122 COrONAviruSES, iNCLuDiNG SArS AND mErS
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Coronaviruses, Including
COrONAviruSES, iNCLuDiNG SArS AND mErS 123
Epidemiology
Coronaviruses were first recognized as animal pathogens in the 1930s. Thirty years later, HCoVs 229E and OC43 were identified as human pathogens, along with other corona- virus strains that were not investigated further and for which little is known about their prevalence and associated disease syndromes.
In 2003, SARS-CoV was identified as a novel virus responsible for the 2002–2003 global outbreak of SARS, which lasted for 9 months, caused 8,096 reported cases, and resulted in 774 deaths. No SARS-CoV infections have been reported worldwide since early 2004.
Most experts believe SARS-CoV evolved from a natural reservoir of SARS-CoV–like viruses in bats through civet cats. Whether or not a large-scale reemergence of SARS will occur is unknown. Finding a novel HCoV sparked a renewed interest in HCoV research, and 2 years later, NL63 and HKU1 were identified as newly recognized HCoVs. Investigations have revealed that NL63 was present in archived human respiratory tract specimens as early as 1981 and HKU1 as early as 1995.
In 2012, MERS-CoV was identified as a novel virus associated with the death of a 60-year- old man from Saudi Arabia with acute pneu- monia and renal failure. As of June 11, 2014, 699 laboratory-confirmed cases and 209 deaths had been reported. MERS-CoV is thought to have evolved from a natural reservoir of MERS- CoV–like viruses in bats. An animal source for MERS-CoV has not yet been determined, but recent studies demonstrated MERS-CoV genetic sequences in dromedary camels.
Human coronaviruses 229E, OC43, NL63, and HKU1 can be found worldwide. They cause most disease in the winter and spring months in temperate climates. Seroprevalence data for these HCoVs suggest exposure is common in early childhood, with approximately 90% of adults being seropositive for 229E, OC43, and NL63 and 60% being seropositive for HKU1.
In contrast, SARS-CoV infection has not been detected in humans since early 2004. MERS- CoV has been reported in people who reside in or have traveled to the Middle East or who have had contact with a person with the infection from the Middle East, including travel-related
cases in the United States. Human-to-human transmission, including clusters of cases, has been observed, but there is no evidence of sustained human-to-human transmission in the community.
The modes of transmission for 229E, OC43, NL63, and HKU1 have not been well studied.
However, on the basis of studies of other respi- ratory tract viruses, it is likely transmission occurs primarily via a combination of droplet and direct and indirect contact spread. For SARS-CoV, studies suggest droplet and direct contact spread are likely the most common modes of transmission, although evidence of indirect contact and aerosol spread also exist.
The modes of transmission for MERS-CoV are still being studied.
Human coronaviruses 229E and OC43 are most likely to be transmitted during the first few days of illness, when symptoms and respi- ratory viral loads are at their highest. Further study is needed to confirm that this holds true for the NL63 and HKU1 viruses. SARS-CoV is most likely to be transmitted during the second week of illness, when symptoms and respira- tory viral loads peak. The peak communicable period or kinetics for MERS-CoV are not yet known.
Incubation Period
Human coronaviruses, 2 to 5 days; SARS-CoV, 2 to 10 days; MERS-CoV, 2 to 14 days.
Diagnostic Tests
The 2002–2003 SARS global outbreak garnered renewed interest in better understanding the etiology of respiratory tract infections, and some clinical laboratories have since started offering comprehensive respiratory molecular diagnostic testing for HCoVs using reverse transcriptase-polymerase chain reaction assays.
Specimens obtained from the upper and lower respiratory tract are the most appropriate sam- ples for HCoV detection. The yield from lower respiratory tract specimens is higher for SARS- CoV and MERS-CoV. Stool and serum samples are also frequently positive using reverse transcriptase-polymerase chain reaction assays in patients with SARS-CoV and have been positive in some patients with MERS-CoV. For 229E and OC43, specimens are most likely to
124 COrONAviruSES, iNCLuDiNG SArS AND mErS
be positive during the first few days of illness.
The optimal timing of specimen collection for MERS-CoV is still being studied.
Serologic testing is a useful tool for diagnosis for SARS and MERS, although these tests are not available widely. Although acute and con- valescent sera are optimal, a single serum spec- imen collected 2 or more weeks from symptom onset may help with the diagnosis of SARS or MERS because these infections are so rare. The CDC should be contacted for additional infor- mation on serologic testing.
Treatment
Infections attributable to HCoVs are generally treated with supportive care. SARS-CoV and MERS-CoV infections are more serious. Ste- roids, type 1 interferons, convalescent plasma, ribavirin, and lopinavir/ritonavir were all used clinically to treat patients with SARS, albeit without evidence of efficacy. In vitro data indi- cate that cyclosporin A and interferon alfa inhibits MERS-CoV replication. No treatment efficacy of antiviral agent for MERS-CoV has been demonstrated.
