Recognizing and treating new and emerging infections encountered in everyday practice STEVEN M. GORDON, MD NFECTIOUS DISEASES, pre- MiikWirj:« Although infectious diseases were once considered a dicted earlier in this cen- diminishing threat, new pathogens are constantly challenging tury to be eliminated as a the health care system. This article reviews the clinical presen- public health problem, re- tation, diagnosis, and treatment of seven emerging infections I main the chief cause of death that primary care physicians are likely to encounter. worldwide and a significant cause of death and morbidity in i Parvovirus B19 attacks erythrocyte precursors; the United States.1 Challenging infection is usually benign and self-limiting but can cause the US public health system are aplastic crises in patients with chronic hemolytic disorders. several newly identified patho- Hemorrhagic colitis due to Escherichia coli 0157:H7 infection gens (eg, human immunodefi- can lead to the hemolytic-uremic syndrome, especially in chil- ciency virus [HIV], Escherichia dren; it also can cause thrombotic thrombocytopenia purpura. coli 0157:H7, hepatitis C) and a Chlamydia pneumoniae causes a mild pneumonia that resem- resurgence of old diseases pre- bles mycoplasmal pneumonia. Bacillary angiomatosis primar- sumed to be under control (eg, ily affects immunocompromised patients, especially those tuberculosis, syphilis). Further, infected with human immunodeficiency virus (HIV). At least multiple-drug resistance in two organisms can cause bacillary angiomatosis: Bartonella hense- strains of pneumococci, gono- lae and Bartonella quintana. Hantavirus pulmonary syndrome cocci, enterococci, staphylo- is spread by exposure to the droppings of infected rodents. cocci, salmonella, and mycobac- Contrary to previous thought, HIV continues to replicate teria undermines efforts to throughout the course of the illness and does not have a latency control the diseases they cause.2 phase. Ehrlichiosis is a tick-borne disease that resembles This paper gives an overview of Rocky Mountain spotted fever. some old and new emerging in- fectious diseases of significance INDEX TERMS: COMMUNICABLE DISEASES; DISEASE OUTBREAKS to primary care clinicians. CLEVE CLIN ] MED 1996; 63:172-178 WHAT IS AN 'EMERGING' From the Department of Infectious Diseases, The Cleveland Clinic INFECTION? Foundation. Address reprint requests to S.M.G., Department of Infectious Diseases, Desk S-32, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Emerging infections either Cleveland, OH 44195. E-mail address: [email protected] have newly appeared or are rap- 172 CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 63 • NUMBER 3 Downloaded from www.ccjm.org on September 27, 2021. For personal use only. All other uses require permission. EMERGING INFECTIOUS DISEASES • GORDON idly increasing in incidence or geographic range. Polyarthralgia syndrome Recent examples include outbreaks of plague in Arthritic symptoms, which are more common in Surat, India and of Ebola virus infection in Zaire. adults, may be the sole manifestation of parvovirus Most emerging infections are not caused by genu- B19 infection. Rubella and parvovirus B19 infection inely new pathogens. Complex ecological, environ- cause similar clinical syndromes in young women, mental, and demographic factors precipitate the but now that the incidence of rubella is decreasing emergence of disease by placing nonimmune people and rubella vaccines have been modified to elimi- in increased contact with a pathogen or its natural nate arthritis-causing strains, parvovirus host or by promoting dissemination. The current arthropathy may be more common. Adults seldom volume, speed, and reach of international travel have the typical slapped-cheek appearance, and make the emergence of infectious diseases truly a only 50% have a rash. Within several days after global problem. infection a symmetrical, self-limiting polyarthritis suddenly appears that most often affects the hands. PARVOVIRUS B 1 9 Like other viral arthritides, parvovirus arthritis is thought to be immune-mediated. Parvovirus B19, a single-stranded DNA virus, was discovered serendipitously in 1975 by electron Aplastic crisis in patients microscopy during a study of transfusion-associated with hemolytic disorders hepatitis. It is the smallest DNA virus known to Parvovirus B19 preferentially parasitizes infect mammalian cells, measuring approximately erythroid precursors in the bone marrow, transiently 25 nm (by comparison, Herpes virus measures 160 suppressing production of red blood cells. This sup- nm, HIV 225 nm). Parvovirus B19 replicates only in pression usually does not decrease the hematocrit in human erythroid progenitor cells, and has been healthy people, as the infection