Page 1007 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

738 PART 5: Infectious Disorders

immunization, there is sudden onset of fever, headache, and myalgia, LASV was first identified in 1969, in a missionary nurse who had
with progression to a severe multisystemic illness (hypotension, lived in Lassa, a Nigerian village. There is a lot of genetic variation
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thrombocytopenia, renal failure, abnormal liver function, respiratory among the strains. 67
failure, pulmonary infiltrates, pleural effusion, myocarditis, and enceph- Pathogenesis LASV binds to the α-dystroglycan receptor on endothelial
alitis) with a 60% mortality rate. Vaccine virus is readily isolated. The risk cells, resulting in a noncytolytic infection and production of high num-
of YEL-AVD is only 0.3 to 0.5 per 100,000 doses overall, but increases bers of virions. In severe LF, there is high, sustained viremia because the
with age over 60 and prior thymus disorder. 56-59 host is unable to control viral replication, probably due to virus-induced
Infection Control and Prevention of Nosocomial Transmission YF requires BSL-3. Strict immunosuppression. LASV impairs endothelial cell function: Increased
precautions for VHFs are required until YF is confirmed. microvascular permeability causes cervicofacial edema and pleural effu-
sions, and endothelial dysregulation causes profound and refractory
Omsk Hemorrhagic Fever: Omsk hemorrhagic fever (OHF) was recog- hypotension. In even severe LF, bleeding is limited to mucosal surfaces,
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nized in 1941 in western Siberia in persons exposed to muskrats or there is no liver failure, thrombocytopenia is mild, and disseminated
their skins. The virus (OHFV) was isolated in 1947. The natural cycle intravascular coagulation is uncommon. 68
involves the meadow tick Dermacentor reticulatus and small animals.
Muskrats introduced from Canada to western Siberia in the thirties are Epidemiology LASV infects an estimated 300,000 to 500,000 and kills 5,000
highly susceptible and shed OHFV for weeks, which amplified the natu- to 10,000 people yearly in Western Africa. 67,69 The prevalence of LASV
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ral cycle. After a short incubation (3-7 days), patients develop sudden antibody ranges from 7% to 20% in endemic regions. LF occurs in
onset of a high fever with headache, myalgias, conjunctival injection, rural areas where Mastomys natalensis lives around homes. The rodent
and flushing of the face and neck. Bleeding from mucosal surfaces is is present in most of sub-Saharan Africa, but the geographic distribu-
typical, and severe cases may be complicated by gastrointestinal bleeding tion of LF is restricted to West Africa, from Senegal to Cameroon, with
and hemoptysis. Some patients have a rash. Most improve within 1 to most outbreaks reported in Sierra Leone, Nigeria, Liberia, and Guinea.
2 weeks but about a third develop a second fever with recurrence of the LASV transmission requires heavy precipitations: Modeling based on
initial symptoms, bleeding, meningoencephalitis, renal involvement, or environmental factors predicts a risk map of LF that covers 80% of Sierra
pneumonia. The mortality rate is 1% to 2%. Leone and Liberia, 50% of Guinea, 40% of Nigeria, 30% of Côte d’Ivoire,
The diagnosis is confirmed by serology (OHFV IgG ELISA). 60 Togo and Benin, and 10% of Ghana. Higher risk of human infection is
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associated with substandard housing and rodent infestation. Persons
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Kyasanur Forest Disease: Kyasanur forest disease (KFD) causes HF in who hunt, cook, and eat these rodents are at increased risk.
Karnataka State in south India. People are infected through the bite Secondary person-to-person transmission occurs within villages
of Haemaphysalis spinigera ticks, which feed on monkeys and other through direct contact with an infected person or a corpse during
animals. After a short incubation, there is sudden onset of fever, along funeral rituals. Infections of health care workers in hospitals have been
with headache, back pain, myalgia, vomiting, diarrhea, cough, and reported in West Africa, always due to contaminated medical equipment
conjunctival injection, followed in some patients by hemorrhagic mani- or direct contact with blood, tissues, respiratory secretions, or excreta
festations and neurological complications. Encephalitis may develop 1 to of an infected person. Aerosol transmission has not been documented.
