Vol

DEPARTMENT OF PATHOLOGY
The Johns Hopkins Medical Institutions

Vol. 18, No. 21
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Monday, June 7, 1999

Provided by Leslie Edwards Reger, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.

(May 31 - June 5, 1999) 6 total outbreaks: 5 outbreaks of foodborne gastroenteritis involving food-service facilities: 3 at restaurants, 1 at a catered event held at the facility, 1 at a catered event held at another location and 1 acute febrile respiratory disease outbreak at a nursing home.

The Johns Hopkins Hospital. Information provided by Stephanie Schreiner, M.D., Department of Pathology.

Clinical Presentation A 57 year-old Hispanic female presented to the Internal Medicine Clinic on 4/9/99 with the chief complaint of persistent fevers. She had been in Puerto Rico visiting her family from 1/26/99 to 4/5/99 and since her return, she had been experiencing persistent fevers to 103⁰ F, generalized arthralgias and myalgias. She denied headaches, neck pain, cough, sore throat, nausea, vomiting, diarrhea, dysuria, rashes, and lymphadenopathy. She had been taking Tylenol and Motrin with limited relief. She did note that her brother in Puerto Rico had had similar symptoms while she was there visiting and that he had been diagnosed with dengue fever (DF). Her past medical history is remarkable for hypertension, asthma, and depression. Physical exam was remarkable only for an elevated temperature of 39.4⁰ C. Laboratory values were remarkable for the following: WBC = 1,990 (53% polys, 29% lymphs), plts = 69K, AST = 111, ALT = 134 and alk phos = 311. Serologies for dengue virus were also sent. She was sent home on Tylenol and ibuprofen PRN. She returned to the clinic for follow-up on 4/15/99 with complete resolution of her fever. She did report, however, that she had had a short outbreak of a rash on her palms which resolved within 48 hours. Results of the ELISA for dengue were positive for IgG and negative for IgM. Dengue virus culture was also negative. Repeat CBC and LFT's were normal. Dengue Viruses

Background

The dengue viruses are flaviviruses (formerly group B arboviruses), which, in addition to DF include the viruses that cause St. Louis encephalitis and yellow fever. There are four antigenically related but distinct viruses, serotypes 1 to 4. Unique genotypes of each serotype also exist and can be traced to specific geographic regions. Dengue viruses occur world-wide in tropical regions but infections are most prevalent in Southeast Asia where all four serotypes are continuously present. In Puerto Rico, dengue serotypes 1,2 and 4 have circulated continuously since 1985. In the United States, most cases of dengue fever have been acquired abroad. It is estimated that greater than 100 million cases of DF occur annually throughout the world. The principal vector is the adult female mosquito Aedes aegypti with humans being the intermediate host. In the United States and parts of South America, another vector, A. albopictus, may play a role in interhuman transmission. Vertical transmission of dengue viruses in Aedes species has also been documented. Dengue virus replication occurs within monocytes/macrophages during an incubation period of 2 to 7 days following the mosquito bite. Virus is present in blood early in the course of illness and may be recovered from serum or mononuclear cells. During this viremic stage, humans are also infectious for other mosquitos. Clinical Presentation Systemic symptoms are believed to result from the release of cytokines as a result of injury to monocytes and their interaction with activated CD4+ T cells. DF begins with the abrupt onset of high fever, chills, headache, retrobulbar and lumbosacral pain, conjunctival congestion, puffiness of the eyelids, and facial flushing. Fever may be sustained for up to 6 to 7 days or may have a biphasic pattern. Initial symptoms are followed by generalized myalgia, bone pain, anorexia, nausea, vomiting, and/or weakness. Respiratory symptoms are often seen in children. Leukopenia is usually present with an absolute granulocytopenia and the platelet count may fall below 100K. A transient, generalized macular rash may appear on the first or second day. A secondary maculopapular or morbilliform rash may also appear at the time of defervescence (day 3 to 5) or shortly thereafter. The secondary rash usually appears first on the trunk, spreading to the face and limbs. A second phase of fever may also occur with accompanying lymphadenopathy, cutaneous hyperesthesia, and metallic taste sensation. Myocarditis and various neurologic disorders have also been associated with DF. Convalescence may be prolonged with generalized weakness, depression, bradycardia, and ventricular extrasystoles.

In a subset of individuals who experience secondary infection with a heterologous serotype, a severe immunopathologic disease occurs, "dengue hemorrhagic fever" (DHF). Although immunity acquired after infection with one serotype confers probable lifelong protection against reinfection with that serotype, it may predispose to DHF on sequential infection with another dengue serotype. Hemorrhagic phenomena include petechiae, epistaxis, intestinal bleeding and menorrhagia. Recent studies have demonstrated structural differences in dengue virus genome sequences from viral types associated with DF versus those that may cause DHF.

Diagnosis Diagnosis may be made by the isolation of virus from blood during the first 3 to 5 days of illness. Mosquitos (Toxorhynchites) inoculated by intrathoracic injection are sensitive hosts for virus isolation. Virus can be identified by this technique within 10 to 14 days using immunofluorescence. Cells of monkey and mosquito origin are most useful for virus isolation and antigen may be detected by immunofluorescence within a few days. More rapid diagnosis has been achieved using immunocytochemical staining of peripheral blood mononuclear cells, but this method has not proven to be reliable. Reverse transcriptase-PCR has also been applied to the rapid diagnosis of dengue infections. Serologic diagnosis uses an ELISA for IgM and IgG antibodies. An acute sample should be obtained during the febrile phase of the illness followed by a second specimen 2-3 weeks later. A positive IgM on a single serum sample provides a presumptive diagnosis but demonstration of at least a fourfold rise (or fall) in antibodies should be documented for a positive result. In primary infections, the IgM/IgG ratio generally exceeds 1.5, whereas secondary infections are characterized by an excess of IgG. The plaque-reduction neutralization test or epitope-blocking ELISA, using monoclonal antibodies, may be used to distinguish specific from cross-reacting antibody responses. Treatment Treatment is supportive and includes bed rest, fluid replacement if indicated, antipyretics and analgesics. Aspirin should be avoided due to a possible association between DF and Reye's syndrome, as well as the possibility of hemorrhagic complications. References

1.   Fields BN ed. et al: Virology, third ed. Lippincott-Raven, Philadelphia, 1996, pp 997-1004, 1016-1023.
2.   Koneman EW et al: Diagnostic Microbiology, fifth ed. Lippincott, Philadelphia, 1997, pp. 1199-1200.
3.   Leitmeyer KC et at: Dengue virus structural differences that correlate with pathogenesis. J Virol 1999 Jun; 73(6): pp. 4738-47.
4.   Richman DD et al: Clinical Virology. Churchill Livingstone, New York, 1997, pp.1164-1171.