**5.10. Respiratory syncytial virus**

Respiratory syncytial virus (RSV) consists of only one serotype and is in the Paramyxoviridae family. Structurally, it consists of 10 viral polypeptides, 4 of which are associated with virus envelope, and 2 of these (F and G) are important for infectivity and pathogenicity. RSV is highly contagious, spreading via droplet and fomite exposure. RSV is the most frequent cause of lower respiratory tract infections among infants and children and the second most common viral cause of pneumonia in adults [54]. The majority of children are infected by the age of 5 years in settings such as daycare centers but the resulting immunity is incomplete. Reinfection when it occurs in older children and young adults is mild. But, with advancing age there is a greater likelihood severe disease and pneumonia. Diagnosed adult RSV hospitalizations have increased significantly in the United States. Respiratory syncytial virus hospitalizations appear to be greater in severity than influenza hospitalizations, especially immunocompromised and in older adults [55].

#### **5.11. Rhinovirus**

Many reports from the literature report that rhinovirus accounts for approximately 30% of cases of all virus-related pneumonia. Rhinovirus is considered the second most frequently recognized agent associated with pneumonia and bronchiolitis in the young. The virus is associated with asthma hospitalizations in both old and young patients [56].

**5.13. Zoonotic viral pneumonias**

ments [62].

failure [63].

causing 774 deaths [65].

rhinovirus or influenza A virus [67].

**5.14. Co-infections**

Zoonotic viral pneumonias include those caused by avian influenza, hantavirus, severe acute respiratory syndrome (SARS), and H1N1 (swine) influenza. In 1997, an influenza virus (H5N1 virus) which normally only infects only birds was found to infect humans In Hong Kong. Manifestations included pneumonia, which in some cases led to fatal acute respiratory distress syndrome (ARDS) or multisystem organ failure. The rising incidence and widespread reporting of disease from H5N1 influenza viruses can probably be attributed to the increasing spread of the virus from existing reservoirs in domestic waterfowl and live bird markets, leading to greater environmental contamination [61]. Recombinations of viruses in animals are a global concern. The H5N1 outbreak in Southeast Asia, H3N2 variant in the USA in 2012, and H7N9 avian cases in China 2013 are examples of such new threats. Effective surveillance is required to monitor such develop-

Pneumonia of Viral Etiologies

201

http://dx.doi.org/10.5772/intechopen.71608

There is a growing danger that in the future avian influenza, a subtype of influenza A, may result in a worldwide pandemic. A/H5N1 exhibits several serious characteristics, such as increased virulence and human-to-human transmission in some cases, rather than bird-to-human transmission. The disease causes high morbidity and mortality due to pneumonia and respiratory

H1N1 was first reported in Mexico and spread to the United States. The infection from a novel swine-origin influenza A (H1N1) virus rapidly spread to become a worldwide pandemic in 2009. Virus-associated hemophagocytic syndrome may play an important role in develop-

SARS is a respiratory infection caused by a coronavirus, which appears to have jumped from animals to humans. The disease was first reported in China in 2003 and rapidly spread from to the rest of the world in a 1 year period. It resulted in more than 8000 patients in 29 countries

Co-infection Infections involving both respiratory bacteria and viruses or are common. Viral infection usually occurs first, followed by a secondary bacterial infection, as observed in the influenza pandemics of 1918, 1957, and 1968 where most deaths occurred due to secondary bacterial infection. In some infections however, especially H5N1 avian influenza, the associ-

Co-infections are particularly common in 45% of children with CAP, and mainly involve pneumococcus [66], Mycoplasma pneumoniae and several species of *Chlamydophila*. CAP of mixed etiology has been characterized less in adults than in children, and prevalence is estimated at less than 5%. The most common combinations reported are pneumococcus with

ment of multiorgan failure and ensuing death in H1N1 infection [64].

ated pneumonia appears to be caused by direct viral action.

Rhinovirus is genetically diverse with more than 100 serotypes identified. In addition to common colds, reports have suggested that rhinovirus is associated with bronchiolitis, bronchitis, pneumonia and acute asthma exacerbation. Rhinovirus has been detected by molecular methods in 10–30% of hospitalized children with lower respiratory tract infections. Rhinovirus is also considered to be the second most common cause of bronchiolitis after respiratory syncytial virus (RSV) [57]. Rhinoviruses have long been known to cause common colds and exacerbations of Chronic obstructive pulmonary disease (COPD), but because rhinoviruses grow poorly at 37°C lower respiratory tract infections were thought to be rare. However, it has been demonstrated that rhinoviruses can replicate at body temperature and infect cells of the lower respiratory tract. Molecular studies have consistently identified rhinoviruses in nasopharyngeal or pharyngeal specimens from children and adults with lower respiratory tract infections. Rhinovirus has also been detected in 2–17% of adults and 4–45% of children with CAP [58].

#### **5.12. Varicella-zoster virus**

Varicella-zoster virus (VZV) is a highly contagious herpes virus and primary infection manifests as chickenpox. The reactivation in later life results in zoster (shingles). It is spread by the respiratory route or direct contact with skin lesions. This pneumonia is rare in otherwise healthy children but does occur in immunocompromised children causing life-threatening complications [59]. VZV-related community-acquired pneumonia (VZV-CAP) has become increasingly recognized as a very serious and life-threatening complication invasive mechanical ventilation in more than half of the cases. Complications include secondary bacterial infections, encephalitis, hepatitis, and, with concomitant aspirin use, Reye syndrome. VZV pneumonia also tends be more severe in individuals who smoke. In fatal cases of pneumonia, laboratory findings include extensive alveolar hemorrhage, pulmonary edema and mononuclear cell infiltration with histological evidence of intranuclear inclusion bodies.

Varicella-zoster virus pneumonia is a serious complication of disseminated varicella-zoster virus infection with mortality rates of 9–50%. In adults prevalence of varicella-zoster virus pneumonia has varied from 5 to 50% of all varicella infections. Varicella-zoster virus is a self-limited benign disease in children known as chickenpox. But in adults it causes significant complications such as varicella-zoster virus pneumonia and over 90% of cases occur in patients with lymphoma and immunocompromised patients. Patients exhibit diffuse alveolar damage, spherical nodules are seen throughout the lung parenchyma. The nodules are composed of an outer fibrous capsule enclosing areas of necrotic tissue [60].
