Toxoplasmosis: an Important Protozoan Zoonosis

Toxoplasmosis is an important infection caused by single celled parasite Toxoplasma gondii which is one of the world's most common parasites. Toxoplasmosis is considered to be the third leading cause of death attributed to food-borne illness in the United States. Most people affected never develop signs and symptoms. But for infants born to infected mothers and for people with compromised immune systems, toxoplasmosis can cause extremely serious complications. Toxoplasmosis was first described in 1908 from a small rodent. The parasite infects almost all worm blooded animals and serological evidence indicates that it is one of the most common of humans' infections throughout the world. The disease is transmitted mainly by ingestion of infective stage of the parasite, organ transplant as well as blood transfusion in addition to the transplacental transmission which is very common. Toxoplasmosis can be presented in various forms of clinical manifestations depending on the immune status of the patient causing life threatening disease in AIDS patient. Pregnant women, cat owners, veterinarians, abattoir workers, children, cooks, butchers are considered as high risk group. Timely treatment of man and animals with proper antibiotic, hygienic measures, proper disinfection, mass education and vaccination are the measures to curtail the disease. Introduction Etiology Toxoplasmosis is the most widespread zoonosis Toxoplasmosis is not a new disease. Cats and an important human disease, particularly in including wild Felidae are the definite host and all other children whom it could cause visual and neurological warm-blooded animals including humans are impairment and mental retardation. Toxoplasmosis is intermediate hosts. Only cats can excrete the resistant caused by the protozoan parasite Toxoplasma gondii. stage of Toxoplasma gondii (the oocyst) in faeces. The (Nicolle and Manceaux,1908). Toxoplasma gondii is a oocysts are formed as a result of a sexual cycle in the cosmopolitan protozoan classified as a coccidian in the intestine of the cats. Only asexual cycle occurs in phylum Apicomplexa. This parasite is an ubiquitous, intermediate hosts. In intermediate hosts Toxoplasma obligate intracellular pathogen in humans and animal gondii is capable of multiplying in virtually any (Tedesco, 2004). The parasite is known to cause nucleated cell of the body. congenital disease and abortion both in human and The major forms of the parasite are: livestock (Dubey and Beattle, 1988). The parasite infects • Oocysts (containing sporozoites), which are shed in most genera of warm-blooded animals, including the feces. humans, but the primary host is the felid (cat) family. …


Introduction Etiology Toxoplasmosis is the most widespread zoonosis
Toxoplasmosis is not a new disease.Cats and an important human disease, particularly in including wild Felidae are the definite host and all other children whom it could cause visual and neurological warm-blooded animals including humans are impairment and mental retardation.Toxoplasmosis is intermediate hosts.Only cats can excrete the resistant caused by the protozoan parasite Toxoplasma gondii.
stage of Toxoplasma gondii (the oocyst) in faeces.The (Nicolle and Manceaux,1908).Toxoplasma gondii is a oocysts are formed as a result of a sexual cycle in the cosmopolitan protozoan classified as a coccidian in the intestine of the cats.Only asexual cycle occurs in phylum Apicomplexa.This parasite is an ubiquitous, intermediate hosts.In intermediate hosts Toxoplasma obligate intracellular pathogen in humans and animal gondii is capable of multiplying in virtually any (Tedesco, 2004).The parasite is known to cause nucleated cell of the body.congenital disease and abortion both in human and The major forms of the parasite are: livestock (Dubey and Beattle, 1988).The parasite infects • Oocysts (containing sporozoites), which are shed in most genera of warm-blooded animals, including the feces.humans, but the primary host is the felid (cat) family.
• Tachyzoites, rapidly multiplying organisms found in History the tissues.
