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eFigure 35–15. Life cycle of Plasmodium vivax, the agent of vivax (tertian) malaria. The female Anopheles mosquito, shown in the typical biting angle, injects sporozoites into the human bloodstream. 1–3: Exoerythrocytic phase of asexual division (schizogony). Within an hour, the sporozoites enter liver cells to initiate the exoerythrocytic phase. Penetration of a hepatocyte is followed by growth and multiplication within a few days (2a), or the parasite may become a hypnozoite, with development delayed for as long as 1–2 years. Asexual multiplication fills the enlarging infected liver cell with merozoites (2a). The cell then ruptures, releasing thousands of parasites (3) to initiate either a second hepatic generation or the erythrocytic phase. 4–9: Erythrocytic phase of schizogony. Invasion of the bloodstream and penetration of red blood cells initiate the blood phase of schizogony. Penetration of the red blood cell may begin as a surface or appliqué (accolé) form (4), after which it enters the cell, rounds up, and ingests hemoglobin to form the ring stage (5), which enlarges and becomes an ameboid trophozoite, with numerous cytoplasmic granules (Schüffner dots) (6) produced as a by-product of hemoglobin breakdown. Nuclear division follows (7), eventually filling the infected cell as the parasites' cytoplasm surrounds each nucleus (8), rupturing it to release more merozoites (9) about 48 hours after onset of the red cell infection (tertian cycle). This asexual erythrocytic schizogony repeats itself with a 48-hour synchronous periodicity. 10a, 10b: Gametogony. Some sporozoites give rise to sexual parasites, gametocyte-producing merozoites that form male (microgametocyte) (10a) or female (macrogametocyte) stages (10b). When taken up in another Anopheles mosquito blood meal, the asexual forms are killed but the sexual stages quickly complete gamete formation. 11–13: Fertilization. "Exflagellation" is the release of male microgametes, which scatter, find a female macrogamete, and fuse. The zygote elongates, becomes a motile ookinete (13), and travels to the mosquito's stomach wall. 14–16: Sporogony. In the stomach wall of the mosquito, the ookinete becomes an oocyst (14). Masses of these oocysts may cover the mosquito's stomach. The oocyst nucleus divides innumerable times (15), and the progeny develop into elongated sporozoites, a process termed sporogony. The oocysts rupture (16), passing sporozoites throughout the female body. Most eventually concentrate in the salivary glands, after which the mosquito becomes infective and can initiate a new malaria cycle. (Reproduced, with permission, from Goldsmith R, Heyneman D [editors]. Tropical Medicine and Parasitology. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, Inc.)

Current Medical Diagnosis & Treatment 2018 > Protozoal & Helminthic Infections

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eFigure 35–17. Life cycle of Entamoeba histolytica. Transmission of infective cysts of this abundant amebic parasite of humans (with pathologic results in 10–20% of infections) may involve fecally contaminated flies, water, fingers, or food. The damage caused by these parasites can involve ulceration of the colon or passage through the intestinal mucosa and spread to other organs. Ingested cysts are acted on by stomach and duodenal enzymes and rapidly excyst. The tetranucleated trophozoite (1) separates into four uninucleated amebae (2), each of which divides mitotically, resulting in eight uninucleated amebulae (3). Occasionally, trophozoites penetrate the mucosa, ingest red blood cells (4), and initiate the ulceration process, which may spread extraintestinally. Normally, the trophozoites multiply in the lumen of the colon and form a commensal colony, feeding on fecal bacteria (5). The trophozoites complete their vegetative phase and begin cyst formation by a process consisting of loss of water and rounding up (6), formation of a central vacuole with chromatoidal particles (7), an early cyst maturation stage with development of typical round-ended chromatoidals (binucleated stage) (8), and final maturation, often completed after passage in the feces, to form the tetranucleated cyst (9), which loses its chromatoidals and becomes infective to humans. (Reproduced, with permission, from Goldsmith R, Heyneman D [editors]. Tropical Medicine and Parasitology. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, Inc.)