is self-limiting and propagated in the laboratory in bone marrow, pe- brief. However, in patients with chronic hemolytic ripheral blood, fetal liver cells, and a few he- disorders (eg, thalassemia, sickle cell anemia), who matopoietic cell lines with erythroid characteristics. depend on a high rate of production of erythrocytes, The virus is heat-stable and can be transmitted via or in patients with chronic immunosuppression (eg, blood products. in patients with HIV infection), parvovirus B19 in- 4 Parvovirus B19 is the only parvovirus known to fection may result in acute aplastic anemia. infect humans, and causes a wide spectrum of ill- nesses (see below).3 Parvovirus infection in pregnancy Parvovirus B19 can cross the placenta and infect Erythema infectiosum (fifth disease) the fetus, leading to hydrops fetalis and, sometimes, This illness has been recognized since the late fetal loss. Because of the considerable (and under- 19th century, when communicable diseases that standable) public concern, it is important to counsel cause rashes were classified using a numbering sys- pregnant patients that the risk to the fetus is rela- tem (1, measles; 2, scarlet fever; 3, rubella; 4, tively low, as the illness is usually self-limiting in Duke's disease or epidemic pseudoscarlatina; 5, immunocompetent patients. There is currently no erythema infectiosum; and 6, roseola)—hence the recommendation to routinely screen pregnant name "fifth disease." Erythema infectiosum is usu- women for parvovirus B19 infection. Parvovirus in- ally a mild childhood illness characterized by a fection is not an indication for therapeutic termina- facial rash (called "slapped-face disease" because it tion of pregnancy. The American Association of features reddened cheeks) and a lace-like rash on Pediatricians does recommend that pregnant health the trunk and extremities. The rash may recur care workers avoid caring for patients at high risk for after exposure to nonspecific stimuli such as tem- active parvovirus B19 infections (patients admitted perature changes, sunlight, and emotional stress. to the hospital with aplastic anemia or known par- Usually, the patient is otherwise well when the vovirus B19 infections). rash appears but reports mild systemic symptoms that began 1 to 4 days previously. The symptoms Diagnosis are usually self-limiting but may persist for several Unlike most viruses, parvovirus B19 infects one months. highly differentiated cell type, the human erythro- MAY • JUNE 1996 CLEVELAND CLINIC JOURNAL OF MEDICINE 173 Downloaded from www.ccjm.org on September 27, 2021. For personal use only. All other uses require permission. EMERGING INFECTIOUS DISEASES • GORDON progenitor. The P antigen, a cellular receptor on the E coli 0157:H7 is a verotoxigenic E coli (VTEC). erythrocyte, has recently been identified as the par- Verotoxins cause diarrhea and are similar to the vovirus B19 virus receptor.5 Persons without the P Shiga toxin produced by Shigella in classic dysentery. antigen are naturally resistant to parvovirus B19 Because the clinical signs of E coli 0157:H7 infec- infection.6 Of note, parvovirus B19 may also infect tion involve hemorrhagic colitis, the organism is endothelial cells. This ability may allow transfusion also referred to as an enterohemorrhagic E coli through the placenta and also may contribute to the (EHEC). Of note, according to an ongoing study facial rash of fifth disease. from the Centers for Disease Control and Preven- Parvovirus B19 infection can be diagnosed by iso- tion (CDC), E coli 0157:H7 causes more cases of lating the virus's DNA from peripheral white blood bloody diarrhea in the United States than Shigella cells (using polymerase chain reaction [PCR] tech- does, accounting for 8% of them.8 However, al- nology) or by serologic testing for specific IgG or IgM though more attention has been focused on E coli (using radioimmunoassay and enzyme immunoassay 0157:H7, Shigella dysenteriae is likely the most com- based on the antibody capture principle with solid- mon cause of the hemolytic-uremic syndrome in phase polystyrene beads). In a patient with anemia children worldwide. and a low reticulocyte count, the presence of a giant pronormoblast in a bone marrow aspirate is very Clinical presentation suggestive of parvovirus B19 infection. E coli 0157:H7 infection causes abdominal pain and watery diarrhea, followed within a few days by Treatment bloody diarrhea (hence the name "hemorrhagic co- Immunoglobulin has been used to treat aplastic litis"). The bloody diarrhea corresponds to the dys- anemia caused by parvovirus B19 infection in im- entery phase of shigellosis, although E coli 0157:H7 munocompromised patients. does not cause true dysentery because it does not invade enterocytes. Sequelae include