Human metapneumovirus (hMPV) is classified in the Pneumovirinae subfamily like human respiratory syncytial virus (RSV). It belongs to the Paramyxoviridae family. Genetically, hMPV is closely related to avian metapneumovirus (formerly known as turkey rhinotracheitis virus). The researchers from Netherlands were the first to describe hMPV in the year 2001. The virus was first isolated from stored nasopharyngeal samples using polymerase chain reaction (PCR). hMPV has been observed and identified across all countries except Antarctica.
Human metapneumovirus is a single-stranded RNA-enveloped virus. There are two major groups (A and B). Also 4 subgroups of hMPV have been identified.
Pathophysiology Of Human Metapneumovirus
Very rare case studies of human metapneumovirus pathophysiology have been reported. Two cases from Argentina have successfully measured the cytokine levels in nasal washes taken from infected subjects. These were compared with cytokine levels found in influenza and RSV. They found that hMPV infection produces a low level of adaptive and innate cytokine response.
Many animals have been used to study the pathophysiology of hMPV. The only animal which demonstrated similar symptomatology with human disease was chimpanzee. Studies on viral time course revealed a peak of viral load at 4-5 days after infection.
Epidemiology In United States And Other Countries
Human metapneumovirus is spread worldwide. This belief is based on the high prevalence of antibodies against the virus in all age groups and the widespread detection of hMPV infection.
In temperate climates, most hMPV infections mimics that in the United States. They usually occur in the winter and spring season. In the tropical regions, peak viral activity occurs during the same months (studies from Hong Kong).
Mortality Rates
hMPV is known to cause disease in all age groups. It is the second leading cause of lower respiratory tract disease in children. It accounts for up to 10% of hospitalizations for pediatric respiratory illnesses.
The Age factor
Initial infections occur in early childhood. Most of the individuals seroconvert by 5 years of age. By age 10, the sreopositivity rate reaches 100%. But reinfection is possible and hMPV disease has been documented in adult patients.
