HISTORY Toxoplasma gondii is a single celled parasite that causes a disease known as toxoplasmosis. It invades muscle and intestinal epithelium. Discovered in 1908 in a desert rodent called gondi. Toxoplasma originated from the Greek word, toxon which means bow. Toxoplasma means ‘bow shaped’ organism. Tachyzoites ( 6 x 2 µm Bradyzoites
Definitive host : Domestic cats and their relatives (Felidae family). Intermediate host : birds, rodents, cows, sheep, humans and other mammals. Geographical range : worldwide. Infection is highest in hot and humid climates and lower altitudes. In the U.S, over 60 million people may be infected i.e % of the population. Toxoplasma gondii is transmitted by three known modes: congenitally, through the consumption of uncooked infected meat and via fecal matter. The parasite has two life cycles: Direct and Indirect
L IFE STAGES Infectious : Tachyzoites - Rapidly multiplying form Bradyziotes - In infected tissue Oocysts – Shed in feces Division: Sexual stages are produced only in the feline definitive hosts (cats). Asexual stages occur in any of the prospective warm blooded animals (birds, dogs, pigs, cattle, humans, etc.).
L IFE CYCLE WITHIN THE INTESTINE The infection is acquired through the ingestion of sporulated oocysts (Oo). Sporozoites (Sz) are release in the intestinal lumen and invade intestinal epithelial cells. Within the epithelial cells the parasite undergoes a round of merogony/schizogony leading to the production of merozoites (Mz). The released merozoites reinvade intestinal epithelial cells and can undergo additional rounds of merogony or develop into either micro- or macrogamonts. Microgametes (ga) will fertilize the macrogametes (ga) to form a zygote (Zy) which develops into the oocyst (Oo). Immature oocysts are passed in the feces and maturation into infectious sporulated oocysts occurs in the environment. Recognizable stages during this maturation (ie, sporogony) include oocysts with a single sporoblast, oocysts with two sporoblasts, and the mature oocyst with two sporocysts, each of which contains four sporozoites.
IN THE INTESTINES OF A DEFINITIVE HOST Sz-Sporozoites Mz-Merozoites Ga-gametes Zy-Zygote Oo-Oocyte Bradyzoites released in the intestine, infects cells forming trophozoites and undergo asexual production called schizogony
1. Oocysts are shed in the cat's feces. o Large numbers are shed, but usually only for 1–2 wk. Oocysts take 1–5 days to become infective. o Cats become reinfected by ingesting sporulated oocysts. 2. Soil, water, plant material, or cat litter become contaminated with oocysts. o Intermediate hosts in nature (eg, birds, rodents, wild game, animals bred for human consumption) become infected after ingesting infected materials. 3. Oocysts develop into tachyzoites shortly after ingestion. 4. Tachyzoites spread throughout the body and form tissues in neural and muscle tissue. 5. Cats become infected after consuming intermediate hosts containing tissue cysts.
6a. Humans can become infected by: Ingesting undercooked meat containing tissue cysts Ingesting food or water contaminated with at feces or other feces-contaminated materials (eg, soil) or contact with a pet cat's litter. 7. Rarely, human infection results from blood transfusion or organ transplantation. 8. Rarely, transplacental transmission from mother to fetus occurs. 9. In the human host, parasites form tissue cysts, most commonly in skeletal muscle, myocardium, the brain, and the eyes; these cysts may remain throughout the life of the host and can reactive if the host becomes immuno-compromised. o Cyst-like accumulations of merozoites called bradyzoites in zoitocyst (cyst) are located in brain tissue.
P ATHOGENESIS * Acute infection: causes painful swollen lymph glands in the cervical, supraclavicular, and iguinal areas. In heavy acute infections the organism can be found free in the blood and peritoneal exudate. Symptoms - flu-like * Subacute: cause extensive lesions in the lungs, liver, heart, brain, and eyes. * Chronic infection: occurs when the host's immune system decreases the formation of tachyzoites. Symptoms - blindness, blind spots, paralysis and myocarditis *opportunistic infection in AIDS patients. Not transmitted from human to human. Exception: mother to fetus. A. Food Borne Transmission: The tissue form of the parasite (microscopic cyst made up of bradyzoites) can be transmitted to humans via undercooked meat.
People become infected by: Eating undercooked, contaminated meat (especially pork, lamb, and venison). Accidental ingestion of undercooked, contaminated meat after handling it and not washing hands thoroughly ( Toxoplasma cannot be absorbed through intact skin). Eating food that was contaminated by knives, utensils, cutting boards, or other foods that had contact with raw, contaminated meat.
