Toxoplasma gondii - IgM, IgA and IgG antibodies; Molecular diagnostics (PCR)

Toxoplasma gondii is an obligate intracellular parasite of the genus Toxoplasma, family Sarcocystidae, with a worldwide distribution. This parasite affects many animal and bird species, as well as people, in which it causes toxoplasmosis.

The biological cycle of Toxoplasma gondii implies a definitive mammalian host where it multiplies and matures, usually domestic and wild cats, which constitute the main reservoir. This biological cycle comprises two phases: a sexual phase that takes place in the organism of mammalian hosts, generally felines, and an asexual phase that takes place in any warm-blooded animal, such as other mammals and birds.

In the definitive mammalian host, including the felines, the parasites invade any type of cells (with the exception of erythrocytes), forming a parasitophore vacuole containing bradyzoites, the form of slow multiplication of the parasite, of size 1.5 μm x 7, 0 μm. The parasitophore vacuoles form cysts in the tissues, especially in the muscles and the brain. Because the parasite is inside the cells, the host's immune system does not detect these cysts. This microorganism propagates inside these vacuoles through a series of binary divisions until the infested cell eventually ruptures, releasing the tachyzoites. The tachyzoites are observed in the acute phase and are responsible for tissue dissemination and destruction, with a size of 6 μm in length and 3 μm in width, oval in shape. The tachyzoites are the form of asexual multiplication of the parasite. Unlike bradyzoites, free tachyzoites are eliminated by the host's immune defenses, although some infect other cells, thus maintaining the life cycle of this parasite. Tissue cysts are ingested by the cat (for example, feeding on an infected mouse) and infect the epithelial cells of the small intestine where sexual reproduction occurs, with formation of macrogametocyte and microgametocytes, which subsequently evolve into macrogametes and microgametos, respectively. When the microgametes fertilize the macrogamate, the zygote is produced, which will eventually give rise to the oocyst, which is released with the feces. The sporulated oocysts are ovoidal, measure between 10 and 12 μm and contain 2 sporocysts, each with four sporozoites. In the course of days to weeks, the oocysts sporulate in a suitable environment (warm and humid) and can remain infective for months.

In animals, the transmission of this microorganism occurs mainly through the ingestion of contaminated meat from birds and rodents with tissue cysts or through oocysts eliminated with the faeces of felines. In people, the transmission of Toxoplasma gondii occurs through the handling of the excrements of infected animals (such as cats), through the ingestion of water containing oocysts, or through the intake of raw or undercooked meat (mainly lamb, pig or beef) containing tissue cysts with bradyzoites and transplacental via tachyzoites, as well as blood transfusions containing tachyzoites or organ transplantation containing tissue cysts with bradyzoites.

Toxoplasmosis is a generally mild disease, but it can be complicated to become fatal, especially in cats, in human fetuses and in individuals with a compromised immune system. The disease can affect the brain, lung, heart, eyes and liver. The majority of Toxoplasma gondii infections (up to 90% of cases) occur asymptomatically. In cases in which the infection presents with clinical manifestations, these usually appear around 10 to 14 days after infection and may include inflammation of the cervical lymph nodes, headaches, fever, muscle pain, abdominal pain and sore throat. In individuals with a depressed immune system, in addition to the aforementioned symptoms, loss of appetite, confusion, blurred vision due to inflammation of the retina, convulsions and encephalitis may occur, which can be fatal. In addition, in pregnant women infection by this agent can cause (depending on the stage of pregnancy in which the infection occurs) the death of the fetus, malformations in newborns and sequelae as serious conditions of the central nervous system, hydrocephalus, cerebral calcifications, hepatosplenomegaly, jaundice, pneumonitis and myocarditis.

Tests carried out in IVAMI:

  • IgM, IgA and IgG antibodies (only in humans).
  • Molecular diagnosis (PCR), to detect DNA of Toxoplasma gondii.

Recommended sample:

  • Serum (only for detection of antibodies in humans).
  • Lymph node biopsy.
  • Brain biopsy.
  • Other tissue biopsies.

Conservation and shipment of the sample:

  • Refrigerated (preferred) for less than 2 days.
  • Frozen: more than 2 days.

Delivery of results:

  • Antibodies (only in humans): 2 to 4 days
  • Molecular diagnosis (PCR): 24 to 48 hours.

Cost of the test: