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Cryptococcosis is a sporadic, cosmopolitan mycotic
disease caused by the yeastlike fungus Cryptococcus neoformans and
its variant, Cryptococcus neoformans gattii.Cryptococcus species
reproduce by budding and vary from 4 to 20 μm in
diameter. The fungus is surrounded by a mucopolysaccharide capsule that
aids in its identification in body fluids and tissues. Of the more
than 30 species in the genus Cryptococcus, C
neoformans and C gattii are the pathogenic
yeasts of cryptococcosis. Both species cause similar clinical manifestations,
primarily in the lung and central nervous system. C neoformans is
most responsible for infection in immunocompromised individuals and
occurs worldwide. C gattii more commonly infects
immunocompetent hosts. C gattii was originally
thought to be limited to tropical and subtropical regions, but a
recent outbreak of C gattii on Vancouver Island
in Canada demonstrated a wider distribution.1
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Cryptococcosis is an opportunistic infection and occurs primarily
in patients with impaired cell-mediated immunity. Susceptibility
to the disease is markedly increased in those with T cell–immune
dysfunction. Cryptococcosis has been described in children with
AIDS, acute lymphoblastic leukemia, hyper IgM and IgE syndromes,
Bruton agammaglobulinemia, as well as in children receiving prolonged
corticosteroid therapy.2 Before the use of highly
active antiretroviral therapy (HAART), cryptococcal infection was
a major cause of morbidity and mortality in adult patients with advanced
HIV, infecting up to 10% of individuals with AIDS. In contrast,
children infrequently develop cryptococcal disease, and prevalence
rates in children with AIDS are reported to be around 1%.3,4 Interestingly,
serologic studies from urban areas in the United States have shown
that healthy asymptomatic children have high titers to cryptococcal polysaccharide.5 In
the past decade, the incidence of cryptococcosis in patients with
HIV/AIDS has significantly decreased due to the use of
aggressive antiretroviral therapy.6 However, due
to increasing numbers of solid-organ transplants and the use of
immunosuppressive agents, the number of cases of cryptococcosis
in immunocompromised, non-HIV patients continues to be high. It
is currently the third-most common invasive fungal infection behind
infections with Candida and Aspergillus in
solid-organ transplant recipients.7 Cryptococcal
basidiospores can be found in soil and in avian excrement. The organism
can withstand prolonged drying and can persist in the soil for long
periods of time. Pigeons are a frequent source, but cases have been
linked to other birds, including starlings. The birds themselves
are probably not infected, but their excreta serve as an excellent
culture medium for the organism. Human disease is believed to be
initiated by inhalation of cryptococcal cells, although infection
via the gastrointestinal tract and direct inoculation into tissues
can also be mechanisms of infection. The initial host response is
thought to be through cell-mediated immunity, and similar to infection
with Mycobacterium tuberculosis, the organism may stay
dormant for long periods of time, only becoming active when there
is a decline in the host’s immune system.
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Clinical Manifestations
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After cryptococcal cells are inhaled, they localize in ...