Search Menu Abstract Toxoplasmosis is caused by infection with the parasite Toxoplasma gondii. It is one of the most common parasitic infections in humans and is most typically asymptomatic. However, primary infection in a pregnant woman can cause severe and disabling disease in the developing fetus. Recent developments have included increased understanding of the role of parasite genotype in determining infectivity and disease severity. Risk factors for acquisition of infection have been better defined, and the important role of foodborne transmission has been further delineated.
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E-mail: moc. This article has been cited by other articles in PMC. Abstract Toxoplasmosis is caused by a coccidian parasite, Toxoplasma gondii. The parasite is highly prevalent both in humans and in warm-blooded animals. Cat family animals are definitive host, and these animals excrete the infective oocysts in their feces. Humans, though not definitive host, get infection by consuming water or food contaminated with cat feces.
Rarely, infection can also take place through transfusing the infected blood, through transplantation of infected organs, or transplacentally from infected mother to fetus. Transplacental infection can cause congenital infection with varied degree of clinical manifestations, which depend on the age of fetus when infection took place. Diagnosis of congenital toxoplasmosis is difficult to establish until it is suspected and laboratory investigations are carried out.
In India, a prevalence rate of It is estimated that approximately between 56, and , children per year are born in India with a possible risk of congenital toxoplasmosis. The diagnosis of congenital toxoplasmosis can be made by serological methods which are most commonly used.
The other methods are parasite isolation by culture and molecular methods. Toxoplasmosis is treatable and transplacental transmission can be prevented by spiramycin, which concentrates in the placenta. However, if infection has done any damage to the fetus or the parasite has passed the placenta, spiramycin cannot reverse the damage. Prevention remains the best remedy. Despite its significant impact on pregnancy outcomes, the toxoplasmosis remains neglected, especially in the Indian subcontinent.
Toxoplasma is also an important opportunistic pathogen in immunocompromised hosts and also a major concern for animal health. However, the topic is vast and it is beyond the scope of this review to give a comprehensive and exhaustive account of toxoplasmosis; hence, I will try to focus only on the management of acute Toxoplasma infection occurring during pregnancy and possibilities of congenital toxoplasmosis.
However, in , a similar structure was reported by Leveran in the spleen and bone marrow of Java sparrow Padda oryzivora. However, this structure was considered as reproductive form of Haemoamoeba danilewskyi. However, after 1 year in , they reconsidered and renamed it as T. They showed that the parasite multiplies in the intestinal mucosa of a cat.
Later on, it was found that all cat family Felidae animals act as definitive host. The young kittens are highly infectious. However, the oocysts are shed in the kitten feces only in the first weeks of infection. However, even during acute infection, the cat does not exhibit any symptom. Other animals in fact, almost all warm-blooded animals including humans get accidentally infected. However, at present, it is well established that there are three primary routes of transmission of T.
There are other rare modes of transmission such as through organ transplantation, blood transfusion, and laboratory acquired.
A wide variation in the prevalence and incidence rates of this infection has been reported. In a recent study, we found that estimated number of children born with risk of congenital toxoplasmosis per year in India is , This also possesses risk of spread of infection to the visitors to that country and to consumers of countries where these food products are exported.
In the USA, food-borne toxoplasmosis is considered to be the third leading food-borne cause of death. Vegetables, salads, and water as source of Toxoplasma infection The oocyst-mediated infection plays major role in developing countries. The oocysts that sporulate in the soil are infectious to intermediate hosts including grazing animals and humans. These oocysts once passed out from cat intestine through feces, these may remain in the soil or the contaminated soil is admixed with water, can adhere to the land vegetables and fruits which are consumed raw by unaware children and adults without washing.
Commonly used ground vegetables and fruits that can get contaminated in this way are carrots, reddish, sweet potatoes, red beet, cauliflower, spinach, etc. Even other vegetables and fruits can be contaminated by humans through the use of soil-contaminated utensils, knives, and if the cut fruits are left open and allowed to access by flies and other insects.
Food handlers and vegetable venders have also been reported to serve as source of Toxoplasma infection as they clean the soiled vegetables with bare hands often with waste water. Transmission through water is most difficult to distinguish from meat-borne infections.
In developing countries where safe drinking water is not available to more than half of the population, water itself or vegetables irrigated and washed with such water and food served using contaminated water can lead to oocysts ingestion. Several epidemiological studies have supported this hypothesis. We reported that in Sub-Himalayan areas of India where natural spring water is drunk by the local inhabitants, the seroprevalence of toxoplasmosis is highest in India.
In this area, the natural water sources are common and are shared by both humans and animals including feline animals. The cats and other members of the cat family are definitive host of this parasite after drinking the water, taking bath, and even defecating in the same water body.
The water flows from higher altitude to lower residential areas, and the inhabitants without knowing that this water is contaminated consume it. It is interesting that as early as only 15 years after its discovery , frequent eating of rabbit meat was considered as a contributory factor for congenital toxoplasmosis.
Serological studies also confirm that several animals are infected with T. Outbreaks of toxoplasmosis associated with raw meat consumption have been reported. On animal toxoplasmosis, maximum work has been done by Dr. Dubey, a doyen in the field. More details of his findings can be found in his recent books and book chapters. Sheep from five flocks in Yorkshire, UK, were identified as having Toxoplasma infection. The prevalence of antibody in the hill flock was lower than the grassland or Worrall flocks.
The Navajo sheep are reared in dry, mountainous areas whereas Kentucky sheep are reared on rich grassland; therefore, it was postulated that environmental factors might have played major role in these varied prevalence rates. Similar findings were reported from India. The seroprevalence trends of human toxoplasmosis in the respective areas have also shown concordance.
