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Parainfluenza Virus Workup

  • Author: Subhash Chandra Parija, MBBS, MD, PhD, FRCPath, DSc; Chief Editor: Mark R Wallace, MD, FACP, FIDSA  more...
Updated: Oct 07, 2015

Approach Considerations

In human parainfluenza virus (HPIV) infection, the complete blood count (CBC) is usually within the reference range. The white blood cell (WBC) count is usually normal; however, lymphocytosis may be noted.

The diagnosis of HPIV infection can be confirmed in either of the following 2 ways:

  • Isolation and identification of the virus in cell culture or direct detection of the virus in respiratory secretions by means of immunofluorescent assay, enzyme-linked immunosorbent assay (ELISA), or polymerase chain reaction (PCR) assay
  • Demonstration of a significant rise in specific immunoglobulin G (IgG) antibodies between appropriately collected paired serum specimens or in specific immunoglobulin M (IgM) antibodies in a single serum specimen

On histologic examination, the epithelium of the respiratory tract may show inflammation and necrosis. Subglottic tissues in particular may appear to be involved.


Viral Testing

Collection and preparation of clinical specimens

Nasopharyngeal aspirations, nasal washings, and nasal aspirations are the optimal specimens, though throat and nasal swabs can also be used. Specimens should be collected and placed in viral transport media, preferably at 4°C, as the infectivity is lost at temperatures above 4°C; if a delay of more than 24 hours is anticipated, specimens should be frozen. In rare situations, nonrespiratory specimens (eg, cerebrospinal fluid [CSF], rectal swabs, or stool samples) may be used.

Paired sera (acute and convalescent phase) should be collected, separated quickly, and stored at either –20°C or –70°C; the 2 samples should be tested simultaneously.

Electron microscopy

Micro drops of secretions or garglings are placed directly on carbon-coated electron microscopy grids and stained with phosphotungstic acid. Virions typical of the Paramyxoviridae may be observed. However, the sensitivity of this study is poor.

Indirect immunofluorescence

Indirect immunofluorescent assay is normally used with antisera against each of the HPIV serotypes. However, the findings from this assay cannot be used as the sole diagnostic criterion, because its sensitivity, like that of electron microscopy, is poor.

Direct detection of viral antigens

Synthesized recombinant HPIV-1 and HPIV-3 nucleocapsid proteins in the yeast Saccharomyces cerevisiae are used as a source of viral antigens.[18] HPIV antigen can be detected with ELISA, radioimmunoassay, fluoroimmunoassay, or immunofluorescent assay; the last two tests are both rapid and specific. Shell vial assay is another method for rapid identification of HPIV. This method yields an average sensitivity of 84% in testing against standard tissue culture-positive HPIV cases.

Isolation of virus

HPIV grows best in primary monkey kidney (PMK) cells (from rhesus, cynomolgus, and African green monkeys). LLC-MK2 cells are also excellent for continued passage and are almost as good as PMK cells for primary isolation. HPIV-2 induces host ADAM8 expression in human salivary parotid adenocarcinoma cell line (HSY) during cell fusion. ADAM8 is responsible for cell-to-cell fusion and formation of multinucleate giant cells, especially osteoclasts.[19]

To recover all HPIV serotypes, trypsin (2-3 mg/mL) must be added to the maintenance medium of LLC-MK2 cells. Proteases are necessary for parainfluenza virus to replicate, and it is hypothesized that proteases present in primary cell cultures are absent in continuous cell lines.

Detection and typing

Cytopathic effects are rarely demonstrated during primary isolation of HPIV in tissue culture, except in the case of HPIV-2, which shows syncytial formation when cultured. All HPIVs demonstrate greater cytopathic effects upon adaptation to a particular cell line; HPIV-3 is the most aggressive, destroying more than 50% of tissue culture monolayer by day 3.

Viral growth is detected with hemadsorption inhibition using guinea pig erythrocytes within 3-10 days of incubation. However, the prolonged incubation time required severely restricts the usefulness of virus isolation in short-term management. The neuraminidase of HPIV-4 appears to be temperature sensitive because this virus hemadsorbs better at room temperature or 37°C, while all of the other serotypes react well at 4°C.

Serologic diagnosis

A 4-fold rise or drop in titer is generally thought to signify acute infection if the testing is performed at the same time on paired acute- and convalescent-phase serum samples. Hemagglutination inhibition, neutralization, complement fixation, ELISA, radioimmunoassay, and Western blotting are frequently used antibody-based serologic tests for diagnosis of HPIV infections.

Genomic detection

HPIV RNA can be detected directly by means of Northern hybridization or a dot blot analysis using virus-specific DNA probes. PCR assay is sensitive and specific in detecting HPIV. In one study, PCR assay yielded twice the sensitivity of cultures and 4 times the sensitivity of immunofluorescent antibody staining.[20] A multiplex reverse transcriptase PCR (RT-PCR) assay for detecting HPIV-1, HPIV-2, and HPIV-3 has been developed.