2 weeks after apparent recovery. The case-fatality rate is 2% to 10%. A Adherence to universal precautions and barrier nursing precautions
formol-inactivated vaccine is used in India, but its efficacy is limited. 61,62 prevents nosocomial transmission.
Alkhurma Hemorrhagic Fever: Alkhurma hemorrhagic fever virus (ALKV) LF is readily exported to nonendemic countries due to the high preva-
causes HF in Saudi Arabia and in travelers returning from Egypt. The lence in West Africa and long incubation period. LF has been identified
natural cycle involves camels, sheep, and soft ticks (Ornithodoros savi- in travelers treated in the USA at least six times. 10,12,13 No secondary cases
gnyi). Humans get infected when butchering camels and sheep, drinking have been documented. 10
unpasteurized milk, or through tick bites. There is sudden onset of fever, The Clinical Spectrum More than 80% of human infections with LASV are
headache, myalgia, arthralgia, vomiting, and in severe cases bleeding mild or asymptomatic. About 5% of infected persons may be hospital-
(epistaxis, ecchymoses, petechiae, hematemesis) or neurologic complica- ized, and only 1% to 2% of all infections result in death. However,
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tions (encephalitis) with a high case-fatality rate. KFDV and AHFV about 15% to 20% of hospitalized patients die. Infection of pregnant
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share >90% sequence homology, suggesting a common ancestral origin. women results in a high fetal demise (75%-92%) and maternal mortality
Alkhurma virus might be a variant of KFD. 62 (7% in the first trimester, 30% in the second or the third trimester, and
■ ARENAVIRIDAE 50% if postpartum). 67
The incubation period is between 3 and 21 days. Onset is insidious, with
Arenaviridae are enveloped, negative-sense, single-stranded RNA gradually increasing fever, headache, myalgia, backache, and arthralgias.
viruses. Arenavirus refers to the granular appearance of virions: These Within a few days, most patients have a severe sore throat (with a pharyngeal
grainy particles are ribosomes acquired from the host cell. The genome exudate or oral ulcerations), cervical lymphadenopathy, a nonproductive
is divided in two segments. 64 cough, retrosternal chest pain, and conjunctivitis. Gastrointestinal symp-
The family Arenaviridae contains a single genus, Arenavirus, divided in toms may appear (vomiting, diarrhea, and abdominal pain).
two groups, the Tacaribe serocomplex (New World arenaviruses), which A minority of patients develop florid LF. They have cervicofacial swelling,
includes Junin, Machupo, Guanarito, and Sabiá viruses, and the Lassa- subconjunctival hemorrhages, and lung involvement. Bleeding is evident
Lymphocytic choriomeningitis serocomplex (Old World arenaviruses), only in a minority (blood oozing from the nose, mouth, gastrointestinal
which includes two African VHF-causing arenaviruses: Lassa fever virus tract, and puncture sites) but is usually not hemodynamically significant.
(LASV) in West Africa and Lujo virus, the cause of a small nosocomial A maculopapular or petechial rash is often observed in Caucasians. Severe
outbreak in South Africa. All are category A bioterrorism agents. LF manifests as shock and multiorgan failure. Neurologic complications
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Each arenavirus causes chronic infection of a specific rodent reservoir (encephalopathy, meningitis, cerebellar syndrome) may appear late in the
and humans get infected when exposed to rodents or their excreta. course. Pericarditis, uveitis, and orchitis are seen. One-third of survivors
develop unilateral or bilateral sensorineural hearing loss.
Lassa Fever Patients with severe LF have thrombocytopenia, lymphopenia, neu-
The Pathogen and the Life Cycle LASV chronically infects the multimammate trophilic leukocytosis, hemoconcentration, elevated BUN, and protein-
rat (Mastomys natalensis), which lives in and around rural houses, food uria. Poor prognosis is independently associated with high viremia,
storage areas, and crop fields. The rodent excretes LASV in its urine, elevated AST above 150 IU/L, and bleeding. Infection during the third
saliva, and respiratory secretions. Humans get infected when exposed to trimester of pregnancy carries a high maternal mortality and universal
the rats or their aerosolized urine. fetal loss. Delivery improves maternal survival. 72

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