Paramyxoviridae (Measles, Mumps, Parainfluenza)

Here we'll learn about pathogenic viruses in the Paramyxovirus family (which includes measles, mumps, and parainfluenza viruses) and, the Pneumoviridae family, which includes Respiratory Syncytial Virus. Be aware that there have been significant changes in the relevant taxonomy; for example, Respiratory Syncytial Virus was formerly classified as a member of the Paramyxoviridae family. Large virions with negative-sense, single-stranded RNA Enveloped helical nucleocapsids Differentiated by surface glycoproteins, which act as viral attachment proteins:

• Hemagglutinin (H)
• Hemagglutinin-Neuraminidase (HN)
• Glycoprotein (G)
• F protein All members have this protein.

Causes fusion of host respiratory cells (F is for Fusion) Pathogenesis Transmitted via respiratory droplets (and, in some cases, via aerosol). Replicate within the cytoplasm (like most RNA viruses). Exit the host cell without lysis. Trigger the cellular immune response Necessary for viral clearance, but also contributes to the symptoms of infection; Many of these viruses are highly contagious and infections are very common. Morbillivirus genus. Hemagglutinin glycoprotein binds protein receptors. Virus enters the host via the respiratory tract, and replicates within immune cells there. Infected immune cells carry the virus to the lymphatic system, which promotes their spread. The virus can spread via direct cell-cell transmission. Viremia distributes the virus systemically. Symptoms: Fever and the "three C's": Cough, coryza (runny nose), and conjunctivitis with watery eyes. Koplik spots in the oral cavity; these white spots surrounded by reddish tissue appear on the inner cheek (buccal mucosa), near the molars. A few days after these early symptoms begin, a maculopapular rash develops; it appears first on the head and neck, then spreads to the torso and extremities. The rash is caused by the infected endothelial cells and the T-cell response. The reddish rash lends measles its alternative name, "rubeola." Measles recovery can occur with full immune protection against future infection. However, many patients experience transient immune suppression that can last weeks to years. Unfortunately, immune suppression renders the patient susceptible to opportunistic infections. Most measles-related deaths are due to complications, which are most likely to occur in adults, malnourished children, and those who are already immune compromised. Complications include: – Diarrhea – Otitis media – Pneumonia – Croup – Bronchitis – Other respiratory illnesses – Corneal ulceration and scarring (which can lead to blindness) – Encephalitis Acute disseminated encephalomyelitis (ADEM) is characterized by sudden, but brief, inflammation of the CNS. Demyelinating damage to the white matter can lead to neurological symptoms such as vision loss, muscle weakness, and jerky movements. Subacute sclerosing panencephalitis (SSPE) is caused by a mutated measles virus. Symptoms appear years after initial infection. It is characterized by relatively slow, progressive symptoms: memory loss, behavioral changes, and motor dysfunction such as myoclonic jerks; as deterioration continues, the patient becomes comatose, and eventually dies. MMR (measles, mumps, and rubella) vaccine is recommended for all children; immunization has significantly reduced child mortality in vaccinated populations. Mumps virus is a member of the Rubulavirus genus (formerly a member of Paramyxovirus genus, which has been dissolved). Hemagglutinin-Neuraminidase (HN) glycoprotein binds sialic acid on host cells. Infection may be asymptomatic. When present, common symptoms include:

• Parotitis, which produces tender, swollen parotid glands as result infection and inflammation. Other salivary glands may also be involved.
• Orchitis (inflammation of the testes), oophoritis (inflammation of the ovaries), or mastitis (inflammation of the breast tissue) may also occur.
• Meningitis or encephalitis
• Other organs, such as the heart, pancreas, and kidneys, may also be affected.

Paralysis and deafness MMR vaccine protects against the mumps virus. Now categorized into two genera (Rubulavirus genus and Respirovirus genus); like the mumps virus, these viruses were formerly classified as members of the Paramyxovirus genus. HN glycoprotein. Often associated with upper respiratory illness. More severe infections may produce lower respiratory illnesses: Croup involves the larynx, trachea, and bronchi Radiographs show a distinctive narrowing of the trachea, often referred to as the "steeple sign." Patients often have a distinctive "seal bark" cough Other lower respiratory illnesses caused by parainfluenza viruses include bronchitis, bronchiolitis, and pneumonia. No specific antivirals or vaccines to protect against parainfluenza. Formerly a member of the Paramyxoviridae, this virus is now classified as a member of the Pneumoviridae family, in the genus Orthopneumovirus. Glycoprotein G binds respiratory cells. In most healthy people, infection causes only a mild upper respiratory illness. However, in children, older adults, and immunocompromised individuals, RSV can cause acute respiratory illness. RSV-associated infections are a leading cause of death in young children worldwide; RSV causes bronchiolitis and pneumonia in children younger than one year old. Some research indicates a correlation between RSV infection and long term respiratory impairment, possibly including the development of asthma. No vaccine available (yet) Palivizumab is sometimes given as prophylaxis. In immunosuppressed patients, Ribavirin may been given to reduce the severity of RSV infection. – However, Ribavirin is not generally recommended for infants, due to inconsistencies in study results.