Image 35.1
Coronaviruses are a group of viruses that have a halo or crownlike (corona) appearance when viewed in an electron microscope. SArS-Cov was the etiologic agent of the 2003 severe acute respiratory syndrome (SArS) outbreak. Additional specimens are being tested to learn more about this coronavirus and its etiologic link with SArS. Courtesy of Centers for Disease Control and Prevention/Dr Fred murphy.
Image 35.2
microscopic appearance of control (A) and infected (B) vero E6 cells, demonstrating cytopathic effects.
The cytopathic effect of SArS-Cov on vero E6 was evident within 24 hours after infection. Courtesy of Centers for Disease Control and Prevention/Emerging Infectious Diseases.
COrONAviruSES, iNCLuDiNG SArS AND mErS 125
Image 35.3
Electron micrograph of a coronavirus. Pleomorphic virions average 100 nm in diameter and are covered with club-shaped knobs.
Image 35.4
This scanning electron micrograph (SEm) revealed the thickened, layered edge of severe acute respiratory syndrome–infected vero E6 culture cells. The thickened edges of the infected cells were ruffled and appeared to comprise layers of folded plasma membranes. Note the layered cell edge (arrows) seen by SEm. virus particles (arrowheads) are extruded from the layered surfaces.
Courtesy of Centers for Disease Control and Prevention/Dr mary Ng mah Lee, National university of Singapore.
126 CRYPTOCOCCUS NEOFORMANS AND CRYPTOCOCCUS GATTII iNFECTiONS
36
Cryptococcus neoformans and Cryptococcus gattii Infections
(Cryptococcosis)
Clinical Manifestations
Primary infection is acquired by inhalation of aerosolized Cryptococcus fungal elements found in contaminated soil and is often asymp- tomatic or mild. Pulmonary disease is charac- terized by cough, chest pain, and constitutional symptoms. Chest radiographs can reveal soli- tary or multiple masses; patchy, segmental, or lobar consolidation (often multifocal); or nodular or reticulonodular interstitial changes.
Pulmonary cryptococcosis can present as acute respiratory distress syndrome and mimic pneumocystis pneumonia. Hematogenous dissemination to the central nervous system, bones, skin, and other sites can occur, is uncommon, and almost always occurs in chil- dren with defects in T lymphocyte–mediated immunity (eg, children with leukemia or lym- phoma, congenital immunodeficiency, HIV infection, or AIDS; children taking cortico- steroids; children who have undergone solid organ transplantation). Usually, several sites are infected, but manifestations of involvement at one site predominate. Cryptococcal menin- gitis, the most common and serious form of cryptococcal disease, often follows an indolent course. Clinical findings are characteristic of meningitis, meningoencephalitis, or space- occupying lesions but sometimes can manifest only as subtle, nonspecific findings such as fever, headache, or behavioral changes. Cryp- tococcal fungemia without apparent organ involvement occurs in patients with HIV infection but is rare in children.
Etiology
Although there are more than 30 species of Cryptococcus, only 2 species, Cryptococcus neoformans (var neoformans and var grubii) and Cryptococcus gattii are regarded as human pathogens.
Epidemiology
C neoformans var neoformans and C neoformans var grubii are isolated primarily from soil con- taminated with pigeon or other bird droppings and cause most human infections, especially infections in immunocompromised hosts.
C neoformans infects 5% to 10% of adults with AIDS, but infection is rare in HIV-infected children. C gattii (formerly C neoformans var gattii) is associated with trees and surrounding soil and has emerged as a pathogen producing a respiratory syndrome with or without neuro- logic findings in people from British Columbia, Canada, the Pacific Northwest region of the United States, and, occasionally, other regions of the United States. A high frequency of dis- ease has also been reported in Aboriginal peo- ple in Australia and in the central province of Papua New Guinea. C gattii causes disease in immunocompetent and immunocompromised people, including children. Person-to-person transmission does not occur.
Incubation Period
C neoformans, unknown; C gattii, 8 weeks to 13 months.
Diagnostic Tests
Definitive diagnosis requires isolation of the organism from body fluid or tissue specimens.
Blood should be cultured by lysis-centrifugation.
Differentiation between C neoformans and C gattii can be made by the use of the selective medium l-canavanine glycine bromothymol blue agar. Sabouraud dextrose agar is useful for isolation of Cryptococcus organisms from sputum, bronchopulmonary lavage, tissue, or cerebrospinal fluid (CSF) specimens. In refrac- tory or relapse cases, susceptibility testing can be helpful, although antifungal resistance is uncommon. A large quantity of CSF is needed to recover the organism because CSF may con- tain only a few organisms. Cerebrospinal fluid cell count and protein and glucose concentra- tions can be normal. Encapsulated yeast cells can be visualized using India ink or other stains of CSF and bronchoalveolar lavage spec- imens, but this method has limited sensitivity.
