Parasitology

Front 1

Back 1

Trypanosoma gambiense.
(African trypanosomiasis)

Front 2

Back 2

Trypanosoma cruzi.
The muscle fibers filled with Leishmania forms of the organism can be identified.

Front 3

Back 3

Trypanosoma cruzi.
The muscle fibers filled with Leishmania forms of the organism can be identified. This is more clearly seen in the high power where the nucleus and kinetoplast in each of the Leishmania forms can be easily seen. These organisms must be distinguished from Toxoplasmosis in which multiple single nuclei are present within the parasitised muscle fibers.

Front 4

Back 4

Cutaneous Leishmaniasis.
The lesion has heaped-up edges and an ulcerated center.

Front 5

Back 5

Cutaneous Leishmaniasis.
The inflammatory infiltrate can be seen to consist of lymphocytes, plasma cells, eosinophils, and foamy histiocytes which have organisms in the cytoplasm.

Front 6

Back 6

Cutaneous Leishmaniasis.
Under oil immersion, the parasites have the morphological features of Leishmania. They are round with an eccentric nucleus, and in some of them a smaller micro-nucleus or kinetoplast can be seen.

Front 7

Back 7

The leptomonad form of Leishmania.
The nucleus, kinetoplast and flagellum are clearly visible. This is the appearance of Leishmania organisms in the sandfly vector.

Front 8

Back 8

Leishmania parasites that have a nucleus and a small kinetoplast.

Front 9

How is leishamaniasis differentiated from histoplasmosis?

Back 9

The distinction is made by identifying the presence of a kinetoplast in association with the nucleus, as seen in Leishmaniasis. In addition, the Histoplasma capsulatum yeast is PAS positive, whereas the Leishmania organisms are PAS negative.

Front 10

Back 10

Visceral lesihmaniasis.
The hepatocytes are morphologically normal, but the sinusoids are markedly distended by proliferating Kupffer cells which are filled with Leishmania organisms.

Front 11

Back 11

Visceral leishmaniasis.
The hepatocytes are morphologically normal, but the sinusoids are markedly distended by proliferating Kupffer cells which are filled with Leishmania organisms.

Front 12

Back 12

Visceral leishmaniasis.

Front 13

Back 13

Visceral leishmaniasis.

Front 14

Back 14

Visceral leishmaniasis.

Front 15

Back 15

Cerebral malaria.
Cerebral malaria presents with a variety of neurological manifestations. It may present as acute psychosis, fitting or abnormal behaviour. These can progress quite quickly to coma and death.Very often the post mortem examination of the brain shows no macroscopic abnormality. The classical abnormality however, is the presence of multiple petechial hemorrhages throughout the white matter.

Front 16

Back 16

Cerebral malaria.
Areas of hemorrhage (low power).

Front 17

Back 17

Cerebral malaria.
Thrombosis of a vessel, destruction of the vessel wall and haemorrhage into the brain substance. Many of the red blood cells contain ring forms of P. falciparum.

Front 18

Back 18

Cerebral malaria.
Shows a cerebral capillary in which the red blood cells contain malaria pigment and ring forms of P. falciparum. This appearance can be seen in the capillaries throughout the brain. This is the usual finding in patients dying of cerebral malaria when no macroscopic abnormality can be seen in the slices of post mortem brain.

Front 19

Back 19

Malaria.
Ring forms and schizonts can be seen. Schizonts are not seen in peripheral blood smears in malaria except as a pre-terminal event. If schizonts are seen in peripheral smears the patient will die quite quickly unless treatment is started as a matter of urgency.

Front 20

How does the size of the various types of malaria in infected red blood cells compare to the size of uninfected red blood cells?

Back 20

P. falciparum - the parasitized red blood cells are the same size and shape as the non-parasitized cells.

P. vivax - the parasitized red blood cells are larger than the non-parasitized ones.

P. malariae - the parasitized red blood cells are not enlarged and are the same size as the non-parasitized ones.

P. ovale - the parasitized red blood cells are enlarged and most of them are oval in shape.

Front 21

What are the parasite size and shape of the various types of malaria?

Back 21

P. falciparum - the trophozoites are all small rings with a red staining nuclear dot and a small amount of blue-staining cytoplasm.

P. vivax - the trophozoite may be in a ring form with a nuclear dot and a crescent of cytoplasm or it may be much larger and have an irregular contour (an amoeboid form)

P. malariae - the trophozoite has a large round nucleus and a solid blue cytoplasm. Very frequently this cytoplasm adopts a shape which looks like a thick band across the red blood cell. P.malariae often has a well defined blob of brown malarial pigment in the red blood cell.

P. ovale - the trophozoite is large with a big nucleus and abundant, irregularly distributed cytoplasm.

Front 22

How do the schizonts of the various types of malaria compare?

Back 22

P. falciparum - schizonts are present in the peripheral blood only in the pre-terminal phase of the infection. The schizonts contain 12 - 24 merozoites (nuclear dots). The red blood cell containing the schizont is not enlarged.

P. vivax - contains 12 - 24 merozoites and the infected red blood cell is enlarged.

P. malariae - the schizont contains 8 - 12 merozoites. The infected red cell is not enlarged.

P. ovale - the schizont contains 12 - 24 merozoites. The infected red blood cell is enlarged and is an oval shape.

Front 23

How do the gametocytes of the various types of malaria compare?

Back 23

P. falciparum - the gametocytes are crescent shaped.

Gametocytes of the other three species are round with a large eccentric nucleus at the edge. Gametocytes are about the same size as the schizont for the particular species.

Front 24

Back 24

A thick blood film from a fairly heavy infection of P. falciparum. Numerous ring forms (trophozoites) can be seen.

Front 25

Back 25

A very occasional ring form of P. falciparum in a thick film.

Front 26

Back 26

Thin film from a patient with a heavy infection of P. falciparum.
Malaria causes a hemolytic anemia. This blood film shows the presence of haemolysis with a polychromatic red cell in the top left hand corner and a nucleated red cell in the bottom right hand corner.
This is P. falciparum because the red cells are all about the same size and shape, and the parasites are all small rings.

