Para Mod 7

• Toxoplasma gondii

• Cryptosporidium parvum

• Cyclospora cayetanensis

• Isospora belli

• Sarcocystis species

Coccidian Parasites

(1) Eimeriida

(2) Haemosporida

3) Piroplasmida

Coccidian parasites can be divided into three orders—

Toxoplasma

is an intracellular parasite that can cause congenital infections and also opportunistic infections (encephalitis) in HIV (human immunodeficiency virus) infected patients

Cryptosporidium, Cyclospora and Isospora

are acid fast parasites that can cause opportunistic infections (diarrhea) in HIV infected patients

Sarcocystis

is a rare parasite infecting man and forms cystic lesions in muscles

Micronemes and rhoptries

are specialized secretory organelles in apicomplexan parasites.

Micronemes

Release adhesive proteins that help the parasite attach to and glide along the host cell before invasion.

Rhoptries

Inject effector proteins that manipulate the host cell, enabling parasite entry and survival.

Toxoplasma gondii

▪ is an obligate intracellular parasite affecting a wide range of mammals and birds including humans.

▪ Though human infection is very common affecting nearly one third of world’s population; clinical manifestations are relatively rare, mostly restricting to opportunistic infections in immunocompromised persons and congenital infection in fetus

arles Nicolle and Louis Manceaux (1908)

were the first to discover T. gondii in Tunisia from a North African rodent called as Ctenodactylus gundi

arc or bow

The name Toxoplasma is derived from a Greek word “Toxon” meaning ____ referring to the curved shape of the trophozoites

tachyzoites

referring to the curved shape of the trophozoites

1. two asexual forms (tachyzoite and tissue cyst) and

2. a sexual form (oocyst).

Morphology of Toxoplasma gondii

Tachyzoite

It is an actively multiplying form (trophozoite), usually seen in acute infection

Tachyzoite

➢ Crescent shaped, having a pointed anterior end and a blunt posterior end

➢ It measures approximately 6 µm in length and 2 µm in breadth; contains several dense granules and a round nucleus situated between center and posterior end

➢ They can infect all mammalian (nucleated) cells except red blood cells (RBCs)

➢ At the anterior end, the tachyzoites contain special organelles like rhoptries, and micronemes which are crucial for the adhesion and invasion into the host cell (Fig. 7.1A)

➢ Inside the host cell, tachyzoites are surrounded by a parasitophorous vacuole within which they divide asexually by a process called as internal budding or endodyogeny by which daughter trophozoites are formed within the parent cell. They often form rosettes surrounding the host nucleus

6 um
2 um

Tachyzoite lenght and bradth

Red Blood Cells

Tachyzoite can infect all mammalian (nucleated) cells except

internal budding or endodyogeny

host cell, tachyzoites are surrounded by a parasitophorous vacuole within which they divide asexually by a process called as

Tissue cyst

Toxoplasma gondii
It is the resting stage of the parasite, usually seen in chronic infection

Bradyzoites

Tissue cyst
The parasite multiplies within the host cells and produces a round to oval cyst containing many crescent shaped slowly multiplying trophozoites called as

Bradyzoites

➢ Measure 7 µm in length and 1.5 µm in breadth

➢ More slender, crescent shaped with a nucleus situated posteriorly

➢ Contains several strongly periodic acid Schiff stain (PAS) positive amylopectin granules h Multiply slowly

➢ Seen in chronic infection

➢ More resistant to gastric juice

Oocyst

Toxoplasma gondii

▪ is the sexual form of the parasite found in cats and other felines.

noninfectious

Unsporulated oocyst excreted in cat’s feces is

Humoral and cellular

Toxoplasmosis in Immunocompetent Patients ▪ In the immunocompetent host, both the ____ immune responses control the infection.

Ingestion of sporulated oocysts

Ingestion of tissue cyst containing bradyzoites

By blood transfusion, needle stick injuries, organ transplantation, transplacental transmission or laboratory accidents (tachyzoites are the infective form)

T. gondii is unique among the protozoa as all the three morphological forms can transmit the infection. Transmission to man occurs by:

ingestion of tissue cysts

Cat and other felines (definitive host) acquire infection by _____ in the meat of rodents and other animals.

