for their efficacy against smallpox and monkeypox. Questions also remain regarding the effective dose and the timing and length of administration of these antiviral compounds. Insufficient information exists on which to base recommendations for any antiviral compound to treat post-vaccination complications or Orthopoxvirus infections, including smallpox. However, additional information could become available, and health-care providers should consult CDC to obtain up-dated information regarding treatment options for smallpox vaccination complications (see Consultation Regarding Complications of Vaccinia Vaccine).
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of poxvirus
Poxviridae
Poxviruses are viruses that can, as a family, infect both vertebrate and invertebrate animals.Four genera of poxviruses may infect humans: orthopox, parapox, yatapox, molluscipox....
es that includes many species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
isolated from mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, such as Camelpox virus, Cowpox virus, Ectromelia virus
Ectromelia virus
Ectromelia virus is a virus of the family Poxviridae and the genus Orthopoxvirus that causes mousepox, a disease of mice. It has only been seen in mouse colonies kept for research purposes. Mousepox causes skin lesions and generalized disease, which can be fatal. It is the only poxvirus to...
, Monkeypox virus
Monkeypox virus
Monkeypox virus is the virus that causes the disease monkeypox in both humans and animals. It was first identified in 1958 as a pathogen of crab-eating macaque monkeys being used as laboratory animals. The crab-eating macaque is often used for neurological experiments...
, and Volepox virus, which causes mousepox. The most famous member of the genus is Variola virus, which causes smallpox
Smallpox
Smallpox was an infectious disease unique to humans, caused by either of two virus variants, Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, which is a derivative of the Latin varius, meaning "spotted", or varus, meaning "pimple"...
. It was wiped out using another orthopoxvirus, the Vaccinia virus, as a vaccine.
Distribution
Some orthopoxviruses have the ability to infect non-host species, such as Monkeypox virus, which is capable of establishing infection in humans. Zoonoses of many of these mammalian isolates have been reported. Others, such as Ectromelia virusEctromelia virus
Ectromelia virus is a virus of the family Poxviridae and the genus Orthopoxvirus that causes mousepox, a disease of mice. It has only been seen in mouse colonies kept for research purposes. Mousepox causes skin lesions and generalized disease, which can be fatal. It is the only poxvirus to...
, are very specific for their hosts.
Laboratory transmission
Aerosols of concentrated virus may result in orthopox infection, especially in non-immunized individuals. Needle sticks, especially with concentrated virus, may result in severe local infection of the skin even in immunized individuals.Signs and Symptoms
The initial symptoms include feverFever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
, malaise
Malaise
Malaise is a feeling of general discomfort or uneasiness, of being "out of sorts", often the first indication of an infection or other disease. Malaise is often defined in medicinal research as a "general feeling of being unwell"...
, head and body aches, and sometimes vomiting
Vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...
. Lesions that developed into crater-like ulcers surrounded by inflammatory tissue and eventually covered by thick black crusts are the characteristic indicators of orthopox infection. Severe edema
Edema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
and erythema
Erythema
Erythema is redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin. It occurs with any skin injury, infection, or inflammation...
may affect large areas in cases of severe infection. Encephalitis
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
(alteration of mental status and focal neurologic deficits), myelitis
Myelitis
Myelitis is a disease involving inflammation of the spinal cord, which disrupts central nervous system functions linking the brain and limbs. The name is derived from Greek referring to the "spinal cord", and the suffix -itis, which denotes inflammation....
(upper- and lower-motor neuron dysfunction, sensory level and bowel and bladder dysfunction), or both may result from Orthopoxvirus infection. Rarely, orthopoxviruses may be detected in cerebrospinal fluid
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...
. Some mammalian orthopox infections are known to result in high instances of mortality.
Treatment
Vaccinia-specific immunoglobulins may be administered to infected individuals. The only product currently available for treatment of complications of orthopox infection is vaccinia immunoglobulin (VIG), which is an isotonic sterile solution of the immunoglobulin fraction of plasmaBlood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
from persons vaccinated with vaccinia vaccine. It is effective for treatment of eczema vaccinatum and certain cases of progressive vaccinia. However, VIG is contraindicated for the treatment of vaccinial keratitis. VIG is recommended for severe generalized vaccinia if the patient is extremely ill or has a serious underlying disease. VIG provides no benefit in the treatment of postvaccinal encephalitis and has no role in the treatment of smallpox. Current supplies of VIG are limited, and its use should be reserved for treatment of vaccine complications with serious clinical manifestations. The recommended dosage of the currently available VIG for treatment of complications is 0.6 ml/kg of body weight. VIG must be administered intramuscularly and should be administered as early as possible after the onset of symptoms. Because therapeutic doses of VIG might be substantial (e.g., 42 ml for a person weighing 70 kg), the product should be administered in divided doses over a 24- to 36-hour period. Doses can be repeated, usually at intervals of 2–3 days, until recovery begins (e.g., no new lesions appear). Future reformulations of VIG might require intravenous administration, and health-care providers should refer to the manufacturer's package insert for correct dosages and route of administration. CDC is currently the only source of VIG for civilians (see Vaccinia Vaccine Availability for contact information). The Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
has not approved the use of any antiviral compound for the treatment of vaccinia virus infections or other Orthopoxvirus infections, including smallpox. Certain antiviral compounds (ST-246) have been reported to be 100% active against vaccinia virus or other Orthopoxviruses in vitro and among test animals. ST-246 has been granted orphan drug status by the FDA and is currently under study to determine the safety and effectiveness in humans . Gleevec, a compound FDA approved for cancer treatment limits the release of enveloped extracellular virions and protects mice from a lethal challenge with vaccinia . Currently Gleevec and related compounds are being evaluated by the CDC for their efficacy against smallpox and monkeypox. Questions also remain regarding the effective dose and the timing and length of administration of these antiviral compounds. Insufficient information exists on which to base recommendations for any antiviral compound to treat post-vaccination complications or Orthopoxvirus infections, including smallpox. However, additional information could become available, and health-care providers should consult CDC to obtain up-dated information regarding treatment options for smallpox vaccination complications (see Consultation Regarding Complications of Vaccinia Vaccine).