Front 27

Back 27

Presence of a characteristic crescent-shaped gametocyte of P. falciparum. It usually takes about eight days from the beginning of the first fever until gametocytes appear in the peripheral blood, so this patient would have had his fever for at least one week.

Front 28

Back 28

P. falciparum.
It shows a neutrophil with malarial pigment in the cytoplasm.

Front 29

Back 29

P. falciparum.
There is a female gametocyte of P. falciparum on the left and a male on the right. The nuclear material in the female is more diffuse than in the male.

Front 30

Back 30

P. falciparum.
It shows a schizont which contains about sixteen or eighteen merozoites, together with some pigment. This patient would have died within a few hours if treatment had not been started at once.

Front 31

Back 31

Thick blood film of P. vivax. There is a schizont in the middle of the field.

Front 32

Back 32

Thin blood smear that shows trophozoites and a gametocyte of P. vivax. The parasitized red blood cells are larger than their neighbours, and the trophozoites are large ring forms. The gametocyte is round and has a single red nuclear dot.

Front 33

Back 33

Thin blood film showing P. vivax. The trophozoite is an amoeboid form. The lower parasite is a gametocyte. Both parasites are in red blood cells that are enlarged.

Front 34

Back 34

Schizont of P. vivax. The red blood cell is enlarged and there are eighteen merozoites in the schizont.

Front 35

Back 35

Ring form of P. vivax. This appearance presents one of the diagnostic problems in the species identification of malaria. The trophozoite is only marginally larger than the trophozoite of P. falciparum but it is P. vivax because the infected red blood cell is enlarged. In such cases one usually finds more characteristic trophozoites of P. vivax in other parts of the smear.

Front 36

Back 36

Peripheral blood smear that shows P. malariae. The infected red blood cell is not enlarged. The trophozoite is large and is forming a band across the middle of the red cell.

Front 37

Back 37

P. malariae infection. The red cell is not enlarged. The trophozoite is in a band form and there is a large blob of pigment associated with the parasite. This prominent malarial pigment is a feature of P. malariae.

Front 38

Back 38

Two schizonts of P. malariae. The red cells are not enlarged. The schizont has ten merozoites and each schizont has a large blob of pigment within it.

Front 39

Back 39

Gametocyte of P. malariae. The red blood cell is not enlarged, the gametocyte is round and there is a single nucleus at one margin.

Front 40

Back 40

Blood smear that shows three schizonts of P. ovale. The red blood cells are enlarged and an oval shape. Each schizont contains approximately twelve to sixteen merozoites.

Front 41

Back 41

P. ovale parasites. The red blood cells are enlarged and their shape is changed. One is a definite oval shape and the other is flattened on one edge. The trophozoites are large and amoeboid in form.

Front 42

Back 42

Histological appearances of toxoplasmosis in a lymph node. The normal lymph node architecture is retained. There is some follicular hyperplasia. Scattered throughout the node there are well circumscribed and tightly packed foci of pale staining histiocytes.

Front 43

Back 43

Histological appearances of toxoplasmosis in a lymph node. The normal lymph node architecture is retained. There is some follicular hyperplasia. Scattered throughout the node there are well circumscribed and tightly packed foci of pale staining histiocytes.

Front 44

Back 44

Histological appearances of toxoplasmosis in a lymph node. The normal lymph node architecture is retained. There is some follicular hyperplasia. Scattered throughout the node there are well circumscribed and tightly packed foci of pale staining histiocytes.

Front 45

Back 45

Toxoplasmosis.
Anterior half of the brain sliced through the mamillary bodies. There is marked dilatation of the frontal and temporal horns of the lateral ventricles with very marked thinning of the cerebral cortex.

Front 46

Back 46

Toxoplasmosis.
Posterior half of the brain showing hydrocephalus of the occipital horns of the lateral ventricles with marked thinning of the overlying cerebral cortex. As the brain was being cut there was a slightly gritty sensation which corresponded to calcification in the thinned cortex. Calcification lining the dilated ventricles can be seen in x-rays of children with Neonatal Toxoplasma Encephalitis.

Front 47

Back 47

Toxoplasmosis.
Cerebral cortex at a higher power. This shows the presence of calcification and a moderately heavy chronic inflammatory cell infiltration in the subarachnoid space.

Front 48

Back 48

Cyst of Toxoplasma that was found in an area of cortex in which there was only a minimal degree of inflammation.

Front 49

Back 49

Toxoplasma cyst.
Frequently such cysts are found in areas of inflammation and active encephalitis. The main differential diagnosis of a Toxoplasma cyst is from (i) an aggregate of Leishmania organisms. This can be done by noting the absence of kinetoplast in the Toxoplasma cyst. (ii) Histoplasma capsulatum. These yeasts are a similar size to the individual Toxoplasma organisms but they stain positively with PAS.

Front 50

Back 50

High power view of individual crescentic Toxoplasma organisms grown in culture in peritoneal fluid of a laboratory mouse.

Front 51

Back 51

The heart of a middle aged male who died from AIDS. The Toxoplasma cyst is expanding the myocardial muscle fiber. In this case there is no inflammatory reaction associated with the cyst. The presence of an inflammatory reaction is variable.

Front 52

Back 52

The heart of a middle aged male who died from AIDS. The Toxoplasma cyst is expanding the myocardial muscle fiber. In this case there is no inflammatory reaction associated with the cyst. The presence of an inflammatory reaction is variable.

Front 53

Back 53

Pneumocystis infection causes focal or diffuse collections of "fluffy" pink staining material in the alveolar spaces. At a low power this pink material looks somewhat like pulmonary edema except that the latter is more homogeneous.

Front 54

Back 54

Pneumocystis carinii.
High power shows that the exudate is rather honeycombed, and even in the Haematoxylin and Eosin stained sections, the blue nuclear dots of the trophozoites of Pneumocystis can be seen. The spaces around the dots are the cysts. The cysts can be more easily seen in silver stains, for example, Grocott.

