Clinical Manifestations
Human bocavirus (HBoV) was first identified in 2005 from a cohort of children with acute respiratory tract symptoms including fever, rhinorrhea, cough, and wheezing. Human bocavirus has been identified in 5% to 33% of children with acute respiratory tract infections.
High rates of HBoV subclinical infection also occur. The role of HBoV as a human pathogen is confounded by simultaneous detection of other viral pathogens in children with HBoV, with coinfection rates as high as 80%. Human bocavirus has been detected in stool samples from children with acute gastroenteritis, but its role in symptoms is uncertain. Nearly all chil- dren develop serologic evidence of infection by 5 years of age.
Etiology
Human bocavirus is a nonenveloped, single- stranded DNA virus in the family Parvo- viridae, genus Bocavirus. Human bocavirus replicates in the respiratory and gastrointesti- nal tracts.
Epidemiology
Detection of HBoV has been described only in humans. Transmission is presumed to be from respiratory tract secretions, although fecal-oral transmission may be possible. The frequent codetection of other viral pathogens of the respiratory tract in association with HBoV has led to speculations that it may be a true copathogen, it may be shed for long periods after primary infection (up to 75 days), or it may reactivate during subsequent viral infec- tions. Human bocavirus circulates worldwide and throughout the year. In temperate cli- mates, seasonal clustering in the spring has been reported.
Diagnostic Tests
Commercial molecular diagnostic assays for HBoV are available. Human bocavirus poly- merase chain reaction and detection of HBoV- specific antibody also are available in research laboratories.
Treatment
No specific therapy is available.
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Borrelia Infections
(Relapsing Fever)
Clinical Manifestations
Two types of relapsing fever occur in humans:
tick-borne and louse-borne. Both are charac- terized by sudden onset of high fever, shaking chills, sweats, headache, muscle and joint pain, altered sensorium, nausea, and diarrhea. A fleeting macular rash of the trunk and pete- chiae of the skin and mucous membranes sometimes occur. Findings and complications can differ between types of relapsing fever and include hepatosplenomegaly, jaundice, throm- bocytopenia, iridocyclitis, cough with pleuritic pain, pneumonitis, meningitis, and myocardi- tis. Mortality rates are 10% to 70% in untreated louse-borne relapsing fever (possibly related to comorbidities in refugee-type settings where this disease is typically found) and 4% to 10%
in untreated tick-borne relapsing fever. Death occurs predominantly in people with under- lying illnesses and extremes of age. Early treatment reduces mortality to less than 5%.
Untreated, an initial febrile period of 2 to 7 days terminates spontaneously by crisis.
The initial febrile episode is followed by an afebrile period of several days to weeks, and then by one relapse or more (0–13 for tick- borne; 1–5 for louse-born). Relapses typically become shorter and progressively milder, as afebrile periods lengthen. Relapse is associated with expression of new borrelial antigens, and resolution of symptoms is associated with production of antibody specific to those new antigenic determinants. Infection during pregnancy is often severe and can result in spontaneous abortion, preterm birth, stillbirth, or neonatal infection.
Etiology
Relapsing fever is caused by certain spirochetes of the genus Borrelia. Worldwide, at least 14 Borrelia species cause tick-borne (endemic) relapsing fever, including Borrelia hermsii, Borrelia turicatae, and Borrelia parkeri in North America. Borrelia recurrentis is the only species that causes louse-borne (epidemic) relapsing fever, and this organism has no animal reservoir.
Epidemiology
Endemic tick-borne relapsing fever is distrib- uted worldwide, is transmitted by soft-bodied ticks (Ornithodoros species), and occurs spo- radically and in small clusters, often within families or cohabiting groups. In the United States, tick-borne relapsing fever can be acquired only in western states but has been diagnosed in other states in travelers returning from these areas. Ticks become infected by feeding on rodents or other small mammals and transmit infection via their saliva and other fluids when they take subsequent blood meals. Ticks can serve as reservoirs of infec- tion. Soft-bodied ticks inflict painless bites and feed briefly (15–90 minutes), usually at night, so people are often unaware of bites.
Most tick-borne relapsing fever in the United States is caused by B hermsii. Infection typi- cally results from tick exposures in rodent- infested cabins in western mountainous areas, including state and national parks. However, infection has also occurred in primary resi- dences and luxurious rental properties.