Gestational age

Congenital toxoplasmosis

is the main factor influencing the fetal outcome. As the gestation proceeds, the chance of transmission increases but the severity of the infection declines

TORCH infection

a term used to denote the agents causing congenital infections

(T) Toxoplasma

(O) Others which includes Treponema pallidum (syphilis), Varicella, etc.

(R) Rubella,

(C)Cytomegalovirus,

(H) Herpes simplex virus,

Meaning of TORCH in “TORCH infection

Sabin-Feldman dye test

This is the gold standard antibody detection method, usually done in the reference laboratories. Other serological tests are evaluated taking this test as standard

1. Sabin-Feldman dye test,

2. enzyme-linked immunosorbent assay (ELISA),

3. indirect fluorescent antibody test (IFA),

4. indirect hemagglutination test (IHA) and

5. latex agglutination test.

Several methods are employed for detecting specific anti T. gondii antibodies like

Detection of IgG in serum

IgG avidity test

Detection of IgM in serum

Differential absorption test

Diagnosis of acute infection with T. gondii

Other antibody tests

intraperitoneal inoculation

T. gondii can be isolated from mice by ____ of the clinical samples into the healthy (T. gondii free) laboratory maintained mice.

Tachyzoites

Mice die in 7–10 days and peritoneal fluid and spleen aspirate smears show

pyrimethamine plus either sulfadiazine or clindamycin and sometimes with prednisolone

Patients with ocular toxoplasmosis are usually treated for 1 month with

pyrimethamine (1 mg/ kg) and sulfadiazine (100 mg/kg) with folinic acid for 1 year

Neonates with congenital toxoplasmosis are treated with daily oral

Encephalitis

Toxoplasmosis is rapidly fatal in immunocompromised patients. If not treated, it may progress to

Primary prophylaxis

Treatment

• Acquired immunodeficiency syndrome (AIDS) patients with Toxoplasma infection, having CD4+ T lymphocyte count of less than 100/µL should receive prophylaxis against Toxoplasma encephalitis (TE).

• Trimethoprim-sulfamethoxazole (cotrimoxazole) is the drug of choice

• Dapsone-pyrimethamine, atovaquone with or without pyrimethamine can be given as alternate

• Prophylaxis can be discontinued in patients who have responded to antiretroviral therapy (ART) and whose CD4+ T lymphocyte count has been more than 200/µL for 3 months.

Secondary prophylaxis (Long-term maintenance therapy)

Treatment

• Required f or HIV positive patients who are previously treated for toxoplasmosis.

• Should be started if the CD4+ T lymphocyte count decreases to less than 200/µL z

• However, it can be discontinued if the patient is asymptomatic, and have a CD4+ T lymphocyte count of more than 200/µL for at least 6 months.

1. Consumption of thoroughly cooked meat

2. Proper hygiene maintenance and hand cleaning of people handling cats and other felines

3. Regular prenatal and antenatal screening to detect Toxoplasma infection in women of child bearing age

4. Avoiding cat’s feces (oocyst) contaminated materials (like a cat’s litter box)

5. Screening of blood banks or organ donors for antibody to T. gondii.

The various methods recommended to prevent toxoplasmosis include:

Cystoisospora belli

Formerly Known as Isospora belli

Isospora belli

Cystoisospora belli formerly known as

Cystoisospora belli

• It is more common in tropical and subtropical countries

• it is a coccidian parasite which causes diarrhea in humans

epithelial cells of the small intestine

In human Cystoisospora belli resides in

elongated, ovoid

Oocysts of C. belli are

25 μm × 15 μm

Oocysts of C. belli are elongated, ovoid and measure

a thin smooth cyst wall

C. belli

Each oocyst is surrounded by

2 sporoblasts

Immature oocyst seen in the feces of patients contains

4 sporozoites

C. belli

Each sporocyst contains

Sporulated oocyst

C. belli

the infective stage of the parasite

enterocytes

C. belli

Some of the trophozoites undergo sexual cycle (gametogony) in the cytoplasm of

macrogametocytes and microgametocytes

Some of the trophozoites undergo sexual cycle (gametogony) in the cytoplasm of enterocytes and transform into _____ and ____

1 host

Cystoisospora belli completes its life cycle in

1 to 4 days

C. belli

Incubation period ranges from

asymptomatic

In C. belli the infection is usually

abdominal discomfort, mild fever, diarrhoea and malabsorption

Clinical Illness of C. belli includes

Ziehl Neelsen stain or Kinyoun acid fast.

