Coccidia

Question 1

Coccidia - generalised lifecycle

Answer 1

Oocyst ingested
Penetrate gut enterocytes
Asexual reproduction cycles producing merozoites
Initiate the sexual cycle
Following fertilsation - ruptures oocysts out of cell and resistant oocysts shed in faeces
Oocyst maturation

Question 2

Cystoisospora belli - diagnosis

Answer 2

Large - up to 30um - oocysts in faeces by light microscopy
-ZN staining - often reticulated

Multiplex PCR - detects cystoisospora, cyclospora, amicrosporidia

Question 3

Cystoisospora belli - criteria for oocysts

Answer 3

Oval shape
Large - normal size 25-30um
May contain undifferentiated mass or two sporocysts
Sporozoites seldom visible

Question 4

Cystoisospora belli - disease

Answer 4

Self-limited watery diarrhoea
-More prolonged and severe in immunocompromised

Question 5

Cystoisospora belli - transmission

Answer 5

Faecal-oral route

Question 6

Cystoisospora belli - treatment

Answer 6

Co-trimoxazole

Question 7

Cryptosporidium species - lifecycle

Answer 7

Unlimited number of asexual cycles [most have limited asexual cycles]
Type 1 meront - propagate asexual cycle
Type 2 meront - go on to sexual cycle
Thin-walled oocyst from zygote can burst causing auto-infection

New evidence:
-3 short [12hr] asexual cycles following single sexual stage
-No type 2 [4N] meronts

Question 8

Cryptosporidium - clinical

Answer 8

Vary from asymptomatic to severe
Watery diarrhoea
-Dehydration, weight loss, abdominal pain, fever, N+V
-Immunocompetent - lasts 1-2 weeks

Question 9

Cryptosporidium - diagnosis

Answer 9

Light microscopy of faecal specimens:
-ZN staining
-Auramine [fluorescent microscopy] = 5um and bright red

Direct FAT and immunochromatographic RDT

PCR

Question 10

Cryptosporidium - organism

Answer 10

C parvum
C hominis

Question 11

Cryptosporidium - transmission

Answer 11

Waterborne
Food borne
Person-to-person
Infected children continue to shed oocysts for up to month after diarrhoea has ceased

Infectious dose small - 100 oocysts
Oocysts highly resistant to chlorine and other disinfectants

Question 12

Cryptosporidium - treatment

Answer 12

No current treatment - paromomycin and nitazoxanide modest benefit

Reason for difficulty in treatment:
-Apicoplast is absent - making a potential drug target unavailable

Question 13

Cyclospora cayetanensis - organism

Answer 13

oocyst with 2 sporocysts with 2 sporozoites in each

Question 14

Cyclospora cayetanensis - diagnosis

Answer 14

Light microscopy:
-Oocysts 8-10um [compared to 5um for cryptosporidium]
-Acid-fastness = variably acid-fast
-‘Broken glass’ contents

Question 15

Cyclospora cayetanensis - clinical

Answer 15

Can be asymptomatic
Watery, sometimes explosive diarrhoea

Question 16

Cyclospora cayetanensis - treatment

Answer 16

Co-trimoxazole

Question 17

Toxoplasma gondii - transmission

Answer 17

Undercooked meat containing cysts
Oocysts in infected feline faeces

Question 18

Toxoplasma gondii - lifecycle

Answer 18

Oocysts hatch in small bowel
Penetration of cell - rapid multiplication - tachyzoites
-Cell ruptures
-Can infect any cell with nucleus
Disseminates from gut to throughout the body
-Tachyzoite invasion of leucocytes promotes their migratory phenotype

After 10-14 days - cyst formation
-Cysts in brain and muscle = slow multiplication [bradyzoites]

Question 19

Toxoplasma gondii - clinical

Answer 19

80-90% asymptomatic
Severe disseminated infections in immunocompromised
Congenital toxoplasmosis

Question 20

Toxoplasma gondii - congenital toxoplasmosis

Answer 20

Tachyzoites can cross the placenta - only the first attack of toxoplasmosis puts baby at risk
Increased risk of perinatal death or stillbirth
Cerebral calcifications
Ocular toxoplasmosis [retinal lesions - bilateral central retinochoroidial lesions]

Question 21

Toxoplasma gondii - population structure

Answer 21

3 clonal lineages - 1, 2 and 3 = genotype 2 most common

Question 22

Toxoplasmosis gondii - diagnosis

Answer 22

Serology - IgG persistent
Maternal IgM - often regarded as new infection
High avidity IgG rules out recent [<4 months] infection
IgM or IgA in newborn indicates infection

Antigen detections by PCR

Question 23

Toxoplasma gondii - treatment

Answer 23

Immunocompetent adults rarely need treatment

Newly infected pregnant women:
-Spiramycin [macrolide]
-Pyrimethamine + sulphonamide [not in 1st trimester as teratogenic]