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Nucleic acid-based tests can be used to identify a number of clinically
important viral and bacterial pathogens that are less common than
cytomegalovirus, hepatitis C virus, HIV, and human papilloma virus.
"These are applications where the market is not big enough for
commercial interests to pursue but for which we need good diagnostics,"
said Stephen Dumler, MD, director of the Division of Medical Microbiology,
Johns Hopkins University Hospitals. Home-brew assays offered by
Dr. Dumler’s laboratory include:
- Epstein-Barr virus and herpes simplex virus types 1 and 2 in
- HSV types 1 and 2 on vitreous humor
- varicella-zoster virus from various tissues
- JC virus in CSF for progressive multifocal leukoencephalopathy
- enteroviruses, mostly on CSF, for aseptic meningitis; also on
na-so-pharyngeal aspirates and stool
- parvovirus B19, both in amniotic fluid for hydrops fetalis and
in serum for individuals with anemia, such as aplastic sickle
- BK virus in urine for hemorrhagic cystitis in transplant recipients
- adenovirus in urine, tissues, and blood of transplant recipients
and other immunocompromised patients, such as persons infected
Dr. Dumler also offers in-house assays for several bacteria not
easily isolated and cultivated:
- Ehrlichia for human granulocytic and monocytic ehrlichiosis
- Bordetella pertussis for whooping cough
- atypical respiratory tract pathogens Legionella pneumophila
and Chlamydia and Mycoplasma pneumoniae.
Currently in a research mode are tests for Bartonella for febrile
bacteremias and catscratch fever and for Leptospira.
Dr. Dumler also offers assays for toxin genes from Staphylococcus
aureus and Streptococcus pyogenes if the clinical severity
doesn’t match what is predicted from the isolate. And he is working
out a molecular assay for Shiga-like toxin in E. coli isolates.
This latter test might make it possible to intervene earlier to
reduce progression to hemolytic-uremic syndrome; performing an additional
test for the toxin up front could lower the total cost of patient
management. "The classic example of that," Dr. Dumler said, "is
the enterovirus assay for aseptic meningitis. If you don’t treat
individuals who have proven enterovirus aseptic meningitis, you
save money overall, even if you spend more up front for diagnosis."
William Check, PhD