B. Animal-to-human (zoonotic) transmission: Cats play an important role in the spread of toxoplasmosis. They become infected by eating infected rodents, birds, or other small animals. The parasite is then passed in the cat's feces in a microscopic oocyst. Kittens and cats can shed millions of oocysts in their feces for as long as 3 weeks after infection. Mature cats are less likely to shed Toxoplasma if they have been previously infected. A Toxoplasma - infected cat that is shedding the parasite in its feces contaminates the litter box. If the cat is allowed outside, it can contaminate the soil or water in the environment as well.
People can be infected by: Accidental ingestion of oocysts after cleaning a cat's litter box when the cat has shed Toxoplasma in its feces. Accidental ingestion of oocysts after touching or ingesting anything that has come into contact with a cat's feces that contain Toxoplasma. Accidental ingestion of oocysts in contaminated soil (e.g., not washing hands after gardening or eating unwashed fruits or vegetables from a garden). Drinking water contaminated with the Toxoplasma parasite. (CDC Photo)
C. Mother-to-child (congenital) transmission A woman who is newly infected with Toxoplasma during pregnancy can pass it to her unborn child via congenital infection. The woman may not have symptoms, but there can be severe consequences for the unborn child, such as diseases of the nervous system and eyes. Generally if a woman has been infected before becoming pregnant, the unborn child will be protected because the mother has developed immunity. If a woman is pregnant and becomes newly infected with Toxoplasma during or just before pregnancy, she can pass the infection to her unborn baby. The damage to the unborn child is often more severe the earlier the transmission occurs.
Potential results can be : a miscarriage a stillborn child a child born with signs of toxoplasmosis (e.g., abnormal enlargement ( hydrocephalus) or smallness of the head). Infants infected before birth often show no symptoms at birth but develop them later in life with potential vision loss, mental disability, and seizures. In the human host, the parasites form tissue cysts, most commonly in skeletal muscle, myocardium, brain, and eyes; these cysts may remain throughout the life of the host.
Rare instances of transmission: Organ transplant recipients can become infected by receiving an organ from a Toxoplasma -positive donor. Rarely, people can also become infected by receiving infected blood via transfusion. Laboratory workers who handle infected blood can also acquire infection through accidental inoculation. Symptoms: Few people show symptoms due to the immune system keeping the parasite from causing illness. "flu-like" symptoms that last for several weeks and then go away. Immunocompetent individuals may present with fever, lymphadenopathy, muscle aches, and headache. Congenitally infected children may suffer impaired vision and mental retardation. Immunosuppressed patients may have central nervous system disease (encephalitis). The parasite remains in the body in an inactive state. It can become reactivated if the person becomes immunosuppressed.
D IAGNOSIS Serologic testing (A test that measures immunoglobulin G (IgG) is used to determine if a person has been infected). Direct observation of the parasite in stained tissue sections, cerebrospinal fluid (CSF), or other biopsy material. These techniques are used less frequently because of the difficulty of obtaining these specimens. Polymerase chain reaction (PCR) also is useful to identify T. gondii DNA in CSF, amniotic fluid, infant peripheral blood, and urine to definitively establish the diagnosis. ELISA
DIAGNOSIS Diagnosis of acute Toxoplasma infection can be established by : Culture of T. gondii from blood or body fluids. Identification of tachyzoites in sections or preparations of tissues and body fluids. Identification of cysts in the placenta or tissues of a fetus or newborn Characteristic lymph node histologic features.
P REVENTION AND CONTROL Cook food to safe temperatures (66 ° C). A food thermometer should be used to measure the internal temperature of cooked meat. Do not sample meat until it is cooked. Freeze meat for several days at sub-zero (0° F) temperatures before cooking to greatly reduce chance of infection. Peel or wash fruits and vegetables thoroughly before eating. Wash cutting boards, dishes, counters, utensils, and hands with hot soapy water after contact with raw meat, poultry, seafood, or unwashed fruits or vegetables. Wash your hands.
If you are pregnant or immunocompromised: Avoid changing cat litter if possible or wear disposable gloves and wash hands with soap and warm water afterwards. Keep cats indoors. Do not adopt or handle stray cats, especially kittens. Do not get a new cat while you are pregnant.
T REATMENT Pyrimethamine (Daraprim) Side effects : bone marrow suppression and liver toxicity, folic acid antagonist. Sulfadiazine: used if unborn child is infected. Spiramycin: used to treat pregnant women. Reduces risk to child. Still experimental in the U.S.
Interesting facts about toxoplasmosis: 1. Infections in rats and mice can lead to them losing their fear of cats and indeed being drawn to cats. 2. Infected male humans have a six fold increased risk of a traffic accident due in part to slower reaction times. 3. Prevalence is affected by climate and climate change may affect its overall prevalence. 5. Countries where raw meat is more commonly consumed have higher rates of the infection, unsurprisingly. 6. Epidemiological studies link infectious agents of Toxoplasma gondii to schizophrenia.