Bocavirus Infection (HBoV, Human Bocavirus)

Respiratory virus

• Bocavirus members of the Parvoviridae virus family are small (20 nm) and non-enveloped viruses with single-stranded DNA.
• Bocavirus is usually found in infants and children who are hospitalized with pneumonia or diarrheal symptoms.
• Bocavirus is often detected in patients who are infected with other viruses.
• Although some investigators suspect bocavirus causes infection and disease, there is no definitive proof that bocavirus causes illness or disease, either alone or with other viruses.
• There are no diagnostic tests or medical treatments for bocavirus; researchers detect bocavirus with a PCR test that is not widely available.
• There is no specific treatment for bocavirus infection, but supportive care, such as rest, fluids, and over-the-counter medications to relieve symptoms, can help manage the illness. 
• There is no vaccine available for bocavirus.
• Research in the next few years should better define what role, if any, bocavirus plays in human infections and diseases.

Bocavirus (also termed HBoV or human bocavirus) is a small (20 nm in size) non-enveloped virus with a single strand of DNA that comprises its genome. The bocavirus genus is a member of the Parvoviridae family, and to date, three strains have been identified: HBoV-1, HBoV-2, and HBoV-3. Bocavirus is a new viral genus that was discovered in 2005 in upper respiratory secretions from acutely ill children. The name bocavirus was derived by combining the names bovine parvovirus with canine minutevirus with which bocavirus shares some genetic and structural characteristics. The ICTVdB (International Committee on Taxonomy of Viruses database) has detailed its genome and structure.

Most bocavirus infections are respiratory and associated with HBoV-1. The symptomatic disease affects the very young, between ages 6 and 24 months. Bocaviruses can infect adults, but adults seem much less likely to have symptoms. The exact cause of bocavirus infection is not fully understood, but it is believed to be spread through respiratory secretions, such as coughing or sneezing.

Although this virus has been found worldwide in humans and animals, there is ongoing research and discussion about this virus as being a pathogen that causes infection, either alone or in conjunction with other virus types. Many investigators consider this newly discovered virus genus as an "emerging viral pathogen" because it is only proven to be associated with infections but not yet proven to be a cause of them, either alone or in conjunction with other viruses. However, another member of the Parvoviridae family, a parvovirus termed B19, causes erythema infectiosum (fifth disease or "slapped cheek" syndrome), hydrops fetalis (severe anemia in pregnant women), and aplastic crisis (cessation of red blood cell production) in individuals that have sickle cell disease. Bocavirus has not been associated with these conditions caused by parvovirus B19.

Because bocavirus is a newly detected virus, many basic studies are still being planned or are ongoing. Consequently, conclusions about how the virus is spread are based on suppositions that are supported by some scientific findings but not yet proved by scientific tests. Since the virus can be detected in high numbers in the respiratory tract and in respiratory secretions of some hospitalized patients, investigators suggest that bocavirus is mainly spread to other humans by respiratory secretions. However, it can also be found in stools (diarrhea) and in blood, so there may be alternative ways for the virus to spread.

Unfortunately, to date, there are no animal or viral cell culture systems to investigate bocavirus strains. It is clear, however, that from the few epidemiological studies done bocavirus can be found worldwide in about 1.5%-19% of the population, usually in sick children.

Because bocavirus is usually only found in individuals (usually in infants, children, and infrequently in young adults) with lower respiratory infections or diarrhea, these are the following common symptoms and signs associated with the presence of bocavirus:

• ARTI (also termed RTIs, acute respiratory tract infections), especially in infants and children
• Cough
• Wheezing
• Fever
• Cyanosis (bluish or grayish tint to the skin due to lack of oxygen)
• Rhinorrhea (runny nose)
• Sore throat
• Diarrhea
• Vomiting
• Difficulty breathing: This is a rare but severe symptom that can occur in infants and your children.

Infants and children with these nonspecific symptoms often are very ill and require hospitalization. It is important to note that it is not clear yet that bocavirus is either completely or partially responsible for these signs and symptoms. Currently, most of the clinical articles that discuss bocavirus describe patients with at least several of the symptoms and signs listed above, with pneumonia as the major problem. Some investigators report months of bocavirus shedding (having tests demonstrate the presence of the virus in body secretions) in patients with cancer (leukemia), but the significance of this shedding is not clear.

Most investigators agree that bocavirus "infection" is a diagnosis by association as the virus has not yet proven to be definitively responsible for a disease state. There are no commercially available tests for any bocavirus strains.

Researchers, however, use a polymerase chain reaction (PCR) to detect viruses in nasopharyngeal aspirates (NPA) and samples of blood and diarrhea. These PCR tests detect the genetic material of the viruses, but the PCR tests are not widely available. Many researchers use the terms "detected bocavirus" or "associated with" instead of "definitively diagnosed with bocavirus infection" when they discuss the patients with symptoms described above. However stated, many investigators who work with these ill children clearly suspect bocavirus is playing some role in the disease process.

There is no treatment, medical or antiviral, that is known to effectively target bocavirus strains. A few investigators suggest that since there is no definitive evidence that bocavirus causes infection or disease, either alone or in combination with other viruses, there should be no treatment directed toward bocavirus.

Other investigators believe that since bocavirus strains are usually associated with patients with respiratory or gastrointestinal symptoms, treatments should be considered. Currently, the only available treatments (for example, oxygen, respiratory support, and hydration) are for the relief of symptoms since no specific anti-bocavirus treatments are available.

Some measures that can help manage and relieve the symptoms of bocavirus infection include:

• Getting plenty of rest: Resting can help the body fight off the infection and reduce symptoms.
• Drinking fluids: Drinking plenty of fluids, such as water, tea, or broth, can help prevent dehydration and keep mucus thin.
• Over-the-counter medications: Over-the-counter medications, such as acetaminophen or ibuprofen, can help reduce fever and relieve pain.
• Humidifiers or steamy showers: Breathing in the steam from a humidifier or shower can help relieve nasal congestion and cough.
• Oxygen therapy or mechanical ventilation: In severe cases where respiratory distress is present, oxygen therapy or mechanical ventilation may be required to support breathing.

The prognosis of patients with bocavirus detected is unclear because it is not known if bocavirus is responsible, alone or in part, for any disease or infection. However, when bocavirus strains are detected, they are frequently found associated (from about 45%-93% of patients tested by experienced investigators) with other viruses known to cause infections. The viruses that are identified in association with bocavirus are of several different types:

• RSV (respiratory syncytial virus)
• Adenovirus
• Parainfluenza virus
• Enterovirus
• Herpes simplex virus

As research on bocavirus progresses, other types of associated viruses are likely to be found. The prognosis for patients with these viruses is usually good, especially if patients are seen and treated by a medical caregiver early in the infection. However, for a few patients who develop severe symptoms with these viral infections, the prognosis may range from fair to poor.

Bocavirus strains have not yet been shown definitively to cause infection; prevention methods await development and are likely to be investigated if these viruses are shown to participate in causing infection. Currently, there is no vaccine in development for human use.