Front 55

Back 55

Pneumocystis carinii.
Low power view of a Grocott stain of lung. The individual cysts stain black.

Front 56

Back 56

Pneumocystis carinii.
Grocott stain of lung. The individual cysts stain black.

Front 57

Back 57

The Pneumocystis infection does not excite a very florid inflammatory cell reaction in the lung. The predominant cell in such inflammatory reactions is the plasma cell. The first descriptions of Pneumocystis pneumonia referred to the condition as "plasma cell" pneumonia.
Interstitial plasma cell infiltration in the lung. The pulmonary macrophage shows a cytomegalovirus within the nucleus. This opportunistic virus is frequently seen in association with a Pneumocystis infection.

Front 58

Back 58

Pneumocystis carinii.
Bronchial lavage preparation stained with Giemsa stain. This outlines the cyst walls and demonstrates the trophozoites within the cyst. Each cyst usually contains four or eight trophozoites. Silver stain or Gram stain are equally useful in staining smear preparations.

Front 59

Back 59

Pneumocystis carinii.
Bronchial lavage preparation stained with Giemsa stain. This outlines the cyst walls and demonstrates the trophozoites within the cyst. Each cyst usually contains four or eight trophozoites. Silver stain or Gram stain are equally useful in staining smear preparations.

Front 60

Back 60

Pneumocystis carinii.
Bronchial lavage preparation stained with Giemsa stain. This outlines the cyst walls and demonstrates the trophozoites within the cyst. Each cyst usually contains four or eight trophozoites. Silver stain or Gram stain are equally useful in staining smear preparations.

Front 61

Back 61

E. histolytica.

Front 62

Back 62

Amebic diarrhea.
Histological examination shows rectal mucosa and purulent exudate on its mucosal surface.

Front 63

Back 63

The rectal mucosa itself does not show significant inflammation but the trophozoites of E. histolytica can be easily seen in the purulent exudate under medium power magnification

Front 64

Back 64

Microscopic section taken across one of the ulcers in E. histolytica. It emphasises the deep erosion into the muscle layer of the bowel and the undermining of the mucosal epithelium at the edge of the ulcer.

Front 65

Back 65

Exudate in E. histolytica.

Front 66

Back 66

Amoebae can be found within the exudate of E. histolytica.

Front 67

Back 67

E. histolytica in exudate.

Front 68

Back 68

E. histolytica in exudate.

Front 69

Back 69

E. histolytica in exudate.

Front 70

Back 70

E. histolytica invading blood vessels.

Front 71

Back 71

Amebic liver abscess.

Front 72

Back 72

Brown colored pus from amebic abscess.

Front 73

Back 73

Cutaneous amebiasis.
Shows normal skin at the edge of an area of very marked epithelial proliferation and thickening.

Front 74

Back 74

Ulcer in cutaneous amebiasis in which pus contains E. histolytica.

Front 75

Back 75

Ulcer in cutaneous amebiasis in which pus contains E. histolytica.

Back 76

Ulcer in cutaneous amebiasis in which pus contains E. histolytica.

Front 77

Back 77

Ulcer in cutaneous amebiasis in which pus contains E. histolytica.

Front 78

Back 78

Ulcer in cutaneous amebiasis in which pus contains E. histolytica.

Front 79

Back 79

The Entamoeba histolytica cyst is fairly small, up to 25 microns in diameter. It contains four nuclei, each with a well-defined central karyosome.

Front 80

Back 80

Naegleria fowleri. Microscopically the meninges are filled with mononuclear inflammatory cells and the amoebae can be seen mixed with this cellular infiltrate.

Front 81

Back 81

Naegleria fowleri.
The amoebae invade the brain by way of the Virchow-Robin spaces. The amoebae are small, approximately 10 microns in diameter. They have a nucleus and very little cytoplasm.

Front 82

Back 82

Within these areas of hemorrhage there are many ameba with morphological features of Acanthamoeba. These organisms are approximately 20 microns in diameter. They have a well-defined nucleus that contains a prominent nucleolus. The cytoplasm is abundant and contains numerous vacuoles.

Front 83

Back 83

Patients who use contact lenses sometimes develop corneal ulceration caused by the free-living Acanthamoeba. The amoebae live in the water in which the contact lenses are kept overnight.

Front 84

Back 84

Patients who use contact lenses sometimes develop corneal ulceration caused by the free-living Acanthamoeba. The amoebae live in the water in which the contact lenses are kept overnight.

Front 85

Back 85

Base of an ulcer in the colon, where Balantidium coli organisms can be seen. These are large organisms approximately 50 microns in diameter. They are round, have a large nucleus and vacuolated cytoplasm.

Front 86

Back 86

Base of an ulcer in the colon, where Balantidium coli organisms can be seen. These are large organisms approximately 50 microns in diameter. They are round, have a large nucleus and vacuolated cytoplasm.

Front 87

Back 87

Balantidium coli.
Oil immersion picture of formalin fixed faeces from stools from a laboratory monkey. The tiny cilia can be seen on the surface of the organism adjacent to the macronucleus.

Front 88

Back 88

The usual appearance of a small intestinal biopsy in a patient with giardiasis. The small bowel is morphologically normal. The villi are of normal length. There is no inflammation. Large numbers of organisms can be seen in the surface mucus and in the recesses between adjacent villi.

Front 89

Back 89

The usual appearance of a small intestinal biopsy in a patient with giardiasis. The small bowel is morphologically normal. The villi are of normal length. There is no inflammation. Large numbers of organisms can be seen in the surface mucus and in the recesses between adjacent villi.

Front 90

Back 90

Giardia.

Front 91

Back 91

Giardia.
An oil immersion view showing the trophozoites on end and "en face". The pear-shape of the organism is best seen in the front face view and then the two nuclei are visible, resembling a pair of eyes.

Front 92

Back 92

Motile trophozoite of Giardia from a wet preparation of duodenal aspirate.

Front 93

Back 93

Small, oval, thick walled cysts of Giardia lamblia as seen in a sample of feces.

Front 94

Back 94

Trichomonas.

