Poxviruses are a complex group of viruses that primarily cause vesicular lesions. They are the largest pathogenic viruses that attack humans, and are the only ones visible under a light microscope. They cause, among others diseases such as smallpox, cowpox or molluscum contagiosum.

Pokswirusy ( Poxviridae , from English pokkes - pocket) belong to the subfamilyChordopoxvirinae , generaOrthopoxvirus andMolluscipoxvirus . With the exception of the three most important viruses: smallpox, vaccinia and molluscum contagiosum, sporadic infections in humans can be caused by numerous zoonotic orthopoxviruses.

Poxviruses - common features

Common features of poxviruses include :

  • complex structure of the virion and lack of spiral or Ixosahedral symmetry
  • dimensions 230-450 / 140-250
  • replication of poxviruses takes place in the cytoplasm, which is unusual for DNA viruses
  • poxvirus genome is linear, double-stranded DNA and is 120-375 kbp long

Thanks to the multi-layer coat with a high protein content, they are quite resistant to disinfectants and antiseptics.

Orthopoxvirus diseases - smallpox

Smallpox is an infectious rash disease with a high mortality rate. Two forms of smallpox were distinguished: the most severe - with a mortality of 50% and a milder one, in which the mortality was about 1%.

The smallpox virus ( Variola virus ) belongs to the genusOrthopoxvirus . It was transmitted mainly by droplets, but the direct contact of infectious material with the pustules also played an important role. The patient was contagious from the time the fever appeared until the last scab fell off.

  • Clinical picture of smallpox

In the first phase of infection, the virus multiplied in the upper respiratory tract and lymph nodes, and then led to primary viraemia, followed by an asymptomatic period lasting about 4-14 days. After an incubation period of 12 days on average, the patient developed prodromal symptoms:

  • fever (usually>40 degrees C)
  • muscle aches
  • feeling unwell

A few days after the onset of the fever, pustules were forming inside the mouth and throat. As a resultThe spread of the virus through the bloodstream during secondary viraemia, a rash occurs that was the result of viral replication in the blood vessel lining and in the dermis. A single skin lesion has undergone changes of the type:

lump → vesicle → pustule → scab

with each stage lasting 1-2 days.

The rash appeared first on the face, then on the hands and feet. It passed over the shoulders and torso, but still dominated the center of the body. There were scars after the scabs had fallen off. Severe patients developed serious complications, such as encephalitis and a hemorrhagic form of disease associated with DIC and general toxaemia.

  • Smallpox diagnosis

The diagnosis was facilitated by inclusion bodies, or Guarnieri bodies found in infected epithelial cells. The virus is able to multiply in chicken embryos and in tissue cultures.

  • Smallpox diagnosis

Each case in which a smallpox infection is suspected must be reported and proceeded in accordance with the action plan of the State Sanitary Inspectorate.

Laboratory virological diagnostics includes electron microscopy of material from skin lesions. Cultivation of the virus in cell lines, evaluation of the cytopathic effect and virus identification. Standard methods are PCR, real-time PCR. The RFLP technique or sequencing of selected regions of the viral genome is used for strain typing or isolation.

The methods used in serological tests are the virus neutralization test with the patient's blood serum and the hemagglutination inhibition test. However, they do not distinguish between a humoral response from an infection and a vaccine one. For serological evaluation of acute infection, an ELISA test for specific IgM antibodies is useful.

  • Smallpox treatment and prevention

Thiosemicarbazones, the antiviral drugs routinely used to treat smallpox prior to eradication, showed limited efficacy.

The treatment regimen for the diagnosis of smallpox includes the intravenous administration of cidofovir and the simultaneous administration of the vaccine after exposure. Human immunoglobulin, which contains a high titer of antibodies to the smallpox virus, is also an effective drug, but its use is currently limited to exceptional situations only.

It is assumed that people vaccinated (in Poland before 1980) have at least partial immunity to the disease.

Diseases caused by poxviruses - cowpox

Cow pox is zoonosis - it means that mainly animals get sick, but the virus can also attack humans. For cow pox, the incubation period for cows is 4 to 8 days, and for pigs it is 2 days.

  • Cowpox symptoms in animals

Domestic Cattle - Symptoms are similar to those of cow pox. They mainly affect the udder and take the form of skin lesions. The disease lasts from 4 to 6 weeks. It ends with recovery.

Pigs - pigs, especially piglets, have skin changes.

  • Symptoms of cowpox in humans

People get sick rarely, so far over 100 cases of vaccinia have been described. The main symptoms are:

  • vesicular-papular rash
  • feeling unwell
  • fever
  • lymph nodes enlargement
  • tonsillitis

The prognosis of patients infected with the vaccinia virus is good. Only symptomatic treatment is applied.

Diseases caused by poxviruses - molluscum contagiosum

  • Clinical picture and course of the contagious mollusc

The virus multiplies only in squamous cells. It is transmitted through direct contact, through sexual contact, and through everyday objects. It manifests as a hard lump, sometimes surrounded by a rim, in adolescents and adults most often on the genitals and inner surfaces of the thighs, in children around the face, and in people with reduced immunity, the lesions are diffuse. Once healed, there may be cavities that disappear or leave scars.

  • Identification of the contagious mollusk

Diagnosis is made on the basis of clinical symptoms, in case of doubt, diagnostics can be extended with microscopic examination.

  • Treatment of contagious mollusks

Invasive treatment

  • laser therapy
  • extraction under local anesthesia or curettage
  • liquid nitrogen cryotherapy

Drug treatment

Diffuse lesions should be treated with antihistamines, immunomodulating and antiviral preparations.

Spot lesions can be treated with preparations with salicylic or glycolic acid, podophyllotoxin, tretinoin, potassium hydroxide.

Other poxvirus diseases

  • monkey pox virus - occurs in Africa, causes a disease very similar to small pox, with a high mortality rate
  • sheep pox virus (ORFV) - zoonosis, if it occurs in humans, does not require treatment
  • alleged viruscowpox (PCPV) - zoonosis, if it occurs in humans, does not require treatment, in the course of the formation of characteristic nodules, the so-called milking machine nodules
  • Tanapox virus(TANV) - occurs in Africa, spreads through bites, causes a minor fever disease
About the authorNatalia MłyńskaStudent of medicine at the Medical University of Lodz. Medicine is her greatest passion. He also loves sports, mainly running and dancing. She would like to treat her future patients in such a way as to see them as a human being, not only a disease.

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