Parvovirus infections
Parvovirus infections are caused by small, single-stranded DNA viruses, primarily affecting humans and presenting through various strains, including B19 virus and human bocavirus (HBoV). Parvovirus B19 is highly contagious, often spreading through respiratory secretions, with peak incidence in late winter and early spring. While many parvovirus infections are asymptomatic, symptoms can range from mild flu-like manifestations to distinct rashes, such as the characteristic "slapped cheek" appearance in children. In vulnerable populations, including pregnant women and individuals with weakened immune systems, parvovirus infections can lead to severe complications like anemia or hydrops fetalis.
Screening for parvovirus infections typically involves blood tests to detect viral presence or antibodies, with no specific antiviral treatments available. Instead, management focuses on alleviating symptoms and monitoring high-risk patients. Preventative measures include proper hygiene practices, as no vaccine currently exists. Recent alerts have indicated an increase in human parvovirus B19 cases in certain regions, prompting further investigation into potential links with the COVID-19 pandemic. Understanding parvovirus infections is essential for identifying risks and implementing appropriate health measures.
Parvovirus infections
- ANATOMY OR SYSTEM AFFECTED: All
- ALSO KNOWN AS: B19 infection, bocavirus infection
Definition
Unknown to scientists until the 1960s, parvoviruses are small, simple eukaryotic viruses that contain single-strand deoxyribonucleic acid (DNA) as their genetic material. There are two parvovirus subfamilies: Densovirinae, which affects insects, and Parvovirinae, which affects vertebrates. No cross-transmission of parvovirus exists between humans and animals.
Infection in humans occurs through four known virus types: adeno-associated viruses (AAV) 1 through 6 (genus Dependoparvovirus), B19 virus (genus Erythroparvovirus; the first human virus type that was identified), human bocavirus (HBoV; genus Bocavirus), and Parv4/5 (genus Parvovirus). Scientists continue to study the potential role of parvoviruses in human disease, and new parvoviruses are still being discovered.
Causes
Knowledge about the cause of parvovirus infection is limited because parvoviruses are extremely difficult to grow in culture, although advances have been made. Routes of transmission for some parvovirus infections such as AAVs and Parv4/5 are unknown. HBoV is transmitted through respiratory droplets. AAVs 1-6 are not known to cause any human diseases. Parv4/5 has been isolated in a relatively small population, intravenous drug users who are also infected with the human immunodeficiency virus (HIV). HBoV has been associated with upper and lower respiratory tract infections and gastroenteritis.
The primary route of transmission for B19, which is highly contagious, is through direct contact with respiratory secretions or through droplet infection. Peak seasonal incidence is during late winter and early spring. More than one-half of all adults are seropositive and immune to the virus, possibly because of asymptomatic infection as children or adolescents.
A secondary route of B19 transmission is transplacental, reported to occur in approximately one-third of B19-infected pregnant women. A tertiary route is through blood and blood products.
B19 is associated with transient aplastic crisis in chronic hemolytic anemia, chronic anemia in immunodeficiency syndromes, arthritis, nonimmune hydrops fetalis, and, most commonly, erythema infectiosum (EI), a mild illness also called fifth disease (so named because it was one of five common rash-producing childhood illnesses).
For EI, incubation and transmission occur four to twenty days after viral exposure. Rash onset, approximately seventeen days after exposure, corresponds to immunoglobulin M (IgM) appearance in serum and signals the clearance of viremia.
Risk Factors
Factors increasing the chance of severe complications are pregnancy, sickle cell anemia, and compromised immunity from AIDS, chemotherapy, congenital or acquired immune disorders, and treatment with immunosuppressive drugs. Screening of persons with these conditions is advisable to determine immunity status.
During pregnancy, B19 infection, especially during the first two trimesters, may cause transplacental transmission and resultant severe fetal anemia and nonimmune hydrops fetalis, a serious condition characterized by possible intrauterine growth retardation, myocarditis, and pleural and pericardial effusions. Intrauterine blood transfusion reduces the rate of fetal death to less than 10 percent. Infection does not result in congenital malformation.
B19 infection may decrease red cell production and result in an anemia crisis in persons with anemia; it also could result in aplastic anemia or severe cytopenias in immunocompromised persons.
Symptoms
Parvovirus infection is frequently asymptomatic. When they do appear, symptoms are often nonspecific and indistinguishable from those of the common flu.
HBoV is associated with the symptoms of upper respiratory tract infection, including acute otitis media (middle-ear infection), conjunctivitis, cough, diarrhea, fever, pharyngitis, rash, rhinorrhea, sinusitis, and vomiting; lower respiratory tract infection symptoms of bronchitis, bronchiolitis, croup, exacerbation of asthma, and pneumonia; and gastroenteritis symptoms of blood in stool, diarrhea, fever, mucus in stool, and vomiting.
B19 is associated with biphasic symptoms, including fever, headache, lethargy, malaise, myalgia, nausea, pharyngitis, and rhinorrhea (five to seven days after infection) and a bright, macular exanthema on the cheeks (termed “slapped cheek”) one week later; these symptoms are followed one to four days later by a diffuse, lacy, maculopapular rash that gradually extends to the distal extremities. Rashes usually remit after one week but may reappear cyclically for several weeks in response to exercise, temperature change, sunlight exposure, or emotional stress.
Less common manifestations of B19 infection are erythema multiforme, pruritus on the soles of the feet, and papular-purpuric “gloves-and-socks” syndrome, which is an erythematous exanthema of the hands and feet ending at the wrist and ankle joints that usually occurs in young adults and is preceded by localized and painful erythema and induration. The primary clinical manifestation in adults is transient small joint arthropathy, with time to onset that parallels a rash onset in children. Symptoms usually remit within one to two weeks but may persist for months. Persons with severe anemia from transient aplastic crisis may experience fatigue, pallor, or signs of an aplastic crisis; persons with thrombocytopenia may experience bruising.
Screening and Diagnosis
Screening is done through blood tests to determine viral presence, which would indicate a recent infection; antibody presence in serum, which would indicate a prior infection and, therefore, immunity; and viral and antibody absence, which would indicate potential susceptibility to infection.
The only known method for diagnosing HBoV is through polymerase chain reaction and viral deoxyribonucleic acid detection using blood, respiratory secretions, or stool samples. For B19, the best-known diagnostic method is the IgM-antibody assay using blood or respiratory secretion samples.
Treatment and Therapy
Treatment is symptom-specific because there is no known antiviral therapy. Most infections are self-limited. Normal human immunoglobulin injections can be administered to persons at risk for severe complications. Pregnant women with a documented infection can be monitored through maternal serum a-fetoprotein screening and with ultrasound examinations to determine if the fetus requires intrauterine blood transfusion.
Prevention and Outcomes
No vaccine exists for human parvoviruses. Frequent handwashing is the most effective means of prevention. In 2024, the Centers for Disease Control and Prevention released a public health alert warning of increases in human parvovirus B19 infections in the United States. Several European countries also reported increases. Research into whether these increases were related to the COVID-19 pandemic of the early 2020s was undertaken.
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