Back 95

Trichomonas.

Front 96

Back 96

Trichomonas.

Front 97

Back 97

Cryptosporidiosis.
An oil immersion view of the oocysts in diarrhoeal feces. The feces sample was concentrated and stained by a modified Ziehl Neelsen stain. The organisms stain a bright pink color.

Front 98

Back 98

Cryptosporidiosis.
The villi are somewhat shortened, the surface epithelium is damaged and there is a moderate increase in the number of chronic inflammatory cells in the lamina propria. The oocysts can be seen on the surface of the epithelial cells as rounded, regular, blue-stained bodies.

Front 99

Back 99

Cryptosporidiosis.

Front 100

Back 100

Cryptosporidiosis.

Front 101

Back 101

Oil immersion magnification of spores of Enterocytozoon bieneusi in diarrhoeal feces of an AIDS patient who was suffering from diarrhoea. The feces sample was concentrated and stained with a modified Giemsa stain.

Front 102

Back 102

Microsporidiosis.

Front 103

Back 103

Microsporidiosis.
Warthin Starry.

Front 104

Back 104

Microsporidiosis.
Warthin Starry.

Front 105

Back 105

Dog tapeworm - E. granulosus. It is a small worm, about 5mm long. It has a head (scolex) with suckers and hooklets. It has one mature and one gravid segment. In the gravid segment the uterus is filled with eggs. The genital pore opens laterally in the middle of the gravid segment.

Front 106

Back 106

Echinococcus.
Liver is the commonest organ in which hydatid cysts develop. The cysts may produce palpable enlargement of the liver. Hydatid cyst in a liver specimen from a 53 year old sheep farmer. It was an incidental post mortem finding. The cyst is composed of a thick white outer membrane one or two millimetres thick. Adjacent to the cyst there is a chronic inflammatory cell reaction with fibrosis in the adjacent tissue. Within the cyst there are multiple daughter cysts of varying size. If the main cyst ruptures these daughter cysts spill into other tissues and continue to grow.

Front 107

Back 107

Echinococcus.
Inner lining of the laminated membrane. The laminated membrane is lined by a single layer of germinal epithelium from which new daughter cysts develop. The developing daughter cysts can be seen as granular projections on the inner lining of the cyst. As these daughter cysts grow, they break off from the germinal epithelium and float freely in the cyst.

Front 108

Back 108

Echinococcus.
Low power view of the laminated membrane lined by the germinal layer with daughter cysts developing from it.

Front 109

Back 109

Echinococcus.
Medium power view. The laminated membrane can be clearly seen. Sometimes in biopsy specimens there is no germinal layer and one cannot see developing daughter cysts. The appearance of the laminated membrane itself is usually enough to make a positive diagnosis of hydatid cyst. At this power the germinal membrane and the developing daughter cysts can be easily seen.

Front 110

Back 110

Echinococcus.
Higher power view to show a developing daughter cyst. A new scolex (or head) is forming within the cyst.

Front 111

Back 111

Ehinococcus.
Scolex from which hooklets are breaking off from the top.

Front 112

Back 112

Echinococcus.
Scolex with intact hooklets.

Front 113

Back 113

Echinococcus.
Chest x-ray from a 10 year old boy who was recovering from an attack of pneumonia. It shows a large opacity in the lower part of his right lung.

Front 114

Back 114

Echinococcus.
The white laminated membrane has begun to pull away from the tissue reaction in the lung. A careful family history failed to reveal any contact with either dogs or sheep. This is not an uncommon story. It is very difficult to explain how such patients develop their infection.

Front 115

Back 115

Echinococcus.
Left kidney which has been bisected longitudinally. The upper two thirds of the kidney has been compressed and replaced by a hydatid cyst. The calyceal system of the kidney is hydronephrotic, being dilated because of the compression on the collecting system by the enlarging hydatid cyst. This kidney came from a six year old male who was investigated for recurrent attacks of urinary tract infection.

Front 116

Back 116

Echinococcus.
A slice of the brain at post mortem with a transparent daughter cyst floating in the greatly dilated lateral ventricle.

Front 117

Back 117

Sparganosis.
Low power view of a section taken from a subcutaneous lump on the back of a 28 year old male. He said that the lump on his back was slowly moving. He lived in a country town and often spent weekends hunting wild pigs. The section shows an inflammatory abscess with a cross section of a "worm" in the center.

Front 118

Back 118

Sparganosis.
Higher power of the "worm" - the sparganum. It has a well defined integument, no internal organs, and no scolices.

Front 119

Back 119

Sparganosis.
The integument at higher power. The surface shows the presence of microvilli and on the inner surface of the integument there is a line of well defined tegumental cells. Within the body of the sparganum there are a number of small muscle fibres. In the centre there is a small focus of calcification (a fairly common finding in this parasite).

Front 120

Back 120

Sparganosis.
Section of a subcutaneous lump removed from the left thigh of an 81 year old farmer. In the centre of an abscess within the lump there is a degenerate worm surrounded by a brisk acute on chronic inflammatory cell reaction.

Front 121

Back 121

Sparganosis.
The wall of a somewhat degenerate sparganum larva.

Front 122

Back 122

Cysticercosis.
An almost complete Taenia solium tapeworm that was passed after the patient had been given treatment to expel the worm. The head end is at the upper part of the photograph. It is thinner than the distal end, which contains the gravid proglottids, filled with eggs. The head of the worm is missing.

Front 123

Back 123

Cysticercosis.
Closer view of the scolex (head) of a Taenia solium. There is a row of hooklets above the part of the scolex which bears the four suckers. The presence of a worm in the intestine usually causes no observable symptoms. Fragments of proglottid may be passed in the faeces, and the patient may notice the presence of motile fragments of flat, white, soft tissue. Otherwise, symptoms are related to the presence of cysticerci.

Front 124

Back 124

Cysticercosis.
Longitudinal section through one of the gravid proglottids. Genital pores occur laterally in the middle of the proglottids. They open on alternate sides of succeeding proglottids.

