Tissue coccida TOXOPLASMA Lecture NO 11 Mrs. Dalia Kamal Eldien MSC in Microbiology

Objectives  Introduction to Coccidia class& the taxonomy  Toxoplasma gondii as example of tissue coccidia  Morphology Toxoplasma gondii (oocyst, tachyzoite & bradyzoite)  Mode of transmission  Pathogenicity  Pregnancy precautions  Life cycle in definitive& intermediate host  Laboratory 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

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-oocyst  Congenital ( By transmission from infected mother to fetus during pregnancy.)- tachyzoite  From 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 baby  Baby born with signs of toxoplasmosis (for example, abnormal enlargement or smallness of the head)  Baby with brain or eye damage.  An enlarged liver and spleen  Yellowing 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.