Table of Contents
Human parainfluenza viruses (HPIVs) belong to the Paramyxoviridae family and cause infections in the upper and lower respiratory tracts. There are four types of HPIVs (1-4), each responsible for different symptoms and diseases. This research paper will thoroughly explore HPIVs. Firstly, it will analyze the characteristics of the virus with emphasis on its genome, capsid shape, envelope, and class according to the Baltimore classification. Secondly, it will cover the diseases caused by the viruses and exhaustively discuss croup, its symptoms, effective prophylaxis, and treatment. Finally, the paper will present estimates of incidence, prevalence, and mortality rate and explore the ways of transmission of HPIVs as well as susceptible populations.
The viral genome contains ribonucleic acid (RNA) with approximately 15000 nucleotides. HPIVs belong to Class V of the Baltimore classification. Class V viruses contain single-stranded, negative-sense RNA. These viruses cannot be directly accessed by the host ribosomes to form proteins; they first should be transcribed by viral polymerases into “readable forms.” HPIVs have a thick nucleocapsid that has a helical shape. HPIVs are pleomorphic enveloped viruses, and their envelope is derived from the host cell (Henrickson, 2003).
HPIVs primarily affect infants and children; however, they may also attack adults. HPIV-1 and HPIV-2 cause croup in children, while HPIV-3 is mostly associated with bronchiolitis and pneumonia (Pringle, 2014). HPIV-4 has two subtypes (4A and 4B) and causes less severe infections. It is rarely included in screening panels for acute respiratory illnesses. The common symptoms of infection caused by HPIVs include chest pain, cough, fever, runny nose, sore throat, wheezing, appetite loss, vomiting, and diarrhea (Centers for Disease Control and Prevention [CDC], 2015).
Croup, caused by HPIV-1 and HPIV-2, is an inflammation of the upper airways, including the voice box (larynx), windpipe (trachea), and bronchial tubes (bronchi). The swelling obstructs airflow and results in labored breathing. It is more frequent in boys than girls, and the peak incidence is at 6-36 months. The first symptoms of croup are similar to the ones of a cold and include a blocked or runny nose as well as fever. When the inflammation progresses, the voice may become hoarse, and the child may develop a rough, barking cough. As the swelling worsens, the breathing becomes labored, and stridor (high-pitched noise) may be heard with inhalation. In serious cases, children develop cyanosis (bluish color of the mucous membranes and skin) due to the lack of oxygen. The symptoms of croup get worse at night or when a child cries (Chamberlain, 2014).
Currently, there are no vaccines to protect individuals against infection caused by HPIVs. However, frequent hand washing and avoiding contact with people having viral infections, especially during the early and most contagious stages, help to prevent infection. Additionally, disinfecting surfaces that may harbor viruses prevents infection as well. Breastfeeding may protect a baby against infection due to antibodies contained in mother’s milk (CDC, 2015).
There is no specific antiviral treatment for croup and other infections caused by HPIVs as they disappear on their own. Most cases are mild, and therapies are mainly aimed at relieving symptoms and making patients comfortable until they recover. Acetaminophen or ibuprofen can be given to children over six months to ease fever and pain. Using a cool-mist humidifier or running a hot shower to create a steam-filled bathroom can help to relieve the patient’s sore throat and cough. Individuals also should have good rest and drink much fluid. Doctors may use corticosteroids to reduce airway inflammation and improve breathing in case of blockage. Oxygen may sometimes be used if the patient experiences labored breathing (Chamberlain, 2014).
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HPIV-1, HPIV-2, HPIV-3, and HPIV-4 have worldwide distribution; however, the epidemics mostly occur with HPIV-1. As it has already been mentioned, the highest rates of serious illnesses occur among young children. Mortality from HPIVs is a rare occurrence in developed countries, and deaths mainly happen in high-risk groups. Infections of the lower respiratory tract cause 25-30% of total deaths in all pre-school children living in developing countries. HPIVs are responsible for 10% of these cases (Parija, 2015).
HPIVs are spread from an infected person to others via respiratory secretions and droplets while coughing or sneezing. They can also be spread through close contact with an infected individual, for example, through a handshake. Additionally, a person can catch the viruses by touching contaminated surfaces or objects and then touching the nose, eyes or mouth. Depending on environmental conditions, HPIVs can stay hours in the air and on surfaces and still cause infections (CDC, 2015).
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HPIVs primarily affect children and cause about 30-40% of all acute respiratory tract infections in infants and young children. The aging population and immunocompromised people are also at high risk of acquiring HPIV infections and developing serious complications. Such factors as malnutrition, vitamin A deficiency, lack of breastfeeding, overcrowding, and environmental contaminants predispose individuals to these infections (Henrickson, 2003).
In summary, there are four types of HPIVs, and their genome contains ribonucleic acid. These viruses are responsible for croup, pneumonia, and bronchiolitis. The symptoms of HPIV infection include a cough, runny nose, sore throat, and wheezing. Such measures as hand washing, avoiding contact with infected people, and disinfecting surfaces help to prevent infection. There is no specific treatment for HPIVs, and therapies mainly aim to relieve symptoms. Corticosteroids, much fluid as well as rest, acetaminophen, ibuprofen, and cool-mist humidifiers help patients to recover. Deaths from HPIVs mainly occur in developing countries. Viruses spread via droplets, handshake, close contact, and touching contaminated surfaces or objects. The risk groups include infants, children, the elderly, and immunocompromised individuals.