Cryptococcus is a
type of fungus that is found in the soil worldwide, usually in
association with bird droppings. The major species of Cryptococcus that
causes illness in human is Cryptococcus neoformans. Another
less common species that can also cause disease in humans, Cryptococcus gattii, has been
isolated from eucalyptus trees in tropical and sub-tropical regions
Infectious agent:
Cryptococcus neoformans, an encapsulated yeast-like fungus. There
are two principal variants:C. neoformans var. neoformans (serotypes A & D) and C. neoformans var. gattii (serotypes B & C).
Identification:
Clinical features :
Cryptococcal infection usually presents as sub-acute or chronic meningoencephalitis
with headache and altered mental state. Lung involvement may cause symptoms of
lower respiratory tract infection or may be asymptomatic. Skin, bone and other
organs are less frequently infected
Method of diagnosis:
Encapsulated budding forms of the fungus may be seen in the CSF,
urine or pus using Indian ink staining. Cryptococcal antigens may also be detected
in the CSF and serum. The diagnosis is confirmed by culture (CSF, blood, sputum
or andurine) or by histopathology (Mayer’s mucicarmine
staining). Pulmonary cryptococcosis in non-HIV infected persons
usually manifests as a nodule which must be distinguished from a malignancy.
Malignancies may co-exist.
Incubation period:
The incubation period is unknown. Pulmonary infection may
precede infection in other sites by months or years.
Public health significance and occurrence:
Human infection is rare in the absence of immunosuppression.
Persons at increased risk of infection include patients with impaired immunity
due to HIV/AIDS infection, corticosteroid therapy, lymphoma or sarcoidosis. Cryptococcal
infections occur sporadically in all parts of the world. Adults are more
commonly infected with males more commonly infected than females.
Reservoir:
Cryptococcus has saprophytic growth in the external
environment. C. neoformans var.
neoformans occurs worldwide,
frequently in association with pigeon or other bird droppings. C. neoformans var. gattii occurs in endemic foci in the tropics and
subtropics where certain eucalypts provide an ecological niche.
Mode of transmission:
Transmission is presumed to be by inhalation.
Period of communicability:
Not spread directly from person to person, nor spread between
animals and
people.
Susceptibility and resistance:
Human resistance is presumed to be considerable given the
widespread distribution of the organism and the rarity of infection. It is not
known whether infection confers immunity. Susceptibility is increased during corticosteroid
therapy, immune deficiency disorders (especially AIDS), and disorders of the reticuloendothelial
system, particularly Hodgkin’s disease and sarcoidosis.
Control measures:
Preventive measures:
No vaccine is available. Some patients may require maintenance
antibiotics to prevent repeat infections
Control of case:
Clinicians should consider referral to a specialist centre for
treatment. Typical treatment often involves amphotericin or flucytosine. Patients
with HIV/AIDS may require continuing maintenance therapy
(secondary prophylaxis), typically fluconazole orally daily.
Control of contacts:
No action required.
Control of environment:
Large accumulations of bird droppings should be removed after
first being wetted or chemically disinfected to reduce aerosolisation.
Outbreak measures:
Case clusters are rare. Environmental investigations focus on potential
reservoirs of infection such as bird droppings, although a definitive source is
rarely found.
sources of information
·
The blue book: Guidelines
for the control of infectious diseases
·
http://www.medicinenet.com
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