• Bradyzoites, slowly multiplying organisms found in First described in 1908, in material from a small the tissues.rodent, Ctenoductyalus gondii (Nicolle and Manceaux, • Tissue cysts: walled structures, often found in the 1908).Rediscovered in 1935 in the brain tissue of muscles and central nervous system (CNS), guinea pigs used for encephalitis experiment .Found containing dormant Toxoplasma gondii bradyzoites.as the cause of encephalitis and chorioretinitis in a 31 (Dubey, 1988).day old infant.This stimulated interest in the disease .First reported Toxoplasma in India in a dog which died Epidemology due to Babesia gibsonii infection (Ray and Approximately one-third of all humanity has been Raghavachari, 1941).exposed to this parasite.Although usually members of the cat family (Felidae) and asexual propagation in a wide variety of warm blooded hosts asymptomatic in immunocompetent adults, it can (Dubey,1977).Three different invasive forms in the life cause severe disease manifestations and even death in immunocompromised patients (Singh, 2003).The cycle mediate survival and spread in the parasite's parasite infects most genera of warm-blooded animals, various hosts.Each invasive form is designed to including humans, but the primary host is the felid (cat) accomplish different modes of transmission: family.Cats are the only animal species to shed the Sporozoites are shed into the environment within infectious stage in their feces (Salvin et al., 1994).
resistant spores (oocysts), which are capable of causing oral infection in herbivorous animals; Prevalence tachyzoites rapidly expand and disseminate within the Serologic prevalence data indicate that definative host; and bradyzoites infect long-lived host toxoplasmosis is one of the most common of humans cells, where they are semidormant, survive in infections throughout the world.Infection is more immunocompetent hosts, and assure oral common in warm climates and at lower altitudes than in transmission into carnivorous hosts.Development in T. cold climates and mountainous regions.High gondii is enormously flexible, as interconversion prevalence of infection in France has been related to a between these stages occurs readily (e.g., sporozoite preference for eating raw or undercooked meat, while to tachyzoite,tachyzoite to bradyzoite, and bradyzoite high prevalence in Central America has been related to to tachyzoite).The entire life cycle can be regenerated the frequency of stray cats in a climate favoring survival from a single cloned organism, which can undergo of oocysts.Until recently the prevalence of T. gondii in differentiation to both male and female gametocytes; the general population of India was considered to be this indicates that mating types are not predetermined.low compared with Western countries (Bowerman, Hence, infection of a cat with a single isolate can give 1991).
rise to progeny through a process of self-Seroprevalence of Toxoplasmosis in Gujarat from mating.(Pfefferkorn et al, 1977).Prepatent period after zoo personnel feeding tissue containing bradyzoites, tachyzoites and feeding sporulated oocystes is 3-5 days, 11-19 days Jani et al. (2006) studied, the prevalence in and 21-24 days,respectively.(Frenkel ,1973).persons was determined based on IgG and IgM level Toxoplasma gondii antibodies were detected in nine Pathogenesis out of 60 persons.The over all prospective prevalence When the organism is ingested, bradtzoites are of toxoplasmosis was found about 15 percent with a released from cysts or sporozoites are released from range of 12-900 iu/ml.The high prevalence in group of oocysts, and the organisms enter gastrointestinal cells.zoo attendant working with feline group followed by Host cell receptors consisting of laminin, lectin, and reptile group.The seroprevalence of parsons working SAG1 are involved in T gondii tachyzoite attachment with avian, herbivores and general group was found and penetration.Tachyzoites multiply, rupture cells, seronegative for toxoplasmosis.
and infect contiguous cells.They are transported via the lymphatics and are disseminated hematogenously Transmission throughout the tissues.

Transmission by ingestion of bradyzoites is
The ability of T gondii to actively penetrate hosts common in case of carnivores, while the herbivores cells results in formation of a parasitophorous vacuole.usually infected by the fecal-oral route by ingesting Following apical attachment, the parasite rapidly sporulated oocysts shed by infected cats.In case of enters host cell in a process that is faster than transplacental transmission tachyzoites multiply within phagocytosis.The vacuole is formed primarily by the placenta and spread to the fetus.Body excretions invagination of host cell plasma membrane, which is and secretions like milk and saliva also play vital role in pulled over the parasite through the concerted action of transmission.(Singh et al., 1997).
the actin-myosin cytoskeleton of the parasite.