B turicatae infections occur less frequently;
most cases have been reported from Texas and are often associated with tick exposures in rodent-infested caves. A single human infection with B parkeri has been reported;
the tick infected with this Borrelia species is associated with arid areas or grasslands in the western United States.
Louse-borne epidemic relapsing fever has been reported in Ethiopia, Eritrea, Somalia, and the Sudan, especially in refugee and displaced pop- ulations. Epidemic transmission occurs when body lice (Pediculus humanus) become infected by feeding on humans with spirochetemia;
infection is transmitted when infected lice are crushed and their body fluids contaminate a bite wound or skin abraded by scratching.
Infected body lice and ticks may remain alive and infectious for several years without feed- ing. Relapsing fever is not transmitted person to person, but perinatal transmission from an infected mother to her newborn can occur and result in preterm birth, stillbirth, and neonatal death.
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Incubation Period 2 to 18 days (mean, 7 days).
Diagnostic Tests
Spirochetes can be observed by darkfield microscopy and in Wright-, Giemsa-, or acri- dine orange–stained preparations of thin or dehemoglobinized thick smears of peripheral blood or in stained buffy-coat preparations.
Organisms can often be visualized in blood obtained while the person is febrile, particu- larly during initial febrile episodes; organisms are less likely to be recovered from subsequent relapses. Spirochetes can be cultured from blood, although these methods are not widely available. Serum antibodies to Borrelia species can be detected by enzyme immunoassay and Western immunoblot analysis at some refer- ence and commercial specialty laboratories;
a 4-fold increase in titer is considered confir- matory. These antibody tests are not standard- ized and are affected by antigenic variations among and within Borrelia species and strains.
Serologic cross-reactions occur with other spirochetes, including Borrelia burgdorferi, Treponema pallidum, and Leptospira species.
Treatment
Treatment of tick-borne relapsing fever with a 5- to 10-day course of a tetracycline, usually doxycycline, produces prompt clearance of spirochetes and remission of symptoms. For children younger than 8 years and pregnant women, penicillin or erythromycin are the preferred drugs. Penicillin G procaine or intra- venous penicillin G is recommended as initial therapy for people who are unable to take oral therapy, although low-dose penicillin G has been associated with a higher frequency of relapse. A Jarisch-Herxheimer reaction (an acute febrile reaction accompanied by head- ache, myalgia, respiratory distress in some cases, and an aggravated clinical picture last- ing less than 24 hours) is commonly observed during the first few hours after initiating antimicrobial therapy. However, the Jarisch- Herxheimer reaction in children is typically mild and can usually be managed with anti- pyretic agents alone.
Single-dose treatment using a tetracycline, penicillin, erythromycin, or chlorampheni- col is effective for curing louse-borne relaps- ing fever.
Image 20.1
Borrelia in peripheral blood smear. The spirochetes can be seen with darkfield microscopy and in Wright-, Giemsa-, or acridine orange–stained smears.
Image 20.2
Borrelia hermsii in the blood of a patient (case 3) stained with rabbit hyperimmune serum and antirabbit fluorescein isothiocyanate (scale bar, 20 mm). Courtesy of Emerging Infectious Diseases.
BORRELIA iNFECTiONS 69
Image 20.3
Borrelia hermsii in a thin smear of mouse blood stained with Wright-Giemsa and visualized with oil immersion bright-field microscopy
(magnification x600) for the confirmation of infection with relapsing fever spirochetes in humans and other animals (scale bar, 20 mm).
Courtesy of Emerging Infectious Diseases.
Image 20.4
This image depicts an adult female body louse, Pediculus humanus, and 2 larval young.
P humanus has been shown to serve as a vector for diseases such as typhus, due to Rickettsia prowazekii, trench fever caused by Bartonella (formerly Rochalimaea) quintana, and relapsing fever due to Borrelia recurrentis. Courtesy of World Health Organization.
Image 20.5
An Ornithodoros hermsii nymph. The length of the soft-bodied tick is 3.0 µm, excluding the legs.
it is responsible for transmitting endemic relapsing fever. Schwan TG, Policastro PF, miller Z, Thompson rL, Damrow T, Keirans JE. Tick- borne relapsing fever caused by Borrelia hermsii, montana. Emerg Infect Dis. 2003;9(9):1151–1154.
Image 20.6
Ornithodoros moubata ticks frequent traditional homes in sub-Saharan Africa and mainly feed nocturnally. Courtesy of Centers for Disease Control and Prevention/Emerging Infectious Diseases and Sally J. Cutler.
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