Front 125

Back 125

Cysticercosis.
Closer view of the genital pore. The vagina opens superiorly as a well defined tube. The vas deferens is a smaller tube and is somewhat twisted as shown by the presence of large numbers of transverse sections leading away from the genital pore. The testis consists of multiple small rounded structures in the connective tissue septum between the branches of the uterus towards the right side of the photograph.

Front 126

Back 126

Cysticercosis.
High power view of the multi-branched uterus filled with eggs.

Front 127

Back 127

Cysticercosis.
Eggs in the feces. They are a brown colour, round with a thick capsule. They measure approximately 36 microns in diameter.

Front 128

Back 128

Cysticercosis.
Under diffracted light (Figure 29.8) radial striations can be seen in the capsule of the egg. Eggs from all species of tapeworm are morphologically identical.

Front 129

Back 129

Cysticercosis.
The lump is 10mm in diameter and it was removed with some surrounding adipose tissue. The lump was a cysticercus. The piece on the right includes the cysticercus with the white nodule of the head (scolex) within it. The remainder of the cyst on the left consists only of cyst wall.

Front 130

Back 130

Cysticercosis.
In the specimen on the left, the membrane of the cysticercus has been cut in two pieces. Both of them have separated easily from the surrounding tissue response of the body. In the specimen on the right the cysticercus has floated out of the cystic cavity. These macroscopic features of the surgical specimen can cause diagnostic confusion for the histopathologist.

Front 131

Back 131

Cysticercosis.
Unless the scolex is included in the section the histopathologist may get a section. Here the only abnormality is an empty cyst lined by granulation tissue.

Front 132

Back 132

Cysticercosis.
The correct approach would be to section not only the cyst wall, but also the cysticercus itself. Now, one sees the head of the new worm and the wall of the cysticercus.

Front 133

Back 133

Scolex of a cysticercus.

Front 134

Back 134

Cysticercosis.
Scolex of a cysticercus.

Front 135

Back 135

Cysticercosis.
multiple, soft, subcutaneous lumps, each approximately 10mm in diameter on the right upper arm and chest. This 29 year old agricultural student from Thailand had multiple similar lumps over all parts of his body. He had a fairly heavy infection of sub-cutaneous cysticerci.

Front 136

Back 136

Cysticercosis.
A number of calcified areas in his calf muscle. These represent degenerate cysticerci that have become calcified.

Front 137

Back 137

Cysticercosis.
A section through muscle in which there are multiple cysticerci present.

Front 138

Back 138

Cysticercosis.
A section through muscle in which there are multiple cysticerci present.

Front 139

Back 139

Cysticercosis.
Undersurface of the temporal lobe of the brain. There are two transparent cysticerci under the leptomeninges at the anterior end of the temporal lobe. This was an incidental post mortem finding in a 72 year old male immigrant to Australia from Pakistan.

Front 140

Back 140

Cysticercosis.
Undersurface of the temporal lobe of the brain. There are two transparent cysticerci under the leptomeninges at the anterior end of the temporal lobe. This was an incidental post mortem finding in a 72 year old male immigrant to Australia from Pakistan.

Front 141

Back 141

Cysticercosis.
Low power microscopic section which shows the head and thin wall of the cysticercus. The surrounding brain shows a thick membrane formed by gliosis.

Front 142

Wet mounts are good for looking for which parasites?

Back 142

Motile trophozoites and cyst forms.

Front 143

Detection of what is enhanced by adding a dilute iodide to a wet mount?

Back 143

Cyst forms.

Front 144

Modified acid-fast stains are positive with which parasites?

Back 144

Cryptosporidium, cyclospora, and isospora.

Front 145

Genital pore injection is used to aid in the diagnosis of what species?

Back 145

Taenia.

Front 146

What does genital pore injection determine?

Back 146

Uterine branching pattern of Taenia species.

Front 147

What are the uterine branching patterns for the various types of Taenia species?

Back 147

T. solium = <13 lateral branches.
T. saginatum = >13 lateral branches.
Dipylidium caninum = 2 genital pores.

Front 148

What are amebae (sarcodinia)?

Back 148

Unicellular organisms that are motile by pseudopodal extension.

Front 149

What is the primary pathogen in the amebae?

Back 149

Entamoeba histolytica.

Front 150

What are the features of E. histolytica?

Back 150

The nucleus is characteristically a small, central karyosome with finely beaded heterochromatin that is applied evenly to the innter nuclear membrane. Can have ingested red cells in the cytoplasm. Display progressive unidirectional motility under direct examination in wet mounts. Cyst forms have up to 4 nuclei and chromatoidal bodies with smooth, rounded, ends.

Front 151

What are the clinical manifestations of E. histolytica?

Back 151

It is acquired through ingestion of cysts in contaminated food or water. It is the main cause of intestinal amebiasis, which consists of protracted diarrhea. Can lead to extraintestinal manifestations such as amebic abscess within the liver, spleen, or brain that are described as having anchovy paste-like material. The lesion if intestinal amebiasis is the "flask-shaped" ulcer in the cecum. Protracted infection can lead to a napkin-ring lesion (ameboma) that mimics adenocarcinoma.

Front 152

Back 152

Entamoeba histolytica

Front 153

Back 153

Entamoeba histolytica.

Front 154

Back 154

Entamoeba histolytica cyst.

Front 155

How is entamoeba coli distinguished from entamoeba histolytica?

Back 155

Entomoeba coli has nondirectional motility, eccentric karyosome, clumped nuclear chromatin, frayed chromatoidal bodies, and has up to 8 nuclei in cyst forms. Also, E coli does not contain ingested red cells.

Front 156

How is entamoeba hartmanii distinguished from E. histolytica?

Back 156

E. histolytica is larger (25 μm) than E. hartmanii (5-10 μm).

Front 157

How is entamoeba nana distinguished from E histolytica?

Back 157

E nana has a large knobby "ball and socket" central karyosome. The cyst form has the same nuclei and lacks chromatoidal bodies.

Front 158

Back 158

Entamoeba coli.
Has the characteristic eccentric karyosome.