In C. belli The staining technique used is modified

co-trimoxazole (160 mg trimethoprim/800 mg sulfamethoxazole orally or i.v. 4 times/day for 10 days)

In C. belli Immunosuppressed patients with diarrhea are treated with

1. Proper fecal disposal

2. Personal hygiene

3. Boiling of drinking water

4. Filtration of drinking water

5. Wash fruits and vegetables with clean water before eating

6. Health education

Prevention and Control of C. belli

Cryptosporidium parvum

• It has a ubiquitous distribution

• Two species, Cryptosporidium hominis (humans are the only natural host) and C. parvum (infects various species of mammals) can cause human infections

• Cryptosporidium causes intractable diarrhea in AIDS patients and immunocompromised persons

small intestine

Cryptosporidium parvum inhabits the _____

thick-walled oocyst

Inferctive form of Cryptosporidium parvum

4-6

C. parvum

he oocyst is small, spherical, or oval and measures about ___ um in diameter

4

C. parvum

Oocysts contain _ crescent shaped sporozoites

60 °C

C. parvum

Oocysts contain 4 crescent shaped sporozoites and can remain viable in the environment for prolonged period and resistant to most disinfectants and temperature up to

ozone

C. parvum
It can survive chlorinated water, but application of ___ is effective in killing the oocysts

ingestion of contaminated water and food

How do humans aquire C. parvum

single host

C. parvum completes its life cycle, sexual and asexual phases in a

2-14 days

Incubation period of C. parvum

10 oocyst

The minimum infectious dose for Cryptosporidium parvum is estimated to be as low as

chlorination

This low infectious dose contributes to Cryptosporidium’s high transmissibility, especially in contaminated water sources where oocysts are resistant to standard

Anti-retroviral therapy (ART)

improves cryptosporidiosis by increasing the host’s immune status

Cyclospora cayetanensis

• It was first reported from Nepal, where it caused outbreaks of prolonged diarrhea

• It is most common in tropical and subtropical areas.

small intestine

C. cayetanensis In human, the parasite is present in the

Sporulated oocyst

infective form of C. cayetanensis

8–10 μm in diameter

C. cayetanensis oocyst measures

2 sporocysts

2 sporozoites

C. cayetanensis contains ____ each sporocyst contains ___

1-7 days

Incubation period od C cayetanensis

autofluorescence under UV ligh

Cyclospora cayetanensis oocysts exhibit _____, which is a key distinguishing feature from other coccidian parasites like Cryptosporidium parvum and Cystoisospora belli.

Blue or green

Under an epifluorescence microscope, Cyclospora oocysts fluoresce ____, making them identifiable without special stains.

• Co-trimoxazole (160 mg trimethoprim/800 mg sulfamethoxazole twice/day for 7 days) is used for its treatment

• Long term suppressive maintenance therapy is given to HIV-infected patients

C. cayetanensis treatment

Sarcocystis

• It is worldwide in distribution • The 3 species that can infect humans

▪ Sarcocystis hominis (transmitted through cattle) ▪Sarcocystis suihominis (transmitted through pig) ▪Sarcocystis lindemanni (unknown mode of transmission)

Sarcocystis

The 3 species that can infect humans are:

Sarcocystis hominis

Sarcocystis that is transmitted through cattle

Sarcocystis suihominis

Sarcocystis that is transmitted through pig

Sarcocystis lindemanni

Sarcocystis that has an unknown mode of transmission

sarcocysts

In sarcocystis When human is the intermediate host, ____are found in the striated muscles

1. Ingestion of cooked beef or pork

2. Freezing meat at −5 °C for several days will kill the sarcocysts

3. Boiling of drinking water

Sarcocystis prevention and control

Blastocystis hominis

• It is globally distributed.

It is a protozoa found in the large intestine of humans, belonging to the Stramenopiles.

stramenophiles

B. hominis is a protozoa found in the large intestine of humans, belonging to the

Vacuolated form

Amoeboid form

Granular form

Cystic form

4 morphological form of Blastocystis hominis