zoonoses and communicable diseases common to ... - PAHO/WHO

CRYPTOCOCCOSIS 329formans,favoring its development and prolonging its survival in the soil. Pigeons donot become ill with cryptococcosis.The environmental source of C. neoformans var. gattii was unknown until a fewyears ago. A study conducted in Australia succeeded in isolating var. gattii from 35samples of bark and plant remains accumulated under the foliage of a species ofeucalyptus, Eucalyptus camaldulensis. Attempts to isolate samples from other eucalyptusspecies were unsuccessful. E. camaldulensis has been exported to variouscountries in the Americas, Africa, and Asia. The air sample taken from beneath thefoliage demonstrated that the presence of the agent in the air coincided with the eucalyptus’blooming season in late spring. These findings would explain the high incidenceof C. neoformans var. gattii among the aborigines in Australia’s NorthernTerritory, where these trees are abundant and the indigenous population lives in closecontact with them (Ellis and Pfeiffer, 1990). Man and animals become infected byinhaling dust containing the causal agent. C. neoformans, which has no capsule innature, becomes encapsulated in the lungs, allowing it to resist phagocytosis.Although all researchers agree that the infection is contracted through inhalation,there is still debate regarding the infecting element. Some believe it is the yeast formof the agent while others believe it is the basidiospores of the agent’s sexual phase. Ithas also been pointed out that the yeast form would be too large (4 to 7 microns) toenter the alveoli, while basidiospores measure only about 2 microns (Cohen, 1982).Role of Animals in the Epidemiology of the Disease: There are no known casesof transmission of the disease from animal to animal, from animal to man, or fromman to man, except in the case of a corneal transplant (Beyt and Waldman, 1978).Diagnosis: Diagnosis can be made through microscopic observation of encapsulatedC. neoformans in tissues and body fluids, and can be confirmed by culture. Theuse of culture media to differentiate serotypes A and D from serotypes B and C nowfacilitates serotyping (Salkind and Hurd, 1982; Kwon-Chung et al., 1982). Thedirect immunofluorescence test can be used for the same purpose for cultures andfor some histological preparations (Kaplan et al., 1981).As the etiologic agent multiplies in the human host, the capsular polysaccharideof C. neoformans neutralizes antibodies. Excess antibodies can be detected in bloodand urine, as well as in cerebrospinal fluid in cases in which the central nervous systemis affected. Cases that come to receive medical attention are frequently faradvanced. Consequently, better results are obtained if the medical examination isdirected toward detecting the specific antigen rather than the antibodies. The platelatex agglutination test with particles sensitized by anticryptococcal globulin is usedto detect the cryptococcal antigen. The enzyme-linked immunosorbent assay(ELISA) test is also available to detect the capuslar polysaccharide antigen of theetiologic agent. This test is much more sensitive than latex agglutination and permitsearlier diagnosis (Scott et al., 1980). In patients with meningoencephalitis, a sampleof the cerebrospinal fluid is used for direct microscopic examination and a cellcount, another examination with India ink to detect encapsulated fungus cells, andculture in Sabouroud’s dextrose agar with incubation at 30°C to 37°C to isolate thefungus. The antigen is sought in serum and cerebrospinal fluid.In England, 828 HIV-positive patients with fever were examined (in the UnitedKingdom, 85% of cases occur in immunodeficient individuals, while in the UnitedStates, 50% of patients apparently have a normal immune system). Sixty-nine of the