An RT-PCR enzyme hybridization assay (RT-PCR-EHA) is available for detecting HPIV types 1-4, respiratory syncytial virus (RSV) types A and B, and influenza A and B virus, with a reported sensitivity of 95-100% and specificity of 97-100% in comparison with the results of tissue culture. The RT-PCR-EHA yields results in approximately 7 hours.

A multiplex RT-PCR assay kit using a dual priming oligonucleotide (DPO) system is now available; this kit is capable of detecting 12 common viruses that cause respiratory tract infections in children.[21] A multiplex PCR assay capable of detecting 15 common viruses that cause respiratory infections has been reported.[22]


Neck and Chest Radiography

Radiographs of the neck or chest are important if epiglottitis, croup, or pneumonia is a possibility.

In patients with croup, anteroposterior views of the neck may demonstrate the classic steeple sign (ie, subglottic swelling with narrowing of the air shadow of the trachea.

Lateral soft tissue films of the neck are normal in most cases. However, such films can be useful if the diagnosis is unclear, especially if conditions such as foreign body aspiration, retropharyngeal abscess, or epiglottitis are in the differential diagnosis. In patients with epiglottitis, lateral views may demonstrate enlargement of the epiglottis and ballooning of the hypopharynx.

Contributor Information and Disclosures

Subhash Chandra Parija, MBBS, MD, PhD, FRCPath, DSc Director-Professor of Microbiology, Head of Department of Microbiology, Jawaharlal Institute, Postgraduate Medical Education and Research, India

Subhash Chandra Parija, MBBS, MD, PhD, FRCPath, DSc is a member of the following medical societies: Royal College of Pathologists, Indian Society for Parasitology, Indian Medical Association, National Academy of Medical Sciences (India), Indian Association of Medical Microbiologists, Indian Association of Biomedical Scientists, Indian Association of Pathologists and Microbiologists, Indian Academy of Tropical Parasitology

Disclosure: Received salary from Jawaharlal Institute of Postgraduate Medical education & Research , Pondicherry , India for employment.


Thomas J Marrie, MD Dean of Faculty of Medicine, Dalhousie University Faculty of Medicine, Canada

Thomas J Marrie, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, American Society for Microbiology, Association of Medical Microbiology and Infectious Disease Canada, Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

Chief Editor

Mark R Wallace, MD, FACP, FIDSA Clinical Professor of Medicine, Florida State University College of Medicine; Clinical Professor of Medicine, University of Central Florida College of Medicine

Mark R Wallace, MD, FACP, FIDSA is a member of the following medical societies: American College of Physicians, American Medical Association, American Society for Microbiology, Infectious Diseases Society of America, International AIDS Society, Florida Infectious Diseases Society

Disclosure: Nothing to disclose.


Jeffrey D Band, MD Professor of Medicine, Oakland University William Beaumont School of Medicine; Director, Division of Infectious Diseases and International Medicine, Corporate Epidemiologist, William Beaumont Hospital; Clinical Professor of Medicine, Wayne State University School of Medicine

Disclosure: Nothing to disclose.

Richard B Brown, MD, FACP Chief, Division of Infectious Diseases, Baystate Medical Center; Professor, Department of Internal Medicine, Tufts University School of Medicine

Richard B Brown, MD, FACP is a member of the following medical societies: Alpha Omega Alpha, American College of Chest Physicians, American College of Physicians, American Medical Association, American Society for Microbiology, Infectious Diseases Society of America, and Massachusetts Medical Society

Disclosure: Nothing to disclose.

Joseph Domachowske, MD Professor of Pediatrics, Microbiology and Immunology, Department of Pediatrics, Division of Infectious Diseases, State University of New York Upstate Medical University

Joseph Domachowske, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American Society for Microbiology, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, and Phi Beta Kappa

Disclosure: Nothing to disclose.

Ashir Kumar, MD, MBBS, FAAP Professor Emeritus, Department of Pediatrics and Human Development, Michigan State University College of Human Medicine

Ashir Kumar, MD, MBBS, FAAP is a member of the following medical societies: American Association of Physicians of Indian Origin and Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Russell W Steele, MD Head, Division of Pediatric Infectious Diseases, Ochsner Children's Health Center; Clinical Professor, Department of Pediatrics, Tulane University School of Medicine

Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, and Southern Medical Association

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Roy M Vega, MD Assistant Professor of Pediatrics, Albert Einstein College of Medicine; Director, Pediatric Emergency Services, Department of Emergency Medicine, Bronx Lebanon Hospital Center, Bronx, NY

Roy M Vega, MD is a member of the following medical societies: American Academy of Pediatrics

Disclosure: Nothing to disclose.

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

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Transmission electron micrograph of parainfluenza virus. Two intact particles and free filamentous nucleocapsid.
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