This document provides an overview of several opportunistic coccidian parasites that can cause disease in immunocompromised individuals: Toxoplasma gondii, Cryptosporidium parvum, Cyclospora cayetanensis, Isospora belli, and Sarcocystis species. It describes the morphology, life cycles, epidemiology, clinical features, diagnosis, treatment and prevention of infections caused by each parasite. Toxoplasma gondii is an intracellular parasite that can cause severe disease in HIV/AIDS patients. Cryptosporidium is an intestinal parasite commonly seen in HIV patients and a major cause of diarrhea. Cyclospora causes intermittent diarrhea and is prevalent

1. Opportunistic Coccidian Parasites
By,
Bajarangi lal Chaudhary
Ph.D. Scholar

2. Chapter Outline
• Introduction
• Toxoplasma gondii
• Cryptosporidium parvum
• Cyclospora cayetanensis
• Isospora belli
• Sarcocystis species

3. Introduction
• Coccidian parasites can be divided into three
orders: (1) Eimeriida, (2) Haemosporida and
(3) Piroplasmida.
• Toxoplasma is an intracellular parasite that can
cause congenital infections and also
opportunistic infections in HIV infected
patients.
• Cryptosporidium, Cyclospora and Isospora
can cause opportunistic infections.

4. TOXOPLASMA GONDII
• Toxoplasma gondii is an obligate intracellular
parasite affecting a wide range of mammals
and birds including humans.

5. Morphology Toxoplasma gondii

6. Life cycle

7. Pathogenicity and Clinical features
• The most common parasitic zoonotic
infections and its prevalence 5–75%
• The geographical area
• Age:
• Food habits:
• Immune status:

8. Toxoplasmosis in
Immunocompetent Patients
• Both the humoral and the cellular immune
responses control the infection.
• Activated macrophages, produce parasiticidal
antibody, production of IFN-γ, and stimulation
of CD8+ cytotoxic T lymphocytes.
• Lymphadenopathy:

9. Toxoplasmosis in Immunocompromised
Patients
• The tachyzoites are disseminated to a variety
of organs, particularly lymphatic tissue,
skeletal muscle, myocardium, retina, placenta
and the central nervous system.
• Toxoplasmosis in patients with HIV mainly
targets CNS leading to Toxoplasma
encephalitis (TE)
• TE develops when the CD4+ T cell count falls
below 100/μL.

10. Congenital Toxoplasmosis
• If the mother becomes infected during the first
trimester, the incidence of transplacental
infection is lowest (15%), but the disease in
the neonate is most severe.
• If the mother is infected before pregnancy,
then the fetus is mostly uninfected except
when the mother is immunocompromised.

11. Laboratory Diagnosis
• Specimens:
• Peripheral blood, body fluids, lymph node
aspirate, bone marrow aspirate, CSF and
bronchoalveolar lavage for HIV infected
patients, biopsy material from spleen, liver and
brain
• These specimens are stained with Giemsa,
PAS, silver stains, immunoperoxidase stain.

12. Toxoplasma gondii (A) Severe, active retinochoroiditis seen in
Toxoplasmosis; (B) Giemsa stain showing comma shaped
tachyzoites in the smear; (C) Histopathology of brain shows
pseudocyst containing numerous tachyzoites; (D) Tissue cyst
containing bradyzoites (section of brain stained with
hematoxylin and eosin)A
B C
D

13. Antibody detection
• Sabin-Feldman dye test
• Detection of IgG in serum:
• IgG avidity test:
• Detection of IgM in serum:
• Differential absorption test:

14. Detection of Toxoplasma Antigens
• ELISA is available to detect specific
Toxoplasma antigens in blood or body fluids or
amniotic fluid.
• Detection of antigen indicates acute infection.
• This is also useful to diagnose congenital
infection.

15. Treatment
• Immunocompetent patients
• Congenital toxoplasmosis
• Immunocompromised patients
(i) Primary prophylaxis
(ii) Secondary prophylaxis (Long-term
maintenance therapy)

16. Prevention
• Consumption of cooked meat.
• Proper hygiene maintenance and hand cleaning of
people handling cats and other felines.
• Regular prenatal and antenatal screening to
detect Toxoplasma infection in women of child
bearing age.
• Avoiding cat’s feces (oocyst) contaminated
materials (like a cat’s litter box)
• Screening of blood banks or organ donors for
antibody to T. gondii.

17. CRYPTOSPORIDIUM PARVUM
• Intestinal coccidian parasite affecting various
animals and men.
• It is an opportunistic pathogen infect
immunocompromised patients (including HIV
infected patients), and causing chronic
persistent life threatening diarrhea.

18. Morphology
(A) Cryptosporidium (B) Cyclospora
(C) Isospora
A B
C

19. Life cycle of Cryptosporidium parvum

20. Epidemiology
• Cryptosporidiosis is a zoonotic disease.
• In immunocompetent people, the prevalence in
developing countries like India varies from 2.4 to
15%;
• western countries it is 1.4–6%
• In immunocompromised hosts (HIV positive
patients),
• The prevalence is 12–46% in developing
countries (46% in Haiti) and 7–21% in developed
countries.

