What is parvovirus B19?

What is parvovirus B19?

Also known as fifth disease, parvovirus infection is often mild but can, in some cases, lead to potentially serious complications. What are the symptoms of this infection? Is it contagious? How to treat it? The answers of Dr Henri Agut, virologist in Paris.

Definition: what is the parvovirus responsible for erythema infectiosum or 5th disease?

Parvovirus B19 is a very small virus whose genome is DNA: we speak of a single-stranded virus. “It has no lipid envelope and is particularly resistant, retaining its infectious power for a prolonged period when it is in the external environment.” specifies Dr Agut. This virus, specific to humans, can infect people at all ages. The emblematic disease it causes is characterized by a rash. “It is called epidermal megalerythema or erythema infectiosum, but is also known as the 5th disease because in an old classification of infectious skin rashes in children, it appeared in 5th place on the list.” says the virologist.

But in addition to this skin condition, an essential property of parvovirus B19 concerns the bone marrow precursor cells which will give rise to red blood cells. “By infecting these precursor cells (or stem cells), parvovirus B19 can compromise the proper renewal of red blood cells, whose short lifespan requires them to be constantly produced.” specifies Dr Agut. Although the infection of these precursor cells has little impact in a healthy child or adult, it can, however, cause a severe deficit in the number of red blood cells, which is say anemia, in fragile subjects suffering from immunosuppression or red blood cell diseases and in the fetus.

Rash, red cheeks, joint pain: What are the symptoms of 5th disease?

A large proportion of people infected with parvovirus B19 (nearly a quarter) are asymptomatic, meaning they show little or no clinical signs of illness. When present, the disease in its benign form, the most common, is characterized by a fever and respiratory signs reminiscent of a cold, followed by a rash that typically affects both cheeks, as if the patient had received a pair of slaps.

Symptoms in children

This skin condition mainly affects children aged 4 to 10, although more discreet rashes can occur in adults. “This rash also affects other parts of the body symmetrically, particularly the trunk, arms and legs. It lasts several days, sometimes weeks, then resolves spontaneously” specifies the specialist. The rash can disappear, and reappear after exposure to heat (hot bath or shower), exposure to the sun or physical exercise and persist for a few weeks.

Symptoms in adults

Mainly in adults, pain and sometimes joint swelling may also be observed which can also last several weeks and disappear spontaneously. “The skin rash, like joint damage, is in fact the result of an interaction between viruses and the antibodies that the human body produces against them. We understand that these clinical signs in fact announce the cure of the infection and the installation of protective immunity which will prevent any new re-infection” explains Dr Agut. These antibodies are type M immunoglobulins (IgM) appearing at the time of primary infection then type G (IgG) characterizing definitive immunity.

Severe forms

Severe forms of the infection manifest themselves differently. “In children or adults suffering from diseases constituting red blood cells (sickle cell anemia or thalassemia), the early attack of the precursor cells of the bone marrow by the virus will lead to the sudden appearance or worsening of anemia with all the complications associated with it: fatigue, shortness of breath, heart problems, dizziness, etc.” describes the specialist.

In immunocompromised subjects, the lack of immune control of the viral infection leads to chronic anemia due to the absence of red blood cell renewal.

In pregnant women first infected with parvovirus B19, the virus crosses the placental barrier and infects the fetus. “Depending on the stage of pregnancy, this infection can cause spontaneous abortion or major anemia associated with fluid retention and cardiac damage with dramatic consequences for the progress of this pregnancy.” says Dr. Agut.

Causes and contagion: How do you catch fifth disease and is it contagious?

Parvovirus B19 is present in the respiratory tract and is particularly resistant. “The infected person spreads the virus into the environment (ambient air, inert surfaces) via droplets produced during breathing. People around them in turn become infected by inhaling these droplets or by putting their hands that have touched contaminated surfaces in their mouths.” explains the virologist. The virus is therefore particularly contagious and circulates constantly in the human population. It regularly causes epidemics, most often at the end of winter or beginning of spring, in nurseries, schools or in families .”It is estimated that 50 to 80% of the adult population has been infected and is therefore immune.” specifies the specialist.

Another route of transmission of parvovirus B19 is through blood. “A person who has an asymptomatic primary parvovirus B19 infection has large amounts of virus in their blood at the start of the infection. If he donates blood at this time, he risks transmitting the infection since at this stage he has not yet produced antibodies” explains Dr. Agut. It is technically very cumbersome to try to detect and exclude these blood donations, so there is no screening of blood donations for parvovirus B19 infection. The recipient of the donation contaminant will only suffer from parvovirus B19 infection if they are not immunized and this infection will only be serious if they present the risk factors (red blood cell disease, immunosuppression, pregnancy).

The last route of transmission of this virus is the transplacental route, since the virus present in maternal blood crosses the placenta and infects the fetus directly through the bloodstream.

What is the incubation period?

When the virus is transmitted by respiratory route, the incubation period of the disease is approximately one to two weeks” indicates the virologist, recalling in passing that the most obvious signs of the disease – namely the skin rash and joint damage – occur with the appearance of antibodies, which explains this relatively long incubation period.

In severe forms causing anemia, this appears within a variable time period depending on the initial state of the blood count and the regeneration of red blood cells. “The anemia is all the more brutal because the patient was already, before the infection, in a state of precarious balance regarding these cells.” specifies the specialist.

Finally, regarding fetal damage, clinical signs are often detected delayed, most often on ultrasound, especially later if the maternal infection was asymptomatic and did not constitute a warning sign.

Diagnosis of the malady

As the virus is very abundant in the blood at the start of infection, it is, in theory, easy to detect its DNA and quantify it using a PCR method. “However, this examination is rarely performed in this context because the clinical signs at this stage are absent or not very specific and the disease which may subsequently occur will be benign in the majority of cases.” explains Dr. Agut. “On the other hand, the direct search for viral DNA by PCR is essential in the face of anemia or fetal damage as soon as the responsibility of parvovirus B19 is suspected.” specifies the latter.

Another way to diagnose parvovirus B19 infection is to look for antibodies in the circulating blood using an ELISA type technique. This diagnosis can only give a positive result after two to three weeks of infection. The detection of IgM diagnoses the recent nature of the infection, that of IgG is a little later and reflects the appearance of protective immunity. “This serological diagnosis is especially of interest in pregnant women, since it allows the diagnosis of a recent infection which will prompt careful fetal monitoring. On the contrary, the notion of the presence of IgG before pregnancy is a sign of immunity protecting the mother and the fetus.” sums up the specialist.

Treatment: How to treat it in adults, children and pregnant women?

There is no vaccine or antiviral medication that can specifically prevent or treat parvovirus B19 infection. Prevention is therefore the main way to protect yourself from this virus.

It is a non-specific prevention, which involves the isolation of infected people (when the diagnosis has been made early, which is rather rare) to prevent respiratory transmission of the virus to those around them. This isolation is all the more useful if this environment is a community or includes a pregnant woman or a person at risk of serious illness.

When the disease is declared, the treatment is symptomatic, and consists of giving analgesics and…