HMPV: Is it a Harbinger of COVID 19 ? Causes and Cure

The Chinese Center for Disease Control and Prevention published data showing that respiratory infections had risen significantly in the week of December 16 to 22, 2024; human metapneumovirus was linked to 6.2 percent of positive respiratory illness tests and 5.4 percent of respiratory-illness hospitalizations in China, more than COVID-19, rhinovirus or adenovirus. Kan Biao, head of the China CDC’s National Institute for Communicable Disease Control and Prevention, announced that the rate of HMPV among children ages 14 and under was on the rise in China. Countries like Malaysia, Hong Kong, and India have also confirmed cases of HMPV infection.

Human metapneumovirus is an important respiratory pathogen that was first discovered in 2001 by researchers at the Erasmus Medical Center in the Netherlands. Despite being relatively new in the context of human viruses, HMPV has become recognized as a significant cause of respiratory illness, especially in young children, the elderly, and immunocompromised individuals. This virus is part of the Pneumoviridae family, which also includes respiratory syncytial virus (RSV), another well-known cause of respiratory infections.

Virology

HMPV is an enveloped, single-stranded, negative-sense RNA virus. It shares structural and functional similarities with RSV, as both viruses belong to the same family. The virus has a lipid bilayer envelope that contains glycoproteins, including the fusion (F) protein and the attachment (G) protein. These proteins play crucial roles in the virus’s ability to infect host cells by facilitating the binding of the virus to cell receptors and enabling viral fusion with the host cell membrane.

The genome of HMPV is approximately 13,000 nucleotides long and encodes for several proteins that are involved in replication and the formation of the virus’s structure. The F protein is critical for viral entry into cells by mediating the fusion of the viral and host cell membranes. The G protein, on the other hand, is primarily responsible for viral attachment to host cells and is considered a key target for immune responses. Other proteins encoded by the virus include the matrix (M) protein, which aids in the assembly of new virions, and the non-structural (NS) proteins, which play a role in modulating the host’s immune response.

Transmission

HMPV is primarily transmitted through respiratory droplets, making close contact with infected individuals a primary route of spread. It can also be transmitted by touching surfaces contaminated with the virus and then touching the face, especially the eyes, nose, or mouth. The virus infects the upper and lower respiratory tract, causing symptoms that range from mild cold-like symptoms to severe respiratory distress.

HMPV infections are most common during the colder months, typically from winter to early spring, similar to other respiratory viruses such as RSV and influenza. The virus is ubiquitous worldwide, and infections occur in both developed and developing countries. Although HMPV can infect people of all ages, it is most frequently seen in children under five years of age, the elderly, and individuals with underlying health conditions such as asthma, chronic obstructive pulmonary disease (COPD), or immunodeficiency. It has also been associated with severe disease in organ transplant recipients and those with compromised immune systems.

The incidence of HMPV infection is difficult to determine accurately because the virus often causes mild symptoms that can be mistaken for a common cold or other respiratory infections. However, studies have shown that HMPV is a major cause of bronchiolitis and pneumonia in young children and is often detected in children hospitalized with respiratory illnesses.

Clinical Manifestations

The clinical presentation of HMPV infection can vary widely, ranging from mild upper respiratory symptoms to severe lower respiratory tract disease. In general, HMPV causes an illness similar to that of RSV and influenza, including symptoms such as: cough, runny nose, fever, sore throat, wheezing, and shortness of breat.

In infants and young children, HMPV infection can lead to bronchiolitis or pneumonia, both of which are characterized by inflammation and congestion in the airways and the lungs. The symptoms in these cases can be severe and may require hospitalization. Pneumonia caused by HMPV may present with fever, cough, difficulty breathing, and crackling sounds in the lungs.

In immunecompromised patients, such as organ transplant recipients or those undergoing chemotherapy, HMPV infection can be more severe and potentially life-threatening. These patients may experience prolonged symptoms and increased risks of complications like secondary bacterial infections or respiratory failure. In the elderly, the virus can also cause significant morbidity and mortality, particularly in those with pre-existing lung or heart conditions.

Diagnosis

Diagnosing HMPV infections can be challenging due to its similarity in clinical presentation to other respiratory viruses like RSV, influenza, and rhinovirus. The gold standard for diagnosing HMPV is the detection of the virus through laboratory methods, such as polymerase chain reaction (PCR) assays, which can identify the viral RNA in respiratory samples like nasal swabs, throat swabs, or bronchoalveolar lavage fluid.

Other diagnostic methods include viral culture and direct immunofluorescence, but these techniques are less commonly used due to their longer processing times and lower sensitivity compared to PCR. Serological tests, which detect antibodies against HMPV, can be useful for understanding past infections, but they are not typically used for acute diagnosis.

Treatment

There is currently no specific antiviral treatment available for HMPV infections. Management of the infection is largely supportive, aimed at alleviating symptoms and preventing complications. For mild cases, treatment focuses on symptomatic relief, such as:

Hydration

Antipyretics (fever-reducing medications like acetaminophen or ibuprofen)

Saline nasal sprays or suctioning to clear nasal congestion

Cough suppressants (if appropriate)

In more severe cases, such as those involving bronchiolitis or pneumonia, hospitalization may be required. Supportive care may include supplemental oxygen, mechanical ventilation, or respiratory support through non-invasive positive pressure ventilation (NIPPV) if the patient has difficulty breathing.

For individuals with underlying health conditions, careful monitoring and more aggressive interventions may be necessary. In immunocompromised individuals, antiviral medications such as ribavirin have been studied, though their efficacy specifically for HMPV remains uncertain. However, ribavirin is not routinely recommended as a treatment for HMPV.

Prevention

Preventing HMPV infection involves reducing the spread of the virus, particularly in settings where individuals at high risk of severe disease, such as young children and the elderly, are present. Standard preventive measures include:

Frequent handwashing

Avoiding close contact with infected individuals

Covering the mouth and nose when coughing or sneezing

Disinfecting commonly touched surfaces

For individuals at high risk, particularly those with chronic respiratory conditions or weakened immune systems, avoiding crowded places during peak respiratory virus seasons and seeking medical advice at the onset of symptoms can help minimize the risk of severe disease.

Vaccines for HMPV are not yet available, although research is ongoing. Given the similarity of HMPV to RSV, there is hope that advances in RSV vaccine development may also provide insights into HMPV vaccine development in the future.

Future Directions and Research

Despite the recognition of HMPV as an important respiratory pathogen, much remains to be understood about the virus, particularly in terms of pathogenesis, immune responses, and vaccine development. Research efforts are focusing on studying how HMPV replicates within the host and the role of the various viral proteins can provide potential targets for antiviral therapies. Investigating how the immune system responds to HMPV, including the role of innate immunity, adaptive immunity, and potential immune evasion mechanisms, is crucial for developing more effective vaccines and treatments. Given the similarities between HMPV and RSV, there is ongoing research into developing vaccines that can protect against both viruses. Advances in RSV vaccine development may offer hope for an HMPV vaccine as well. As HMPV is often clinically indistinguishable from other respiratory infections, improving diagnostic methods for rapid and accurate detection of HMPV remains an important area of research.