21. Pathogenesis and Clinical features
• Attachment: Sporozoites attach to the brush
border epithelium of the small intestine with
the help of a unique protein called as CP47 (47
kDa C.parvum protein)
• Penetration:

22. Laboratory Diagnosis
A. Direct microscopy (Stool examination):-
shows round 4–6 μm size oocyst
a) Direct wet mount
b) Acid fast staining
c) Direct fluorescent antibody staining
B. Antigen detection from stool—ICT, ELISA
C. Antibody detection from serum—ELISA
D. Molecular diagnosis—PCR
E. Histopathology of intestinal biopsy specimen

23. (A) acid fast stain shows red color oocyst against blue back ground;
(B) direct fluorescent antibody staining shows brilliant green
fluorescent oocysts; (C) hematoxylin and eosin stain of intestinal
biopsy shows numerous oocysts at the luminal surface of the
intestinal crypt (marked by arrows)
A B C

24. Treatment
• Mild cases are self limited, requires fluid
replacement like ORS, with lactose-free gluta-
mine supplemented diet.
• Severe cases: Nitazoxanide is given to adults
(500 mg twice daily for 3 days).
• Paromomycin can be given as an alternate.
Macrolide antibiotics including spiramycin,
azithromycin and clarithromycin have some
activity against Cryptosporidium species.

25. Prevention
• Requires minimizing exposure to infectious
oocysts in human or animal feces
• Proper hand washing, use of submicron water
filters, improved personal hygiene are some of
the efforts to prevent transmission

26. Cyclospora cayetanensis
• Cyclospora cayetanensis is the most recently
described coccidian parasite as human
intestinal pathogen.
• It is named by Schneider in 1881 and human
infection was described by Ashford in 1979

28. Epidemiology
• Disease is prevalent in Central America and
South Asia.
• More cases are reported from Haiti (11% of
AIDS related diarrhea), children of Nepal
(32%) and travelers coming to India, Pakistan
and Morocco.
• less common in African countries.

29. Laboratory Diagnosis
• Stool examination-Shows round oocysts
• Wet mount examination
• Acid fast stain—shows variably acid fast
oocysts
• UV epifl uorescence microscopy—shows auto
fluorescence oocysts
• Molecular diagnosis—rt-PCR
• Serology (antibody detection)
• Histopathology of intestinal biopsies

30. Cyclospora species
(A) saline mount preparation showing unsporulated
Oocyst (B) epifluorescence microscopy showing
autofl ourescent oocysts
A B

31. Cyclospora species modifi ed acid
fast stain shows variable acid fast oocyst
(A) acidfast oocysts, (B) non acid fast oocysts

32. ISOSPORA BELLI
• Isospora belli is the only species that infects
man.
• It belongs to the family sarcocystiidae.
• It was first described by Virchow in 1860 and
was named by Wenyon (1923).

33. Morphology
• Oocyst
• Th e sporulated oocyst is
oval/elliptical, 23 to 36 μm ×
12 to 17 μm in size, contains
two sporocysts, each with
four sporozoites. The oocyst
is surrounded by a thin,
smooth, two layered cyst
wall

34. Life Cycle

35. Epidemiology
• Isosporiasis is found worldwide but
predominantly in tropical and subtropical
climates, especially in South America, Africa,
and Southeast Asia including India.
• It is frequently associated in AIDS patients,
prevalence ranging from 3% (USA) to 37%
(Zambia).
• However, it is rare in HIV infected children
(different from cryptosporidiosis).

36. Clinical Feature
• Profuse watery diarrhea and extr-aintestinal
infections such as involvement of biliary tract.

37. Laboratory Diagnosis
• Stool examination (by wet mount, acid fast
stain)—detects oval oocysts
• Molecular diagnosis—PCR
• Histopathology of tissue sections from small
bowel

38. Treatment
• Twice daily for 7 days followed by suppressive
therapy three times weekly)
• Nitazoxanide has also been used successfully.

39. SARCOCYSTIS SPECIES
• Sarcocystis is a zoonotic parasite.
1. Intestinal sarcocystosis: Caused by S.
hominis and S. suihominis
2. Muscular sarcocystosis: Caused by
• unidentified species of Sarcocystis
• collectively known as S. lindemanni.

40. Morphology
• Oocyst
• Sporocyst
• Sarcocyst

41. Life Cycle

42. Clinical Features
• Intestinal Sarcocystosis: It is usually
asymptomatic but patient may develop nausea,
vomiting, abdominal pain and diarrhea.
• Muscular sarcocystosis: Larger cysts can
cause muscle pain, weakness in muscle or
rarely focal myositis and eosinophilic myositis.

43. Laboratory Diagnosis
• Intestinal sarcocystosis
• Stool microscopy (wet mount)-detects
sporocysts
• Muscular sarcocystosis
• Histological Examination of muscle biopsy
detects sarcocysts
• Serum antibodies—by Western blot

44. Sarcocystis sporocysts containing sporozoites
(A) saline mount;
(B) autofluoresce under UV light sporozoites
are clearly seen

45. Sarcocysts in skeletal muscle biopsy

46. Treatment
• No specific treatment for Sarcocystis infection
is known.
• Infection, if symptomatic, is generally self-
limited.
• Corticosteroids may provide symptomatic
relief in cases of eosinophilic myositis.

47. References
• Essentials Medical Parasitology by Apurba
Sankar Sastry.