Cryptococci are the causative agents of cryptococcosis
Last reviewed: 23.04.2024
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Cryptococcosis (synonyms: thorulosis, European blastomycosis, Busse-Busch disease) - subacute or chronic disseminated mycosis, observed in persons with severe immunodeficiency.
The causative agent is a conditionally pathogenic yeast-like fungus Cryptococcus neoformans (the perfect form is Fibbasidielia neoformans). Among the fungi of the genus Cryptococcus, only two species are pathogenic to humans and cause cryptococcosis - C. Neoformans (the main causative agent) and S. Laurentii (sporadic diseases).
Cryptococcal morphology
The fungus has the shape of round, less often oval yeast cells 6-13 microns in size, sometimes up to 20 microns, which are surrounded by a capsule, the size of which can reach 5-7 microns, and sometimes exceeds the diameter of the vegetative cell. The capsule consists of an acidic polysaccharide, its dimensions are directly dependent on the virulence of the strain. Invasive forms are represented by yeast cells surrounded by a large capsule, giving them considerable dimensions (up to 25 microns).
[6], [7], [8], [9], [10], [11]
Cultural properties of cryptococci
Cryptococcus is unpretentious, it grows well on conventional media (Saburo, wort agar, MPA), the weak acid or weakly alkaline reaction of the medium is optimal. C. Neoformans equally well grows both at 25 ° C and at 37 ° C, while saprophyte cryptococci can not reproduce at 37 ° C. Forms typical shiny juicy colonies mediated by the presence of a polysaccharide capsule. On agar, Saburo can form shiny creamy-brown colonies.
[12], [13], [14], [15], [16], [17], [18]
Biochemical activity of cryptococci
Low.
Antigenic structure of cryptococci
For capsular polysaccharide antigens, 4 serovars are isolated: A, B, C and D. Among the pathogens, serovars A and D predominate. Serovars B and C cause sporadic lesions in the tropics and subtropics.
[24], [25], [26], [27], [28], [29], [30],
Ecological niche of cryptococci
Cryptococci are widespread in nature, most often they are isolated from humans, animals, from pigeon droppings, from soil, from various fruits, berries, vegetables, leaves.
[31], [32], [33], [34], [35], [36],
Sustainability in the environment
High enough; sensitive to temperature effects.
Sensitivity to antibiotics
Sensitive to amphotericin B and fluconazole.
Sensitivity to antiseptics and disinfectants
Sensitive to the action of commonly used antiseptics and disinfectants.
Factors of pathogenicity of cryptococci
Capsule protecting the causative agent from the action of phagocytes and humoral protective factors, nonspecifically activating T-suppressors and inducing cleavage of complement components and serum opsonins. The causative agent does not form toxins. As a possible pathogenicity factor, the enzyme phenoloxidase, secreted by the fungus, is considered.
[37], [38], [39], [40], [41], [42]
Pathogenesis of cryptococcosis
Cryptococci form the primary focus of inflammation in the lungs with the involvement of regional lymph nodes. In most cases, the process ends in a spontaneous recovery, it is possible to disseminate the fungus from the primary focus in the lungs. Inflammatory response varies depending on the patient's immune status. Risk groups for dissemination form a linden with a violation of the functions of T-lymphocytes. In the elimination of the causative agent, the main role is played by cytotoxic reactions.
Immunity cellular
Antibodies and complement do not provide resistance to the organism against the pathogen. The presence of antibodies in patients with negative HRT to fungal antigens is a poor prognostic sign. As a rule, the patient has cellular immunodeficiency.
Epidemiology of cryptococcosis
The source of infection is the soil. Cryptococcus fungus is isolated from the soil, nest and droppings of pigeons, fruit juices, milk, butter. The transmission mechanism is aerogenic, the transmission path is air-dust. From the soil, where the fungus has small dimensions (2-3 μm) with a lack of moisture, it enters the lungs with dust. Primary lesions are localized in the lungs, although the possibility of introducing the fungus into the skin and mucous membranes can not be ruled out. The susceptibility of the population is low and depends on the state of cellular immunity. Diseases are sporadic, among the sick majority are men. Group diseases associated with the inhalation of infected dust when working in old buildings contaminated with pigeon pigeons are described. The patient is not contagious to others. The main conditions predisposing to the development of the disease are AIDS, leukemia, Hodgkin's disease, metabolic disturbances, conditions after organ transplantation.
Symptoms of Cryptococcosis
The main symptoms of cryptococcosis are meningeal lesions (up to 80% of cryptococcal meningitis in AIDS patients).
Primary cryptococcosis often occurs asymptomatically or its manifestations are insignificant and do not require medical care. The cases of revealing primary forms are extremely rare. Significantly less often observe primary skin lesions. The main clinically diagnosed form of the disease is cryptococcal meningitis. The day of lesions is characterized by slow development and the absence of specific signs in the initial stage. Typical intermittent headaches, the intensity of which increases, dizziness, visual impairment, increased excitability. In the dynamics of the disease, in a week or months after the onset, there are disturbances in consciousness. The clinical picture includes typical signs of meningitis - high body temperature and rigidity of the occipital muscles. Epileptic seizures, edema of the optic nerve disk and symptoms of cranial nerve damage are possible. More than 50% of patients have residual neurological disorders.
Laboratory diagnostics of cryptococcosis
The material for the study is sputum, pus, scrapings of ulcers, cerebrospinal fluid, urine, bones, tissue biopsy.
In native preparations, the causative agent, surrounded by a mucous yellowish capsule, has the appearance of rounded or ovate cells measuring 2x5-10x20 μm. Fungi can easily be found in wet smears of liquor stained with mascara. The capsule is found in carcasses or stained with Buri-Hinsu preparations. Histological preparations for the detection of C. Neoformans are stained with mucicarmin.
To isolate the pure culture, the test material is inoculated on sugar agar, Saburo medium, beer wort with the addition of antibiotics. The crops are incubated at 37 ° C, the colonies are formed after 2-3 weeks. Dense colonies form colonies from a whitish-yellowish to a dark brown color, a creamy consistency, on a carrot-potato agar, the fungal colonies have a dark brown or brown color. Identification of C. Neoformans is carried out taking into account the formation of urease in the Christainsan environment and the inability to absorb lactose and inorganic nitrogen, virulence, growth at 37 ° C.
Bioprobo is put on mice, which are intraperitoneally infected with blood, urine sediment or exudate from the patient. After 2-4 weeks, animals are killed, the homogenate of the liver, spleen and brain are opened and cut into media with antibiotics. The isolated fungal cultures are identified by their cultural, morphological and enzymatic properties.
In the serum of patients, agglutinins, precipitin, complement-binding antibodies are detected in low tigers and unstable. Antibody titers in RSK rarely make up 1:16 and as an exception 1:40. The appearance of antibodies and an increase in their titer serve as a favorable prognostic sign. Absolute diagnostic value is the detection in the latex-agglutination reaction of the circulating antigen, with the reaction titers sometimes being 1: 1280 or more.