Front 159

Back 159

Entamoeba coli.
Eccentric karyosome.

Front 160

Back 160

Amebae

Front 161

Back 161

Entamoeba nana.
Trichrome stain.

Front 162

What is the appearance of Iodamoeba butschlii?

Back 162

The cyst has a prominent iodine-staining vacuole. The trophozoite and cyst form have a large "ball and socket" central karyosome, but the nuclear membrane is inconspicious.

Front 163

Back 163

Iodamoeba butschlii.

Front 164

Back 164

Iodamoeba butschlii.

Front 165

What is the classic history of infection with Naegleria fowleri?

Back 165

Fatal meningoencephalitis arising in children who have been swimming in fresh-water pools. The frontal lobe is infected via the cribriform plate, and the infection is fatall within days.

Front 166

What does Acanthamoeba cause?

Back 166

Granulomatous amebic encephalitis (GAE) and contact lens-associated acanthamoebic keratitis.

Front 167

Where can Naegleria fowleri and Acanthamoeba be found?

Back 167

Soil, water, and other environmental substrates.

Front 168

How is Naegleria fowleri cultured?

Back 168

N. fowleri found in CSF can be cultured on a lawn of inactivated Escherichia coli. A visible trail formed when the ameba moves across the plate ingesting the E. coli is confirmatory.

Front 169

Back 169

Naegleria fowleri.
The clear spaces around the trophozoites represents shrinkage of the amebae.

Front 170

What is the microscopic appearance of Giardia lamblia?

Back 170

They are kite-shaped when viewed from the top with a central axostyle running along their length. The flagella are not easily seen. From the side view, the organisms are comma-shaped. The cysts are oval, thick-walled, and have 4 nuclei located along a central axostyle.

Front 171

What is the characteristic motility of Giardia lamblia on wet mount called?

Back 171

"Falling-leaf" motility.

Front 172

What is the most common cause of protozoal gastroenteritis?

Back 172

Giardia.

Front 173

Back 173

Giardia lamblia cyst.
Trichrome stain.

Front 174

Back 174

Giardia lamblia.

Front 175

What is Chilomastix mesnili?

Back 175

It is a nonpathogenic lumen-dwelling flagellate. It lasck a central axostyle, has rotary motion, and has only anteriorly located flagella. The cyst form has a single nucleus located adjacent to a safety pin-shaped structure. There is tapering of the end opposite the nucleus.

Front 176

Back 176

Chilomastix mesnili.

Front 177

Back 177

Chilomastix mesnili.

Front 178

What is the microscopic appearance of Dientamoeba fragilis?

Back 178

It is a round binucleate structure that has a nucleus with a fragile central karyosome. There is a single flagellum which appears attached to the wall of the organism at several points.

Front 179

What does Dientamoeba fragilis cause?

Back 179

It can cause diarrhea and anal pruritus, particularly in children.

Front 180

What is the microscopic appearance of Trichomonas vaginalis?

Back 180

It is a pear-shaped organism with 2 nuclei located at the anterior end of a central axostyle. Has an undulating membrane that extends halfway down the organism.

Front 181

What is Trichomonas hominis?

Back 181

It is a nonpathogenic organism that has a single nucleus located at the anterior end of a central axostyle. Has an undulating membrane that extends along the top of and all the way down the organism.

Front 182

Back 182

Trichomonas vaginalis.

Front 183

Back 183

Trichomonas vaginalis.

Front 184

Back 184

Trichomonas hominis.

Front 185

What is Trypanasoma cruzi?

Back 185

It is the cause of Chagas disease (American trypanosomiasis). It is a cause of congestive heart failure and achalasia. It is acquired from the reduviid bug, whose inoculation site (Chagoma) when present about the eye is called the Romaña sign.

Front 186

What is Trypanasoma brucei?

Back 186

It is the cause of African sleeping sickness (African trypanosomiasis), an acute febrile illness that results in death. Acquired through the tsetse (glossina) fly. East African trypanosomiasis is caused by T. brucei rhodesiense. West African trypanosomiasis is caused by T. brucei gambiense.

Front 187

Which has the larger kinetoplast: T cruzi or T brucei?

Back 187

T cruzi.

Front 188

On what medium can trypanasoma species be culture?

Back 188

Novy-MacNeal-Nicolle medium.

Front 189

Back 189

Trypanasoma cruzi.

Front 190

Back 190

Trypanasoma cruzi.

Front 191

Back 191

Trypanosoma cruzi.
Amistigotes in heart.

Front 192

Back 192

Trypanosoma brucei.
Delicately curved structures with an undulating flagellum that is attached along its length, ending in a whip-like tail.

Front 193

Back 193

Trypanosoma brucei.
Delicately curved structures with an undulating flagellum that is attached along its length, ending in a whip-like tail.

Front 194

What is the only ciliate?

Back 194

Balantidium coli.

Front 195

What is the microscopic appearance of Balantidium coli?

Back 195

A 50-70 μm organism with cilia uniformly covering its surface. Has a kidney bean-shaped macronucleolus. The cyst form has cilia that can be seen beneath the outer cyst wall as well as the kidney bean-shaped macronucleolus.

Front 196

Back 196

Balantidium coli trophozoite.

Front 197

Back 197

Balantidium coli cyst.

Front 198

What does Cryptosporidium parvum cause?

Back 198

It is a major cause of protracted diarrhea in immunocompromised patients. It can also ascend the biliary tree to cause strictures.

Front 199

What is the microscopic appearance of Cryptosporidium parvum?

Back 199

It is a dome-shaped 8-15 μm, basophilic structure that appears to be adherent to the small intestine brush border but is in acutality located within an apical vacuole.

Front 200

Back 200

Cryptosporidium parvum.

Front 201

Back 201

Cryptosporidium parvum.
The eggs are weakly acid-fast.

Front 202

Back 202

Isospora belli.

Front 203

Back 203

Isospora belli.

Front 204

Back 204

Isospora belli.

Front 205

What is the microscopic appearance of Isospora belli?

Back 205

Thin elliptical structures with weakly acid-fast eggs with one (unsporulated) or two (sporulated) sporocysts.