Focal pulmonary or skin lesions can be biop- sied for fungal staining and culture.
CRYPTOCOCCUS NEOFORMANS AND CRYPTOCOCCUS GATTII iNFECTiONS 127
The latex agglutination test, lateral flow assay, and enzyme immunoassay for detection of cryptococcal capsular polysaccharide antigen in CSF are excellent rapid diagnostic tests for those with suspected meningitis. Antigen is detected in CSF or serum specimens from more than 98% of patients with cryptococcal meningitis; however, antigen test results can be falsely negative when antigen concentra- tions are low or very high (prozone effect), if infection is caused by unencapsulated strains, or if the patient is less severely immunocompromised.
Treatment
Amphotericin B deoxycholate in combination with oral flucytosine is indicated as initial ther- apy for patients with meningeal and other seri- ous cryptococcal infections. Serum flucytosine concentrations should be maintained between 30 and 80 mcg/mL. Patients with meningitis should receive combination therapy for at least 2 weeks followed by consolidation therapy with fluconazole for a minimum of 8 weeks or until CSF culture is sterile. Alternatively, the ampho- tericin B deoxycholate and flucytosine com- bination can be continued for 6 to 10 weeks.
Lipid formulations of amphotericin B can be used as a substitute for amphotericin B deoxy- cholate in children with renal impairment. If flucytosine cannot be administered, amphoter- icin B alone is an acceptable alternative and is administered for 4 to 6 weeks. A lumbar punc- ture should be performed after 2 weeks of ther- apy to document microbiologic clearance. The 20% to 40% of patients in whom culture result is positive after 2 weeks of therapy will require a more prolonged treatment course. When infection is refractory to systemic therapy, intraventricular amphotericin B can be admin- istered. Monitoring of serum cryptococcal
antigen is not useful to monitor response to therapy in patients with cryptococcal menin- gitis. Patients with less severe disease can be treated with fluconazole or itraconazole, but data on use of these drugs for children with C neoformans infection are limited. Another potential treatment option for HIV-infected patients with less severe disease or patients in whom amphotericin B treatment is not possible is combination therapy with fluconazole and flucytosine. The combination of fluconazole and flucytosine has superior efficacy compared with fluconazole alone. Echinocandins are not active against cryptococcal infections and should not be used.
Increased intracranial pressure occurs fre- quently despite microbiologic response and is often associated with clinical deterioration.
Significant elevation of intracranial pressure is a major source of morbidity and should be managed with frequent repeated lumbar punc- tures or placement of a lumbar drain.
Children with HIV infection who have com- pleted initial therapy for cryptococcosis should receive long-term suppressive therapy with fluconazole. Oral itraconazole daily or ampho- tericin B deoxycholate, 1 to 3 times weekly, are alternatives. Discontinuing chronic suppressive therapy for cryptococcosis (after 1 year or lon- ger of secondary prophylaxis) can be consid- ered in asymptomatic children 6 years or older who are receiving antiretroviral therapy, have sustained (≥6 months) increases in CD4+ T lymphocyte counts to 100 cells/mm3 or greater, and have an undetectable viral load for at least 3 months. Most experts would not discontinue secondary prophylaxis for patients younger than 6 years.
128 CRYPTOCOCCUS NEOFORMANS AND CRYPTOCOCCUS GATTII iNFECTiONS
Image 36.1
This photomicrograph depicts Cryptococcus neoformans using a light india ink staining preparation. Courtesy of Centers for Disease Control and Prevention/Dr Leanor Haley.
Image 36.2
Cryptococcus neoformans, thin-walled encapsulated yeast in cerebrospinal fluid (india ink preparation, original magnification of cerebrospinal fluid x450).
Image 36.3
This photomicrograph depicted numbers of Cryptococcus neoformans fungi, the etiologic agents responsible for the disease cryptococco- sis. This slide was created from a lung specimen and stained using the hematoxylin-eosin staining technique. Courtesy of Centers for Disease Control and Prevention/Lucille K. Georg, mD.
Image 36.4
Cryptococcosis of the liver (original magnification x810) in an immunodeficient patient with disseminated disease. The mucinous capsules are prominent. Courtesy of Edgar O. Ledbetter, mD, FAAP.
Image 36.5
Cryptococcus meningitis. Cystic lesions resulting from accumulation of organisms in perivascular spaces. Courtesy of Dimitris P. Agamanolis, mD.
Image 36.6
This micrograph depicts the histopathologic changes associated with cryptococcosis of the lung using mucicarmine stain. Cryptococcosis, caused by the fungal pathogen Cryptococcus neoformans, is transmitted through inhalation of airborne yeast cells or biospores. At risk are those who are immunocompromised, especially those with Hiv infection. Courtesy of Centers for Disease Control and Prevention/Dr Leanor Haley.