Toxoplasmosis

Learning outcomes By the end of the lecture, you should be able to: 1- Mention Causal Agent of Toxoplasmosis. 2- Mention systematic position of Toxoplasma gondii. 3- Mention geographic distribution of Toxoplasmosis. 4- Mention Intermediate and definitive hosts of Toxoplasma gondii. 5- Describe Forms and morphology of Toxoplasma gondii. 6- Mention habitat of different forms of Toxoplasma gondii. 7- Explain life cycle of Toxoplasma gondii. 8- Mention routes of disease Transmission. 9- Mention pathology and clinical features of Toxoplasmosis. 10- Diagnose Toxoplasmosis.

Suggested Reading http://www.dpd.cdc.gov/dpdx/HTML/Toxoplasmosis.htm Chiodini, P.L.; Moody, A.H. and Manser, D.W. (2001): Atlas of Medical Helminthology and Protozoology. 4th ed. Churchill Livingstone, P. 59-60.

Causal Agent of Toxoplasmosis Toxoplasmosis is caused by Toxoplasma gondii. Toxoplasma gondii is a protozoan parasite that infects most species of warm blooded animals, including humans, causing the disease toxoplasmosis.

Systematic position of T. gondii Phylum: Apicomplexa (Sporozoa). Class: Coccidea. Genus: Toxoplasma (T.) e.g. Toxoplasma gondii

Geographic distribution of Toxoplasmosis Toxoplasmosis is one of the most common of humans infections throughout the world. Infection is more common in warm climates and at lower altitudes than in cold climates and mountainous regions. 

Hosts of Toxoplasma gondii Definitive host: Cats. Intermediate hosts: Human. Cattle. Sheep. Camel. Pig. Dogs. Rodents. Chickens

Forms of T. gondii Tachyzoite (acute stage, free or in pseudocyst in brain, liver, lung, spleen, bone marrow, eye, etc.) Bradyzoite (chronic stage, in True cyst in different organs)

Stages of the asexual cycle (in intermediate Host) Morphology Stages of the asexual cycle (in intermediate Host) A- Trophozoite : - proliferative form , 6x3 µ - crescent in shape with one end pointed & the other rounded - has a nucleus.

B- Pseudocyst A host cell containing rapidly multiplying tachyzoites. No cyst wall. In acute infection.

C-True Cyst Dormant stage. Contains bradyzoites Surrounded by a cyst wall 50-100µ In chronic infection

Stages derived from cat (D.H) Sporulated oocyst: Oval,10x12µ, transluscent Di-sporocystic tetrazoic Unsporulated oocyst: Shed in faecs of cat, contains one sporoplast

Different forms of T. gondii

Life cycle of T. gondii I- Sexual enteric cycle in cat: Cats can acquire infection by ingestion of cysts (when they eat an intermediate host as rat), or mature oocysts in food and drinks contaminated with faeces of infected cats  release of trophozoites or sporozoites in the intestine  penetrate the enterocytes  multiple schizogony cycles. Then development of gametes occurs fertilization  zygotes  immature oocysts  external environment with faeces  mature within 3-4 days and become disporocystic tetrazoic oocysts. Moreover, asexual exoenteric multiplication may occur in tissues of the cat i.e. cat is a complete host

Life cycle…..cont Asexual exoenteric cycle in Intermediate host (as human): Ingestion of the infective stage(oocyst, cyst, or pseudocysts)  release of organisms (sporozoites or trophozoites) in the small intestine  penetrate the small intestinal wall, multiply in lymphoid macrophages in the lamina propria and then via lymphatics they reach the mesenteric lymph nodes where they proliferate  haematogenous spread to various organs pseudocysts in acute infection. In chronic infection, cysts are formed due to the developed host immunity. Then the intermediate host is infective if eaten by cats. Human is a blind intermediate host.

Life Cycle of T. gondii

Unsporulated oocysts passed in faeces Infected fetus Unsporulated oocysts passed in faeces

Routes of disease Transmission Human and other animals infection may be acquired in several ways: 1- Ingestion of undercooked infected meat containing Toxoplasma cysts (true or pseudo-cyst) 2- Ingestion of the sporulated oocyst from fecally contaminated hands or food. 3- Organ transplantation or blood transfusion. 4- Transplacental (congenital) transmission. 5- Accidental inoculation of tachyzoites. 

Clinical Features Infection with Toxoplasma in immuno-competent persons is generally an asymptomatic infection. However, 10% to 20% of patients with acute infection may develop: A flu-like illness. Cervical lymphadenopathy. Atypical pneumonia. Acute encephalitis. Chorioretinitis. Symptoms usually resolve within a few months to a year. 

Clinical Features…cont. In immunodeficient patients or infants (congenital) infection lead to: 1- Toxoplasmic encephalitis (hydrocephalus)

Clinical Features ….…cont. 2- Myocarditis. 3- Retinochoroiditis (Ocular Toxoplasma infection)

Laboratory Diagnosis of Toxoplasmosis 1-The detection of Toxoplasma-specific antibodies (IgM & IgG) is the primary diagnostic method to determine infection with Toxoplasma. 2- Observation of parasites in patient specimens, such as bronchoalveolar lavage or lymph node biopsy. 3- Isolation of parasites from blood or other body fluids, and intraperitoneal inoculation into mice or tissue culture.  4- Detection of parasite genetic material by PCR.

Laboratory Diagnosis of Toxoplasmosis Microscopy Findings T. gondii cyst in brain tissue stained with hematoxylin and eosin T. gondii tachyzoites