Front 206

What is the microscopic appearance of microsporidium?

Back 206

Microsporidia appear in small intestinal biopsies as numerous tiny intracellular organisms within the apex of enterocytes.

Front 207

Back 207

Microsporidium.

Front 208

What is Cyclospora?

Back 208

It is an organism acquired from ingestion of contaminated fruit and leafy vegetables in Nepal, Peru, Haiti, and Guatemala. It is acid-fast by modified techniques.

Front 209

What is the characteristic syndrome of Cyclospora infection?

Back 209

Several days of fever, severe watery diarrhea, followed by an extended period of anorexia and fatigue.

Front 210

What is the pathogenesis of Sarcocystis?

Back 210

It is acquired from beef or pork and leads to self-limited gastroenteritis.

Front 211

What is the microscopic appearance of Sarcocystis?

Back 211

It appears as an hour glass-shaped eggs with two sporocysts.

Front 212

Back 212

Sarcocystis.

Front 213

What is the definitive host for Toxoplasma gondii?

Back 213

Cat. Infection is acquired through ingestion of material contaminated with cat feces.

Front 214

What is the risk if maternal infection of Toxoplasma gondii occurs in the first trimester of pregnancy?

Back 214

Risk of fetal loss.

Front 215

What is the risk if maternal infection of Toxoplasma gondii occurs in late pregnancy?

Back 215

Risk of fetal CNS infection that centers around the retina and ventricles, with the residual effect of periventricular calcification and chorioretinitis.

Front 216

Are women previously infected with Toxoplasma gondii safe from intrauterine toxoplasmosis infection?

Back 216

Yes.

Front 217

With what symptoms does a person present with Toxoplasma gonddi infection?

Back 217

Mononucleosis-like syndrome (fever and posterior cervical lymphadenopathy).

Front 218

What laboratory values suggest recent Toxoplasma gondii infection?

Back 218

IgG titers >1:1024 or still rising.

Front 219

What establishes the diagnosis of congenital and acute infection of Toxoplasma gondii?

Back 219

Anti-toxoplasma IgM.

Front 220

What is the microscopic appearance of Toxoplasma gondii?

Back 220

The tachyzoite is a small curved, 3-5 μm free form of the organism. The bradyzoite is a pseudocyst form of the organism in which numerous organisms are packed into the cytoplasm of a histiocyte. Giemas is good for demonstrating the organism.

Front 221

Back 221

Toxoplasma gondii.
Tachyzoite.

Front 222

Back 222

Toxoplasma gondii.
Bradyzoite.

Front 223

Fever spikes every 48 hours (tertian fever) for which species of Plasmodium?

Back 223

P. falciparum, P. ovale, P. vivax.

Front 224

Fever spikes every 72 hours (quartan fever) for which species of Plasmodium?

Back 224

P. malariae.

Front 225

Which species of Plasmodium is called malignant tertian malaria and why?

Back 225

P. falciparum due to its lethality and every other day fever.

Front 226

Which species of Plasmodium are called benign tertian malaria?

Back 226

P. vivax and P. ovale.

Front 227

Which Plasmodium is associated with nephrotic syndrome?

Back 227

P. malariae.

Front 228

Which Plasmodium is associated with CNS involvement?

Back 228

P. falciparum.

Front 229

Relapse is seen in which species of Plasmodium?

Back 229

P. vivax and P. ovale.

Front 230

Which species of Plasmodium infect younger erythrocytes?

Back 230

P. vivax and P. ovale.

Front 231

Which species of Plasmodium infects older erythrocytes?

Back 231

P. malariae.

Front 232

Which species of Plasmodium infects any erythrocytes?

Back 232

P. falciparum.

Front 233

Where do most cases of P. ovale infection occur?

Back 233

Western Africa.

Front 234

What blood group antigen mediates attachment of P. vivax?

Back 234

Duffy.

Front 235

What condition is protective against P. falciparum?

Back 235

Hemoglobin S trait (HbSA).

Front 236

What condition is protective against all Plasmodium species?

Back 236

Glucose-6-phosphate dehydrogenase (G6PD).

Front 237

What are the morphological features of P. falciparum?

Back 237

Only early ring forms and gametocytes are seen within peripheral blood erythrocytes. Multiple rings may be seen in a single erythrocyte. Schizonts are not usually seen. Gametocytes are banana-shaped. Infected RBCs are not enlarged.

Front 238

What are the morphological features of P. malariae?

Back 238

Infected erythrocytes are not enlarged, no Schuffner dots, schizonts have 6-12 nuclei, coarse malarial pigment may be present.

Front 239

What are the morphological features of P. vivax and P. ovale?

Back 239

Infected RBCs are slightly enlarged, gametocytes are amoeboid in shape, schizonts have 12-14 nuclei, P. ovale is associated with fimbriated erythrocytes.

Front 240

Back 240

Plasmodium ovale.

Front 241

Back 241

Plasmodium vivax.

Front 242

What is the microscopic appearance of Babesia microti?

Back 242

The trophozoites are usually multiple, located within RBCs, and form tetrads or Maltese cross arrangements. Extraerythrocytic ring forms are present, unlike Plasmodium species.

Front 243

How is Babesia microti acquired?

Back 243

The tick Ixodes dammini.

Front 244

What are the clinical features of Babesia microti infection?

Back 244

Nonperiodic fever and hemolysis, leukopenia, abnormal liver function tests, death.

Front 245

What are the clinical features of Pneumocystis carinii infection?

Back 245

Presents as a bilateral (butterfly) pulmonary infiltrates in an immunocompromised patient.

Front 246

What is the microscopic appearance of Pneumocystis carinii?

Back 246

The trophozoite appears as 5 to 8 μm concave discs when their walls are stained with GMS. There is a characteristic frothy exudate which suggests the organisms presence.

Front 247

Back 247

Pneumocystis carinii.

Front 248

Back 248

Pneumocystis carinii.

Front 249

Back 249

Pneumocystis carinii.

