Human parainfluenza viruses are the etiologic agents causing 'human parainfluenza.' hPIVs are a group of four distinct serotypes of enveloped single stranded RNA viruses belonging to the paramyxovirus family. These viruses are closely associated with both human and veterinary disease. hPIV remains the second main cause of hospitalisation in children under 5 years of age suffering from a respiratory illness (only respiratory syncytial virus causes more respiratory hospitalisations for this age group).

Classification The taxonomic division is broadly based on antigenic and genetic characteristics, forming four major serotypes. These include: 1- Human parainfluenza virus type 1 (hPIV-1) (most common cause of croup) 2- Human parainfluenza virus type 2 (hPIV-2) (causes croup and other upper and lower respiratory tract illnesses) 3- Human parainfluenza virus type 3 (hPIV-3) (associated with bronchiolitis and pneumonia) 4- Human parainfluenza virus type 4 (hPIV-4) (includes subtypes 4a and 4b). Parinfluenza virus 1 and 3 belong to the paramyxovirus genus. Parainfluenzavirus 2, 4a and 4b belong to the rubullavirus genus along with mumps. Respirovirus (hPIV-1 & hPIV-3) and the Rubulavirus (hPIV-2 & hPIV-4) No common group antigen, though some degree of cross reactivity can be demonstrated with the different serotypes and the mumps virus.

Viral structure and organisation

Disease Virus type Minor upper respiratory disease 1, 3, 4 Bronchitis 1, 3 Bronchopneumonia 1, 3 Croup 1, 2, 3 In general, types 1 and 2 cause outbreaks of respiratory disease in the fall, which include colds, pharyngitis, tracheobronchitis and croup. Although parainfluenza 3 may produce croup, more typically, it produces a spectrum of infection that closely mimics that produced by RSV, including bronchiolitis and pneumonia.

Pathogenesis Parainfluenza viruses enter the host through the inhalation of infected droplet nuclei. Virus multiplication occurs throughout the tracheobronchial tree, inducing the production of mucus. The vocal cords of the larynx become grossly swollen, causing obstruction to the inflow of air, which is manifested by inspiratory stridor. In adults, the virus is usually limited to causing inflammation in the upper parts of the respiratory tract. In infants and young children, the bronchi, bronchioles and lungs are occasionally involved, which may reflect on the small size of the airways and the relative immunological immaturity. Viraemia is neither an essential nor a common phase of infection. Reinfections with parainfluenza viruses are common. Duration of parainfluenza virus shedding is about 1 week after onset of illness; some children may excrete virus several days prior to illness. Type 3 may be excreted for up to 4 weeks after onset of primary illness. This persistent shedding from young children facilitates spread of infection.

Interactions with the environment : Parainfluenza viruses last only a few hours in the environment and are inactivated by soap and water. Furthermore, the virus can also be easily destroyed using common hygiene techniques and detergents, disinfectants and antiseptics. Environmental factors which are important for hPIV survival are pH, humidity, temperature and the medium the virus in found within. The optimal pH is around the physiologic pH values (7.4 to 8.0), whilst at high temperatures (above 37°C) and low humidity, infectivity reduces. The majority of transmission has been linked to close contact, especially in nosocomial infections. Chronic care facilities and doctors surgery's are also known to be transmission 'hotspots' with transmission occurring via aerosols, large droplets and also fomites (contaminated surfaces).

Mumps Virus Infections : Mumps is an acute contagious disease characterized by nonsuppurative enlargement of one or both salivary glands. Mumps virus mostly causes a mild childhood disease, but in adults complications including meningitis and orchitis are fairly common. More than one-third of all mumps infections are asymptomatic. Pathogenesis & Pathology :- Humans are the only natural hosts for mumps virus. Primary replication occurs in nasal or upper respiratory tract epithelial cells. Viremia then disseminates the virus to the salivary glands and other major organ systems. Involvement of the parotid gland is not an obligatory step in the infectious process. The incubation period may range from 2 weeks to 4 weeks but is typically about 14–18 days. Virus is shed in the saliva from about 3 days before to 9 days after the onset of salivary gland swelling. About one-third of infected individuals do not exhibit obvious symptoms (in apparent infections) but are equally capable of transmitting infection. It is difficult to control transmission of mumps because of the variable incubation periods, the presence of virus in saliva before clinical symptoms develop, and the large number of asymptomatic but infectious cases.

Prevention, & Control :- An effective attenuated live-virus vaccine made in chick embryo cell culture is available. It produces a subclinical, noncommunicable infection. Mumps vaccine is available in combination with measles and rubella (MMR) live-virus vaccines. Combination live-virus vaccines produce antibodies to each of the viruses in about 78% to 95% of vaccinees. There is no increased risk of aseptic meningitis after MMR vaccination. Measles (Rubella) Virus Infections :- Measles is an acute, highly infectious disease characterized by fever, respiratory symptoms, and a maculopapular rash. Complications are common and may be quite serious. Pathogenesis & Pathology :- Humans are the only natural hosts for measles virus, although numerous other species, including monkeys, dogs, and mice, can be experimentally infected.

The virus gains access to the human body via the respiratory tract, where it multiplies locally; the infection then spreads to the regional lymphoid tissue, where further multiplication occurs. Primary viremia disseminates the virus, which then replicates in the reticuloendothelial system. Finally, a secondary viremia seeds the epithelial surfaces of the body, including the skin, respiratory tract, and conjunctiva, where focal replication occurs. Measles can replicate in certain lymphocytes, which aids in dissemination throughout the body. During the prodromal phase (2–4 days) and the first 2–5 days of rash, virus is present in tears, nasal and throat secretions, urine, and blood. The characteristic maculopapular rash appears about day 14 just as circulating antibodies become detectable, the viremia disappears, and the fever falls. The rash develops as a result of interaction of immune T cells with virus-infected cells in the small blood vessels and lasts about 1 week.

The most common complication of measles is otitis media (5–9% of cases). Pneumonia is the most common life-threatening complication of measles, caused by secondary bacterial infections, while the central nervous system Complications are the most serious one. Treatment, Prevention, & Control :- Vitamin A treatment in developing countries has decreased mortality and morbidity. Measles virus is susceptible in vitro to inhibition by ribavirin, but clinical benefits have not been proved. A highly effective and safe attenuated live measles virus vaccine has been available since Measles vaccine is available in monovalent form and in combination with live attenuated rubella vaccine (MR) and live attenuated rubella and mumps vaccines (MMR).

Risk factors : Numerous factors have been suggested and linked to a higher risk of acquiring the infection, inclusive of malnutrition, vitamin A deficiency, absence of breastfeeding during the early stages of life, environmental pollution and overcrowding.