Tissue coccida TOXOPLASMA

Lecture NO 11Mrs. Dalia Kamal Eldien

MSC in Microbiology

Objectives

Introduction to Coccidia class& the taxonomyToxoplasma gondii as example of tissue coccidiaMorphology Toxoplasma gondii (oocyst, tachyzoite

& bradyzoite)Mode of transmissionPathogenicityPregnancy precautionsLife cycle in definitive& intermediate hostLaboratory diagnosis

Introduction

Coccidia (Coccidiasina) are a subclass of microscopic spore-forming, single-celled, obligate intracellular parasites belonging to the  Apicomplexa phylum and class Sporozoa.

As obligate intracellular parasites, they must live and reproduce within an animal cell.

The common of the tissue coccidia that infect humans is Toxoplasma

Taxonomy

• Kingdom Animalia• Subkingdom Protozoa• Phylum Apicomplexa• Class Sporozoa• Order Coccidia• Genus Toxoplasma• Species gondii

Toxoplasma gondii

Is an obligate intracellular parasitic protozoan that causes the disease toxoplasmosis.

Found worldwide,  In humans, it is one of the most common parasites, serological studies estimate that up to a third of the global population has been exposed to and may be chronically infected with T. gondii

The parasite infects most genera of warm-blooded animals, including humans, but the primary host is the felid cat family

The definitive host of T. gondii is the cat, but the parasite can be carried by many warm-blooded animals (birds or mammals).

Morphology

3 forms :Oocyst : oval in shape, contains 2 sporocystes each

contains 4 sporozoites, which are shed in the feces. Tachyzoite: rapidly multiplying trophozoite, acute state,

found intracellularly in phagocytic cells, cresentic in shape, one rounded end & other pointed end, one nucleus towards the rounded end.

Bradyzoite: slowly multiplying form, found intracellularly in tissues chronic stage-pseudocyst

Tissue cysts: walled structures, often found in the muscles and central nervous system (CNS), containing dormant T. gondii bradyzoites.

Oocysts of Toxoplasma gondii

Tachyzoite

Tachyzoite

Bradyzoite

Bradyzoite

Transmission

Carnivores and omnivores, including humans, can become infected when:-

Consumption of raw or undercooked tissues containing tissue cysts or, occasionally, tachyzoites( especially pork, lamb, or venison)-

Contaminated food or water or hands-oocystCongenital ( By transmission from infected mother

to fetus during pregnancy.)- tachyzoiteFrom a blood transfusion or organ transplant

Incubation Period

Incubation Period In humans, the incubation period is 10 to 23 days after ingesting contaminated meat, and 5 to 20 days after exposure to infected cats.

Toxoplasmosis is the most common work-related parasitic infection in laboratory workers. Infections can be acquired by accidental inoculation, splashing, inhalation or ingestion. The source of infection may be blood or blood products, feces or tissues.

Toxoplasmosis, the disease of which T. gondii is the causative agent, is usually minor and self-limiting but can have serious or even fatal effects on a fetus whose mother first contracts the disease during pregnancy or on an immunocompromised human.

Toxoplasma gondii is known to change the host's behavior. Studies show the capability for the parasite to make rats fearless near cats.

Pathogenicity

Healthy people who become infected often do not have symptoms because their immune system keeps the parasite from causing sickness.

10–20 % of patients develop sore lymph nodes, muscle pains and other minor symptoms that last for several weeks and then go away (acute toxoplasmosis).

Symptoms similar to those of the flu, including: Body aches, Swollen lymph nodes, Headache, Fever& Fatigue

The parasites remain in the body as tissue cysts (bradyzoites) and reactivate, if the person becomes immuno-suppressed by other diseases or by immunosuppressive drugs.

Pregnancy precautions

Usually if a woman has been infected before becoming pregnant, the born baby is safe because the mother has developed immunity.

If a woman is pregnant and becomes infected with toxoplasmosis during or right before pregnancy, she can transmit the disease to her unborn child (congenital transmission).

The earlier transmission occurs the bigger effects. A simple blood draw at the first prenatal doctor visit can

determine whether or not a woman has had previous exposure and therefore whether or not she is at risk

Pregnant women should avoid handling raw meat, drinking raw milk (especially goat milk) .

• Symptoms might include:Miscarriage or stillborn babyBaby born with signs of toxoplasmosis (for example,

abnormal enlargement or smallness of the head)Baby with brain or eye damage.An enlarged liver and spleenYellowing of the skin and whites of the eyes (jaundice)Usually the babies have no symptoms initially, but can

develop mental disability, vision loss (ocular toxoplasmosis) .

Life Cycle In definitive host

A cat ingests either: a pseudocyst in an infected animals flesh or an oocyst from the environment

The tissue cyst or oocyst wall is dissolved during digestion, releasing bradyzoites or sporozoites, which enter the lamina propria of the small intestine and begin to multiply as tachyzoites.

The tachyzoites can disseminate to extra-intestinal tissues within a few hours of infection, via the lymph and blood.

The parasite multiply sexually & asexually within the intestinal epithelium to form the zygote which secrete a wall around its self forming un-sporulated oocyste

Oocyst sporulates 1 to 5 days after excretion.

Life Cycle In Intermediate host

Following ingestion of infective oocyst, the parasite becomes intracellular & multiply in the lymph glands , liver, muscle, CNS, placenta, etc

In the early acute stages of infection, the parasites tachyzoites invade phagocytic mononuclear cells.

In chronic stages the parasites bradyzoites multiply intracellularly in the tissues forming pseudocysts.  in the brain, the eyes, and striated muscle (including the heart)

Tissue cysts usually cause no host reaction and may remain for the life of the host.

Laboratory diagnosis

Toxoplasmosis can be diagnosed by direct observation of the parasites in tissues, including broncho alveolar lavage material and lymph node biopsies.

PCR techniques can be helpful, particularly for detecting congenital infections in uterus, By detecting the parasite's DNA in the amniotic fluid .

Immunohistochemical staining and electron microscopy

are also used.

The diagnosis of toxoplasmosis is typically made by Serologic testing:

A test that measures immunoglobulin G (IgG) is used to determine if a person has been infected.

If it is necessary to try to estimate the time of infection, which is of particular importance for pregnant women, a test which measures immunoglobulin M (IgM) is also used along with other tests such as an avidity test.

The IFA and ELISA tests are used most often in humans.