Human infection can occur either by Ingestion of
Tachyzoites proliferate, producing necrotic foci undercooked infected meat containing cysts or by surrounded by a cellular reaction.Upon normal ingestion of the sporulated oocysts from contaminated immune response, tachyzoites disappear from tissues.hands or foods.Organ transplantation, Blood In immunodeficient individuals and in some apparently transfusion (iatrogenic), Transplacental transmission immunologically healthy patients, the acute infection and accidental inoculation of tachyzoites in the skin are progresses, resulting in potentially lethal the other modes of transmission.(Parija, 1996) The detection of Toxoplasma-specific antibodies Conditions of transmission may be when is the primary diagnostic method to determine infection infection during parasitemia -in unexposed mother with Toxoplasma.Antibodies are detected by with an active primary infection during pregnancy or numerous serologic tests and most of the test kits are previously exposed mother before pregnancy with commercially available to detect T. gondii specific IgG, immune compromise (eg.AIDS) and tachyzoites IgM , IgA or IgE antibodies.The Sabin-Feldman dye cross placental barrier.The risk of the baby's infection test (DT),indirect fluorescent antibody test (IFAT), depends partly upon the timing of the mother's indirect haemagglutination test (IHAT), latex infection.When mothers are infected in the first agglutination test (LAT), direct agglutination test (DAT), trimester, 15 percent of fetuses become infected,as and enzyme linked immunosorbent assay (ELISA) are compared to 30 percent in the second trimester and 65 some of the tests used to detect T. gondii antibodies.percent in the third trimester (Jeffrey, 2003).
Although the DT is the most specific test, it is rarely Toxoplasmosis is often asymptomatic in used now because it uses live virulent T. gondii (Singh, immunocompetent individuals, but ocular lesions may 2003).be present in up to 20% of infected patients.It is Public health importance common to find cysts and tachyzoites in the retina of T.
Persons at high risk are pregnant women, cat gondii-infected subjects.Lesions are often necrotic, owners, veterinarians, abattoir workers, children, with destruction of the architecture of the neural retina cooks, butchers.There is no significant difference and choroids (retinochoroiditis) (Vallochi et al. 2002).
between the prevalence in men or in women.High Toxoplasmosis in AIDS patients and other prevalence of infection is in pregnant women of child immunocompromised patients can be life threatening.
bearing age (Singh and Neutiyal, 1991).Prevalence of Disease in these individuals can be due to recently infection in vegetarians and non-vegetarians was acquired infection or more commonly due to similar (Rawal, 1959).Infection is asymptomatic in 80reactivation of a latent infection.severe in infants whose mothers become The early symptoms include lethargy, persistent infectedduring the first trimester than those during the fever despite treatment with some antibiotics, and third trimester.Although most congenitally infected anorexia.In some animals, toxoplasmosis may be children are asymptomatic at birth, they will develop characterized by hepatitis or pancreatitis.Central some symptoms later in life.nervous system (CNS) signs, particularly common in Treatment in human older animals, vary with the site of the lesion and may Antibiotics may be used in pregnant women, include convulsions, restlessness,somnolence, head immunocompromised patients with organ involvement, pressing, teeth grinding, personality changes, congenitally infected infants or individuals with ocular hyperesthesia, atypical vocalizations, incoordisease.Antibiotics cannot destroy tissue cysts and dination,trembling, opisthotonos or circling.Abortion, may not be able to eradicate actively dividing parasites metritis and the birth of premature, can occur but seem If the presence of acute T. gondii infection in a pregnant to be rare.Ocular signs are common and may include woman is confirmed, treatment with spiramycin generalized retinitis or irregular reddish, dark or pale (Rovamycine) can be initiated in an effort to prevent retinal foci;.Chronic lowgrade infections may cause transmission to the fetus.If fetal infection is confirmed glaucoma, corneal opacity and panophthalmitis.
through amniocentesis, the woman may be switched to Diagnosis pyrimethamine (Daraprim) and sulfadiazine after the The diagnosis is mainly carried out by first trimester (Daffos et al., 1988).Folinic acid