These trends are indicative of oocyst infection; the presence of cats and survival of oocysts in those environmental conditions. Toxoplasma has been isolated from tissues skeletal muscle and brain tissue of naturally infected sheep; parasite was more commonly seen in the musculature than the brain.
However, even though mutton word used for both sheep and goat meats is most commonly consumed meat in most of the Asian countries including India, the chances of toxoplasmosis through meat as such are rare because in the Indian subcontinent meat is cooked well and semi-cooked and raw meat is rarely consumed.
However, in low socioeconomic populations, precooking processing and cleaning of meat and improper cleaning of hands and meat utensils can be potential sources of toxoplasmosis.
For a comprehensive data on toxoplasmosis in sheep, readers are encouraged to go through a recent review by Dubey.
Various experimental and histopathological studies have revealed that most commonly infected tissues of goat are skeletal muscle, diaphragm, intestine, heart, kidneys, and liver, in the same order. A few outbreaks of food-borne human toxoplasmosis have been reported after consuming raw goat meat. Although in Indian continent goat meat called mutton in this continent is the most common meat consumed, the chances of toxoplasmosis through this route are rare as the meat is cooked adequately.
In several other countries, the natives hunt and consume raw meat of wild goats. The seroprevalence of toxoplasmosis in breeding swines was reported as high as The access of cats to the pig farms has unequivocally been associated with infection of Toxoplasma in pigs.
Toxoplasma has been isolated from various tissues skeletal muscle, heart, and brain of naturally infected pigs. Outbreaks of human toxoplasmosis after consuming uncooked pork have been reported from Asian countries also. The major reason is that these countries eat pork minimally due to their cultural and religious beliefs.
The dye test DT is too unreliable for the diagnosis of toxoplasmosis in cattle as false positive results are caused by bovine serum protein. Although the prevalence of tissue cysts in cattle is low, beef is one of the most common meats eaten in Britain.
However, no work has been done to find the prevalence rate of toxoplasmosis in snow cattle, for example, yaks which are used not only as baggage careers and source of wool but also as source of meat for Himalayan tribes. Dubey et al. These studies indicated that prevalence rates varied from as low as 6.
Most of these studies were done on free-ranging chicken, and the authors concluded that prevalence of T. The quail meat is used as special feast in India.
Other meats and meat products Only a little information is available about Toxoplasma infection in other animals such as horses, camels, kangaroos, water buffaloes, and elephants whose meat is often consumed in some countries.
However, parasite has not yet been isolated from the eggs commonly consumed by human. If at all, the infection can occur through contaminated and broken egg shell if eggs are laid on the soil-containing Toxoplasma oocysts. Although Toxoplasma has been demonstrated in the milk of experimentally infected cat, sheep, goat, and mice, whether these reports can be considered indicative of milk-borne transmission in human is yet to be established.
The survival of Toxoplasma has been reported for up to 10 days in milk and unprocessed home-made cheese. For more details, readers are encouraged to read a recent review by Singh and Munawwar.
Toxoplasmosis is more severe in infants whose mothers become infected during the first trimester than those during the third trimester.
Although most congenitally infected children are asymptomatic at birth, they may develop some symptoms later in life. Hydrocephalus, retinochoroiditis, chorioretinitis, intracerebral calcification, mental retardation, loss of hearing, and very rarely death may also occur.
Because these symptoms are nonspecific, postnatal toxoplasmosis is rarely diagnosed. Toxoplasmosis in AIDS patients and other immunocompromised patients can be life-threatening.
Heart and other organ transplantation recipients are at risk for developing toxoplasmosis because of lowering of host resistance by immunosuppressive medication. Similarly, cancer patients are also at risk of developing clinical toxoplasmosis. Although any organ may be involved, encephalitis is the predominant presentation of toxoplasmosis in AIDS patients.
The term bad obstetric history BOH or bad obstetric outcome has been coined to associate Toxoplasmosis by Indian microbiologists and obstetricians, based on serology findings. However, my team has been against associating Toxoplasma with these conditions.
There are several flaws in linking habitual abortion with Toxoplasma infection. In most of these studies which associated prevalence of anti-Toxoplasma antibodies with multiple abortions, the number of patients was low, studies were uncontrolled, and serologic data before pregnancy were not obtained. In many cases, poor-quality test kits were used which yielded high false positivity. Even isolation of T.
E-mail: moc. This article has been cited by other articles in PMC. Abstract Toxoplasmosis is caused by a coccidian parasite, Toxoplasma gondii. The parasite is highly prevalent both in humans and in warm-blooded animals. Cat family animals are definitive host, and these animals excrete the infective oocysts in their feces. Humans, though not definitive host, get infection by consuming water or food contaminated with cat feces. Rarely, infection can also take place through transfusing the infected blood, through transplantation of infected organs, or transplacentally from infected mother to fetus.
Congenital toxoplasmosis: Clinical features, outcomes, treatment, and prevention
Parasitology[ edit ] In its lifecycle, T. Tachyzoites are also known as "tachyzoic merozoites", a descriptive term that conveys more precisely the parasitological nature of this stage. The formation of cysts is in part triggered by the pressure of the host immune system. Bradyzoites, once formed, can remain in the tissues for the lifespan of the host. In a healthy host, if some bradyzoites convert back into active tachyzoites, the immune system will quickly destroy them. However, in immunocompromised individuals, or in fetuses, which lack a developed immune system, the tachyzoites can run rampant and cause significant neurological damage.