Current Medical Diagnosis & Treatment 2018 > Protozoal & Helminthic Infections

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eFigure 9–41. Normal lung ventilation with xenon-133. With the patient's single full breath, inhaled radioxenon is evenly distributed to all lung areas, reaching the terminal airways and alveoli in the normal patient (A, posterior view). There is a less noticeable gradient of activity from the upper to the lower lung fields than is seen in perfusion lung images. Fifteen-second images obtained during closed-system rebreathing of a xenon–oxygen mixture show uniform distribution at 120 seconds (B). Serial 15-second frames after switching the patient to room air breathing (C to G) show a homogeneous pattern of washout from all lung areas. This sequence mainly evaluates the posterior lung regions. To better localize gas trapping in specific lung segments or more anterior regions, the acquisition may be modified after the rebreathing phase by rotating the patient into posterior oblique positions. Selected images from a complete study include single breath (H, posterior view), the late phase of rebreathing (I, posterior view), posterior washout (J), left posterior oblique washout (K), and right posterior oblique washout (L). No gas is retained in this patient, which is normal, but in obstructive airway disease gas retention persists and is better localized in the oblique views than in a posterior view alone. A small amount of alveolar xenon normally crosses the alveolar membrane to reach the blood and be distributed throughout the body. Because it is highly soluble in lipids, xenon accumulates in adipose tissue, including the liver, which is faintly seen with prolonged rebreathing. Liver activity should not be mistaken for delayed washout of xenon from the base of the lung. Occasionally, splenic blood pool radioactivity or swallowed xenon in the stomach may also be seen. (SIN BRE = single breath, L REB =late rebreathe, WO =washout.) (Reproduced, with permission, from Baum S et al. Atlas of Nuclear Medicine Imaging, 2nd ed. Originally published by Appleton & Lange. Copyright © 1993 by The McGraw-Hill Companies, Inc.)

Current Medical Diagnosis & Treatment 2018 > Pulmonary Disorders

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eFigure 9–41. Normal lung ventilation with xenon-133. With the patient's single full breath, inhaled radioxenon is evenly distributed to all lung areas, reaching the terminal airways and alveoli in the normal patient (A, posterior view). There is a less noticeable gradient of activity from the upper to the lower lung fields than is seen in perfusion lung images. Fifteen-second images obtained during closed-system rebreathing of a xenon–oxygen mixture show uniform distribution at 120 seconds (B). Serial 15-second frames after switching the patient to room air breathing (C to G) show a homogeneous pattern of washout from all lung areas. This sequence mainly evaluates the posterior lung regions. To better localize gas trapping in specific lung segments or more anterior regions, the acquisition may be modified after the rebreathing phase by rotating the patient into posterior oblique positions. Selected images from a complete study include single breath (H, posterior view), the late phase of rebreathing (I, posterior view), posterior washout (J), left posterior oblique washout (K), and right posterior oblique washout (L). No gas is retained in this patient, which is normal, but in obstructive airway disease gas retention persists and is better localized in the oblique views than in a posterior view alone. A small amount of alveolar xenon normally crosses the alveolar membrane to reach the blood and be distributed throughout the body. Because it is highly soluble in lipids, xenon accumulates in adipose tissue, including the liver, which is faintly seen with prolonged rebreathing. Liver activity should not be mistaken for delayed washout of xenon from the base of the lung. Occasionally, splenic blood pool radioactivity or swallowed xenon in the stomach may also be seen. (SIN BRE = single breath, L REB =late rebreathe, WO =washout.) (Reproduced, with permission, from Baum S et al. Atlas of Nuclear Medicine Imaging, 2nd ed. Originally published by Appleton & Lange. Copyright © 1993 by The McGraw-Hill Companies, Inc.)

Current Medical Diagnosis & Treatment 2018 > Pulmonary Disorders

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