Parovirus B19


Parvovirus B19

Description, Causes and Risk Factors:

The large Parvoviridae (A family of small viruses containing single-stranded DNA. Virions are 18-26 nm in diameter, are not enveloped, and are ether-resistant. Capsids are of cubic symmetry, with 32 capsomeres. Replication and assembly occur in the nucleus of infected cells. Three genera in the subfamily Parvoviridae are recognized: Parvovirus, Erythrovirus, and Dependovirus, which includes the adeno-associated virus. A second subfamily, Densovirinae, has 3 additional genera, all of which infect arthropods) family includes many pathogenic animal viruses that have long been of interest to veterinarians and virologists. These viruses include feline panleukopenia virus, canine parvovirus, Aleutian mink disease virus, and porcine parvovirus, adeno-associated viruses, also members of the Parvoviridae family, appear to infect humans without causing clinical manifestations and have been used as vectors for gene transduction and gene therapy. The parvoviruses are dependent on help from host cells or other viruses to replicate. The autonomous parvoviruses propagate in actively dividing cells, whereas the adeno-associated viruses grow in tissue cultures infected with adenoviruses and herpesviruses.

Parvovirus B19 is the type member of the erythrovirus genus, which includes similar simian viruses, all of which propagate best in erythroid progenitor cells. Parvovirus B19 is a common pathogen worldwide. The virus infects and lyses erythroid precursor cells leading to a drop in reticulocyte count and transient anemia. Other cells can also be infected and their function impaired, though they do not produce infectious virus. Parvovirus B19 infection is transmitted via the respiratory route, via parenteral blood products, and vertically from viremic mother to fetus. Antibody prevalence increases progressively throughout life, reaching 30-60% in adults and 85% in the elderly. Infections occur year-round, but peak in late winter and spring. Every 3-4 years, transmission may reach epidemic levels. The highest occupational risk is found in people caring for children, such as teachers, day care workers, and homemakers.

Many infections are subclinical; however, a number of clinical manifestations can occur. Erythema infectiosum (EI) or fifth disease is a common rash illness of childhood associated with primary B19 infection. Symmetric arthropathy can occur in childhood, but is more common in adults, and can last for weeks or months. Parvovirus infection is often mistaken for Lyme disease, and occasionally for systemic lupus or rheumatoid arthritis since transient ANA and RF can occur. Less common presentations are also observed. Both the rash of EI and the arthropathy are immune mediated; therefore, IgM antibody is detectable when the patient first presents to the physician.

Transient aplastic crisis (TAC) is seen in patients with increased red cell turnover, due to B19 lysis of RBC precursors and a precipitous drop in reticulocyte counts. Patients with B19 aplastic crisis present earlier in infection, and serum IgM may not yet be detectable. Development of neutralizing antibody leads to eventual resolution of symptoms. Immunocompromised hosts, such as patients with AIDS and hematologic malignancies, can fail to produce neutralizing antibodies. Persistent B19 infection with chronic anemia can result.

Parvovirus B19 has been found in the respiratory secretions (e.g., saliva, sputum, and nasal mucus) of infected people before the onset of the rash, when they appear to "just have a cold." The virus is probably spread from person-to-person by direct contact with those secretions, such as sharing drinking cups or utensils. In a household, as many as 50% of susceptible people (those who are exposed to a family member who has parvovirus B19) may become infected. During school outbreaks of the virus, 10 to 60% of students may get fifth disease.

Symptoms:

About 25% of people infected with parvovirus B19 never develop any symptoms. Another 50% will only have flu-like symptoms, such as fever, excessive tiredness, headache, and muscle pain. The remaining 25 percent will have the classic symptoms of infection, including a rash, joint pain, and/or joint swelling. These people might have flu-like symptoms for the first week, followed by the rash and joint pain or swelling the second week.

Diagnosis:

Parvovirus B19 can cause a number of different conditions. Your healthcare provider may suspect a parvovirus infection based on your symptoms, history of medical conditions, or other findings during a physical exam.

In cases in which it is important to confirm the diagnosis, a blood test may be done to look for antibodies to parvovirus.Antibodies are proteins produced by the immune system in response to parvovirus B19 and other germs. If the immunoglobulin M (IgM) antibody to parvovirus B19 is detected, the test result suggests that the person has had a recent infection.

    Healthy Host: IgM and IgG antibodies for immunestatus, EI and arthropathy. PCR in addition to antibody ifunusual presentation, or if IgMand IgG are negative.

  • B19 infection in pregnancy: IgM and IgG antibodies in motherPCR in amniotic fluid and fetaltissues.

  • Immunodeficient host: PCR; IgM and IgG antibodies.

The finding of parvovirus B19 IgM antibodies in a blood sample is consistent with a recent infection. By comparison, only finding parvovirus B19 IgG antibodies indicates an infection some time in the past and the patient now has life-long immunity. The absence of both parvovirus B19 IgG and IgM antibodies indicates there has been no recent or previous infection and the patient remains susceptible to the disease.

Treatment:

There is no specific treatment available. If necessary, patients are given medicines to relieve their symptoms, such as analgesics for joint pain. Severe anemia in patients whose immune system is deficient or those who have chronic blood disorders can be treated with blood transfusions.

At present there is no vaccine to prevent this infection. Pregnant women should be given advice about parvovirus but there is no indication for routine antenatal screening for parvovirus B19 immunity. Any pregnant woman who comes into contact with a known or suspected case of parvovirus should consult their general practitioner or midwife. There is no reason to keep a child with parvovirus infection off school unless the child is unwell.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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