Para Lab 11

PARASITOLOGY LABORATORY 11 – Trypanosomes etc. USTMED ’07 Sec C – AsM, AnnePonce; Photos provided by JV.N. Gomori methenaminesilver nitrate stain.

Female mosquito head

Cysts in human impression smear

lung

Male mosquito head

Pneumocystis carinii

PNEUMOCYSTIS CARINII

H&E stained section of human

CLASSIFICATION

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Protozoa

Alveoli appear to be filled with a pink-staining, foamy material,

DISEASE

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Pneumocystosis, interstitial plasma cell pneumonia

Neither cysts nor organisms can be seen in this stain

GEOGRAPHIC DISTRIBUTION – cosmopolitan LOCATION IN HOST

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lung tissue

MORPHOLOGY

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Trophozoites: small, 1-5µ in diameter, with ovoid or amoeboid appearance Cysts: 3.5-7.0µ in diameter, have an outer membrane of variable thickness and usually contain 4 to 8 nuclei, each of which measures 1-2 µ in diameter

LIFE CYCLE

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DIAGNOSIS

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Although the life cycle has not been clearly elucidated, Pneumocystis probably exists in the environment and in the lungs of rodents and humans without causing apparent disease. However, in hosts that are immunosuppressed for extended periods of time or in premature and malnourished infants, the organisms may proliferate in lung tissue, leading in consolidation, dyspnea, and even death. Usually established by demonstrating organisms in lung tissue. Specimens obtained by lung biopsy, lung aspirates, or bronchial brushings are more satisfactory for examination than are sputum or bronchial washings because more organisms are likely to be detected. Although a variety of stains (Giemsa’s, methylene blue, hematoxylin-eosin) have been used, the Grocott modification of the Gomori methenamine-silver nitrate stain is especially useful because organisms stain darkly and are readily identifiable against an unstained background. DIAGNOSTIC PROBLEMS. Obtaining a suitable specimen for examination is essential. Pneumocystis must be differentiated from yeasts, fungi and other organisms

Pneumocytsis carinni cyst Involved in: 1. Upper and Lower Respiratory Tract Infections 2. Eye Infections

Characteristic cysts stained with Gomori methenamine-silver nitrate are seen at high magnification

TRYPANOSOMA SPECIES 145 & 146 Trypanosoma cruzi in human blood film. The causative agent is T. cruzi. It occurs characteristically in blood films as short “C” or “S” shaped trypomastigotes with a prominent kinetoplast. It is otherwise monomorphic (x900)

147 Typical vector biting. Reduviid bugs (also known as “assassin” or “kissing” bugs), particularly in the genera Triatoma, Rhodnius and Panstrongylus, transmit T. cruzi while feeding, not by inoculation but by fecal contamination. 148 & 149 Life cycle in vector. Trypomastigotes picked up in the blood meal transform to epimastigotes in the midgut of the bug. They reproduce as epimastigotes, then pass to the hindgut where they transform again to the infective stages (metacyclic trypomastigotes). The figures show epimastigote stages in the vector.

Trypanosoma gambiense

Figure 1. This is a thin blood film containing the trypomastigote stage of T. gambiense. These trypomastigotes, indistinguishable from those of T. rhodesiense, have a small kinetoplast near the somewhat blunted, posterior end, and a conspicuous, undulating membrane with a flagellum. At the extreme right margin note the two dividing forms; this is characteristic for the African trypanosomes, but is not seen in T. cruzi.

TOXOPLASMA GONDII Toxoplasma gondii

bradyzoite

Cyst in H & E stained tissue section of mouse brain cyst

Trypanosoma cruzi trypomastigote

Figure 2. “Broad: form of T. cruzi trypomastigote in mouse thin blood film. Note the large kinetoplast close to the short, pointed, posterior tip of this organism. Broad forms, such as this usually assume an S or C shape in stained preparations. The centrally located nucleus is subspherical, and the undulating membrane inconspicuous. T. cruzi does not undergo division in the trypomastigote stage.

Toxoplasma gondii

Giemsa-stained trophozoites in tissue culture

Toxoplasma gondii

Trypanosoma cruzi Figure 3. “Slender” form of T. cruzi trypomastigote in mouse thin blood film. Slender forms are commonly found during acute infections. Note the elongate nucleus and the large kinetoplast followed by a long, pointed, posterior tip. The undulating membrane may be inconspicuous in stained preparations.

Giemsa-stained trophozoites in peritoneal fluid of mouse called Tachyzoites found in tissues and fluids during the acute stage of infection.

Toxoplasma gondii

Giemsa stained cyst in an impression smear

Trypanosoma cruzi

Figure 4. Two typical C forms are visible in this mouse thin blood film of trypomastigotes of T. cruzi. Note the very large kinetoplasts that seem to bulge from the body at the posterior end. In contrast, the kinetoplasts in the African trypanosomes are small and subterminal

CRYPTOSPORIDIUM Cryptosporidium oocyst

Trypanosoma cruzi

Figure 5. In this illustration of T. cruzi epimastigotes in culture, note the small, S-shaped trypomastigote above and to the left of center. It has a large kinetoplast near the posterior end and a flagellum that extends along its length, projecting beyond the anterior end. An undulating membrane is present between the flagellum and the body of the organism. This form – the infective stage for humans – is found in cultures and in feces of infected triatomid bugs.

15-26, 27 Cryptosporidium parvum. Oocysts, Feces, Acid-fast and fluorescence stain. In acid-fast stained preparations, the oocyts of C. parvum appear round to oval, measuring approximately 4 to 6 um in diameter. Several black granules can be observed, usually in the periphery of the cyst. Under fluorescence, the wall of the cysts may appear smooth or wrinkled. Cryptosporidium oocyst

Trypanosoma cvnasi

ISOSPORA BELLI Trypanosoma sp.

Isospora belli, immature oocyst

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