Front 250

What is the pathogenesis of Echinococcus?

Back 250

It is acquired when ingesting food contaminated with stool of an infected dog. Sheep and cattle are intermediate hosts. Results in the formation of cysts in various organs, particularly the liver.

Front 251

How many cysts are seen in Echinococcus granulosis?

Back 251

One or several unilocular hydatid cysts.

Front 252

How many cysts are seen in Echinococcus multilocularis?

Back 252

Multilocular cysts are seen.

Front 253

Polycystic hydatid cyst disease is seen with which species of Echinococcus?

Back 253

Echinococcus vogeli.

Front 254

Back 254

Echinococcus granulosis egg.

Front 255

Back 255

Echinococcus granulosis larvae.

Front 256

Back 256

Echinococcus granulosis.

Front 257

What is the microscopic appearance of Dipylidium caninum?

Back 257

It occurs in globular packets of 5-6 eggs enclosed by a thin membrane. The proglottis has a double genital pore, one exiting out of each side.

Front 258

What is the pathogenesis of Dipylidium caninum?

Back 258

It commonly infects cats and dogs and occasionally children.

Front 259

Back 259

Dipylidium caninum.
The proglottis has a double genital pore.

Front 260

Back 260

Dipylidium caninum.
The egg consists of globular packets of 5-6 eggs enclosed by a thin membrane.

Front 261

What is the microscopic appearance of Hymenolepsis nana (dwarf tapeworm)?

Back 261

The egg consists of an inner shell and an outer shell with a wide space in between. The inner shell has two polar thickenincs, pairs of filaments that look like tiny bows.

Front 262

What is the pathogenesis of Hymenolepsis nana infection?

Back 262

It is a cestode that follows ingestion of contaminated water or food, the typical contaminant being rodent droppings.

Front 263

How is Hymenolepsis nana distinguished from Hymenolepsis diminuta?

Back 263

H. diminuta does not have the pairs of filaments that look like bows.

Front 264

Back 264

Hymenolepsis nana.

Front 265

Back 265

Hymenolepsis nana.

Front 266

Back 266

Hymenolepsis diminuta.

Front 267

What is the pathogenesis of Diphyllobothrium latum?

Back 267

It is a fish tapeworm found in temperate zones and acquired through the ingestion of poorly-cooked freshwater fish. Infection can become complicated by vitamin B12 deficiency.

Front 268

What is the morphology of Diphyllobothrim latum?

Back 268

The egg is a 60-70 μm oval structure with a smooth shell and an unshouldered operculum ("hatch door) at one end and a small abopercular knob on the other end. The scolex appears as an elongated almond with longitudinal grooves. Each proglottid is characteristically wider than it is long.

Front 269

Back 269

Diphyllobothrium latum.
The uterus is rosette-shaped.

Front 270

Back 270

Diphyllobothrium latum.
Almond-shaped scolex.

Front 271

Back 271

Diphyllobothrium latum.
Egg.

Front 272

Back 272

Diphyllobothrium latum egg.

Front 273

What is the pathogenesis of Taenia solium?

Back 273

The pork worm is seen in the US most commonly with recent imitration. Infection occurs with ingestion of encysted organisms (cysticerci) in pork. Cysticersosis is a condition in which cysts containing larvae are found in the brain and elsewhere.

Front 274

What is the microscopic appearance of Taenia solium?

Back 274

The eggs are spherical with a thick radially striated wall and contains 3 pairs of hooks. The scolex has 4 suckers and many tiny hair-like hooks on its surface (armed rostellum). The proglottids are short and have <13 lateral uterine branches. An invaginated scolex with a double row of hooklets that are acid-fast and birefringent is key.

Front 275

Back 275

Taenia solium.
Scolex.

Front 276

Back 276

Taenia solium.
Eggs.

Front 277

What is the pathogenesis of Taenia saginata?

Back 277

It is common in South and Central American and acquired by ingestion of encysted organisms (cysticerci) in beef. Results in small bowel infestation by the adult worm.

Front 278

What is the microscopic appearance of Taenia saginata?

Back 278

The egg is spherical, 30-40 μm, has a thick radially striated wall, and contains 3 pairs of hooks. The scolex has 4 suckers and a smooth surface (unarmed rostellum). Each proglottis is elongated and has >13 lateral uterine branches.

Front 279

Back 279

Taenia saginata.
Scolex.

Front 280

Back 280

Taenia saginata.
Proglottid.

Front 281

What is the microscopic appearance of Leishmania species?

Back 281

They appear as multiple tiny 2-5 μm intracellular amastigotes within histiocytes. THe amastigote lacks an external flagellum. Appear as oval structures with a nucleus adjacent to a bar-like kinetoplast.

Front 282

How is Leishmania species cultured?

Back 282

It is cultured on Novy-MacNeal-Nicolle medium.

Front 283

Which form of Leishmania species is seen on culture?

Back 283

Promastigote.

Front 284

What is the pathogenesis of Leishmania?

Back 284

It is acquired from the sandfly (genuses Phlebotomuc and Lutzomyia).

Front 285

What are the clinical manifestations of cutaneous leishmanias?

Back 285

L. tropica, L. major, and L. aethiopica can result in a solitary cutaneous lesion that is self-limiting (L. aethiopica can dissieminate). Seen principally in the Mediterranean.

Front 286

What does Leishmania donovani cause?

Back 286

Widespread systemic disease (visceral leishmanias or kala azar) associated with hepatosplenomegaly and bone marrod infection. Found in Africa, Asia, India, and the Middle East.

Front 287

What does Leishmania mexicana cause?

Back 287

It resutls in new-world leishmania, which is a self-limiting solitary cutaneous lesion (chiclero ulcer of the ear lobe) seen in SOuth America and Texas.

Front 288

What does Leishmania braziliensis cause?

Back 288

It results in a form of new-world leishmaniasis known as mucocutaneous leishmaniasis that is characterized by persistent cutaneous and mucosal lesions. Seen in South and Central America.

Front 289

Back 289

Leishmaniasis.

Front 290

Back 290

Leishmaniasis.