Parvovirus B19 and infections
Parvovirus B19 (or Erythrovirus B19) is the first human virus officially recognized as belonging to the family of Parvoviridae and the genre of Erythrovirus.
Parvovirus B19 owes its particular name to the (purely random) way in which it was discovered: the pathogen was first isolated in 1975, in a petri dish labeled precisely "B19", during a screening study to search for a hepatitis antigen in a serum.
Incidence of infections
Infections sustained by Parvovirus B19 are extremely common: from the medical statistics reported in the journal Red Book: Report of the Committee on Infectious Diseases, it is clear that:
- 5-10% of children between the ages of 2 and 5 are HIV-positive for Parvovirus B19
- 50% of children between the ages of 6 and 15 are HIV-positive for Parvovirus B19
- 60% of adults (from 30 years of age) are HIV-positive
- 90% of the elderly (aged> 60 years) have been affected by Parvovirus B19
The initial attack of Parvovirus B19 confers permanent immunity.
The death rate associated with Parvovirus B19 infections is extremely low: infections tend to resolve within a short time.
Parvovirus B19 affects males and females equally, with no sex predilection. However, it appears that females are significantly more prone to developing complications (especially arthritis) after Parvovirus B19 infections. Immunocompromised patients are more at risk of Parvovirus B19 infections.
Characteristics of the virus
Parvovirus B19 is a single-stranded DNA virus of rather small size (18-25 nanometers). It is equipped with an icosahedral capsid, consisting of 2 structural proteins (which enclose the DNA), endowed with immunogenic activity; the capsid is not equipped with a casing. The DNA strands show a positive or negative polarity: they are incorporated separately in the virions (viral particles).
B19 is a fairly stable virus: it is resistant to temperatures of 60 ° C for 16 hours, and survives in ether and chloroform.
Parvovirus B19 shows a marked predilection for nucleated cells of the erythroid series (precursors of erythrocytes): these cells have a specific receptor (globoside P) and are in continuous proliferation. From what has been said we understand how simple viral replication is.
Transmission
Parvovirus B19 is mainly transmitted by air through the inhalation of respiratory secretions (droplets of saliva). However, Parvovirus B19 can also be transmitted through infected blood transfusions, bone marrow transplant or maternal-fetal route ( during the passage of the fetus through the birth canal).
Parvovirus B19 has an estimated incubation time of around 13-18 days: the infection is contagious until the skin rash appears (distinctive element of Parvovirus B19 infections).
Infections
In most cases, Parvovirus B19 triggers acute infections, sometimes asymptomatic (25% of affected patients), accompanied by nonspecific prodrome, such as fever, skin rash and flu-like symptoms.
The most recurrent infection of all, carried by Parvovirus B19, is the INFECTIOUS ERITEMA, also known as the fifth disease (in reference to the fifth typically childhood infectious pathology described in medicine).
Along with rubella, the sixth disease and measles, the fifth disease is one of the protagonists of childhood rashes related to viruses.
The disease is therefore a "contagious viral infection, even if of a minor entity, and self-limiting: it is characterized by the formation of immune complexes in the endothelium".
In some sensitive or predisposed individuals, however, Parvovirus B19 can trigger serious complications, such as:
- Loss of the fetus (when contracted during pregnancy)
- Hydrops fetalis (accumulation of fluid in two or more fetal compartments)
- Reactive arthritis
- Hemolytic sickle cell anemia
- Acute haemolytic anemia + leukopenia + reduction in the number of erythrocytes
- Chronic myeloid leukemia
Less frequently, Parvovirus B19 triggers different skin reactions, such as PURPLE, Erythema MULTIFORME, rubella-like SKIN RUSH, and papulopurpuric lesions.
Parvovirus B19 rarely causes ARTHROPATHIES in the hands, wrists, knees and ankles.
- A certain correlation has been observed between genetic predisposition to rheumatoid arthritis / juvenile arthritis, and propensity to arthropathies after Parvovirus B19 infections.
Other possible correlations have been hypothesized between Parvovirus B19 infections and idiopathic thrombocytopenic purpura, fulminant hepatitis, vasculitis, myocarditis and meningoencephalitis.
Therapy
Therapy depends on the symptoms triggered by Parvovirus B19. Fifth disease, for example, does not require any specific therapy, since it tends to self-resolve spontaneously within a few days. In any case, children affected by Parvovirus B19 can take antipyretic drugs to reduce fever, thus reducing the healing times Antihistamines are indicated in case of itching.
In the event of complications from Parvovirus B19 (e.g. fetal hydrops), intrauterine blood transfusion (transfusion of fetal blood into the uterus) may be necessary.
Patients with sickle cell anemia, also affected by Parvovirus B19, require blood transfusions.
Immunocompromised patients should be treated by injection of human immunoglobulins: by doing so, Parvovirus B19 is more easily removed.
